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US 8068800 B2 Abstract A method of tuning an antenna circuit includes: (a) receiving a signal on an antenna, (b) producing a received signal strength indication based on the received signal, (c) using the received signal strength indication to produce a control voltage, (d) using the control voltage to control a capacitance in an antenna matching circuit, (e) changing the control voltage to minimize a ratio of a change in the received signal strength indication to a change in the control voltage and (f) repeating steps (a), (b), (c), (d) and (e). An apparatus that implements the method is also provided.
Claims(43) 1. A method of tuning an antenna circuit, comprising:
(a) receiving a signal on an antenna;
(b) producing a received signal strength indication based on the received signal;
(c) using the received signal strength indication to produce a control voltage;
(d) using the control voltage to control a capacitance in an antenna matching circuit;
(e) changing the control voltage to minimize a ratio of a change in the received signal strength indication to a change in the control voltage; and
(f) repeating steps (a), (b), (c), (d) and (e).
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14. The method of
producing a digital control signal;
applying the digital control signal to a digital-to-analog converter to produce the control voltage; and
applying the control voltage to a varactor.
15. The method of
filtering the control voltage prior to applying the control voltage to the varactor.
16. The method of
17. The method of
18. The method of
19. The method of
20. The method of
the control voltage is updated in a plurality of cycles; and
wherein for each cycle, the received signal strength indication is produced at the start of each cycle, the control voltage is produced, the control voltage is filtered and applied to varactor diodes, a remaining portion of the cycle allows for settling time of control voltage filtering.
21. The method of
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24. The method of
25. An apparatus, comprising:
an antenna;
a circuit for producing a received signal strength indication based on the received signal;
a processor for using the received signal strength indication to produce a control voltage; and
an antenna matching circuit including a capacitance controlled by the control voltage;
wherein the processor changes the control voltage to maximize signal gain by minimizing a ratio of a change in the received signal strength indication to a change in the control voltage.
26. The apparatus of
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37. The apparatus of
a digital-to-analog converter receiving a control signal from the processor and producing the control voltage.
38. The apparatus of
a filter for filtering the control voltage.
39. The apparatus of
40. The apparatus of
41. The apparatus of
42. The apparatus of
43. An apparatus comprising:
means for receiving a signal on an antenna;
means for producing a received signal strength indication based on the received signal;
means for using the received signal strength indication to produce a control voltage; and
means for using the control voltage to control a capacitance in an antenna matching circuit;
wherein the means for using the received signal strength indication to produce a control voltage changes the control voltage to maximize signal gain by minimizing a ratio of a change in the received signal strength indication to a change in the control voltage.
Description This invention relates to antenna systems, and more particularly to impedance matching in antenna systems. The size and aesthetics of many AM/FM receivers constrain the dimensions of their antennas and their ground planes to suboptimal limits. For simplicity and performance, the desired size of a good-performing antenna is about one-half wavelength at the tuned frequency (e.g., a halfwave dipole). Although longer antennas can offer better antenna gain, their narrow beamwidths make them impractical for most applications. At FM frequencies, a half wavelength is about 1.5 meters, while for AM frequencies it is about 150 meters. Due to the presence of sensitivity-limiting ambient noise, which is greater at lower frequencies, it turns out that 1.5 meters is a sufficient length for both FM and AM receivers. A vertical quarter-wave whip antenna mounted over a large ground plane (e.g., a metal car body) exhibits performance similar to a halfwave dipole antenna, and affords good FM and AM reception in cars. AM/FM receivers are available in many configurations, including automotive, tabletop, MP3 players, and cell phones. Smaller devices are typically characterized by poor signal reception, since halfwave and quarter-wave antennas are too large and impractical. An antenna size less than a half wavelength is considered electrically small. Electromagnetic interference (EMI) caused by antenna proximity to electronics, signal variability due to human body effects, and variable antenna orientation all have a significant impact on antenna performance. Because these effects are more pronounced at lower frequencies, many small devices have FM-only receivers. The impedances of any antenna and receiver can theoretically be matched to achieve maximum power transfer. This can be realized by conjugate matching antenna and receiver impedances. Although it is well-known that conjugate matching of the antenna and receiver input impedances maximizes power transfer into the receiver, it is not necessarily optimum for receiver sensitivity. Conjugate impedance matching is practical for half wavelength antennas with relatively low reactance, and resistance nearly constant across the band, but this approach is not practical for the electrically small antennas used in many devices. The radiation and loss resistance of these antennas is very low, and the reactance is high. This high ratio of reactance to radiation resistance leads to matching techniques that maximize the voltage (not power) delivered to the receiver input. The reactance of electrically small antennas can be tuned out using a resonant matching circuit. The Q of the resonant circuit thus formed must be held sufficiently high to increase the signal voltage to an acceptable level at the input to the receiver low noise amplifier (LNA). To achieve a sufficiently high Q, the receiver LNA must present a high parallel resistance to the antenna resonant circuit. Although higher values may be possible and could improve reception, a Q of about 30 is a practical goal for AM and FM reception. Since a high Q circuit has a narrow bandwidth, it must be tunable across the AM or FM band as the receiver is tuned. This was common practice for AM tabletop superheterodyne receivers with internal loop antennas. The receiver mixed the RF input signal to a fixed intermediate frequency (IF) using a local oscillator (LO), mixer, and IF filter. The antenna for these receivers was either an air-loop (typical of older tube receivers) or a smaller ferrite-core loop antenna, both having similar characteristics. Since the inductance of this internal loop antenna was fixed and not significantly affected by external factors (such as the human body), a preselection filter was tuned along with the receiver LO to maintain a high Q resonant peak at the tuned frequency. This preselection filter, comprised of the loop antenna's inductance and a variable capacitance, also served as an image reject filter. Older superheterodyne receivers used a ganged-capacitor method to synchronize the preselection filter tuning with the LO tuning. More modern receivers typically perform a similar function with varactor diodes acting as voltage-controlled capacitors. The voltage for the varactor diode of the preselection filter is derived from the tuning voltage of the LO varactor diode. Factory calibration is usually necessary for these