Loose (Open) Squelch Improves LSM (Simulcast) Reception

[DaveIN]

It's been an ongoing problem since I've been monitoring simulcast systems. I'll bet Uniden has a real solution for this problem in the works. I can't wait to see what's next!

 

[jpm]

we want p2

 

[AZScanner]

In regards to the lower squelch helping P25 decoding, hell I noticed that with my old BC250D back when the Phoenix digital system was first being tested! On my trusty old BC796D, the squelch is set all the way wide open. Works pretty good that way, too.

Here in Phoenix where we have the RWC (which stands for Simulcast Radio System from Hell ) the best solution to this problem has been to put up a Yagi antenna and position it so that signals are only coming from ONE site. Once you do that, it comes in very very well. Not quite perfect, but considering the fact that you can buy a decent Yagi for less than 50 or build one yourself for less than 20, good enough.

If you want mobile use, set up your scanner on a yagi anyway, and become a feed provider so you can listen to your scanner anywhere you have cell service on your smartphone. :twisted:

-AZ

 

[SCPD]

I don't believe it. LSM simulcast systems are hard for consumer scanners to deal with it period. Best bet is to use a yagi antenna.

 

[rdale]

I don't believe it.

Believe it.

LSM simulcast systems are hard for consumer scanners to deal with it period. Best bet is to use a yagi antenna.

I've yet to see one work while mobile My testing took conversations with 30-40% audible to 80-90%.

 

[jcardani]

I believe the real issue is where the scanner's DSP is taking the radio signal from. If it is from the discriminator's baseband audio it would be flawed. It has been proven that CQPSK modulation (LSM) in a simulcast system is distorted due to multipath if discriminator baseband audio is used. The DSP needs to take the the I&Q signal from the last IF stage (450 or 455 KHz in most scanners). Example 455 KHz IF ---> IQ demodulation ---> DSP

 

[AZScanner]

Rdale got banned?? Darn it, I always miss all the excitement.

For what it's worth, I've found two things help my poor tired old BC796D cope with LSM simulcast systems: FM (not NFM) modulation and loose squelch. Believe me, I've tried EVERYTHING else I can think of, short of the Yagi antenna because I want to use my scanner when mobile. Why does it work? I have no idea - but I can attest that it certainly does help.

If you're struggling with simulcast hell, try using FM along with a loose squelch. It won't be a huge improvement, mind you, but it will help.

-AZ

 

[KC8ESL]

What works for me is using a junk (and I mean JUNK) antenna. I monitor 2 simulcast systems without any distortion issues. The Cleveland P25 system and the MARCS-IP system in CuyCo, LakeCo, and GeaugaCo. Back down your input gain to the reciever and voila, you localize to one tower. Try an attenuator if your radio has one built in or add one in-line on your coaxial cable feed.

Don't buy a yagi antenna that doesn't help you with all of your other listening habits. That yagi is for monitoring a system far far away, not localizing a single tower 3 or 4 miles from your house. Find an old JUNK antenna. If you have a very high RSSI value, it wouldn't hurt to use a dummy load of sorts. Maybe you could convert that LMR400 run to RG58 to attenuate from the external antenna. Getting a hotter signal from one single tower that is already screaming hot isn't what I've found is the most effective method.

 

[kayi4cle]

I’ve been experimenting with my 996T ever since Paul started this thread. Using his open squelch suggestion, I’ve tried it out on 3 floors at every window in the house. It helped a little, but I still wasn’t able to decipher whole sentences (just a word here and there). Next I set the site modulation to FM and entered some talkgroups selecting “Digital Only” for audio type. That still didn’t do it. So I finally ordered the smallest yagi I could find.

With the yagi (please don’t laugh) attached to a lamp next to a window on the 3rd floor, I am finally able to make out whole sentences and sometimes entire transmissions. It’s a HUGE improvement. But it only works on that floor at that window, and reception is better some days than others. Before the system went simulcast, I could receive it crystal clear anywhere in the house.

My biggest challenge was wrestling with 25 feet of LMR-400. That stuff is huge and stiff as a board. It took a couple weeks of working with it to finally tame it into a neat looking coiled-up mess next to my desk. I wish someone made a small indoor yagi on its own stand with flexible coax attached and BNC connection (a desktop yagi, LOL!).

 

[OpSec]

How does Motorola do it so well?

By using LSM voodoo.

 

[kaiserfan]

loose sqeec

What do you mean by loose squelch having serious problems on simlcast system in Saginaw Mi audio garbled and sometimes no reception at all have tried two other antennas other than original will pickup stations 30 miles away but not within 2 to 3 miles any suggestions

 

[ofd8001]

Kaiserfan-

You appear to be experiencing distortion which comes as a result of your scanner hearing transmissions from multiple sites on the same frequencies. Essentially your scanner is being bombared with transmissions from two (or more) sites and it's having trouble making up its mind on which signal to decode and thus the audio comes out garbled or not at all.

Or put another way: It's like a person on your left side shouting at you with another person on your right side also shouting at you. You can "hear" them fine, but you can't "understand" what they are saying because they aren't using the same words at the same precise moment in time.

There are several threads describing this in detail found in these forums along with some options. Do a search for "simulcast distortion"..

Oddly enough, if you were to go 30 miles away from Saginaw, you'll hear it better. I'm in Louisville KY and have the same predicament. If I 20 miles away from Louisville, I hear our system better.

