 Posted:  Wed Aug 07 2019, 11:54pm | |
| Posted by: w2lie | Posts: 2802
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Old Display Name: w2lie
| Location: Long Island, NY
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Your Admin
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Is anyone using a Whistler TRX-1 or TRX-2 to monitor the new Suffolk P25 system? If so - are you having any luck using it? I know this scanner isn't made for simulcast, but there shouldn't be any reason that from Nassau County I miss +90% of the voice traffic on this system, and the inverted S never goes inverted T. I shoudl be far enough outside of Suffolk where simulcast is not an issue for me. My goal here is to see if it is an issue with my scanner, programming, or the radio in general.
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| Posted: Thu Aug 08 2019, 01:38am | |
| Posted by: GTR8000 | Posts: 146
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| Joined: Fri Nov 25 2016, 07:07am
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It's actually a two-fold issue with most scanners.
The first is that there is actual simulcast distortion, whereby the scanner is getting hit with signal from two or more sites at once, and the timing is slightly off which gives the scanner fits trying to cleanly decode it. Normally this can be mitigated with some form of attenuation, or by using a directional antenna in order to make the capture from one site so strong that it drowns out the other sites. Attenuation can be in the form of the scanner's attenuator feature, by using an antenna that has less gain (e.g. using a rubber ducky indoors vs a big outdoor antenna), or by being well outside the intended coverage area of the simulcast cell.
Unfortunately, being well outside the intended coverage area gives no guarantee that you're only going to capture one site strong enough to drown the others out. It may seem like you're far enough away, but it only takes one monster site that is further away from you than the nearest site on the map, and it can still wreak havoc. I have seen this numerous times with simulcast cells around the region, where a site in the center of the county is actually stronger than a site at the edge of the county. Because of that phenomenon, your distance outside of the intended coverage area may not matter all that much.
The second issue is the modulation used with these simulcast cells. Motorola favors LSM (their own flavor of QPSK) while Harris and others favor the H-DQPSK standard. This is always the case with Phase II TDMA systems, as TDMA requires linear amplifiers and thus some form of QPSK modulation. Most modern P25 simulcasts will use a form of QPSK even when the system is only capable of FDMA, with C4FM modulation largely being restricted to non-simulcast FDMA standalone sites. In the case of the latter, while the control channel will use C4FM modulation, TDMA traffic channels will use QPSK.
The trouble with QPSK is that it's not straight FM, there is some AM involved that is fairly critical to attaining good demodulation. Unfortunately because nearly all scanners except for the SDS series use an FM discriminator, they kill that important AM component of the signal, thus crippling their ability to cleanly decode most P25 simulcasts.
Of course some scanners do better than others, so a 436HP might decode the system adequately while a TRX fails miserably. I for one never got into all of the smoke and mirrors of adjusting P25 wait times and all that crap...it's easier to just listen with an APX and call it a day lol.
[ Edited Thu Aug 08 2019, 01:43am ] |
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| Posted: Wed Sep 04 2019, 02:50pm | |
| Posted by: LIScanner101 | Posts: 381
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| Location: Hicksville, NY
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| Joined: Sun Jun 16 2013, 09:29pm
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Phil,
I have a Radio Shack PRO-668 that has fits with this system. Right now I'm just monitoring from my home office with a RS 800MHz duck and sometimes I have to move the scanner around my desk a few inches here & there to get it to decode. Most of the time it's clean, but once in a while I get the garbled mess that I'm sure you're dealing with as well. I live in Hicksville only a few blocks from the Northern State (northernmost part of Hicksville).
I know a few guys that have sprung for the Uniden SDS100 and say that it's like a dream come true for LSM, but I'm just not ready to plunk down that kind of cash just yet. |
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| Posted: Wed Sep 04 2019, 02:53pm | |
| Posted by: LIScanner101 | Posts: 381
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| Location: Hicksville, NY
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| Joined: Sun Jun 16 2013, 09:29pm
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GTR8000 wrote ... I for one never got into all of the smoke and mirrors of adjusting P25 wait times and all that crap...it's easier to just listen with an APX and call it a day lol.
Agreed 1000%. Those things are just a stopgap measure, they have almost no effect on the scanner's performance on these systems. However, I do NOT have an APX lol.
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| Posted: Thu Oct 17 2019, 05:39am | |
| Posted by: PFD Mike | Posts: 433
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Old Display Name: PFD Mike
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Donating Member - 2008-2010
Premium Member | Joined: Wed Aug 02 2006, 12:31am
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| Using a GRE-PSR800 I get Command Band crystal clear, but the radio stops on the 1st Pct and I get no sound. Nassau county - Wantagh. Just giving some input to Phil - Stock antenna |
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| Posted: Thu Oct 17 2019, 11:17am | |
| Posted by: Dave3825us | Posts: 1006
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Old Display Name: Dave
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| Premium Member | Joined: Fri Mar 24 2006, 10:47pm
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PFD Mike wrote ...
Using a GRE-PSR800 I get Command Band crystal clear, but the radio stops on the 1st Pct and I get no sound. Nassau county - Wantagh. Just giving some input to Phil - Stock antenna
What system is this happening on? The P25? If so, what site is this happening with?
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| Posted: Thu Oct 17 2019, 06:14pm | |
| Posted by: PFD Mike | Posts: 433
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Old Display Name: PFD Mike
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Donating Member - 2008-2010
Premium Member | Joined: Wed Aug 02 2006, 12:31am
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Dave3825us wrote ... PFD Mike wrote ...
Using a GRE-PSR800 I get Command Band crystal clear, but the radio stops on the 1st Pct and I get no sound. Nassau county - Wantagh. Just giving some input to Phil - Stock antenna
What system is this happening on? The P25? If so, what site is this happening with?
Suffolk P25 is the system - It doesn't show which site it is receiving.
It just seems that the "Command Band" the audio is clearer. I get a get a lot more of a chopping sound on other talkgroups. When I say chopping its like the radio has nott locked onto the group (usually in the beginning of the reception). The audio sounds better after the start of a message.
My original post said 1st Pct - That was the 1st Pct Talkgroup - not the site.
Sometimes it sounds great from the start.
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| Posted: Thu Oct 17 2019, 06:56pm | |
| Posted by: Dave3825us | Posts: 1006
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Old Display Name: Dave
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| Premium Member | Joined: Fri Mar 24 2006, 10:47pm
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PFD Mike wrote ...
My original post said 1st Pct - That was the 1st Pct Talkgroup - not the site.
Sometimes it sounds great from the start.
That where I was going. I pick up site 4 much better than site 6 and on 6 many times it won't decode well enough for any audio. Site 4 on the other hand, all talk groups come in basically the same and clear.. |
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