a device consisting of 2 back-to-back diodes providing protection for the receiver's front end. The output of the preamplifier is sent to a helical resonator filter. The output of the filtered and amplified 70 cm path is passed through and coupled into the receive mixer. For 70 cm receive, PIN diode bias is provided to the PA unit, through the MAIN unit and then through an RF-decoupler network, a parallel-output shift register. A 2m signal goes to a relay and then the signals are diplexed, with 2m and < going to a lo-pass filter. The signal gets diplexed again using a hi-pass filter, separating out the 2 m signal from the HF-6 meter signal path. The rx signal passes through the VHF directional coupler/power detector (not used in rx) to a lo-pass filter and then passes by 2 PIN diodes (both HSU277). These diodes and related components form T/R isolation switches that operate similar to that of the 70 cm front end. Rx signal passes through the half which is not used for 70 cm and then to the RX RF output and is then passes to the MAIN unit. Here the signal enters and then passes through a transformer, along with a varactor and related components and forms an electrically-tuned filter/matching network, the 2 meter preamplifier. The output of the preamplifier goes through 2 electronically tuned transistors. Finally, the output goes through to get to the rx mixer. For 2 m rx, the PIN diode bias is provided by the PA unit to 2 m preamplifier. Aircraft band Rx path (108-154 MHz) is the same as that of the 2 m path on the PA unit. On the MAIN unit, it goes through the same part as the 2 m signal, but it then goes through the diode portion that was not used for 2 m into an electronically tuned bandpass filter. The output passes through the rx mixer. The PIN diode bias is provided by the PA unit and flows through the primary transistor. On the output, current is provided and goes through the secondary transistor. Both current paths are completed using the aircraft band rx preamplifier. WFM broadcast band rx path (76-108 MHz) is identical to the 2 m path on the PA unit. On the MAIN unit it passes through the same portion as the 2 m signal, then through a HSC277 diode. This signal then