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Showing posts from January, 2016

Tuning the receiver front-end of a Kenwood TKR-750 repeater

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Tuning the receiver front-end of a Kenwood TKR-750 repeater Introduction I bought a second-hand Kenwood TKR-750-1 VHF repeater. However it was not clear what band the receiver was tuned to. The actual receiver and transmit frequencies can be programmed with a computer. However the the receiver band width is tuned with a spectrum analyser and tracking generator.

This post describes how to re-tune the receiver front end.

The band pass filters for a 2m repeater RX are quite critical as they are the only selectivity. With a 600 kHz spacing, the cavity filters are usually just isolating the TX and RX when sharing the same antenna, but providing no bandpass to strong nearby signals.

Starting point and instrumentation I have an old HP8591A spectrum analyser and tracking generator, circa the 1990s, but still a capable instrument. The basic procedure is to connect the tracking generator output to the RX antenna input and the spectrum analyser input to a test point after the RX bandpass filter…