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Author Topic: Repeater noise along with audio when TX enters the air ..!  (Read 1362 times)

PY2HR

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Re: RE: Repeater noise along with audio when TX enters the air ..!
« Reply #15 on: April 20, 2020, 12:58:19 PM »

OK, need more info.
First eliminate the obvious, no RG-58 or LMR anything for cable.
If you are working on the cheap and are running PL-259 connectors and not N connectors, then locate some FSJ1-50 cable and get the Amphenol stlye connector and RG-8X reducers and solder the sheild to the reducer and assemble the end and solder the center pin.  This is still hard line and for VHF it will be plenty good for jumpers.

Now tell us about the environment that the repeater is in.  I assume it's at a tower site, but what else is there?  AM/FM broadcast, TV, commerical and public safety?  Or are you the only one on the site?
Do you have an actual service monitor to take readings with and a spectrum analyzer or are you just winging it?

Dear,KB8VUL, thanks for trying to help, not my case the RPT is installed in the rural area, far from sources of interference.

Att,
Moises C.
PY2HR
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PY2HR

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Re: RE: Repeater noise along with audio when TX enters the air ..!
« Reply #16 on: April 20, 2020, 01:01:29 PM »

Abs. Moises PY2HR - It sounds like what you are talking
about is NOT RF related but in fact may be the CTCSS
level on the repeater audio output. This level may be
a little on the high side and your receiver is not filtering
it out and passing it on to your receiver speaker.

Dear, N2AYM thanks for trying to help, not my case I would know how to safely detect it.
This is PIM.

73 "
Moises C.
PY2HR
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PY2HR

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Re: RE: Repeater noise along with audio when TX enters the air ..!
« Reply #17 on: April 20, 2020, 01:07:42 PM »

What are you seeing on the receiver limiter and discriminator when the transmitter is keyed? This sounds like an externally generated IMD product.  Can you try a temporary antenna on the system?


I changed antenna, without, same thing.
73 "
Moises C.
PY2HR
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WB8VLC

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Re: Repeater noise along with audio when TX enters the air ..!
« Reply #18 on: April 20, 2020, 01:08:50 PM »

Any poor conductors, be they rusty screws, rusty tower sections or dissimilar metals can produce a pseudo diode junction resulting in PIM so yes this can be a challenging search to find out where the noise is coming from.

 I work on a lot of 6 meter and 10 meter systems and the best search tool for me is a 4 to 6 foot long two by four piece of wood which I use to smack and bang on anything nearby that is metallic such as the tower itself, nearby metal buildings, building doors, siding on buildings, ground connections.

Anything that is remotely close to being metallic near my systems  have caused the PIM issue, I use the wood two by four board to search out the noise source while listening with a hand held radio to the repeater output and this has been the best tool for me.

One 6 meter repeater in central Arizona took us a couple of months to first eliminate a nearby cellphone companies switches and Multiplexers which were creating noise masking some poor metallic connections that were resulting in unknown PIM sources.

Once the cell companies noise sources were lowered by around 15 to 20 db we next faced finding several latent PIM sources which showed up and these then took another month or two to search and eliminate.

For this 6 meter repeater it took so long because it was on a 8000 foot mountain in the dead of winter with 4 feet of snow on the ground.

Do not overlook any nearby metallic on anything, look at buildings, doors on buildings, metal or aluminum siding on buildings, loose connectors on anything, light fixtures poor screws on electrical wall plates.

Look at nearby lighting systems, poor AC electrical systems, everything and anything metallic or closely metallic should be considered suspect to causing PIM issues.

If your repeater is in a more mild environment then it may only take a couple of weeks or even days to search and eliminate the noise sources.
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WB0DZX

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Re: Repeater noise along with audio when TX enters the air ..!
« Reply #19 on: April 28, 2020, 10:07:12 PM »

KB8VUL, WB8VLC and others have given excellent possible remedies which you have tried. Yet the problem still persists, having started during (your) winter until now (your summer). May I add some questions and thoughts?
 
A. According to the model number given your Icom IC-F211 mobile acting as a repeater receiver is UHF. According to the model number given your Motorola M120 mobile acting as a repeater transmitter is VHF. Is the Icom model number incorrect? Is it correct that you are operating a cross-band repeater? Or are you operating a remote base?
B. Confirm that the Icom is NOT programmed to:
     1. "auto transmit"
     2. SmarTrunk II operation
     3. Scan
     4. A frequency other than the desired input
     5. An improper DCS or CTS
     6. A programmable function key (P0-P3)
     7. Wide bandwidth (via the W/N softkey)
     8. The same frequency as the Motorola and vice versa.
C. Confirm that IC-F211 microphone is on a grounded holder.
D. Confirm the audio level is not overdriving the transmitter input.
E. Would it be possible for you to upload from a cellphone a public YouTube video showing a ten second keyup and resulting "snore" audio? Do this with the repeater antenna connected AND, understanding there will be little or no audio, ten seconds on "dummy" load. If you do this, please post the link(s) on this forum.
F. What is the brand and model number of the duplexer?
G. Please say whether the repeater uses digital coded OR continous tone OR carrier squelch.
H. Was anything changed on your system or the nearest system(s) just prior to the problem's first occurrence? If so, what?
I. Are you aware of any continuously transmitting transmitter(s) or trunked system(s) nearby? If so, what frequency band(s)?
J. Is there any radio programmed cross-band repeat in reverse on the system?
 
There will probably be additional questions as the effort drills down.
 
Mike WBØDZX
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WB0DZX

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Re: Repeater noise along with audio when TX enters the air ..!
« Reply #20 on: April 29, 2020, 12:06:43 AM »

Might as well take this to the next level to save you a trip. If I heard the noise both on dummy load and antenna I can often tell if it is RF caused or ground caused, or ... -120dbm is a very weak signal, of course!
 
Did the system as configured before the antenna change ever properly work?
 
What were the results of using the hair dryer/cold spray to induce or find the problem?

RF getting into the audio circuitry between the receiver and the transmitter - need ferrite beads on the output and input lines
 
Ground loop - ensure single point grounding for power and audio
 
One or more components has failed in the audio interface and/or the receiver audio output and/or the transmitter audio input - ideally use optoisolators on the output and input for protection
 
The power supply and/or the receiver has failed filter capacitors and/or the power supply is a switching power supply that is underpowered and/or failed
 
Check the grounding of the power outlet - sometimes it is loose, missing, or improperly connected. Likewise the hot and neutral wires could be reversed. If a three wire-to-two wire adapter is used ground the ground lug.
 
However, what you report back may cause me to go off on one or more tangents.
 
Mike WBØDZX
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W9IQ

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Re: Repeater noise along with audio when TX enters the air ..!
« Reply #21 on: April 29, 2020, 04:14:43 AM »

Moises,

If you are fairly well convinced that it is PIM, have you monitored your AM and FM broadcast stations for the time of their power change in the evening? Brazil is well known for its high power AM stations, at least one of which (ZYH-707 in Brasília) jumps to 600 kW at night. Closer to you, São Paulo has several +100 kW night time stations.

Then consider that it may not be PIM but simple receiver front end overload. If you can detect the station that is causing the problem, some common mode ferrite chokes and perhaps a band stop filter would cure it. The common wisdom is that the duplexers should filter this out but common mode current allows it to pass through easily.

Or you could just invite me to spend some time in your beautiful area to help you find the problem!

- Glenn W9IQ

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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.
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