BCD325P2: confusion on trunking sites

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paulmohr

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I am not entirely sure if this question should go here, the Michigan forums or the Antenna forums. If this is the wrong place feel free to move it where it belongs.

Ok, so as most of you know by now I am trying to pick up the next closest trunking tower to me. I can get the local one, but I am trying to pick up a different one a bit farther away. I would say it is about 25 miles from me.

I live in Adrian MI and I am trying to pick up the Michigan Public Safety Communications System. Like I said, I can get the local tower in Adrian easily, but I want to try to pick up another one, like Monroe Simulcast in Monroe County.

I constructed a high gain 850mhz yagi antenna using the calculator from K7MEM's website. 40 inches long, 11 elements and says 12db gain. Basically I took apart an old TV UHF antenna and re purposed the parts. Trimming and placing the elements where the program told me to. It seems to work fine, but I have no testing equipment to really know. But aiming it around at stuff it seems to pick up fine. It has a folded dipole feed element that is supposed to be 300 ohms. I have a 300-75 ohm adapter on it with 25 feet of RG6 cable. The antenna is on a fiberglass pole 15 feet in the air.

I am using the Uniden 325p2 and programmed in the tower sight and associated groups. I am using the built in spectrum analyzer on the 325p2. If I hold on the control channel and aim the antenna the analyzer shows me getting a signal, and fairly strong one. However when I switch it back to scan mode (just scanning that site) I get nothing. If press hold and toggle through the groups and ID's the little antenna bar at the top shows a signal but the screen says "searching for control channel".

I am confused at this point, anyone have any ideas? My guess is that even though I think I am getting a signal my antenna still isn't strong enough to actually "lock on" to anything. But that is just a wild freakin' guess lol. I am beginning to think this is something that will never happen regardless of what I try. Am I correct?
 

RoninJoliet

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I have a RS groundplane in the attic which the attic is about 20' above ground using 30' of LMR400 coax, if I move the antenna 6" from where it is I loose the 5 bars on a Starcom site 28 miles away, that's how critical those 700mgz digital systems are...If I move my 325P2 with 800mgz rubber duck in the correct spot on the second floor of my home I pick up the same "site" with 4 bars perfect also...Its really a experiment for this stuf.....The "hot spot" is what counts....
 

marksmith

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Your noting that it is searching for control channel is a solid determination that the signal is not strong enough for it to decode the control channel.

Comment by Ron in is also useful. Using a radio mounted antenna, often 4-6 inches of radio movement is the difference between good and bad signal.

On 700-900mz, this is a very real phenomenon.

Very small adjustments to your antenna location or orientation can produce huge differences in signal strength or signal quality.

Having said that, 25 miles away for a 700 - 900 mz system, especially if the site is not in your specific jurisdiction area is at max limits.

P25 system sites are specifically designed directionally to propagate where that system is to work, and specifically avoid being any interference other than that area. It could be directionally away from you purposely.

I have a tower site on a p25 system a couple miles from me that does not come in where I am. If I go mobile a mile in either direction it comes in. It is designed not to cross over one jurisdiction to another.

536/436/ws1095/996p2/996xt/325p2/396xt/psr800/396t/HP-1/HP-2 & others
 

paulmohr

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Ok so basically it is probably never going to happen, and if it does it will be by shear luck and if a bug farts on my antenna I could lose the signal lol.

I think this is pretty much what everyone has been telling me all along and I have just been too dense to listen. So instead I have beating a dead horse for no reason.

However I did entertain myself for a day and learned how to build a highly directional 800mhz antenna.

Thanks for the help and I PROMISE I won't ask about picking up another tower again LOL.
 

marksmith

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If it was a Motorola Type II system, 35 miles away would probably be much more doable, as those sites were generally more brute force repeaters than the new P25 sites, which are now designed to protect more spectrum, etc.

The newer systems, especially the simulcast sited systems, are much harder for scanners to lock on properly and decode.

You may not be missing a lot. The statewide system I monitor allows me to monitor stuff thru my local site that is not in my area. Depends on how your state does channel grants and radio affiliations to various towers on your system. It is a new P25 Phase 2 only a few years old.

You could get a cheap $20 dongle and Unitrunker and survey that second site and see what traffic it is carrying.