receivers to accommodate component tolerances. Unfortunately, it is impractical for some modern receivers to utilize preselection filter tuning. The receiver IF is sometimes incompatible with this type of tuning, and calibration and consistency over operating temperature become impractical. Furthermore, external and portable antennas have time-varying impedance characteristics, making fixed factory calibration impossible. In a first aspect, the invention provides a method of tuning an antenna circuit including: (a) receiving a signal on an antenna, (b) producing a received signal strength indication based on the received signal, (c) using the received signal strength indication to produce a control voltage, (d) using the control voltage to control a capacitance in an antenna matching circuit, (e) changing the control voltage to minimize a ratio of a change in the received signal strength indication to a change in the control voltage, and (f) repeating steps (a), (b), (c), (d) and (e). In another aspect, the invention provides an apparatus, including an antenna, a circuit for producing a received signal strength indication based on the received signal, a processor for using the received signal strength indication to produce a control voltage, and an antenna matching circuit including a capacitance controlled by the control voltage, wherein the processor changes the control voltage to maximize signal gain by minimizing a ratio of a change in the received signal strength indication to a change in the control voltage. In another aspect, the invention provides an apparatus including means for receiving a signal on an antenna, means for producing a received signal strength indication based on the received signal, means for using the received signal strength indication to produce a control voltage, and means for using the control voltage to control a capacitance in an antenna matching circuit, wherein the means for using the received signal strength indication to produce a control voltage changes the control voltage to maximize signal gain by minimizing a ratio of a change in the received signal strength indication to a change in the control voltage. In one aspect, this invention provides an Adaptive Impedance Matching (AIM) technique designed to overcome the practical limitations of current techniques, while offering superior performance. AIM is an adaptive feedback technique which attempts to maintain maximum signal gain at the tuned frequency. In one example, resonant tuning of a high Q preselection filter is achieved using a signal metric from a baseband processor. As the received signal level decreases (due to listener tuning, antenna orientation, human body effects, etc.), the baseband processor adaptively retunes the preselection filter to provide maximum signal voltage to the low noise amplifier (LNA). AIM eliminates the need for receiver calibration associated with existing preselection filter tuning techniques, and is independent of the intermediate frequency (IF), since local oscillator (LO) tracking is not performed. For portable AM receivers, a small ferrite loopstick antenna is often the best choice. Although the sensitivity of an AM receiver with a small loopstick antenna is generally not very good, it is relatively easy to construct a varactor-tuned circuit with high Q to increase signal gain. AM reception is especially challenging for a portable receiver. FM broadcast signals are generally transmitted with both vertical and horizontal polarization, making the receiver antenna orientation less critical than for AM, which has only vertical polarization. This makes positioning and orientation of the AM loopstick antenna more crucial than for FM. Furthermore, placement of a loopstick antenna within a receiver makes it more susceptible to EMI generated by the receiver electronics, especially at AM frequencies. Portable and hand-held analog FM radio receivers often use an earbud wire antenna, which may be configured as either a short dipole or monopole. Although one might imagine an earbud wire as a dipole with one leg for each ear, this would yield poor performance due to the limited distance between elements of the antenna (much less than a half wavelength). Another short dipole configuration places the antenna feed and receiver in a small accessory that clips to the listener's lapel. One leg of the dipole would extend up toward the ears, while the other would drape down to the waist where it would connect to the main device (e.g., MP3 player). This dipole configuration is not common and suffers from poor performance because it is shorter than a half wavelength. The more common monopole earbud wire antenna requires a ground plane to replace the lower element of a dipole. Ideally, the ground plane for an FM monopole should be at least one square meter, and a ground plane the size of a metal car body is preferred. However, hand-held portable devices are typically much smaller than a quarter wavelength, which seriously compromises performance. One way to effectively increase the ground plane size is to add a meander spiral to the receiver printed circuit board (PCB). The inductive reactance of the spiral cancels some of the highly capacitive reactance of the small ground plane, thereby improving signal coupling into the receiver. Although this approach has some utility at higher frequencies, it provides little sensitivity improvement at FM (and especially AM) frequencies. Another portable FM antenna option is a small loop located within the receiver. This is an especially attractive choice for portable FM receivers that do not use earbud wires (e.g., a wireless Bluetooth headset). Location within the receiver makes it aesthetically pleasing and easy to use. Receiver size is not important because loop antennas do not require a ground plane. On the other hand, its small size makes a loop a less-efficient signal collector than an earbud wire, and its placement within the device leaves it more susceptible to EMI. It has been shown, however, that human body proximity to a loop actually improves reception sensitivity, whereas the sensitivity of earbud wire antennas is generally degraded. Furthermore, it has been demonstrated that a small loop antenna can achieve a higher Q than an earbud wire, partially offsetting its smaller size. As a result, a loop antenna could be an attractive diversity element in a receiver that also includes an earbud wire antenna. As stated above, a practical technique for matching electrically small antennas is to maximize the signal voltage at the receiver low noise amplifier (LNA) input. This can be done by conjugate matching the antenna and receiver input reactances. The Q of the resulting parallel resonant circuit determines the voltage delivered to the receiver LNA. Resonant circuit Q is largely determined by the LNA parallel input resistance. The higher the input resistance, the higher the Q, and therefore the higher the signal voltage. Of course, resistor noise also increases with receiver input resistance, so the net effect of Q on reception sensitivity is not as pronounced. Consider a small square loop antenna in free space connected to a receiver with a high-impedance input. This configuration can be modeled as the resonant antenna circuit filter shown in The transfer function of this antenna circuit filter is:
Evaluating at resonance, the magnitude of the antenna circuit filter transfer function is:
Since the loop is small, its radiation and loss resistance can be considered negligible. In this case, All antennas have an effective height he which, when multiplied by the electric field strength E, yields the open circuit induced antenna voltage:
The effective height of a loop antenna depends upon the frequency f in Hz, loop area A in square meters, permeability μec, and number of turns N: From
