GR 1225 Audio Fading

Dean Buccheri · Post by **Dean Buccheri** » Mon Jan 20, 2003 6:24 pm

I have been trying to troubleshoot a problem with a GR1225 repeater. I have narrowed the problem down to the repeater as multiple portable, mobile, and base station equipment experience the same problem. When a using is talking (usualy for at least 5-10 seconds), the audio will disappear in the middle of the transmission. Sometimes it will come back on longer transmissions, and othertimes it will not come back until PTT is released. This is a very intermittant problem, but seems to be getting more noticiable. Of course, I can never duplicate it when on site. I've only been able to "see" the problem by playing back recordings of the problematic transmissions. I can't guarantee it, but it appears that the carrier stays active, but the audio is gone. I've checked everything that I can think of of. Has anyone seen this problem? or does anyone have any ideas what may be causing it. I should have most of the necessary test equipment at my disposal, but don't know what else to check.
Thanks

Post by **wavetar** » Tue Jan 21, 2003 12:18 pm

Hmmm, strange problem. Can't say I've seen/heard it as a common thing, if it indeed is just the audio dropping. Are the field radios set up with PL/DPL? If so, is the repeater set-up as CSQ, and just passing the signal transparently (flat)? Or is it set-up to strip PL & repeat (EIA)? If set as CSQ, then the PL is likely being repeated at a much lower level (~0.2 KHz) than it should be (~0.75KHz). This could possibly cause your drop out issues. I would normally start with that. If all seems well programming wise, then it would appear you have an intermittant somewhere in the repeat audio path, which will be difficult to find while the unit is in service. Times like that it's nice to have a loaner GR1225 or even MTR2000 to give while you're checking out the customer unit at the shop. But, most shops (mine included) don't have that option. Hopefully others will have further suggestions.

Dean Buccheri · Post by **Dean Buccheri** » Tue Jan 21, 2003 6:27 pm

Thanks for the reply. You idea makes sence. Part of the problem is that I inhereited this from another shop, and all the portables and mobiles were programmed wrong, so you may be on to something. We are using CTCSS PL on TX and RX. I'll have to check the programming at the repeater to see if they set it as CSQ. I would think the receiver would automatically strip off the tone whether or not set for CSQ. But with the other programming nightmares, it is certainly worth checking. Is there actually a setting that force it to regenerate PL or does it automatically do it if you turn RX and TX tones on?

I do have a model 25 zetron controller and spare radios for loner purpsoes, but nothing that will do narrowband.

perthcom · Post by **perthcom** » Tue Jan 21, 2003 8:04 pm

Hi
You may have power supply problems. When transmitting, the repeater takes much more current.... if the voltage level from the power supply drops under load or becomes noisy, the transmitter will become unstable and flutter and rumble. This masks the PL code at the recieving end so you lose the audio. When you release the PTT, the power supply recovers.
If the power supply is real bad, the VCO might go out of lock and then the radio will inhibit TX until the PTT is released.
If you are using a digital service monitor, you might not even see the VCO flutter... use a good old analog unit like IFR1200.
Intermittents can take for ever to track down if you can't get it to act up in front of you! Try subbing a power supply...
Another thing.. would the repeater location be subject to brownouts? Try a switching power supply then as they can usually still regulate under load with a lower input voltage.
I have a number of GR1225 units out in the field... the only problem has been the connector to the front control panel... it loses Rx or Tx audio... but I think you are talking about repeat audio and this is done internally and not though this connector.

Nand · Post by **Nand** » Tue Jan 21, 2003 8:31 pm

perthcom · Post by **perthcom** » Tue Jan 21, 2003 9:23 pm

I know the early ones came with an analog supply.. My back reminds me of that everytime I lift my demo unit!!
I must say that most of mine are actually the R1225 in a wall mount cabinet... can't say that i have sold the desktop GR1225 version in a couple years so they may have changed the power supply

Dean Buccheri · Post by **Dean Buccheri** » Sun Feb 09, 2003 7:45 am

Thanks for all the replies, I've been away from the board for a while but this is where I'm at with this problem.

The audio was set for flat by a previous technician. I changed it to EIA which I assume will filter and regenerate the CTCSS tones. You could actually see the deviation fluctuate proportional to the voice modulation on the monitor. Now it stays right at .70K. That solved that problem.

Now, however the repeater just goes deaf for 5-15 minutes at a clip. I don't know if we are looking at a loss of AC power, DC Power, Power Amp Problem or a Desense Problem or just a deaf receiver.

The biggest pain is that it corrects it self by the time we get there. I've check AC and DC power both under load and with tx idol. This is the only device in the building other than a heater. I've even turned the heater o and off during TX to see if that is affecting things. The power supply is right at 13.96 VDC and fluctuaties < .01 V during TX even with extened talk times.

When we are on site, all levels are in spec.

I've installed a battery backup on the AC side to eliminate that, and going up this week to replace DC power to rule out those components.

I love a challange in troubleshooting, but how the hell do you fix a problem when it corrects itself by the time you get on site.

Any other ideas?

April · Post by **April** » Sun Feb 09, 2003 9:26 pm

Perthcom, you are right on the nose with you evaluation, I have had simmular dealings with the R1225/GR1225.
Also, is anything pluged into the accessory connector that might screw up the audio?
The was a known issue with both the lineir and switching power supplies.
A lot of them (power supplies)were "fixed" (read butchered) by who knows.

I always check the R1225 radio for posible corrosion and have to remove the boards to check with a magnifier glass.

Post by **wavetar** » Mon Feb 10, 2003 7:17 am

We just recently had the very same problem with a customer's GR1225. They would call & say the repeater was down, we'd arrive 20 minutes later to find it working perfectly. Drove us batty for a few days, until we finally caught it in the act. No tx power out. Simply required resoldering the PA to fix. You may want to open it up & have a look at it. Resolder it whether it looks good or not, see if it solves the problem. I'm not sure how helpful your customer might be, but if someone could go to where the repeater is when it acts up & listen with the internal speaker, you'd at least know if it's receiving the field units or not. I'm putting my money on the tx PA. I'm assuming you've checked the duplexer & verified it to be tuned properly.

Todd

Dean Buccheri · Post by **Dean Buccheri** » Mon Feb 10, 2003 5:55 pm

OK I'll resolder the PA. This is the type of idea I was looking for. If that doesn't do the trick, it really sounds like the power supply. I did check the duplexer because that was one of the first things I suspected because it is clearly labled wrong. 2 Meg off on both TX and RX. I don't have enough equipoment to due a complete duplexer tuning, but the isolation seems to be on (or close) the correct frequencies injecting frequencies with a portable directly connected and reading on monitor on other side.

Correct me if I'm wrong, but if the duplexer were tuned wrong, wouldn't the problem be less intermittant or more noticable on longer transmissions?

Thanks for all the help.