ll change the antenna matching, particularly with internal and/or electrically undersized antennas. A gloved hand will have a different but similar effect. Mismatches also happen as phones move from band to band and from one end to the other end of a band. TX matching is done by measuring the TX signal at the antenna. In practice, the antenna impedance match (VSWR) can be anything between 3.1 and 5.1 (and can approach 10 to 1). This reduces to between 1.1 and 1.5 to 1 when optimally matched. Adaptive matching of the TX path is claimed to realise a 25% reduction in DC power drain in conditions where a severe mismatch has occurred and can be corrected. However, in a duplex spaced band matching the antenna on the TX path to 50 ohms could produce a significant mismatch. Ideally therefore, the RX path needs to be separately matched (noise matched rather than power matched). This is dependent on having a low-noise oscillator in the handset such that it can be assumed that any noise measured is from the front end of the phone rather than the oscillator. Matching can then be adjusted dynamically. Note that low phase noise is also needed to avoid reciprocal mixing to avoid desensitisation. Adaptive matching is by present indications one of the more promising new techniques for use in cellular phones. The technique is essentially agnostic to the duplexing method used. It does, however, offer the promise of being able to support wider operational band- widths though this in turn depends on the tuning range of the matching circuitry, the loss involved in achieving the tuning range and the bandwidth over which the tuning works effectively. Note that most of these devices and system solutions depend on a mix of digital and analogue functions. A strict definition of tunability would imply an analogue function, whereas many present device solutions move in discrete steps - eighty switched capacitors on a single die being one example. Of course if the switch steps are of sufficiently fine resolution the end result can be very muc