Reception sensitivity is a function of not only the gain of the antenna circuit filter, but also of the LNA, resistor, and ambient noise. For an electrically small loop antenna, the radiation resistance is very low, so the ambient noise can be considered negligible. Furthermore, one can assume that the resistor noise dominates the LNA noise in a well-designed receiver. The antenna circuit filter used to determine the resistor noise contribution in the small loop antenna configuration is shown in The transfer function of the resistor noise antenna circuit filter is:
Again, assuming negligible radiation and loss resistance for the small loop antenna, and evaluating at resonance,
From The open circuit noise voltage of a resistor R is given by the well-known relation:
Reception sensitivity is defined as the electric field strength needed to achieve a desired signal-to-noise ratio at the receiver LNA input. Using equations (2) and (3), the signal-to-noise ratio at the LNA input for a small loop antenna is:
Solving for reception sensitivity E:
For a parallel resonant circuit:
Using this definition to substitute for R in the previous expression for E yields:
Equation (1) indicates that, for a small loop antenna at resonance, the received signal gain is equal to the Q of the antenna circuit filter. However, equation (4) shows that reception sensitivity improves only as the square-root of Q, due to effects of resistor noise. Thus, one would expect that for a received signal level increase at the LNA input of N dB, the net sensitivity increase would be only N/2 dB. Although illustrated for a small loop antenna, this relationship between signal gain and sensitivity applies in general to all antenna types. So the sensitivity of the receiver in dB includes a 10�log(Q) term. Although high Q antenna circuit filters can improve signal gain and reception sensitivity, they must be accurately tuned. The higher the Q, the more demanding are the tuning requirements. Antenna reactance can be variable and unpredictable, depending on listener movement and relative orientation of the antenna to the human body. As a result, impedance matching to the receiver is generally very lossy. To overcome this problem, existing portable receivers often include the antenna in a docking station. This solution is undesirable, however, because the antenna element is not portable and cannot travel with the listener. It is desirable to have an antenna design that overcomes these and other problems, particularly for use with a portable, hand-held receiver for receiving analog and digital radio broadcast signals. Resonant tuning of a high Q circuit can be achieved by controlling the voltage applied to a varactor diode with variable capacitance depending upon this voltage. As the received signal quality degrades (due to listener tuning, antenna impedance changes, human body effects, etc.), the receiver adaptively retunes the circuit with the tuning voltage to provide maximum signal voltage to the LNA. This process, referred to as Adaptive Impedance Matching (AIM), is illustrated in The AIM seeks to maximize antenna gain at the receiver tuned frequency. A feedback control loop is used to accomplish this goal. A simplified, generic functional block diagram of a receiver 10, antenna 12, and antenna circuit filter 14 is shown in The tuned antenna circuit filter is comprised of the inductance L of the loop antenna and the capacitance C of the varactor diodes, along with any other stray capacitance or inductance, including human body effects. A damping resistor Rdamp, in concert with the LNA input resistance, is used to set the Q of the tuned circuit. The receiver is shown to include a low noise amplifier 30 having a high input impedance, an IF or baseband signal filter 32 and other components commonly found in receivers such as a demodulator, detector, etc. as shown in block 34. Tuning the antenna circuit filter to a desired frequency is accomplished by applying a voltage to a varactor diode that provides the appropriate capacitance for the tuned frequency. This tuning control voltage is the feedback signal generated by the AIM algorithm, shown in block 36. The AIM algorithm receives a received signal strength indication (RSSI) estimation 38 from the filtered IF or baseband signal on line 40. The AIM algorithm outputs a control value on line 42, which is converted to an analog control voltage on line 44 by a digital-to-analog converter 46. The analog control voltage is filtered by a filter 48, comprised of resistors 50, 52 and capacitor 54 to produce a filtered control voltage at point 56. A back-to-back varactor diode pair, as shown in Assuming negligible radiation and loss resistance, the simple loop antenna circuit shown in the example of
The resonant frequency fres is defined as the frequency where the transfer function is real. The imaginary portion of the complex transfer function can be set to zero to arrive at the well-known result for fres.
However, the resonant frequency is not necessarily the peak magnitude of the transfer function, but it is generally close to it, especially for high Q circuits. The AIM algorithm attempts to find the peak of the magnitude of the tuned circuit. The magnitude of the transfer function is:
Its peak frequency is found by setting its derivative to zero, then solving for the frequency fpeak.
However, the quantity of interest is the capacitance C required to maximize the magnitude of the gain at the tuned frequency fdes. Solving for capacitance yields:
In this case the magnitude peak of the transfer function is achieved when C is selected at the true resonance frequency, or fdes=fres. This is due to the fact that Q changes with C. Since the AIM algorithm generates a control voltage (CV), that is applied to the varactor, it is useful to express the capacitance of the varactor as a function of the AIM feedback control voltage CV.
The target feedback control voltage to maximize the tuned circuit gain at frequency fres in this example is then:
If all conditions of the circuit are known and constant, as in this example, then it is relatively straightforward to develop a circuit (especially under digital control) to provide the appropriate control voltage CV for each desired tuned frequency fdes, according to the expression above. This technique can be used for antennas with fixed characteristics, while component tolerances can be accommodated with factory calibration. Although variations with temperature can still be a concern, limiting the value of Q (and some performance) may suffice to accommodate parameter variation. This technique is typical for preselection filters of superheterodyne receivers. However, portable antennas can have greatly varying impedances. Human body effects, small ground planes, and varying antenna characteristics due to movement and orientation (e.g., earbud wire), make this technique impractical without some means to adapt to the varying impedance characteristics. The AIM algorithm is included in a feedback control loop which adaptively determines the control voltage feedback signal needed to maximize the signal gain at the desired frequency. Unlike the analytical derivation for the required control voltage CV presented above, there is no practical method to directly compute the appropriate CV for the tuned circuit with unknown or varying impedance parameters in this nonstationary process. Therefore, an indirect heuristic algorithmic approach is taken to dynamically solve for CV. A Received Signal Strength Indication (RSSI) estimation or measurement is used to indicate the signal and noise level in the tuned signal bandwidth of the receiver. This RSSI is used as a proxy for the gain of the tuned circuit. The RSSI can be estimated by computing the (near) instantaneous power of the input signal in a digital signal processor (DSP)-type device. Other techniques for estimating RSSI, such as diode/capacitor detectors used in analog AGC control circuits, are also possible for some receiver implementations. RSSI samples can be computed over discrete time intervals, for example. For the purposes of adjusting a multiplicative gain in this case, it is convenient to compute RSSI(k) in dB as the log of the sum of the energies of a plurality of signal samples r(t) of the received and filtered signal in the interval k, that is:
