First of all you do not have enough isolation between antennas with only two wavelenghts horizonal seperation. A single bandpass cavity will not be enough. I would try 2 bandpass/bandreject cavities. Reject set for the TX freq and the other set for the RX freq. I believe that RF from your repeater is exciting the RF amp in your aprs tranceiver, see if the problem is still present with the aprs hooked up to the antenna but with your power supply disconnected. Most people used a simple mobile for aprs which creates alot of headaches where several transmitters are used. They just dont have the filtering needed for this application. You should also use a circulator on your aprs radio. This will help keep RF out of your aprs transmitter.
David Epley, N9CZV Winchester, In --- In [email protected], "bullmus" <kf7...@...> wrote: > > Here's a weird one. I have my ideas, but I need to bounce it off a couple > brains bigger than mine. > > APRS on 144.39, and FM Voice repeater at 147.24/147.84. Antennas are > identical Telewave 4-bay stacked dipole. Both antennas are horizontal to each > other, and roughly two wavelengths from each other center loop to center > loop. > > The problem... When folks are using the voice repeater, then APRS transmits a > packet, it generates noise on the voice repeater the listener hears. However, > when APRS stops transmitting, the noise continues on the voice repeater until > the voice repeater is unkeyed. > > In our effort to troubleshoot, we found a couple extra oddities. For example, > with APRS antenna unhooked and the APRS radio turned off, when we attempt to > reattach the APRS antenna, we get all kinds of popping and crackling on that > turned off radio. > > We've checked grounding until we're blue in the face, and everything appears > to be in order. > > We have tried different cables on everything, one at a time, bypassing the > polyphaser, rack bulkhead connectors, etc... No fix. > > We discovered the problem when we began noticing APRS wasn't getting out. > Troubleshooting identified that the single band-pass can we had on the APRS > was reflecting 100% of the transmit power. We do not know the history or > condition of this can in the first place. It is very possible it has been > faulty for years, and only recently began to degrade to worthless. We have > temporarily bypassed the can, and expected possibly a little noise on the > voice repeater because of it, but we didn't expect the weird things we're > getting now like the noise continuing even when APRS isn't transmitting, and > the level of desense it creates. APRS is transmitting 5 watts. The Voice > repeater is I believe 25 watts. > > Thanks for the help... >
