Thanks for the input folks!
I missed a couple critical pieces of information that are about to get me shot!
;-)
Our FM Voice repeater is running through a 6-cavity duplexer. The APRS setup
had a single cavity, tuned to the 144.39 APRS frequency. I am assuming this
single cavity is acting as a low pass filter or maybe a notch to prevent the
voice repeater from overpowering the APRS, but I honestly don't know. APRS is
running on a rack-mounted mobile rig. We don't have to contend with too many
neighbors on this hill. Only have two, they're government, and the nearest
frequency is 30Mhz up the band.
I should elaborate a little more too. We realize the APRS and Voice repeater
antennas are way too close, and our APRS setup was ridiculously overpowered.
We've already dropped our output from 40 watts to 5 on the APRS. We're going to
be replacing the APRS antenna with something with quite a bit less gain, and
we're going to put as much vertical spacing between it and the Voice repeater's
antenna as we can. In other words, I think we already have a plan to fix the
issues, but I want to understand the issues. My curiosity is in what is causing
the affects were are currently seeing/hearing. Noise and desense are one thing,
but the popping and crackling when trying to hook the antenna to a powered off
radio, and the weird noise on the voice repeater that is initiated by keying
the APRS, but won't leave until the voice repeater is unkeyed has me scratching
my head.
...and I'm trying to spout a lot of jargon, with very little experience in
their use, so before getting your exercise flying (off the handle) and jumping
(to conclusions), keep in mind I may not be saying it right. I'm fairly new at
using these here new fangled words... ;-) Finally, please note we're trying to
fix issues we inherited, we didn't do this, and want to make it "best
practice", while actually learning something in the process. Crazy huh?
Thanks again for the feedback.
--- In Repeater-Builder@yahoogroups.com, "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...
>
