P25 simulcast distortion and other questions

I believe that I have seen that I can eliminate P25 simulcast distortion by only programming one system site as opposed to all of them?

The particular system is Dauphin County, PA (Dauphin County Trunking System, Steelton, Pennsylvania - Scanner Frequencies) and has 10 total sites listed with the first being "Simulcast". I assume that, if I am at home, I would only want to have the site programmed the coverage of which overlaps the area where I live? The same thing with when I am at work...I would only want to have the closest site to my office programmed. Since it a simulcast system, as long as I am hitting one site, I will still receive all radio traffic in the county according to which TGIDs I have programmed?

dmg1969 said:

I believe that I have seen that I can eliminate P25 simulcast distortion by only programming one system site as opposed to all of them?

The particular system is Dauphin County, PA (Dauphin County Trunking System, Steelton, Pennsylvania - Scanner Frequencies) and has 10 total sites listed with the first being "Simulcast". I assume that, if I am at home, I would only want to have the site programmed the coverage of which overlaps the area where I live? The same thing with when I am at work...I would only want to have the closest site to my office programmed. Since it a simulcast system, as long as I am hitting one site, I will still receive all radio traffic in the county according to which TGIDs I have programmed?

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Oh if it were only that easy...

You are correct in that you may only want to "enable" the site that is closest to your current location (work, home, etc.).

However, in general, there is no guarantee you'll hear everything / all talkgroups on all sites. In fact, that's very unlikely. That somewhat defeats the purpose for the system to have separate sites.

The simulcast site typically covers a large area like a city. In this system, it looks like the simulcast site is designed to handle coverage and traffic for the greater Harrisburg area. Individual sites typically cover smaller areas and many times are designed to keep area specific activity inside that site (vs. being heard countywide). The Lykens site is an example which is limited to that northeastern corner of the county.

In general, you will only hear a talkgroup across multiple "sites" when a user/subscriber radio is switched onto that talkgroup inside the site(s) you are trying to monitor. For example, if a talkgroup is usually only active on the simulcast site, you may hear it for a brief time on one of the other sites if/when a user radio switches to that talkgroup and is inside or near the coverage area for the "other" site. But when that radio leaves that talkgroup (on that site) the talkgroup will go silent (on that site). Talkgroups that are unlikely to leave the intended site (say for example - downtown Harrisburg police or fire units) are unlikely to be heard on the Lykens site (but it's possible for several different reasons).

There are exceptions --- for example, Prince George County Maryland has two* main (simulcast) sites - North and South. There are a few fire talkgroups that are common and heard on both sites but there are others that are site specific and typically only heard on one or the other because they are specific to the area of coverage - north county or south county.

Every system and it's sites (1 or more) is configured in a different way depending on that needs for the customer and coverage.

I've found that the best reception comes from
(a) selecting only the site(s) you want to monitor for you location - unless there is a single simulcast site for a given system, the days of trying to hear the entire area/county are fading fast
(b) program only the control channel frequencies for each site - even better (but can be risky if the site changes to an alternate CC), only program the primary control channel frequency; this speeds up re-acquisition of the control channel when it gets lost due to the simulcast problems
(c) find the "sweet spot" at your current location for each site; many (but not all) times, distorted and/or poor reception can be overcome if you can find that perfect spot to place your scanner; however users are situated smack in the middle of several site towers/transmitters and have trouble even making this work.

It doesn't so much matter for me when I am at home because I am only within range of two of the sites...Peters Mountain and Mahantango. I'm going to create two FLs...using only one of each of those sites and see which one I am hitting here at home. I have a feeling that it is Peters Mountain. Whichever one I hit, I will use that FL at home and see if I can hear u its from the from side of the county (Derry Township in the Hershey area). Then, I will create another using the simulcast site for when I am at work. Technically, I could run on the Peters Mountain site from home to work as I am within the coverage area the whole way. I am just going to experiment and see what happens. It's part of the fun of scanning.

dmg1969 said:

I am just going to experiment and see what happens. It's part of the fun of scanning.

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That's the correct attitude!

In my situation, I have two radios (a PSR800 and a WS1080) with "sweet spot" positioning in my den - one positioned to listen to the site of our state system that I am sitting inside (Anne Arundel) of and the other to receive an adjacent site (Baltimore). The two radios are sitting less than 2 feet apart to accomplish this but if you move them even and inch or two, the voice becomes unintelligible. Occasionally, as conditions change (seasons, leaves on trees, etc.), some slight adjustments and movements are sometimes required to maintain reception.

FWIW - the Unidens (436 and 536) aren't a whole lot better as far as required placement. The 536, being wired to the power outlet, has to be stationary anyway. The 436 allows me to have a slight bit more mobility but still requires being positioned properly to get decent reception. Most times I can hear voice on the Anne Arundel simulcast site of the Maryland FiRST system but it still is distorted most times. In contrast, I many times get better reception from the Baltimore site - probably because one transmitter/tower of the Baltimore site is much stronger than any other of the transmitters on that site (since I'm outside the intended area of coverage). Therefore, the simulcast distortion is less of an issue. The problem with the x36 radios is that for more distant systems/sites and/or these newer systems/sites that are designed to stay inside the intended area of coverage, the reception "comes and goes" like the wind (there is activity but the radios don't receive it consistently - I know this based on other indicators including other radios). Such is the basic nature of digital communications. In the days of analog, it might just be really "scratchy". Digital may just stop being received if/when sufficient signal strength and decode quality drops off. Even Uniden has said "YMMV" (your mileage may vary).... Every situation is different.

