PSR500 P25 --- Need some input

[GrumpyAeroGuy]

OK, given that P25 reception in my home of the county just south of me is next to non-existant, had an opportunity to drive 1-1.5 miles down the road (INTO the county that I am trying to monitor). Sat in my wife's office and listened for a while.

The system is received like I am sitting in the units I am listening to. It actually has changed my opinion of this scanner tremendously. No distortion, no nothing. Incredible P25 performance.

at my home, 1 mile north, the control channel is choppy, or not received at all. This is all with an RS 800 antenna. On occasion, I can get this system at home, but it is never great. One mile south, unbelievably good---actually--- beyond excellent.

What is the answer for me at home? Outdoor antenna? Is there an answer?

I am astounded about the performance difference. is it possible that there can be this big a descrepency 1 mile away?

I am going to check if there is a cell tower near by my home. Would this matter, and why? Seem to have read some threads that this can be an issue...


I'm not giving up without trying something else.

The system in question is Ohio---Hamilton County. This has me a little intrigued.

[Spitfire8520]

Originally Posted by GrumpyAeroGuy

What is the answer for me at home? Outdoor antenna? Is there an answer?

I am astounded about the performance difference. is it possible that there can be this big a descrepency 1 mile away?

While I have no experience with antennas, I would definitely believe some kind of outdoor antenna would improve your reception with the house itself probably reducing reception of some signals. You should probably wait for a lot more experienced members to reply with suggestions.

As for the performance differences, digital signals are notorious for what is known as the "digital cliff." Basically digital signals are really an all or nothing situation where a middle does not exist like with analog where you steadily get more and more scratchy as you move farther away. Here's a link to a Wikipedia article regarding digital cliffs.

https://en.wikipedia.org/wiki/Cliff_effect

Hope I helped somewhat!

[Mike_G_D]

I'll try and shed a little light on some possibilities concerning your situation. Firstly, judging by what I see in the RR database concerning the county system you mentioned, Hamilton County, Ohio, I gather it is a large simulcast P25 system. If truly simulcast and you are trying to receive it outside of its designed for coverage area (you indicate you are north of the county it was designed to cover by a couple of miles or so), then this is likely part of your problem and such systems are notorious for causing grief to scanner listeners using consumer grade radio equipment. Here is a link to the RR wiki describing simulcast distortion: Simulcast digital distortion - The RadioReference Wiki.

Although I generally go along with what is stated in the wiki I will add that I think there is more to it based on my past experience in RF engineering for mobile TDMA digital cellular equipment. I worked with a brilliant individual who was responsible for cleaning up multipath phasing distortion in the RF signals carrying the digital information. We had a whole subsection in the unit's design with dedicated hardware and software/firmware devoted to this issue. It was, as I recall, termed as the "equalizer". In that case, the distortion was primarily caused by multipath signals resulting from multiple signal paths being received out of phase when the vehicle was moving rapidly through varying terrain. However, I can see similarities with the intended multi-signal simulcast generated by these simulcast P25 systems. I still think that there is a whole category of signal processing devoted to dealing with this issue in the "real" subscriber radios that is simply missing altogether from consumer grade scanner equipment. This is, no doubt, for cost reasons. Also, if I am to believe what some have reported who have access to schematics and block diagrams for some of these "real" radios, the design of the receiver's digital demodulation circuits has a lot to do with the issue in that the "real" radios (or at least some of them, according to some folks with the aforementioned information) have two different demodulation circuits (the common FM discriminator and the less well known, at least among non-technical folks, I/Q demodulator) that they can switch between on the fly according to how well the quality is on either; both demodulation methods have advantages and disadvantages given different digital modulation modes and different signal degradation characteristics. If such information is to be believed (I cannot verify it myself) using the two types of circuits together and being able to switch between them on the fly (I assume with some sort of advanced digital signal processing algorithm that characterizes the incoming signal in near real time thereby selecting the circuit with the best signal - I don't know for sure) gives them a "bet hedging" capability that I suspect is lacking in consumer scanners. To keep things simple, most hobbyist oriented articles concerning simulcast distortion simply lump all of this together under the term "error correction" and I really don't think it is that simple nor a fully accurate description of the problem. Back when I was involved in the TDMA cellular stuff, we didn't consider either the phase "equalization" or the demodulator design as "error correction" - the real error correction came after demodulation and equalization. But, I have to admit I am not up on the most current designs and I can also understand the need to "keep things simple" for non-technical readers (even if I don't agree with the methodology to do such).

Sorry if I got overly technical there but this has always been a fascination for me and I wish I could get the whole real story but have been out of the loop on things for too long now and no longer have any contacts in the industry to consult.

In any case, the above plus the nature of the simulcast systems themselves being designed to work well within only a very specific area makes this a likely cause of your problems. As described in the wiki article, using an external directional antenna pointed to a specific site antenna may help - this may not be the closest site but the site with the least phase distortion present on its signal. Also, you may find that the antenna needs to be pointed not at the site itself but at the point where the best least phase distorted signal comes in - you will have to experiment. There is much discussion concerning this on this site in the forums. Obviously, this is only a good solution for fixed use and does not address mobile operation - pretty much you are out of luck in that respect, at least while outside of the area the system was designed to support.

