Re: Interference on a 6 meter repeater You are living one of my past nightmares... Let me give you the probable fix first.
If you have them, try a number of attenuator pads in series with the Yaesu Radio. First might be a 10 dB pad and back the values down while testing for grunge. I ended up using a 3 dB pad in series with the Yaesu Radio... the problem generator radio still worked just fine in the intended operation and the 3dB pad fixed the problem. Of course the pad will have to take the attenuated transmit power value. Yes I tried cavities and shook my head when they didn't work (even multiple cavities and really high insertion loss settings) regardless of configurations. The front end of some Yaesu Radios can be a real serious problem maker... been there, done that, coffee mug and tee shirt. You can tell the Yaesu Owner their radio is probably causing other problems besides your issue and they should deal with it as best possible. My fix was the pad option short of replacing the radio. Try the high power pad... and hope the 3dB value is enough to knock the problem out of the ball park. Let us know if it works for you. cheers, s. > Joe <[EMAIL PROTECTED]> wrote: > > I've been working on an interference problem on a 6 meter repeater and > would like to pass it by the "brain trust" for some input. > > The repeater is on 53.85Mhz with the input on 52.85Mhz. When the > repeater is keyed up, NOAA weather radio comes through the repeater > output loud and clear. (Decode PL turned off) I identified the problem > as intermodulation in a Yaesu VX-2500V transceiver at the site used for > telemetery on a simplex frequency of 173.3375Mhz. The mix is: > > 4(53.85)-162.55=52.85 (repeater input) > > The VHF transceiver frequency is not involved in the mix, but the PA > stage of the Yaesu is where the mix is being created. I proved this by > disconnecting the coax to the Yaesu and the IM goes away. Also, when > the Yaesu keys up on 173.3375, the interference goes away on the > repeater. The IM is only being caused when the Yaesu transceiver is in > the receive mode. No cavity is on the Yaesu, it goes directly to the > antenna. > > The site is on a water tank, so there is only about 10 feet of > horizontal separation between the telemetry antenna and the 6 meter > repeater antenna. The NOAA station is running 500 watts 1.6 mile away, > line of site. I added a VHF cavity tuned to 173.3375 to the Yaesu > telemetry radio, but it did not fix the problem. (The can had about > 25dB rejection at 162.55Mhz and about 40dB rejection at 53.85Mhz.) > Prior testing showed that reducing the 6 meter repeater output from 25 > watts to 2 watts solved the problem. > > My next thought is to put a highpass filter and the VHF cavity in series > with the telemetry radio antenna. I am thinking of using a 6/2 meter > diplexer, terminate the 6 meter port with 50 ohms, and connect the > telemetry radio to the 2 meter port. The diplexer should give good > rejection to the 6 meter signal going into the telemetry radio (along > with the additional isolation of the VHF cavity) and the VHF cavity > would give rejection of the NOAA radio signal. If this works, I will > contact TX/RX and see what they can provide to make the installation > professional. We are guests at the site and need to provide something > professional to the water company. > > Any ideas? We already thought of changing frequency on the 6 meter > repeater, but that would be difficult to coordinate. > > 73, Joe, K1ike >
