![]() ![]() The solution found at each site was to add a bandpass filter on the OUTPUT of the 220 repeater. Luckily, this harmonic lands in the 440 ham band, so the only people we are interfering with is ourselves. It also makes a 2nd harmonic that is only 50dB below the primary signal. It also made the public safety amp not work properly. ![]() A perfectly readable signal on the VHF repeaters would turn into total noise. The symptom was any time the 220 repeater keyed, the 146MHz repeater and fire dept repeater would lose about 12dB of sensitivity, the 440MHz about 2dB, and the input level on the bi-directional amp jumped by 8dB. There were also other users on a neighboring site that I did not do testing with. For an example, one site had a 146MHz VHF repeater, 150MHz fire dept repeater, 440 MHz repeater, and an 8MHz wide Class B Public Safety bi-directional amplifier at 770 MHz. The amount of drop is related to the orientation of the 220 transmitting antenna to the receiver antenna, the resonance of the TX antenna on those frequencies, and the type of duplexer used on the 220 repeater. Basically, any time the repeater keyed (high or low power), it would cause the sensitivity of anything receiving at the site to drop. I know there are a not a lot of solutions for 220 repeaters for ham use, but I have run into 3 of these units in the local area that all had very high wideband TX noise.
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