The interference & noise on one of our MTR2000s is back with a vengeance. It occurs daily, sometimes on each transmission for a lengthy period of time. I've read a number of posts on the "Batboard" of this type of problem occurring on MTR2000 repeaters. Many of the described problems sound the same as ours. These posts seem to indicate that other MTR2000s are having a similar issue.
We have checked and rechecked to find a source of interference but have found nothing. There is no rhyme or reason as to when it occurs. We thought it may have been from NOAA weather equipment but they came & turned their monitors & modem on with no interference.
I am beginning to think this is somehow being self generated from the MTR itself. Either that or an outside source is causing the repeater to remain keyed with this noise but not sure from where. There is no other radio equipment at our site except a ham repeater which has been turned off eliminating it as the cause. There is a cell site about 100 yards away with several companies on the tower.
The problem only occurs when a mobile or portable talks. It will not key the repeater on it's own but the noise is present after a transmission. It keeps the repeater keyed until the noise fades out or the time-out timer expires. I don't understand how the repeater remains keyed as it is programmed for PL to be present for TX to hold.
The noise sounds like some sort of feedback as if the repeater is in a "loop". A "honking" noise was described in another post and that is also what our noise is like.
Here is the repeater info:
MTR2000 UHF 100w Standard Duplexer Single Circulator
TX = 460.225 MHz 100.0 Hz 25.0 KHz
RX = 465.225 MHz 100.0 Hz 25.0 KHz
The repeater has been checked and everything looks good.
I have wav files of the noise if anyone wants to e-mail me at mlucas@tnacso.net.
I'm at my wit's end trying to figure out this noise. This is our primary repeater and is now much more than an annoyance.
Thanks.
Mark
MTR2000 Noise/Interference
Moderator: Queue Moderator
It sounds very much like a duplexer desense problem. It would explain the repeater remaining keyed as the valid PL would still be present. Something you could try is programming a different PL for the TX and set-up a half dozen portables to work on it & test it out. See if the problem goes away...or at least drops out after the hang-time expires.
Has the tuning of the duplexer been checked by a qualified service person/company?
Todd
Has the tuning of the duplexer been checked by a qualified service person/company?
Todd
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Dan562
- Posts: 533
- Joined: Mon Aug 23, 2004 7:30 pm
- What radios do you own?: Kenwood, Yaesu, ICOM, Motorola
This sounds more like a classic case of Inter-Modulation Distortion IMD mixing problem when two or more transmitters are up and transmitting RF signals producing a third frequency. They do not necessarily need to be on same frequency band. Once the Subscriber unit keys up, activating the repeater's PL / CTCSS Squelch, it does not matter which PL you're using on decode as the unwanted IMD mixing signal will hold the repeater's receiver open for any length of time until the Time Out Timer inhibits the repeater's transmitter or the IMD mixing signal drops out.
What causes the IMD problems? Well, strange enough things like dissimilar metals on roof top mechanical doors assemblies, chain link fences and mechanical hardware can set up the "Diode Action" causing the frequency mix. The mechanical doors do not need to be on the same building as your repeater's mounted antenna and these mechanical problems can be miles away from your site. There's factors such as Spurious Transmitters on 150 - 174 MHz or 450 - 512 MHz mixing with Commercial FM Broadcast stations (but not always) that can produce frequencies in the receiver's I.F. Mixing frequency range either above or below the carrier frequency and generally on 3rd, 5th & 7th harmonics.
Trying to track these type of problems can take days, months and years to find. I would recommemd to have a good quality Spectrum Analyzer such as a H-P / Agilent, TekTronix or IFR products that have a dymanic range of -110 to -130 dBm receiver sensitivity, a couple of Yagi antennas, one for VHF and one for UHF for Fox Hunting the unwanted signal and a Bearcat or Radio Shack Programmable Scanner set up on know RF Business Channels listening for same kind of interference signal.
I've even talked to the former /\/\ MSS, COSC and FTR technicians chasing IMD problems. They have indicated that some times the intereferring signals are caused by construction companies that take their Base Stations around the country, setting them up without a qualified service technician and/or shop to check the equipment before use and have no clue their transmitter is at fault for the interference signal. The former /\/\ MSS, COSC and FTR service personnel just stumble across the interference problem(s) with everyone in the shop listening for that type of a signal. This will take you some time to find who's Business Band transmitter / user is a fault. It's not a tried and true one solution fits all IMD problems or neccessarily a MTR2000 Base Station / Repeater problem.
