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XTS3000 analog simulcast receive help

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KD6RRR

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So here's a weird one; I didn't know this was even a thing among analog FM systems.

The local law enforcement dispatch uses a single analog narrowband VHF frequency (155.5350 MHz) on their repeater output. They have several repeaters covering the county; two sites are above the local town and both completely blanket the local area with their signal. Both of these sites have the same transmitter power, both transmit the same CTCSS tone, and both transmit at the same time with all radio traffic.

I sometimes use an XTS3000 to listen in. When it receives traffic on this particular frequency, the signal is, I'm assuming, getting wiped out by the two transmitters being used simultaneously. It will receive clearly for a couple of seconds, then static quickly builds until the audio goes completely quiet, then will suddenly receive clearly for a couple of seconds, then static, then nothing, and repeat. It will do this cycle repeatedly in perfect time as long as the frequency is being used. This issue only started in the last few months; prior to that, never had a problem.

I can forcefully attenuate the signal by gripping the radio's antenna in my hand, and doing this causes the received audio to stop the on/off cycle described above, and I then hear everything clearly. So I am assuming that this fade in and out issue is due to the receiver getting overloaded by the two different equal signals off the two repeaters covering the local area.

For comparison, I have a Uniden SDS200 with an outside antenna that can actually "see" THREE of this system's repeater sites, all of which are transmitting same frequency, same CTCSS tone, and it is able apparently to ignore two of them and clearly receive just one no problem.

So finally the question: is there a setting of some sort that I'm missing in my XTS3000 CPS that somehow enables the radio to properly deal with the simulcast interference it's getting? Or is that ability too new for this model radio to do? Or is this maybe a problem with the two repeater site transmitters somehow not being configured correctly and causing the issues?

Interesting side note- the local fire dispatch uses the exact same setup as far as simulcasting sites with same analog frequency and CTCSS tone, but the XTS3000 has no problem receiving it clearly. Not sure if maybe the two fire transmitters are somehow more synced somehow so they don't have the same problem as the law transmitters, or maybe they just have different transmit power so one always wins, or some other cause.

Thank you for your help figuring this one out!
 

KD6RRR

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That would definitely make sense. It hasn't been tuned in the 14 years I've owned it, and I'd assume the agency I got it surplus from didn't either considering what a small department they were. So probably no tuning since manufactured.
 

NVAGVUP

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For analog simulcast, there are no programming settings to change in radio.

Simulcast is closely synchronized/aligned/timed. Since these systems are narrowbanded, subscriber alignment requires tight tolerances. Additionally, (per your comments) are in a simulcast overlap area. You are likely experiencing some time delay differences. (The distance from site A vs site B (C, etc) is different to your subscriber radio receiver. So arrival time is different. This can manifest itself by summing of signals or negating each other.
 

mikewazowski

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Have you tried disabling the ctcss tone to see what happens?

Typically a when you're in the overlap zone of two transmitters, you will hear a heterodyne signal. I'm wondering if this signal is confusing your ctcss decoder.

A signal dissolving into static doesn't sound like a simulcast issue though since both transmitters should still be received at the same signal strength.
 

KD6RRR

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Thank you all for your replies! Based on your (very much appreciated!) insight, I'm wild guessing it may be a combination of these things. This particular simulcast system setup has been in place for about four years now and has always been received clearly on this XTS3000 with zero issues. The system has three different frequencies in use regularly in this simulcast setup (law dispatch, fire dispatch, & road department), and the issue literally appeared suddenly one afternoon a few months ago in the dead of winter. So I am thinking perhaps some work was done on the only site that is accessible in the winter that may have changed something. Couple that with my very well aged and well used radio, and it would explain a lot.

As I mentioned in my original post, I can eliminate the issue by wrapping my fingers around the (very stubby and no gain at all) antenna. I can also stop the issue temporarily by holding the radio pressed up against my body and then turning so the one particular site that's easily accessible in winter is behind me. This trick does not work when putting the other local site in the same position.

So I also need to see if I can find a radio shop that does alignments on this model as well.

Thank you all again!
 

KD6RRR

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I forgot to reply to Mike; I have had it programmed both with CTCSS decode as well as just CSQ, and same issue either way. Something else I just thought of- the fire dispatch will go quiet upon transmission stopping with zero squelch crash; the law dispatch, ever since this problem started, now has a monster, at least a second long if not more, squelch static crash after any transmission. I need to go make sure I don't have a setting incorrect in the law dispatch personality that might be allowing that.
 

IAmSixNine

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You know, there is always the possibility that there is an issue with 1 of the sites. You mention your radio has worked with this set up for 4 years. A few months ago it started to cause issues. The trailing squelch tail on the law dispatch channel could be an issue starting to creep up and get worse over time on their system.
Its more noticeable to you due to your location to the sites while the public safety users wont notice it unless they are very close to your spot.
Test out and see if the issues is still there when your in different part of the city/county. While your radio might be old it may not actually be your radio (alignment) but rather a system issue. But after 14 years it wouldnt hurt to have it aligned.
 

RFI-EMI-GUY

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I would try bringing the radio to a location outside where it can see the strongest of the three sites . Also, is that radio programmed for narrow band RX? It should be..

"I can forcefully attenuate the signal by gripping the radio's antenna in my hand, and doing this causes the received audio to stop the on/off cycle described above, and I then hear everything clearly. So I am assuming that this fade in and out issue is due to the receiver getting overloaded by the two different equal signals off the two repeaters covering the local area. "
 

wgbecks

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I seriously doubt it's radio alignment. I live in a county that has thirteen VHF transmitters in simulcast with numerous areas where the overlap causes way more problems than it was intended t solve. The system is aging and the problem with overall alignment has been exponentially increasing over time. Piss poor maintenance and a general lack of understanding of simulcast by the shop maintaining the system!
 

NVAGVUP

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Also keep in mind, simulcast systems are basically "Controlled Transmitter Interference" They are designed with overlap areas in mind. Overlap areas can be "moved" by adjusting transport by microseconds. A fairly common practice is to adjust transport delays to "move" an overlap area from footprints with a high number of public safety calls. (Directional and/or downtilt antennas are also other techniques) It is plausible the overlap has been adjusted (And now affects your location moreso than another footprint) As someone lese mentioned, try your radio in a different location. Not within your house, but miles away. Does the issue follow your radio, or your location?
 

KD6RRR

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Well after some wandering around town over the last few days, it is just as has been suggested; I just happen to live in the "bad spot" for the system here locally. Traveling not even a half mile in three directions gets me clear reception again. Traveling as far as I can without trespassing in the fourth direction actually makes it worse, then going a couple of miles beyond in that same direction by driving the long way around on public roads, it will get better again until I'm up against a mountain.

So it's obvious that whatever work that was done that fateful sudden change afternoon must have moved the bad spot to my neighborhood. Maybe I should be thankful that they don't need great reception for law enforcement around my area!

Thank you all again for your insight and time spent sharing your ideas and experience!
 
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