In the above equations, n is n-th sample of the N signal samples comprising RSSI interval k, he is the effective height of the antenna, and Ha is the transfer function of the antenna circuit. The received signal includes a desired signal s(t), if present, scaled by the channel gain a(t), with additive noise n(t), and the antenna circuit gain comprising the product he(fdes)�|Ha(fdes)| of the effective height of the antenna and the tuned circuit filter, both approximated at their desired center frequencies fdes. The goal of the heuristic AIM algorithm is to solve for the desired CV which maximizes the gain of the tuning circuit at the desired frequency. The solution for CV involves a stochastic derivative expression for the nonstationary process, that is:
The AIM algorithm, in effect, varies the value of CV such that the expected value of this derivative over sufficiently small time-spans (or time averaging) tends toward zero. The antenna tuning parameters experience little variation over the time interval wherein CV is near-stationary. The solution for CV is continually updated to allow it to provide a solution when the tuning parameters are slowly changing. In one example, the algorithm is implemented using discrete RSSI differences, instead of d(RSSI); in addition, d(CV) is replaced with a change in CV by an amount delta, having a �1 polarity, or direction, at each interval. The stochastic derivative is modified to be the solution to a stochastic difference equation, that is:
The AIM algorithm adaptively varies CV, with the goal of maximizing the varying RSSI values, by seeking zero RSSI differences. This feedback loop also accommodates changes in antenna tuning circuit parameters due to antenna movement and human body effects, for example. The feedback control algorithm is an heuristic approximation to solving the problem of changing the control voltage to minimize the ratio of a change in the received signal strength indication to a change in the control voltage. AIM is a peak-maintaining feedback control loop, attempting to maximize the RSSI with the appropriate values of CV. It is the heuristic approach to the solution to the stochastic derivative expression above. Feedback control techniques for tracking maxima (i.e., peaks of RSSI) or minima are inherently more difficult than tracking a parameter that monotonically crosses the target value (or zero), such as a PLL. This is because the peak-finding algorithm, in effect, operates on the derivative of the function to be maximized. The above process converts the peak of the function to a zero crossing function whose derivative is zero at its peak, and monotonically crosses the zero value. The derivative is generally noisier than the original function. The derivative, or difference in this case, also requires dynamic action of the controlled variable to estimate its change with respect to time. This dynamic action generally results in dither of the feedback control signal, resulting in variations (i.e., of RSSI) about its peak value. The peak value of the RSSI may vary due to other effects on the signal and noise that are not due to antenna tuning. The AIM algorithm must also accommodate these conditions. Several assumptions are made about the elements supporting the AIM algorithm to aid in defining its operational characteristics. It is assumed that the tuning circuit resonant peak frequency is unique, so there is only one peak over the varactor control voltage range for a given frequency at a point in time. However, this peak can move both in frequency and in amplitude with movements of the receiver and antenna. The RSSI values may also vary due to fading, automatic gain control (AGC), or other effects. Some algorithmic functions and parameter settings deal with the dynamics of the RSSI. In one example, the AIM algorithm is implemented as a periodic repetitive process, although strict periodicity is not a requirement. For portable FM or AM broadcast receivers, the AIM algorithm can be updated on the order of roughly 10 cycles per second. The sequence within each cycle is as follows:
This AIM cycle is illustrated schematically (not to scale) in More details of an implementation of the heuristic AIM algorithm are presented next. Assume that the receiver (not yet the antenna tuning circuit) is tuned to the desired signal frequency, and RSSI values are periodically computed at each cycle. Also assume that the RSSI values are maximized when the varactor control voltage CVF is near a particular value which causes a resonant peak of the antenna tuning circuit at the desired frequency. However, CV is initialized at some other value, perhaps at the center of its range. Define a variable delta, and a binary value direction (+1 or −1), which are intermediate variables used in the AIM algorithm. The AIM algorithm outputs a new control voltage CV at each cycle. The filtering of CV to produce CVF is used to avoid the introduction of phase and amplitude steps into the desired signal. The filtering should smooth these steps so that it minimizes the impact on demodulation performance, and it is especially important for coherent demodulation. A 2-pole filter is preferred (over a 1-pole filter) to ensure continuous slope smoothing immediately after the step. A simplified AIM algorithm is described first, then additional complexity is added to deal with the special conditions. A single AIM simple cycle can be described as follows:
The AIM simple algorithm cycle example simply changes the direction of the control voltage delta (also referred to as an increment) when it detects that the signal level (RSSI) is decreasing. Ideally, in the absence of noise or other effects, CV and the corresponding resonance peak of the antenna circuit will move in the direction that increases successive RSSI values until the tuning peak frequency passes the desired frequency. After the resonance peak passes the desired frequency, the RSSI value will decrease, changing the direction of CV and the resonance peak. Then CV will continue to dither, or vary from side to side, about the peak. Notice that the CV must change every AIM cycle (by an increment or step value delta); otherwise, there would be no useful information on the slope of the RSSI. The size of the increment or delta determines the span of dithering around the resonant peak. In a real system with noise and other factors that dynamically affect RSSI, the dithering span tends to be larger. Low Q antenna circuits will result in a greater dither span than high Q circuits. Also the dithering may cause CV to reach the extreme limiting values and get stuck, because RSSI does not change. So some modifications to the AIM algorithm are needed for a practical implementation. The variable CV, previously considered as the analog control voltage applied to the varactor diodes, being the same as the AIM control voltage will now be considered an integer, since it is used to set the voltage output of a Digital-to-Analog-Converter (DAC). We will now distinguish this variable label CV from the analog filtered control voltage by defining the variable CVF. CVF is the actual voltage applied to the varactor diodes, a filtered version of CV. For this example, assume an 8-bit DAC, where 0≦CV≦255. However, there may be some implementations where the range of CV results in resonant frequencies that are too far out of band. To avoid potential undesirable effects when the tuning range is much larger than the FM or AM band, some other more restrictive limits can be placed on CV, i.e., CVmin≦CV≦CVmax. The following modified AIM algorithm shown below addresses these concerns.