What causes the IMD problems? Well, strange enough things like dissimilar metals on roof top mechanical doors assemblies, chain link fences and mechanical hardware can set up the "Diode Action" causing the frequency mix. The mechanical doors do not need to be on the same building as your repeater's mounted antenna and these mechanical problems can be miles away from your site. There's factors such as Spurious Transmitters on 150 - 174 MHz or 450 - 512 MHz mixing with Commercial FM Broadcast stations (but not always) that can produce frequencies in the receiver's I.F. Mixing frequency range either above or below the carrier frequency and generally on 3rd, 5th & 7th harmonics.
Trying to track these type of problems can take days, months and years to find. I would recommemd to have a good quality Spectrum Analyzer such as a H-P / Agilent, TekTronix or IFR products that have a dymanic range of -110 to -130 dBm receiver sensitivity, a couple of Yagi antennas, one for VHF and one for UHF for Fox Hunting the unwanted signal and a Bearcat or Radio Shack Programmable Scanner set up on know RF Business Channels listening for same kind of interference signal.
I've even talked to the former /\/\ MSS, COSC and FTR technicians chasing IMD problems. They have indicated that some times the intereferring signals are caused by construction companies that take their Base Stations around the country, setting them up without a qualified service technician and/or shop to check the equipment before use and have no clue their transmitter is at fault for the interference signal. The former /\/\ MSS, COSC and FTR service personnel just stumble across the interference problem(s) with everyone in the shop listening for that type of a signal. This will take you some time to find who's Business Band transmitter / user is a fault. It's not a tried and true one solution fits all IMD problems or neccessarily a MTR2000 Base Station / Repeater problem.
I would disagree with that since you can set the MTR2000 'hold in' to require the proper PL in order to continue the transmission, not just initiate it.Dan562 wrote: Once the Subscriber unit keys up, activating the repeater's PL / CTCSS Squelch, it does not matter which PL you're using on decode as the unwanted IMD mixing signal will hold the repeater's receiver open for any length of time until the Time Out Timer inhibits the repeater's transmitter or the IMD mixing signal drops out.
.
Of course, this won't help you if one of the offending frequencies happens to use the same PL....
Otherwise, yes it could be an intermod issue...which I don't envy you if it is, as Dan pointed out it can take weeks/months/years to track down.
I agree it isn't a specific MTR2000 issue, it's just the repeater of choice for mid to high-tier analog applications in the past almost 10 years or thereabouts, so that's why people report these types of problems while using MTR repeaters.
Todd
No trees were harmed in the posting of this message...however an extraordinarily large number of electrons were horribly inconvenienced.
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psapengineer
- Posts: 175
- Joined: Thu Oct 07, 2004 10:00 am
Intermod and PL
I agree that the problem could be intermodulation, perhaps even intermodulation where your repeater transmit frequency is one of the offending transmitters. In this case, since your transmitter would be involved, it has the required PL for the receiver if your Rx and Tx PL tones are the same.
You could try this as a test:
Change the portable (and mobile) Tx PL to something new, unique and different than you use now. Reprogram the Rx PL on the repaater to match the same tone you just chose for the portable.
Test the system. If the problem is gone (masked by the PL change) you then know what the problem is.
You then have three choices, change the Tx PL tone on all of the mobiles and portables to match the test PL chosen, fix the intermodulation, or do both.
Good Luck, Bob
You could try this as a test:
Change the portable (and mobile) Tx PL to something new, unique and different than you use now. Reprogram the Rx PL on the repaater to match the same tone you just chose for the portable.
Test the system. If the problem is gone (masked by the PL change) you then know what the problem is.
You then have three choices, change the Tx PL tone on all of the mobiles and portables to match the test PL chosen, fix the intermodulation, or do both.
Good Luck, Bob
IMD Issues
The best desciption I've come up with for self induced (multicoupler issues) desense is a "hoarking" sound thru a tube... the kind of sound that you would make when mustering some mucus from deep within your throat.... sorry... a bit more graphic than you want... but it is exactly that sound.
If the sound itself doesn't give it away, you have to run with this systematically, by the numbers.....
My favourite moto: "If in doubt, go to the victim receiver!" Thats where you will find your answers.