536/436/ws1095/996p2/996xt/325p2/396xt/psr800/396t/HP-1/HP-2 & others
 

paulmohr

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I can get some stuff that isn't local, but not a lot. May main goal was to increase my state police coverage. Right now I can only get the local post which is in Monroe. We used to have one in Adrian but they closed it and combined with Monroe county. Actually they closed a ton of them. They shut down a lot of locations but managed to keep all the people and officers. Just assigned them to different posts.

I will check out this Unitrunker thing. I was looking into the software controlled scanner things earlier but it looks VERY complicated and confusing. Look at the questions I ask with a simple 325P2, imagine if I tried to figure one of those things out lol. I would probably get banned from the forums for flooding it with questions.
 

paulmohr

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With the dongle and the software based radio thing I am still limited to what my antenna will pick up right? I mean it still isn't going to let me pick up a tower that isn't range from what I can tell. Or am I missing something.
 

jonwienke

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No hardware can demodulate a signal that is not first received by your antenna.
 

JamesO

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You did turn the TV antenna so the elements are Vertical? TV antennas are Horizontal polarized, not Vertical polarized like typical Public Service service transmit antennas.

You may also want/need a Low Noise Amp at the base of the antenna.

For a long time I suffered with antennas on the back of my radios in the house. I then installed an attic antenna, but I cannot use high quality, larger coax, so I had a long run of RG6. It worked ok, however, I was still missing traffic from neighboring systems. Then I spend a lot of time and money experimenting with different Low Noise Amps and FM Broadcast filters. I now have a very sensitive receive antenna system that allows me to monitor many of the neighboring systems that I could not receive before.
 

paulmohr

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Yes I did turn it on its side. I basically just took an old UHF yagi antenna and removed all the elements and everything so I had a bare boom. Then I used that website to calculate the length and position of the elements to change it to a 850mhz antenna. Then I cut the elements to the correct sizes, marked out the positions on the boom and re attached everything. Then made a folded dipole feed element and attached it with the plastic part that the original feed elements was on.

I think that since the towers are made to have limited coverage I am just out of luck regardless of what I try. I can live with that.

What I would like to do is climb my 30 foot tower and flip my large TV antenna on its side to see how it performs. Since I am afraid of heights though I don't see that happening. I might get up the courage some day though.
 
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You've done pretty much all you can do, if you lose the control channel signal, you won't get the Talkgroups. There is also a possiblity that you may get the control channel okay enough to register, but the voice freqs channels will be too weak to come in, because of the distance. Also the scanner may be trying to latch onto a different CC signal which is in a different system, but in your channel site freqs lineup. I had this happen to a distant system. Something didn't seem right. It was locking onto a different system's CC frequency that happened to be in my voice freqs lineup. That particular (voice channel) was also a Control Channel for a different system. So it was ignoring the (really weak) control channel I wanted in favor of a stronger one it found on that voice channel in my programmed lineup. And it wouldn't lock at all when in Scan mode. I gave up on this one as I couldn't trick the scanner to ignore the bad CC without locking out one of the voice channels in the system I wanted.

If you've done all this, a USB dongle with Unitrunker isn't that hard. The worst is getting it first setup with the Zadig driver and then Unitrunker & your computer, being able to find it as a device. I actually tried it on 3 PC with Win7 as I was just using a discriminator tap before this. The USB dongles work great in UniTrunker. It works great to monitor the total activity of a P-25 system, what TG's are currently in use on what freqs and where they bounce to. But it is visual data to look at. The scanner does give you the "actual audio calls". If the system is analog, you will get sound, for a P-25 digital system, you need two dongles. One to monitor and one to decode the digital data output (to get real sound) with DSD+. I tried it. I couldn't make it work to do sound. You will need the same antennas you are testing, (and also an F connector adapter cable to work with the dongle). Unfortunately, I don't think it will be that useful to you or give you any more than the scanner does. Unless you wanna see what their radio system is doing with what channels every second and log it. This is badly addictive. You see how their radio system works.
 
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JamesO

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Since the scanner is a handheld unit, get in the car and drive over near the tower/site you want to monitor. Then make sure the scanner is programmed correctly by monitoring the site.

Then drive back toward home and stop every so often and see how far the radio can still monitor this tower/site with the stock antenna on the hand held. Figure out where the service drops out. Then you will have an idea how close/far the site signal is from you.

You may need a decent Low Noise Pre-Amp setup similar to what I am using. I am sure a number of people will claim if the antenna cannot pick up a decent signal the Amp will not help, not true it you are using a very Low Noise Pre-Amp.

See this thread - https://forums.radioreference.com/s...mp-10-off-december-other-useful-rx-items.html
 
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