A flowchart of the above algorithm is shown in Consider the fixed-point resolution of RSSI. For example, RSSI can be computed on a log scale having 0.25 dB resolution. If successive signal level changes are small compared to the RSSI resolution, then the RSSI could remain constant. This could be due to a low Q circuit over that frequency range. Since there is not sufficient resolution for AIM to observe the RSSI decrease over this sequence, then the same direction will be maintained until RSSI decreases. The �if� condition in the AIM algorithm shown in block 66 of
In this example, the size of the increment or delta is adaptive to better accommodate the unknown Q, to speed-up acquisition, and to track a varying peak frequency due to changing parameters. The maximum value of delta is limited to ⅛ of the total range for this example, and this maximum value is also applied as the initial value. This limit prevents overly coarse CV resolution, and its initial value aids fast acquisition. The minimum value of delta is set to one, the finest achievable DAC resolution. The value of delta is adapted to accommodate an arbitrary Q of the tuned circuit. The adaptive delta also offers fast tracking when needed for acquisition, changing parameters, or low Q. The value of delta is decreased when RSSI decreases, and the direction is reversed. This is because a decrease in RSSI is indicative of tuning away from the RSSI peak. The dither span and delta should be reduced after reversing direction since the dither about the peak should eventually be minimized for best performance, keeping the resonance peak close to the tuned frequency. The value of delta is increased if the direction is not changed, which has the effect of decreasing the number of steps while dithering back and forth across the peak. This increase is useful in improving the ability to track parameter changes, and adapt to low Q tuning. The delta affects the average number of AIM cycles as it dithers, as this can affect the response time to changes in tuning parameters, e.g., caused by movement. Using the simple adaptive rules for delta, it approaches a value such that the dither requires several AIM cycles to traverse the peak in each direction, regardless of Q, and in the absence of RSSI noise. A �dither cycle� is defined to be a CV traversal in both directions. This dither cycle starts with an AIM cycle enforcing a direction change, it traverses the dither span for another direction change, and then ends with the AIM cycle immediately prior to the next AIM direction change cycle. Also define a delta increase factor U (e.g., U= 9/8 in the AIM algorithm example above), and a delta decrease factor D (e.g., D=� in the AIM algorithm example above). Both U and D affect the AIM response time to parameter changes, as well as dither sensitivity to noise. The U and D factors are adaptively controlled to ensure stability and a balance between response time and tracking accuracy. Consider the minimum number of AIM cycles required in a dither cycle. A steady-state dither of 2 AIM cycles cannot be sustained. A dither cycle was previously defined to require exactly 2 direction-changing AIM cycles, so there would be no other AIM cycles. A direction reversal would be required at every AIM cycle, also requiring a persistent decrease in RSSI at every AIM cycle. This could happen only if the signal and noise power continue to decrease more than the RSSI resolution at each AIM cycle, and this is not steady state. However, this is a desirable response for a monotonically decreasing signal fade, since the CV remains in the same range as before the signal fade. If the signal is monotonically increasing faster than the decrease in gain away from the tuning peak, as it recovers from a fade, for example, then the CV will continue to advance in the same direction. Although the signal gain is actually decreasing in this case, the RSSI is not decreasing, and the signal quality should be improving. Once the signal stops increasing, the CV will quickly find its way to the tuning peak. It can be shown that a dither cycle can be sustained with 3 AIM cycles, but it is unstable since delta decreases to its lower limit. In one example, a dither cycle has been defined to require exactly 2 direction-changing AIM cycles, so the third AIM cycle must not change direction. Consider a perpetual deterministic dither cycle consisting of 3 AIM cycles (AIM1, AIM2 and AIM3), with corresponding RSSI1<RSSI3<RSSI2. The AIM1 cycle will decrease delta by factor D, because RSSI1<RSSI3. The AIM2 cycle will increase delta by factor U, because RSSI2>RSSI1. The AIM3 cycle will decrease delta by factor D, because RSSI3<RSSI2. Since this dither cycle consists of 2 AIM cycles decreasing delta by factor D, and a single AIM cycle increasing delta by factor U, then this deterministic dither cycle can be sustained if D2�U=1. If D2�U<1, then delta will continue to decrease at each dither cycle until it reaches its lower limit of one, and the dither cycle is broken. Conversely, if D2�U>1, then delta will continue to increase at each dither cycle until it reaches it maximum limit (e.g., CVmax/8) and the dither cycle is broken. However, whenever a dither cycle requires 4 or more AIM cycles due to changing parameters or noise, for example, the value of delta is increased over the previous dither cycle. Even if D�U=1, the occasional extra AIM cycles will eventually bring delta to its maximum limit, so it is too unstable to consider. If the RSSI values are completely random due to large RSSI noise, and there is a 0.5 chance of changing directions for any single AIM cycle, then the number of AIM cycles that do not change direction is the same as the number that do change directions (i.e., 2 by definition). Then there are 4 AIM cycles per dither cycle, on average, in this random case. If D�U<1, then delta will continue to decrease at each dither cycle until it reaches its lower limit of one. Conversely, if D�U<1, then delta will continue to increase at each dither cycle until it reaches its maximum limit (e.g., CVmax/8). So it is important that D�U<1, especially considering that RSSI quantization tends to suppress direction changes and increases the rate of U. The average number C of AIM cycles per dither cycle can be computed for an equilibrium condition where delta is maintained between its minimum and maximum values. Since a dither cycle requires exactly 2 direction-changing AIM cycles, then the remaining number of AIM cycles with no direction change must be C−2. The average value of delta at equilibrium is maintained if UN−2�D2=1. Then the average number of AIM cycles per dither cycle is:
For this example, where U= 9/8 and D=�, C=6.885. Simulation and product testing have indicated that these values of U and D are appropriate to balance adaptation time (C) and noise immunity. When delta reaches its minimum (e.g., one in this case), there is a possibility that it gets stuck in a dither limit cycle consisting of 4 AIM cycles, assuming D�U<1. This could be desirable, especially for high Q tuning. When delta reaches its maximum, even temporarily, there is a possibility that it gets stuck in a dither limit cycle consisting of 6 AIM cycles. This is because the D factor of the first AIM cycle following a maxed-out delta value limits the product of the second pair of U factors by the first D factor. So the second U factor is reduced due to the limit on delta. The sequence is as follows: RSSI1<RSSI0 resulting in the first D in the dither cycle RSSI2>RSSI1 resulting in U RSSI3>RSSI2 resulting in Ux, limited such that Ux*U=1/D. The second half of the dither cycle is similar: RSSI4<RSSI3 resulting in the second D in the dither cycle RSSI5>RSSI4 resulting in U RSSI6>RSSI5 resulting in Ux, limited such that Ux*U=1/D. Therefore, to prevent this undesirable limit cycle case, impose the condition