FM & C4FM/WIRES-X Users: Performance Improvements on 146.88 🥳

[RATS Technical Committee]

An FM broadcast notch filter was installed on the receive side of the 146.88 repeater Saturday morning.  This has significantly improved the performance of the repeater's receiver.  The repeater still experiences a small amount of de-sense when operating at full power (50 watts).  Additional filtering and/or a cavity duplexer tune-up may be needed.  Transmitter power is set at 50 watts.  Performance observations and feedback are requested by our Technical Committee, tech...@rats.net.

Might this simple $22 part be the solution to years of increasing noise in the repeater's receiver?  Time will tell if this is "the" fix, but it sure is helping.  The filter attenuates signals in the FM broadcast band (88-108 MHz) by about 60-70 dB.  There are several powerful FM broadcast transmitters co-located at our repeater site and on other nearby towers.  The high RF generated by those transmitters was making it past our 6-cavity duplexer, de-sensitizing the repeater.  The filter prevents those unwanted signals from overpowering the receiver.  The amount of de-sense was influenced considerably by the repeater's transmitter power.  Over the past couple of years, power had been reduced to 20 watts, and then to 5 to combat the noise.  This de-sense has been nearly eliminated and the repeater is back to full output power.

The 146.88 repeater carries analog FM and digital C4FM traffic, and it's connected to the global WIRES-X network.  Digital traffic is primary on this repeater;  analog users must yield to C4FM and WIRES-X activity.

Take it for a spin and let us know how it goes!

[50W coverage estimation]