Dan562 has made mention of the best approach to this. Get a good spectrum analyzer with a wide dymanic range and high TOI (at LEAST +10 dbm, usually +18dBm is appropriate)! The analyzer must be at sensitve enough to see your desense which it can do with some BP filtering. You must start by replacing your rx with the analyzer and look at what your rx is seeing.
In some rare cases where the noise was below the noise floor of the analyzer, I've used a lab grade receiver (R&S for instance) to see if the results are the same as the victim receiver. The noise can be visible by spec 'A in an amplified manner at the IF output.
Do you know how strong this desense is in dBm? Have you measured the deviation of any PL tone that is apparently keeping the squelch open? The multiplier participants in an IMD will also multiply their deviation. For instance, a 2A-B=C IMD will have double modulation on the 2A participant. How wide does the desense appear to be? Often, the shape of the noise can be a useful clue or if it is centered on your rx freq, or offset.
Do you have any way of looking at the general RF environment? What else is multicoupled? Co-located? Any other carriers seen by your antenna stronger than -30 dBm? Can you draw a co-relation between the presence of those carriers and your noise? Very strong co-located transmitters will still be visible through your multicoupling at some subdued level consistent with the frequency delta from your rx freq. Or you can use a rubber ducky antenna and sniff around. Look at the other bands too, but I prefer to use the victim antenna.
If you suspect IMD and have a mathematical mix/child identified, you can sniff for it at the base of the multicoupling chain where the termination load is. One trick is to prepare a BP filter for the mix so that you can safely (and without overload) connect the analyzer. It depends of this type of by the numbers analysis must be carried out or not to solve. One example is IMD in the MC chain, cable, or antenna.
If it is self induced IMD, you may find that "all hell breaks loose" and you have little birdies and mixes up and down the band. This could be anything and is difficult to track down. In my experience fighting the forces of IMD, a 5 dB of contribution at an oxidized connector here, 10 db on a cable there, another 10 dB at the antenna, perhaps 3 db from that rusty tower and you find that cumulatively it can force a complete replacement of infrastructure. Dealing with each source yields only partial success. But since you have the issue with only one repeater.... this is probably not the case or you would be seeing them mixing with each other up and down the band.
Can you provide more numerical insight when you have it?
I've always enjoyed dealing with a good interfence issue. Like a puzzle, the answer is right in front of you. Just have to see it from the right angle.
You can sniff the spectrum elsewhere or with different equipment to make it more convenient, but only after you have proven that there is a co-relation. Of course, you are then well on your way to solving the puzzle.
Good luck. RF Dude
If the sound itself doesn't give it away, you have to run with this systematically, by the numbers.....
My favourite moto: "If in doubt, go to the victim receiver!" Thats where you will find your answers.
Dan562 has made mention of the best approach to this. Get a good spectrum analyzer with a wide dymanic range and high TOI (at LEAST +10 dbm, usually +18dBm is appropriate)! The analyzer must be at sensitve enough to see your desense which it can do with some BP filtering. You must start by replacing your rx with the analyzer and look at what your rx is seeing.
In some rare cases where the noise was below the noise floor of the analyzer, I've used a lab grade receiver (R&S for instance) to see if the results are the same as the victim receiver. The noise can be visible by spec 'A in an amplified manner at the IF output.
Do you know how strong this desense is in dBm? Have you measured the deviation of any PL tone that is apparently keeping the squelch open? The multiplier participants in an IMD will also multiply their deviation. For instance, a 2A-B=C IMD will have double modulation on the 2A participant. How wide does the desense appear to be? Often, the shape of the noise can be a useful clue or if it is centered on your rx freq, or offset.
Do you have any way of looking at the general RF environment? What else is multicoupled? Co-located? Any other carriers seen by your antenna stronger than -30 dBm? Can you draw a co-relation between the presence of those carriers and your noise? Very strong co-located transmitters will still be visible through your multicoupling at some subdued level consistent with the frequency delta from your rx freq. Or you can use a rubber ducky antenna and sniff around. Look at the other bands too, but I prefer to use the victim antenna.
If you suspect IMD and have a mathematical mix/child identified, you can sniff for it at the base of the multicoupling chain where the termination load is. One trick is to prepare a BP filter for the mix so that you can safely (and without overload) connect the analyzer. It depends of this type of by the numbers analysis must be carried out or not to solve. One example is IMD in the MC chain, cable, or antenna.