U2�D<1. The values used in this example (U= 9/8, D=�) satisfy the inequality (U2�D=243/256). The value of delta should have sufficient precision to prevent truncation or limiting after multiplication with the increase or decrease factors. This effect is similar to the finite-precision effects of fixed-point infinite impulse response (IIR) filters. In this example, delta should have a precision of ⅛, or finer, to avoid finite-precision effects. Results of a simulation of the AIM algorithm are shown in Care must be taken to control AIM interaction with an automatic gain control (AGC). Since AIM uses RSSI as a metric, there is potential interaction with an AGC, which also uses some kind of RSSI metric. These interactions should be examined for any receiver design, and the solution for both may be somewhat synergistic. In one example, the AIM computation cycle is disabled when the receiver automatic gain control (AGC) adjusts its gain. This prevents unwanted interaction between AGC and AIM algorithms. Ideally the AGC control voltage (or AGC information) is used for RSSI estimation, so AGC should not have a significant effect on AIM performance. This AGC control information alone may be sufficient for RSSI, although further estimation of the signal level after AGC adjustment may also be useful if the AGC control is not �tight�. Some receivers may employ autonomous continuous AGC ahead of the RSSI estimation, and the AGC information may not be available for RSSI estimation. In this case, the update rate of the AIM cycles should be shorter than the AGC time constant. This should prevent or minimize the effects of the AGC that would tend to cancel the gain changes due to AIM tuning. Some receivers use step-controlled AGC, where a DAC-like attenuator is under digital control. If accurate information on this step AGC control is available for RSSI estimation, then this AGC should have minimal effect on AIM performance, assuming RSSI is compensated for AGC gain. Alternatively, it may be simpler to avoid AGC effects by temporarily disabling AIM whenever an AGC gain change is imposed. It is important to consider that when the AGC gain is updated, instead of AIM, then this actually consumes 2 AIM cycles instead of one because the differential RSSI is the metric. The flowchart of If there is no information available to the receiver regarding the preferred CV value for a tuned frequency, then CV should be initialized to the center of the band. When tuning to a new frequency channel, instead of using a default center control voltage value, the initial control voltage value is determined from previously filtered control voltage values when this frequency was previously tuned. If the receiver uses presets to store favorite stations, for example, then the initial CV for any preset frequency could be stored with the preset. The stored preset CV could be the last CV used for that frequency. When tuning to a new frequency channel, instead of using a default center control voltage value, the initial control voltage value can be determined from a known a priori relationship between tuned frequency and control voltage. A known a priori relationship between tuned frequency and control voltage can be refined and updated based on the latest filtered control voltage information for each tuned frequency. Preferably, a filtered version of CV would be more accurate. An example of this filtered CV is CVavg, as computed in block 92 of the flowchart of AIM can also be used more as a preselector filter for receivers where the antenna characteristic is constant: some tabletop receivers with loop antennas, for example. If the relationship between tuned frequency and CV is known a priori, then the initial CV value can be computed for each frequency. Furthermore, AIM can refine the accuracy after tuning to that frequency. The receiver could also use this CV refinement to update the CV versus frequency relationship. This feature replaces the need for a preselector varactor voltage that is derived from the LO voltage for superheterodyne receivers. The Adaptive Impedance Matching (AIM) technique described herein provides a means for improving the signal gain of electrically small antennas, and can be implemented in a digital radio receiver. Although AIM is designed to enhance the reception of AM and FM broadcast signals, including HD Radio signals, the technology is not limited to AM or FM broadcast receivers. While the invention has been described in terms of several examples, it will be apparent to those skilled in the art that various changes can be made to the disclosed examples without departing from the scope of the invention as defined by the following claims. The implementations described above and other implementations are within the scope of the claims. Patent Citations
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4.5 Brilliant Suz1584 | 03/09/2007 | See all Suz1584's reviews (7) I love this game - I am so adicted - the story line is a bit cheesy but you take it all in good humor and you'll enjoy. I lvoe this game so much, good fun and not too gruesome as I first thought it was going to be - Must Buy
4.5 The doctor is in ChooseYourFate | 01/09/2007 | See all ChooseYourFate's reviews (49) Right ill start off by saying that i loved the ds version of trauma center and although the stroyline is very similar (well i think it might be nearly identical) dont let that put you off.The game is fantastic and the input of the wii's controls are amazing and well used, although the nunchuk for me was annoying switching between all the instruments (i think i have a weak thumb) its still a fantastic game for young and old adults.A MUST HAVE
4.5 amazing Boroboy1 | 01/09/2007 | See all Boroboy1's reviews (18) actually feels like ur operating on someone a great game.
4.5 Well worth a purchase! barryslee | 29/08/2007 | See all barryslee's reviews (1) Bought this game on a friends recommendation of the ds game, loved it from the start, the feeling of interaction with the wiimote makes you feel in the game and the different surgeries and inreasing difficulty make for a game that keeps you hooked right to the end
4.5 Dont waste your money on Trauma Centre Wii Positivepresents | 27/08/2007 | See all Positivepresents's reviews (2) Not worth the money, very boring game indeed. No gameplay long wonded storyline and far too easy.
4.5 Good testing game! PaulyStyle | 25/08/2007 | See all PaulyStyle's reviews (4) This is a testing and sometimes difficult game - saw another review saying that it doesn't work on the Wii, simply not the case, like any software you just have to know how it works and adapt to it!Playing it on hard mode is even more interesting and I've not found a game that makes me feel so involved in a while, mainly due to the Wiimote and the feeling of real interaction rather than just a move of a thumb like with most other consols!Buy this game but not for the sunday gamer!
4.5 Trauma Center TomTom21 | 25/08/2007 | See all TomTom21's reviews (6) I thought that when i first bought it, i would be buying a bit of an odd game that was worth perhaps selling within a week, but i was surprised to find that the game is as most say "unique", i am really pleased with the game, and the fact that the originality is very well incorporated with the wii. The only let down in my view of the game is the fact that the graphics on the video are a little bit basic for the game. overall a very good game 7/10
4.5 Docter To E.R Please Madr0x | 21/08/2007 | See all Madr0x's reviews (28) Maybe This Game Worked On The Ds But Its Really Really Hard On The Wii. I Loved To Ds Version And That Was The Reason I Brought This Version But Im Struggling To Play It. Greaphics Are Good But Gameplay Is Lacking. I Seem To Forget How To Do Certain Operations Most Of The Time. Great Thought Tho And Im Sure Alot Of People Are Going To Enjoy It.
