Repeater keys but without voice

[emtprt]

I recently upgraded a r1225 uhf repeater from 40watts to 100 watts. I purchased and had a local shop tune a decibal 100 watt duplexer that is attatched via 2 4 foot RG58 cables. I also purchased a TPL 110 watt amplifier.

The amplifier was placed between the transmitter and the duplexer. The antenna system is a 3.8db omnidirectional that works fine with another repeater.

Here is the problem. The portable radios keys up the repeater but there is no audio. I turned off the amplifer and the problem did not change. So at 40 watts and 100 watts portables only key up the repeater. Mobile radios have audio and receive fine.

I hooked up another 40watt r1225 repeater to the antenna and the portables have audio from the same location (3 miles away).

Is the duplexer bad or should I be using differant coax?

Mark

[batdude]

well, for what it's worth, never use RG58 on anything.


it should be illegal to use it on anything except "TANDY" or "RADIO SHACK" products



doug

[mancow]

The duplexer and amp have nothing to do with the audio as long as a signal is present.

If the signal is being received and re-broadcast you should have audio.

Something must have changed somewhere but I wouldn't start with the RF components.


mancow

[emtprt]

Motorola used RG 58 so I gave it a shot. I did use Belden cable instead of RS>

[kcbooboo]

There's some stuff, maybe RG142 or RG143 (I don't use it and am not sure about the number) that's the same size as RG58 but much, much better. Sometimes it has a clear outer cover and you can see the braid inside. It's often confused for RG58 and is sometimes used on low power duplexers (150 watts or so).

But as others have said, if you're getting RF power but no audio, then your amplifier, duplexer, coax, and antenna are NOT the problem.

Bob M.

[emtprt]

Portables open up the repeater but don't have audio mobiles seem to do fine. I Took the repeater in queswtion to another site with another duplexer (the one that was installed when purchased) an every thing seems fine. The small lengths of coax that came from Motorola are being utilized and I am using a 8.5db omidirectional antenna.

[kcbooboo]

Perhaps the repeater is now interfering with itself. With the extra power, maybe the duplexer just can't provide enough isolation between the transmitter and the receiver, so what you think is keyup without audio is really the portable keying the receiver, the transmitter comes on and wipes out the receiver, but the repeater stays on the air for a few seconds (normal hang-time) during which time you don't hear anything. Mobile signals are usually a lot stronger so they break through the transmitter's interference.

This could be caused by a poorly tuned duplexer, insufficient shielding in the interconnect cables (i.e. using RG58), too much transmitter power (from that TPL amplifier), or spurious emissions from the transmitter and power amplifier.

If you press the PTT button on a hand-held and keep it pressed for, say, 20 seconds, does the repeater stay on the air the entire time, or does it drop out for a split second then come back on? If so, this would indicate a desense problem as described above. If the repeater stays on the entire time and drops out only when you let go of the PTT button, then you've got one very strange problem on your hands!

Bob M.

[jim]

With the new PA and cables, do you have RF leaking from a cable or through the duplexer back into the receiver? The mobiles working properly, but low power portables not is a sign that it really may be an RF problem here.


Disconnect the 100W PA from the TX port on the duplexer and install a good dummy load with a GOOD coax onto the output of the amplifier and try it. Also, install a small dummy load on the TX port of the duplexer to keep the impedance correct. If it works now, it IS an RF problem with feedline or duplexer. Now, connect everything back to normal and substitute the dummy load in place of the antenna of the duplexer antenna port and try again to disprove an antenna/feedline problem.

Also, what is your reflected power from the antenna?

[commtek]

Sounds like a desense problem. I have seen wierd things like this at times. Especially if you are using RG-58 and not the good stuff that is the same size as the 58. There are many brands available for this purpose.

You might also try to hook up the amp to the transmitter and then to tha antenna, eliminating the duplexer. For test purposes, use another antenna for receive, any type will do, and see if the problem goes away.

If it does, look at your cabling and duplexer.

[transistor747]

I would hazard a guess that the repeater is being keyed by PL tone, but squelched audio is what is repeated. Portables are not opening the squelch.
If no programming has been changed in the repeater, and since it works elsewhere, it's gotta be desense.
A GR1225 has a crummy front end, and the duplexers generally used on that tier of repeater are not much either.