If it is self induced IMD, you may find that "all hell breaks loose" and you have little birdies and mixes up and down the band. This could be anything and is difficult to track down. In my experience fighting the forces of IMD, a 5 dB of contribution at an oxidized connector here, 10 db on a cable there, another 10 dB at the antenna, perhaps 3 db from that rusty tower and you find that cumulatively it can force a complete replacement of infrastructure. Dealing with each source yields only partial success. But since you have the issue with only one repeater.... this is probably not the case or you would be seeing them mixing with each other up and down the band.
Can you provide more numerical insight when you have it?
I've always enjoyed dealing with a good interfence issue. Like a puzzle, the answer is right in front of you. Just have to see it from the right angle.
You can sniff the spectrum elsewhere or with different equipment to make it more convenient, but only after you have proven that there is a co-relation. Of course, you are then well on your way to solving the puzzle.
Good luck. RF Dude
MTR2000
Our problem doesn't appear to "desense" the receiver as it checks good. The noise only appears at the hang time after a mobile or portable unkeys. No problem in re-keying during the interference or talking over the noise. The radio shop is going to re-check the repeater once again including the duplexer and we may use an antenna analyzer to check the feedline and antenna. Thanks for your help.
Re: MTR2000
Perhaps 'desense' isn't the proper word for this case, as you don't really seem to have a range issue. But I do beleive a small portion of the TX signal is getting back into the receiver through the duplexer.mark102 wrote:Our problem doesn't appear to "desense" the receiver as it checks good. The noise only appears at the hang time after a mobile or portable unkeys. No problem in re-keying during the interference or talking over the noise. The radio shop is going to re-check the repeater once again including the duplexer and we may use an antenna analyzer to check the feedline and antenna. Thanks for your help.
I would try a quick test by changing the TX PL of the repeater to a value different than the RX & test it with a few matching portables. If the repeater doesn't hold the TX after that, it'll pretty much verify it's a self induced problem with your system, as opposed to external interference.
Todd
No trees were harmed in the posting of this message...however an extraordinarily large number of electrons were horribly inconvenienced.
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We have tried that as well as a number of other programming changes. We've went through several settings with RX activation and hold. Noise still occurs. Our next step is to change the TX PL to something different than RX. As this is one of our primary repeaters, I'll have to make some changes in our control station but I believe we can run a test without much disruption. The problem is the interference is so intermittent it may be weeks before it shows up again. Thanks.
The crystal filter trick might not work if the problem is coming from the repeater transmitter. There could be too much energy for the filter and as such it could possibly roll over. I tend to side with the others that think it is self induced.
Problem is trying to locate the cause. It could be almost anything from a rusty loose bracket on the tower to water in the coax connector. Only checking one thing at a time will find it. One hint for the outside, pay attention to the weather. If it gets better and goes away when it's damp, then spend your time on the tower. If weather has no effect, then look at the inside issues.
Jim
Problem is trying to locate the cause. It could be almost anything from a rusty loose bracket on the tower to water in the coax connector. Only checking one thing at a time will find it. One hint for the outside, pay attention to the weather. If it gets better and goes away when it's damp, then spend your time on the tower. If weather has no effect, then look at the inside issues.
Jim
MITYTONE wrote:Maybe you could try a crystal filter on your rx front end.These have a very sharp pass band and are fairly cheap.
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mattgraves
- Posts: 10
- Joined: Sun Jul 23, 2006 3:54 pm
My God!!!
This started at our County Tower site about a week ago and we are working on this problem as I write this. We have 2 MTR2000's , 2 Johnson
and 1 GE UHF repeater at our site. The kicker is that 4 other counties in our region have been dealing with this "EXACT" issue....one has been wrestling with issue for 2 years! He has spent 4 grand on a techs coming out looking at the spectrum ....all no avail. He even called the FCC office in Dallas and they sent out a field rep. He came out in a completely "stealth" Ford Excursion...no anntennas at all. Even with the best gear from the "Commission" nothing conclusive resulted.
Download soundfile here:
http://www.yousendit.com/download/2gvDOjTHwLh5TA==
If anyone can help us give me call at 1-360-515-3233. Thanks.
and 1 GE UHF repeater at our site. The kicker is that 4 other counties in our region have been dealing with this "EXACT" issue....one has been wrestling with issue for 2 years! He has spent 4 grand on a techs coming out looking at the spectrum ....all no avail. He even called the FCC office in Dallas and they sent out a field rep. He came out in a completely "stealth" Ford Excursion...no anntennas at all. Even with the best gear from the "Commission" nothing conclusive resulted.