The nearby cell tower you mentioned could also be a problem. Again, this is because of the limitations in the design of the consumer grade scanning equipment. Specifically, in this case, the RF (radio frequency) "front end" which includes the RF amplifier and band filtering components. Cheaper less robust or less well designed RF front ends do not handle strong in band and near in band undesired signals as well as the better designed and more expensive variety. The current GRE front end is especially notorious for having this issue. Again, the specifics of the problem are more complex than what is generally described in non-technical hobbyist literature - the problem has more to do with the RF amplifier's dynamic range handling ability than with"filtering" which is what most folks usually harp on. In any case, yes, this could also be your problem. No easy cures for this either though using the attenuator that is built in to the unit is worth a try. Also, if the problem is really more to do with the cell tower issue than using a "lesser antenna" might help - in essence you are trying to reduce the level of the signals coming into your scanner rather than boost them. The hope is that you can reduce the interfering signal enough that it no longer badly affects your scanner's ability to hear what you want. Of course, the problem is that you also reduce the signal strength of what you want to hear as well - if that signal is sufficiently strong, however, it may be a viable solution.

It's entirely possible you have both simulcast issues as well as undesired front end signal overload issues. In such a case, that directional antenna may help the most if you can point it away from the source of the interfering signal and toward the best least phase distorted signal that you want to hear!

One other thing I would do which is least troublesome but "quick and dirty" and may help is to manually listen to all of the red and blue highlighted control channel frequencies noted in the RR database for the system you are interested in and try and find the best sounding least distorted signal (I can usually tell when phase distortion is occurring even on "digital" trunking control channel type signals by listening to them as there is a fluctuating high pitched "ringing and buzzing" that is inconsistent with what you hear on a good non-distorted signal of the same type - try listening to the control channel signal when in your wife's office and then doing the same at home to see how different they sound to you). You might find that you can get more than one system control channel where your home is but the scanner may not be locking on the best one.

So, pretty much, all of this means you will have to do some experimenting and "fiddling" but doing so may solve your problem - at least when stationary at home.

-Mike

[wingmaker]

I got some LMR 400 coax and a yagi antenna from this CellAntenna: Yagi and Panel Directional Antennas it is the CAY810 for 39.95, and in my expierence work good. I have 1 of the 3 yagis pointed at 1 of 4 of the towers for the Lake County Simulcast system in my state and I get 100% perfect reception of the Control Channel, its about 15 miles away or so.

If you can alreay get it, but not to good and you just go a mile down the road, if you had a yagi antenna pointed at the tower, with some good coax, mounted on your roof, you should definitly be all good

LOVE AND BLESSINGS

[GrumpyAeroGuy]

I appreciate all of the input. Mike_G_D: thanks for thanks for the tutorial. I enjoy reading and learning.

When the weather becomes a little more cooperative, I may try a YAGI. My gut tells me that when set up correctly, it'll probably make things a lot better.

[LarrySC]

An additional question for Mike. I'm just North of a P25 -5- tower system but out of range for the other 4 towers so I think my problem is not simulcast but maybe the 4 program settings like threshold or timeout. Signal shows full 5 bars but audio breaks up. Any idea. Larry

[krokus]

The system you are listening to is not simulcast?

It sounds like you have a signal corruption, which Mike went into detail about.

[LarrySC]

First of all I clearly posted that I am out of range of the other 4 towers so it could not be a simulcast issue.Second of all ------ I;ll just stop right here. Thanks for reply. Mike? Any idea on settings?

[wingmaker]

Originally Posted by GrumpyAeroGuy

I appreciate all of the input. Mike_G_D: thanks for thanks for the tutorial. I enjoy reading and learning.

When the weather becomes a little more cooperative, I may try a YAGI. My gut tells me that when set up correctly, it'll probably make things a lot better.

Cool let us know how it works out. I agree it is very good if your like me and only pick up really in one direction. I actually got 3 pointing 3 different directions LOVE AND BLESSINGS

[GrumpyAeroGuy]

Originally Posted by wingmaker

Cool let us know how it works out. I agree it is very good if your like me and only pick up really in one direction. I actually got 3 pointing 3 different directions LOVE AND BLESSINGS

I shall. Taking the PSR500 to my wife's office completely changed my opinion of that scanner... live and learn.

Gotta wait for the snow and ice to melt off of the roof..... lol

[Mike_G_D]

Originally Posted by LarrySC

First of all I clearly posted that I am out of range of the other 4 towers so it could not be a simulcast issue.Second of all ------ I;ll just stop right here. Thanks for reply. Mike? Any idea on settings?

What system are you trying to listen to? Also, I believe the admins would consider your post a thread hijack which is frowned upon - not trying to be difficult here just giving you a heads up. It's usually better to start your own thread with a separate problem - you're in a different area than the OP and with maybe a technically unrelated issue so it's always better to start your own thread when such is the case.

That having been said, I'll be glad to help if I can - just let me know which system you are interested in (best to include a link the exact system in your reply).

Given what you did say, yes, it might seem unlikely that you have a simulcast issue IF you really are only getting one tower. But it's not always that easy. Even though the other towers are further away, if it is a simulcast system due to terrain and other factors the signals could still be interacting in destructive ways at your location. Difficult to say given the current info. I would refrain from tweaking the scanner's settings yet. Also what scanner model are you using and what kind of antenna?

Also, you might try the area specific forum threads as someone there can probably help you best - based on your profile tag I'm guessing South Carolina?! Just something to try. Not being in the area and not being familiar with the system you are interested in I can only give possible generalities in terms of technical advice.

-Mike

[LarrySC]

Thanks, I'll try this from another source. Larry