Well, I did indeed create FLs with just one site in each. It turns out that I can only pick up The Peters Mountain site at home. I am not within range of the Mahantango site. Rather than my normal Dauphin County FL that I scan with my other FLs...I will scan just the one with the Peters Mountain site on the way into work tomorrow morning. I should have coverage the whole way into work. When I get to work, I will take the HP-1 into the office and monitor FL I created using just the simulcast site.

From what I heard at home after casting the single site FL, I had no distortion. Whether I heard all the radio traffic is unknown. However, I was hearing traffic for calls outside of the radius of the coverage of that site, so I would say that I was hearing all radio traffic countywide.

dmg1969 said:

However, I was hearing traffic for calls outside of the radius of the coverage of that site, so I would say that I was hearing all radio traffic countywide.

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You will - as long as at least one radio is on a given talkgroup is active within the site you're monitoring. Peters Mountain overlaps into the Simulcast (Harrisburg) area/site so it makes sense.

As far as all traffic countywide - I'm willing to bet that you won't hear the same things on other more distant sites such as the Lykens site.

dmg1969 said:

I believe that I have seen that I can eliminate P25 simulcast distortion by only programming one system site as opposed to all of them?

Click to expand...

Going back to the this original question on a simulcast system, one cannot program a single site for the simulcast system. The nature of a simulcast system is such that you have several transmitting towers (sites) all operating on the same frequencies. Thus you cannot isolate just one of the sites via programming - it is all or nothing.

Your county appears to have a mix, consisting of several sub-systems one of them being a simulcast system, the rest are "stand alone" sites.

You may wish to program all ten of those sites. You can get into site settings for the simulcast system and tinker with the attenuator, P25 Threshold Mode and P25 Threshold Level settings to find some combination that improves the decoding of the simulcast site.

For the other "non simulcast" sites, distortion should not be an issue.

If you are out of range of a site, the scanner more or less skips over them. You can also eliminate the too far away sites from even being scanned with location control turned on.

Checking the fcc licenses for the Simulcast system and Peters Mountain confirms this:

- the simulcast "site" has 10 frequencies and 6 transmitters sites around Harrisburg
- Peters Mountain "site" has 6 frequencies and 1 transmitter site north of Millersburg

You can expect that reception on the Peters Mountain site to be very good because there is only one transmitter/towers and will likely notice the simulcast distortion on the Simulcast site.

Also, give the Simulcast site has 10 frequencies and the Peters Mountain site only has about 55% of the capacity of the Simulcast system, it is another indicator that is is unlikely both will carry the exact same traffic.

OK. I am still a little unclear on exactly how the multi-site trunked systems and simulcast works. I did tinker around with the P25 audio settings in the HP-1 and never really found any improvement. I need to do some online research (or in the RR wiki) for a good explanation of the mechanics of trunked and simulcast systems. Not being into amateur radio and doing analog conventional scanning most of my life, I am still fairly new to trunking and simulcast. It's still fun to experiment though....

How can I tell if a site is part of the simulcast. Can I tell by looking at the system site information here in the RR database (https://www.radioreference.com/apps/db/?sid=5502) or do I need to look on the FCC website?

Dave- Do you have the HP Extreme Upgrade? You're getting into details which would make the Extreme option a good thing to have on your HP-1.

dmg1969 said:

How can I tell if a site is part of the simulcast. Can I tell by looking at the system site information here in the RR database (https://www.radioreference.com/apps/db/?sid=5502) or do I need to look on the FCC website?

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In the RR database, simulcast "sites" are often labeled "Simulcast". If you click on the word "Simulcast" on that page, it will take you to another page which says "Six-Site Simulcast". Then on that page, if you click on the FCC license call letters near the bottom, the page that will appear will show you the locations of the towers that make up that simulcast "site."

The word "site" can be used two different ways. A site can be a group of towers that make up a simulcast "site", or it can be a single tower at a single geographic point.

The problem with simulcast sites is that they share frequencies. So when a transmission takes place, the signals are coming at your scanner on the same frequency from different locations, and basically are competing with each other. If you are closer to one tower than another, the signals will be out of sync. That's not an issue with towers that have their own, unique frequences.

popnokick said:

Dave- Do you have the HP Extreme Upgrade? You're getting into details which would make the Extreme option a good thing to have on your HP-1.

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No, Mark. I never really considered it, but I may now. I'm going to do more research into the issue of P25 distortion...particularly on the HP-1. I know that the newer firmware has the P25 settings in the audio options. I played with them for some time and never really got any positive results.