4.5 truma center is great taz8892 | 18/08/2007 | See all taz8892's reviews (2) this game is the best game i have played yet on the wii although the controles could be better and their is far to much talking once you work out where all your tools are you can get qucikthis is not 1 for the kids as some bad language but still a great game
4.5 A Unique Game, Stat! HiKickRy | 17/08/2007 | See all HiKickRy's reviews (11) This game is really unique, as you have probably heard everywhere.I never played the DS one so didnt know the story or characters so i didnt mind reading through the text to move the plot and characters along.The operations vary in style and difficulty; the game has you defusing a bomb with your surgical tools at one stage, all are do-able but some may take a few turns and you never feel like you dont' want to give them another try anyway.I just havent played anything like it before and it something you will only ever find on the Wii, you really feel in control; it's weird how natural it feels gripping something with the forceps with the 2 trigger buttons on the remote and nunchuck.It's unique and fun, recommended.

subset: commoncrawl


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After nearly two months at sea, an important part of the port city is coming home today.
The US Coast Guard cutter Diligence left in early August to help patrol the windward pass to stop illegal immigration. The crew stopped dozens of Haitian migrants from coming into the US.
During their time at sea the Diligence crew encountered hurricanes Fay, Gustav, Hanna and Ike. The crew also went to the Bahamas to help in recovery efforts from Hurricane Ike.
The Diligence will dock around noon today.


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Results 1 to 15 of 20
Thread: May/June '10 SF BOTM Nominations
April 4th, 2010, 09:30 PM #1
May/June '10 SF BOTM Nominations
Let's see if we can get this thing going again. Time for some nominations for a May/June BOTM. If this goes well, I'll go back into monthly nominations for a SF book.
April 5th, 2010, 03:56 PM #2
Seeds of the Earth (Book 1 Humanity's Fire) - Michael Cobley
Released in 2009, I have never read any of his books before and its a start of a new series. Plus its available at my local libraries :-)
Hope we can get this started up again. I am quite excited about it.Last edited by mrpolley; April 5th, 2010 at 04:04 PM.
April 5th, 2010, 07:51 PM #3
Course of Empire by Eric Flint and K. D. Wentworth.
Flint's books seem to have good reviews and I've been wanting to try him out.
This one also has a sequel called Crucible of Empire.
I agree with MrPolley. Let's get this rolling.
There are no science fiction book clubs in Tulsa (that I know of...), so might as well start here!
April 6th, 2010, 09:37 AM #4
I nominate Blindsight by Peter Watts.
Great book and plus its available for free on his website in several e-formats
April 6th, 2010, 12:06 PM #5
April 6th, 2010, 10:57 PM #6
I also go for Blindsight because I've been meaning to read it. I heard him read a short story of his and it was wickedly good. If you do it for May/June, I'll try. I love the idea of book clubs; I just don't manage to keep up with them.
April 7th, 2010, 10:45 AM #7
yes blindsight looks pretty good. Ok I guess I can second that too. Plus I can get it from my local library.
EDIT: Hmmm. Blindsight has been read before in this book club back in June 2007. Don't know if you want to read it again Erfael lol. But I am willing toLast edited by mrpolley; April 7th, 2010 at 10:51 AM.
April 7th, 2010, 10:53 AM #8
How does this work, do we take nominations till the end of the month and then vote on it?
April 9th, 2010, 09:47 AM #9
read this thread, it should give you an idea, and it should be the same even though this time round we have 2 months to read and complete.
April 9th, 2010, 01:33 PM #10
April 11th, 2010, 01:11 PM #11
There seems to be a lot of interest in Blindsight. I think, as the personnel have totally changed, that it would be fine if we picked it again. That's the only thing that's gotten seconds so far. I'll leave this up another day or two to see what else happens then see if we need a vote or if we just go ahead with the Watts.
April 11th, 2010, 02:34 PM #12
Sounds good.
I made an epub book from the files the author offers on his website.
If anybody wants a copy, shoot me a pm with an email address and I'll send it to you.
I believe this is ok, if I read the Creative Commons thing correctly:
April 12th, 2010, 03:57 PM #13
April 13th, 2010, 03:13 AM #14
- Join Date
- Feb 2008
- Posts
- 188
Haven't read Blindsight, but it looks good and is available at my local library. So I'm all for it.
April 29th, 2010, 06:25 AM #15
Nice to see some new blood. Will see about tracking down blindsight as I missed it the first time round (even if amazon says 1-3 weeks)


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Mar 14, 2010, 09:57 PM | ||
Here's a link to my blog. I have entered in a couple of things that I thought people might be interested in as well as links to my friends. It's more community friendly on RCGroups. There is no worries on security either. If you don't want to be friends with someone you can always ignore... not an obligation. http://www.rcgroups.com/forums/member.php?u=149102 |
Mar 14, 2010, 10:07 PM | ||||
It's a neat sight. Like any other, it does take some getting used to. There are pros and cons to preference but I've found things run very smoothly on RCGroups. It's very electric friendly Hey Rick, Do you have the SR on a DX6 or DX7? A friend, the one in the video flinging dirt, said there was not enough throws on the included transmitter to hold in inverted.
Mar 14, 2010, 10:21 PM | ||
Joined Mar 2010
3,435 Posts
LMAO...I got a beagle and a lab, we hook 'em to a chain on the back porch out the sliding glass doors...what a nightmare this year. All winter, and it too rotten to go out and clean it up as yet. I take the Ford 861 tractor with an 8ft grading blade...I drag it across the yard...gone after about 3 good rains. Right now, it's just too muddy to do that...it'll be there next week too...I aint worried. |
Mar 14, 2010, 10:58 PM | |||
What is happening BOBs?
I see there is talk of Blade SR in here. I absolutely love mine. I am flying mine on the DX7 with +11 -10 pitch and 7.5° cyclic. I removed all the flybar weights and have installed a 10T Blade 400 pinion which replaced the SRs 9T. It is capable of flips, rolls, loops, funnels etc but that is not its strong point. Where I find it to really shine is in FFF. Just like my CPP2, it is just a blast to carve with and I can FFF aileron better than any other heli I have. Here is a vid of mine in action. Feel free to check out my other BSR vids.