Download soundfile here:
http://www.yousendit.com/download/2gvDOjTHwLh5TA==
If anyone can help us give me call at 1-360-515-3233. Thanks.
So that just means by opening your receiver with the proper PL, you have provided a path for the offending signal to enter. But, how is the repeater staying keyed up without the proper PL? Do you retransmit PL or is it generated and sent to the tx audio line continously with a repeater PTT command?Our problem doesn't appear to "desense" the receiver as it checks good. The noise only appears at the hang time after a mobile or portable unkeys.
What about just eliminating the hang time of the repeater until a solution is found?No problem in re-keying during the interference or talking over the noise. The radio shop is going to re-check the repeater once again including the duplexer and we may use an antenna analyzer to check the feedline and antenna.
I am having an identical problem with a VHF quantar. We have a 2 second hang time and every once and a while we get a second of white noise. The freq's are pretty close, but we have a brand new tower, antenna, duplexer, and cable. Currently the user is running the system CSQ. I've read the posts and I'll be heading out with a spectrum analyzer and dummy load to start investigating. We are planning to reprogram the fleet with TPL, so I'll make sure I use different PL's for Tx and Rx. I'm interested to see what any of the other users/techs find.
Me too, but on a Quantar. Problem went away completely.MITYTONE wrote:I had a similar problem and I found that the cure was in the rss mapping..In analog rx activation; if you are using "carrier and PL&dpl" change it to "PL&DPL".
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If at first you don't succeed,.....then maybe skydiving isn't for you.
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If at first you don't succeed,.....then maybe skydiving isn't for you.
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Dan562
- Posts: 533
- Joined: Mon Aug 23, 2004 7:30 pm
- What radios do you own?: Kenwood, Yaesu, ICOM, Motorola
Mark102,
You've stated that the UHF MTR2000 is your "Primary" repeater on your original Post. Does this mean your system has Redundancy as in a Back-Up repeater unit? If you have a Back-Up repeater unit or Hot / Standby, "Is this an older /\/\ or GE repeater?" Before the new MTR2000 Base Station Repeater was installed, "Did your older repeater have the same intermittent noise interference on the system?"
Dan
You've stated that the UHF MTR2000 is your "Primary" repeater on your original Post. Does this mean your system has Redundancy as in a Back-Up repeater unit? If you have a Back-Up repeater unit or Hot / Standby, "Is this an older /\/\ or GE repeater?" Before the new MTR2000 Base Station Repeater was installed, "Did your older repeater have the same intermittent noise interference on the system?"
Dan
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chpalmer
- Posts: 105
- Joined: Mon Jun 17, 2002 9:01 pm
- What radios do you own?: Astro Specta, MT1500, HT1550LS
Winegard TV antenna amplifiers built around 2000 for a two year period were defective and generated rf that seemed to be repeating what it was hearing (i.e. itself plus power supply hum) and caused many a headache.
Ive located 50 now in my area causing us issues.
Look at your receive antenna with your spectrum analyzer. Look for a carrier up and down the spectrum that may be moving or still but stays on.
See if the modulation is identical to what you are hearing. If your near a hwy. then your just gonna have to change pl's
Our first one was 10 miles accross the water on an island, where the driveway of the rv faced our repeater antenna.
My link to the Winegard page has since disappeared but Winegard techs will still know of the issue.
They can sound a bit like your description.
Ive located 50 now in my area causing us issues.
Look at your receive antenna with your spectrum analyzer. Look for a carrier up and down the spectrum that may be moving or still but stays on.
See if the modulation is identical to what you are hearing. If your near a hwy. then your just gonna have to change pl's
Our first one was 10 miles accross the water on an island, where the driveway of the rv faced our repeater antenna.
My link to the Winegard page has since disappeared but Winegard techs will still know of the issue.
They can sound a bit like your description.
Last edited by chpalmer on Mon Feb 05, 2007 10:18 pm, edited 1 time in total.
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chpalmer
- Posts: 105
- Joined: Mon Jun 17, 2002 9:01 pm
- What radios do you own?: Astro Specta, MT1500, HT1550LS
This is what the link used to say...
Dear Winegard Customer,
Winegard Company has received reports that some of our Sensar II television reception antennas may be emitting spurious signals. While these inquiries have been relatively few when compared to the number of Sensar II antennas in use today, Winegard Company takes this matter very seriously. Please note that this problem will not be apparent to you the consumer, as it typically does not affect the performance of the antenna. However, if this problem exists with your antenna it may cause interference to the two-way radio signals of other parties.
