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Author Topic: Odd VHF repeater problem...  (Read 8661 times)
WA0MNA
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Posts: 21




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« on: December 13, 2006, 10:50:06 AM »

Our club has a VXR-7000 Vertex repeater, couple years on the air.  New duplexors, new MaxRad 4-bay antenna, and heliax fed.  Problem is...in the last 2-3 weeks the repeater has been "distorting" the first couple words of a transmission when the repeater comes up.
Then the rest of the audio is clear as a bell.  This seems to happen only when the box has been inactive for a long period of time (like overnight) then seems fine when used during the day.  A site visit didn't reveal anything connection wise, temperature,etc.  Some members think it's the antenna, I do not.  Repeater output is always strong.  I KNOW THIS IS AN "OFF THE WALL" REQUEST...BUT, ANY TIPS AT THIS POINT WOULD HELP.
Tnx 73
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KA4P
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« Reply #1 on: December 13, 2006, 10:59:39 AM »

I'm thinking power supply. Maybe a regulation problem. The transmitter comes up. The supply voltage drops, but only for 2 or 3 seconds and then it's back up to snuff.

I may be all wet but that is where I would look first.
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KZ1X
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Posts: 3294




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« Reply #2 on: December 13, 2006, 11:17:30 AM »

Can you be more specific abou the "distortion" ?

Is it audio distortion, coming from the controller?  or is it the receiver, as if the icoming signal is off frequency?  

Does it happen on everyone's signal, or, just to some people?  

How long do you have to wait until the problem comes back?
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HA5RXZ
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Posts: 380




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« Reply #3 on: December 13, 2006, 11:32:37 AM »

How about an antenna changeover relay with dirty contacts?

HA5RXZ
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WB2WIK
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« Reply #4 on: December 13, 2006, 11:36:00 AM »

Distortion on an FM signal is often the result of being slightly off frequency.

Anybody look at the repeater's transmit frequency when it first comes up?  Based on symptoms, I'd say it drifts for the first second or two, starting out off frequency and then drifting on.

If that's the case, then de-bug that condition.

WB2WIK/6
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K6AER
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Posts: 3810




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« Reply #5 on: December 13, 2006, 12:50:38 PM »

Also check the receive frequency as well as the transmit frequency. In the winter time the Phase lock loop may be on the ragged edge in the cold. Also check power supply regulation. Cold weather operation is always problematic.
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WA0MNA
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Posts: 21




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« Reply #6 on: December 13, 2006, 03:35:48 PM »

Thanks to all for your quick replies.  Great tips!!!
Appreciate it guys.  Going out to the site tommorrow.
Will keep you posted.  73  Vance
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WA0MNA
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« Reply #7 on: December 13, 2006, 03:45:21 PM »

I will try to describe what I call distortion abit better.  At the very start of a transmision from the repeater, the "audio/speech" is weak with lot's of noise (like you are using an HT standing in a hole).
This happens for only a few seconds, then boom, the signal is loud and full quieting.
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KZ1X
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« Reply #8 on: December 13, 2006, 06:44:08 PM »

Sounds like a start-up spur on the transmitter, desensing your input.
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KV6O
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Posts: 96




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« Reply #9 on: December 14, 2006, 09:11:31 PM »

Those symptoms are a sure sign of demonic possession. Open up one of the duplexer cans and look inside. If you see a portal to an alternate plane of existence, or any other folding of space-time, time for a new repeater. I hear the new D-Stars are niceā€¦

Steve
KV6O
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K4III
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« Reply #10 on: December 20, 2006, 11:03:07 AM »

My MSR-2000 ocassionally does this when the power comes back on after after a 20 minute or more period of power-loss when the temps are around freezing or lower. Yes, ICM temperature compensates "burns" them. I believe since my "rocks" (crystal elements) are temperature-compensated and the power is off long enough, when it comes on and they are "cold", the crystals are a hair off frequency. I never really have much of a problem as it only happens a couple of times during cold times of the year (here in N Florida) and the crystals usually tune-up within 5-10 minutes of the power returning at the site.
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K7KLA
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Posts: 4




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« Reply #11 on: January 01, 2016, 02:21:03 PM »

Was there any conclusion or solution to this problem? I am experiencing an almost identical issue only the distortion is lasting for about 10 to maybe 15 seconds and then completely resolves. The distortion never occurs during the hang timer. The repeater is always transmitting a very strong signal. The issue seems to be isolated to radios accessing the repeater from a further distance away. Users in close proximity to the repeater never seem to experience this problem almost as if they are able to overpower the distortion. There has not been any recent changes the hardware or equipment of the repeater system. This issue seems to exist when powered off of both AC and DC supplies. The repeater is at a ski resort and is the only radio equipment at it's location and a long distance from any other transmitters. We have operated this repeater for several years with no issues until now.
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ONAIR
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Posts: 2297




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« Reply #12 on: January 02, 2016, 01:06:40 AM »

I will try to describe what I call distortion abit better.  At the very start of a transmision from the repeater, the "audio/speech" is weak with lot's of noise (like you are using an HT standing in a hole).
This happens for only a few seconds, then boom, the signal is loud and full quieting.
   Can you post a YouTube video of the distortion?
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K7KLA
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Posts: 4




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« Reply #13 on: January 03, 2016, 10:17:50 AM »

I was trying to get a good video of the distortion the other day when I was on location at the site however never could get one. I always seemed to be in the wrong place at the wrong time without my phone. I made some simple observations and performed some basic troubleshooting. I found a few things that seemed suspect to say the least.

1) The antenna feed line has about a 6" section of the plastic sheathing/protective covering that is partially missing.

2) The coax cable between the transmitter and the duplexer is LMR400 and seems to have a little excessive length.

3) The coax cable between the receiver and the duplexer has a couple different types of coax. The first section is about 18" and appears to be standard RG8 and the second section is about 36" of RG142.

4) There was not any distance separating the transmitting and receiving coax before they reached the duplexer.

All the connections seemed to be snug and no obvious signs of corrosion or oxidisation. The SWR reading of the feed line and antenna was 1.4:1. I created some separation between the TX and RX cables before they reach the duplexer. The duplexer is a VHF Telewave TPCD-1554 4 cavity duplexer. We are running 4.5MHz frequency split. I put some electrical tape around the antenna coax feed line for a little protection until it can be replaced. Making these small changes seemed to help a fair amount however there is still some background noise but no distortion to the level that we were experiencing. I haven't heard any feedback from the guys working since then that the distortion has come back.
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WA3SKN
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Posts: 6047




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« Reply #14 on: January 03, 2016, 12:06:41 PM »

As I recall, double shielded coax all cut to frequency, was the normal install from the repeater through the duplexor, and heliax up the tower to the antenna(s).  This was needed for the 100 dB separation between transmit and recv desired to keep de-sense at bay.
Sounds like you might want to replace some of those cables.

-Mike.
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