 

[Ronaldski]

having serious problems on simulcast system in Saginaw Mi audio garbled and sometimes no reception at all have tried two other antennas other than original will pickup stations 30 miles away but not within 2 to 3 miles any suggestions

What radio are model are you using? I'm in Bay City doesn't garble too much nor if I'm in Saginaw.
Take a look at my reception FAQ's -
Mid-Michigan scanner frequency list

You can contact me through my website if you want.

 

[kaiserfan]

I'am using an HP1 have tried 3 antennas moved scanner multiple times it works for a day or two but then not sometimes it won't pickup anyy saginaw at all not just distortion it's like the decoder adjusts to not pickup signal and the 800mghs antenna you referenced wont attatch to HP1

 

[Ronaldski]

Be sure you have the latest firmware.
Uniden Home Patrol FAQ - The RadioReference Wiki

As mentioned you can contact through my webpage link is below, and then maybe meet up?

 

[kaiserfan]

also no one answered what loose squelch means is it more or less squelch?

 

[SB-Wi]

Here's a refresher from the first post:
"For now, though, we strongly recommend that you set your squelch level as low as you can without having conventional channels w/no tone programmed break squelch w/no signal present. If you are only scanning trunked systems, for example, you could effectively set squelch to 0 (always open)"

In recent studies, we've determined that the squelch setting can dramatically affect P25 decode quality, especially on Simulcast (LSM) sites. For more background on Simulcast issues, see the wiki article with the caveat that it is not fully correct on the root cause of the problem. Here is a quick bullet-point summary that more correctly describes the root cause:

• Any receiver dropout during digital reception creates data loss that results in bad decoding.
• Because multiple towers are transmitting the same signal, simulcast systems can have many areas that have “nulls” where the same signal from different towers arrives at slightly different times, causing the signal strength to drop and/or vary suddenly.
• Even atmospheric changes or someone opening/closing a door can affect where the nulls are, so even optimizing antenna location cannot prevent dropouts 100%. Moving a receivers antenna even a few inches can sometimes move it out of a null zone. Vehicle and fixed-location radios typically avoid the problem by use of a diversity antenna system. Also, system engineers try to design the system so that predicted null areas occur in areas that system users are not likely to be, such as over water or unpopulated areas. Even then, nulls cannot be 100% eliminated in intended service areas. Handheld radios w/single antennas and scanners are both subject to a higher level of signal amplitude changes.
• When the signal strength drops below the squelch threshold point, the scanner’s squelch action immediately stops the receiver from providing a signal to demodulate/decode, even if the drop is very brief. This results in data loss and choppy or no decoding.

We are studying to determine what things we can do in the scanners themselves to mitigate these drops (no guarantee that we can do anything for an existing model, but we are looking). For now, though, we strongly recommend that you set your squelch level as low as you can without having conventional channels w/no tone programmed break squelch w/no signal present. If you are only scanning trunked systems, for example, you could effectively set squelch to 0 (always open) with a couple of caveats:

• You must have End Code detect enabled. Otherwise, when an analog comm ends on a trunked system, the scanner will remain on the voice channel and you will either hear open squelch or the next comm assigned to the voice channel.
• It will take longer for the scanner to acquire the trunked control channel (normally, it only looks on those programmed frequencies that have a signal strong enough to break squelch). You can mitigate this delay by only programming control channels into your scanner.

If you have any conventional channels programmed with no CTCSS/DCS, then you must set the squelch to threshold: typically 3 or 4. Even if all your conventional channels have CTCSS/DCS, you might want to keep the squelch at threshold, as it will take much longer to scan conventional channels with squelch fully open. The scanner will have to evaluate every channel for the presence of CTCSS/DCS before moving to the next channel. Typically, this check is only made for those channels with a signal strong enough to break squelch.

 

[walter900]

In recent studies, we've determined that the squelch setting can dramatically affect P25 decode quality

I may be thinking about something different here and not quite understanding your post... But when I monitor a Motorola ll Trunking System in my area.. After imputing all frequencies.. I noticed I was missing conversations as a few of the entered frequencies were having signal strength issues.. Opening the Squelch helped out greatly, but when it comes off trunking and back onto conventional scanning I had to close it back down to normal. In my situation it was signal strength of all the entered trunking frequencies (especially the control channel) not being equal in quality.. I realized, for reliable trunking/digital scanning all channels need to have good signal strength... I have recommended in the past that Uniden include a mini signal AMP that can be turned on/off globally or per channel... Like the ATT can, but in this case to boost signal.. This would be a very useful feature and help solve a lot of reception issues from scratchy channels unreliable digital decoding.

 

[Bote]

One solution is for the scanner squelch to have better hysteresis. I notice on the analog simplex railroad channels that since reprogramming them for NFM the squelch is ridiculously stingy, even when set on 1.

Give the scanner a chance to recover from a fade, don't close the squelch the very microsecond the signal drops below threshold.

Better yet, develop a squelch action that approximates the MICOR squelch without running afoul of somebody's patents and you'll have a real winner. There are still a lot of analog radio systems out there and will be for some time.

 

[wa8pyr]

How does Motorola do it so well?

Having just spent several days in Schaumburg, I can tell you that Motorola tests the dickens out of their stuff. I was very impressed, so much so that I now feel better about the slightly higher prices.

In fact, I can't overemphasize how impressed I was by the incredibly stringent testing and attention to detail.