As part of our normal program of long-term quality assurance, Winegard has been surveying various RV campgrounds, dealers, and rallies throughout the United States. When a problem is identified with a Winegard Sensar II antenna, it is replaced with a new antenna free of charge and a renewed two-year warranty.
Winegard continues to search actively for and replace potentially affected antennas. Winegard is a responsible company and takes this matter very seriously. Customer satisfaction is extremely important to us.
If you have questions regarding this matter please call us at (800) 856-4350.
© 2003 Winegard Company. All Rights Reserved
I can not find it any longer on their site.
Dear Winegard Customer,
Winegard Company has received reports that some of our Sensar II television reception antennas may be emitting spurious signals. While these inquiries have been relatively few when compared to the number of Sensar II antennas in use today, Winegard Company takes this matter very seriously. Please note that this problem will not be apparent to you the consumer, as it typically does not affect the performance of the antenna. However, if this problem exists with your antenna it may cause interference to the two-way radio signals of other parties.
As part of our normal program of long-term quality assurance, Winegard has been surveying various RV campgrounds, dealers, and rallies throughout the United States. When a problem is identified with a Winegard Sensar II antenna, it is replaced with a new antenna free of charge and a renewed two-year warranty.
Winegard continues to search actively for and replace potentially affected antennas. Winegard is a responsible company and takes this matter very seriously. Customer satisfaction is extremely important to us.
If you have questions regarding this matter please call us at (800) 856-4350.
© 2003 Winegard Company. All Rights Reserved
I can not find it any longer on their site.
Noise & Interference
Dan562,
Sorry. I missed your post. The noise was present on a new MTR2000 which was our main repeater. No stand-by at this location but we have multiple repeater sites. We placed a temporary repeater. It too had noise at times. We now have a new Quantar at this location. We still have interference at times but not as frequent. No luck in finding the cause. We've checked everything from antenna & feedline to the AC power.
Mark
Sorry. I missed your post. The noise was present on a new MTR2000 which was our main repeater. No stand-by at this location but we have multiple repeater sites. We placed a temporary repeater. It too had noise at times. We now have a new Quantar at this location. We still have interference at times but not as frequent. No luck in finding the cause. We've checked everything from antenna & feedline to the AC power.
Mark
I will give you one to think about. A number of years ago, one of
the public safety repeaters in town had a strange problem. Once
in a while the input would have a signal that would over power
the weaker signals. It would kind of pulse on and off at times.
At other times it would stay on steady. The pulse rate kind of
sounded like the time sequence of a scanner.
Managed to track it down to a scanner in town about a half mile
from the repeater. The owner would lock it up on the fire channel
and when they did that, the local oscillator would radiate just
enough signal on the police repeater input. When in the scan
mode, it would cause the pulse type signal.
Managed to track it down by using another receiver on the
input channel and started driving around. Had a variable
attenuator in line to drop the signal level as we got closer to
the source. Managed to get it down to only 2 houses. Had
a police officer go knock on the door and ask if there was a
scanner in the house. One said no and the other said yes.
then asked them to turn it off and the signal went away.
We informed the owener that he was causing a problem.
They said they would take the scanner back to where
they bought it. In the mean time it remained unplugged.
Not saying this is your issue, but that is how strange it
becomes when trying to locate problems.
Jim
the public safety repeaters in town had a strange problem. Once
in a while the input would have a signal that would over power
the weaker signals. It would kind of pulse on and off at times.
At other times it would stay on steady. The pulse rate kind of
sounded like the time sequence of a scanner.
Managed to track it down to a scanner in town about a half mile
from the repeater. The owner would lock it up on the fire channel
and when they did that, the local oscillator would radiate just
enough signal on the police repeater input. When in the scan
mode, it would cause the pulse type signal.
Managed to track it down by using another receiver on the
input channel and started driving around. Had a variable
attenuator in line to drop the signal level as we got closer to
the source. Managed to get it down to only 2 houses. Had
a police officer go knock on the door and ask if there was a
scanner in the house. One said no and the other said yes.
then asked them to turn it off and the signal went away.
We informed the owener that he was causing a problem.
They said they would take the scanner back to where
they bought it. In the mean time it remained unplugged.
Not saying this is your issue, but that is how strange it
becomes when trying to locate problems.
Jim