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The Finca is in a very peaceful setting, approximately 2 km from nearest houses and 8km from nearest shop. To make the most of the area a car is vital and if you get suggestions from James the owner there are very reasonable deals available from the airport. The Finca is staffed by a delightful local staff who despite their... More
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We stayed three nights at Limetree Farm to have a day's bird watching and another to climb Blue Mountain Peak. Our expectations were greatly exceeded. Our hosts were helpful and friendly, the facilities of the first order and the situation spectacular.
Our bird guide, Lyndon, for the day at Hardwar Gap was knowledgeable, and with the ability to seek out birds and to help us see them. This was an enjoyable and rewarding experience.
The following morning our guide, Rodger, had us away on the road to Blue Mountain early, and we climbed Blue Mountain Peak in good order. Another rewarding day, spent with an excellent guide.
Suzy's meals at Limetree were the best we enjoyed throughout our extended stay in Jamaica.
If hills and birding are your passions, this is a good place to stay and deserves your serious consideration.
- Official Description (provided by the hotel):
- Lime Tree Farm is the perfect Jamaican holiday retreat for the independent traveller. Our beautiful ecological holiday cottages are set in a working coffee plantation that's nestled high in the magnificent Blue Mountains of unspoilt Jamaica. Combined with our first class, locally sourced organic cuisine, our Jamaican holiday cottages are the perfect luxury to come back to after exploring Jamaica's Blue Mountains with its rich flora, fauna and wildlife, whether hiking or by 4x4 jeep. ... more less
- Also Known As:
- Lime Tree Farm Hotel Blue Mountains National Park
- Lime Tree Farm Jamaica/Blue Mountains National Park


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i had a headache and asked the kid next to me for aspirin. he gave me esctacy instead. gotta love college.
Last night I ate the rest of the salsa with my hands. And i DONT have a hangover? Glorious.
she was dressed as a doctor claiming that after she was done i would have a "permaboner"
You were so drunk that some guy dressed as Harry Potter pointed his wand at you and screamed "Accio SHITSHOW"
I am going to be the most sexually active ladybug that he has ever seen
I should have known there'd be issues when he included "beautiful soul" in our playlist
I love seeing the creepers that friend request me outside of facebook. its like seeing a unicorn in the middle of campus.
im having a hard time not telling ppl about ur bathroom story
Just burped. Tasted like beer and cherios...Beerios. This is gonna be quite a day.
i cant finish this easy-mac because i need it for a chaser.
I convinced her last night that my actual nickname was "No Condom John"
remind me not buy ky at kmart ever again. Had to get a manager to open the locked case. then he stood there and watched me look through the selection
I hate that ur telling me this.
but really, i care about skinny girls as much as michael vick cares about rotweilers
he kind of looks like leonardo dicaprio...in whats eating gilbert grape
He told me he had herpes after I put his hotdog in my mouth
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The Atlanta Apparel is home to wide range of clothing and includes coats, outwears and furs for men and women, bath accessories and fixtures, bridal wear, bridal accessories, bridal fashion, bridal handbags, bridal intimate apparel, bridal jewelry, garment bags and packaging, footwear and accessories for men and much more to add to the list. The event displays the largest single product collection of Atlanta. It is also a great platform for both the shoppers and sellers and creates huge business opportunities.
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Founder/owner at Dove Sports
Hartwell, United States
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Atlanta Apparel is attended by a large number of well targeted professional exhibitors, displaying a wide array of products and accessories. More than 1000 temporary exhibits and 550 permanent showrooms are set up along with 8000 different product lines and categories. Some of the prime exhibited items at the event are contemporary apparels for men, women, children, clothing, shoes, fashion accessories, jewelry, fashion products, trendy designer garments along with innovative juvenile products for children. Several renowned companies also take part in the show to exhibit their products in front of the world and generate desired number of sales leads to augment their annual revenue


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Ah, 'tis the season! Treats abound everywhere. Food is the hallmark of celebrating the holidays, and it seems to be everywhere! Even this supermom has to stop and admire fancy Christmas cookies, ponder a cup of peppermint hot chocolate, and seriously consider my own Cinnabon cinnamon roll with an extra side of dipping sauce! What makes these treats even more irrestistable is that so many are offered out as free samples to lure you in for more. Alas, my dear, even these small bites come with their fair share of calories, sugar, and fat...sorry! Best to stay away, lest those free munchies at the head of every aisle at Costco come back to bite you later. Bah, humbug, you say? What's the fun in not splurging...it's the holidays after all, right?
If you're like me, I've worked too hard all year to throw it all away, by throwing the floodgates wide open. So, I pick and choose my battles, and it's an easy choice...eat my weight in holiday food samples or save myself for the good stuff. I give myself permission to enjoy a meal of whatever I want on Thanksgiving and Christmas, including the day or so of leftovers that follow, and give my calorie counting a rest. Weightloss experts, tips, and shows be damned, I will not forgo a second of enjoying these meals. So, knowing I will happily soak my turkey, potatoes, and stuffing in a puddle of gravy, I have made the trade-off with indulging in the endless parade of nibbles lurking around every storefront or aisle I pass.
So, for the sake of your dress size, consider an eating strategy that will allow you to get in the spirit of the holidays, while guaranteeing you'll still fit into your fave pair of jeans come January!
What will you do this weekend? Get out and enjoy the weather or stay in for a leisurely weekend?
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Save [1] Print [2] Crunchburgers! Ingredients 1½ pounds ground chuck (80 percent lean) or ground turkey (90 percent lean) Kosher salt and freshly ground black pepper 1½ tablespoons canola oil 8 slices American cheese, each ¼ inch thick 4 potato hamburger buns, split; toasted if desired 4 slices beefsteak tomato 4 leaves romaine lettuce 4 slices red onion Horseradish Mustard Mayonnaise 4 handfuls of potato chips Instructions 1. Divide the meat into 4 equal portions (about 6 ounces each). Form each portion loosely into a ¾-inch-thick burger and make a deep depression in the center with your thumb. Season both sides of each burger with salt and pepper. 2. Cook the burgers, using the oil and topping each one with 2 slices of cheese and a basting cover during the last minute of cooking. 3. Place the burgers on the bun bottoms and, if desired, top with tomato, lettuce, onion, and a dollop of horseradish mustard mayonnaise. Pile on the potato chips, top with the bun tops, and serve immediately. 3.2.2925
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