Improving 850-860 mhz reception

[SevenMaryFour]

Are you sure you aren't getting too much signal? Too much will cause this kind of popping etc.. I know from experience. I thought for the longest time I wasn't getting a good signal. Turns out these scanners aren't great at filtering UHF, thus any amplification of signal just overloads the filters and lets all the crud through.. Try attenuation on your signal and see if it helps. Can you get a signal with no antenna or very little antenna at all? If so, you probably have overload problems.. Example, on my 785D if I have full bars on an 800mhz trunked system, it sounds like crap. If I cut the signal down to about 3 bars, it sounds much better. Hiss in the background, but much much better to listen to. My 668 is really good at attenuation on the systems I listen to. Makes a system that is hard to even listen to, to something that sounds rather good.

I'm glad you brought that up because I thought that might be part of the problem as well. On the Plano/Allen/Wylie/Murphy P25 digital system, I get a full 4 bars on my HomePatrol-1 with my external antenna at comparable distances from the transmitters. Since it's P25 digital, the audio sounds more or less the same regardless. The county's analog system control channel hovers between 2-3 bars (and swings between 0-4 bars on the talk channels). As an experiment, I turned on the attenuator feature last night. The PAWM system stayed strong at 3-4 bars and did seem to remove some of the digital distortion that happens from time to time, but the County system disappeared completely, so I think it's more a weak signal issue than a strong signal issue.

Re: the use of an external antenna vs rubber ducky, I do have an RS-800 that I've tried. The PAWM system comes in pretty well on it, but the county system is too weak. With the stock HomePatrol-1 antenna, neither system can be monitored from inside my apartment.

 

[bharvey2]

You might also consider running RG6 or RG6Quad instead of the RG58. You'll get much less loss at 800-900MHZ and it will probably be easier to come by than LMR400 and such. It is 75ohm instead of 50ohm but I don't think you'll notice an appreciable hit it performance in a receive only application.

bharvey2

 

[prplehz]

I have a similar situation. I have a site that is about 10 miles from me. No matter what I do it still pops etc. Now if I listen to the same system on a site that is say 15 miles or more away. It's much better. That same poppy system when put in trunker gets 70 percent decode rate, until I hit the attenuation, then it gets 99 percent.. However the voice channels still pop and such. I gave up trying after trying everything. I think it may just be intermod. I would change your cable to RG6 coax if I were you, that is the only thing I use especially when it comes to 800 stuff.. It does make a difference, even if it doesn't completely get rid of the problem, it will help. Best of luck.

 

[fredva]

so I think it's more a weak signal issue than a strong signal issue.

I think you are probably right.

Earlier I believe you mentioned trees nearby. Are those trees still in between you and the transmitter when you have the antenna on the patio?

The fact that you were able to make an improvement by cutting the line length is encouraging.

 

[sparklehorse]

As mentioned earlier, RG174 is pretty crappy coax for 800MHz. According to the coax calculator that was linked to earlier in this thread, even at 13 feet the RG174 still has nearly 4 dB of signal loss at 855 MHz. Keep in mind that just a 3 dB loss means your signal strength is cut in half. LMR-400 by contrast has just .491 dB of loss over a 13 foot length. A better antenna and better coax should really help your situation out. Unless your problem is just overload from that nearby cell tower or something. It might be worth trying that inexpensive 800 MHz yagi type antenna that was linked to earlier (the Supersonic 602 I think, or something like that). That design is directional. It will give you some gain when pointed at your target site, while helping to reduce any overload you might be getting from nearby cell towers (assuming the cell towers aren't between you and your target). I know you mentioned monitoring more than one site, but you might just be surprised how well it will still pick up your other sites even if it's not pointed in their direction. This is the kind of radio problem that just requires experimenting, trying different ideas until you find something that works. Try taking your radio for a little road trip. You've already got a mag-mount antenna for the job. Drive around and see what you can learn about the reception pattern for the analog site. You might drive a block away and find that it sounds great. Clues like that can help you figure it out.

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[SevenMaryFour]

I did order one of those cheap yagi antennas, and I should get it tomorrow. Good idea on the driving around, too. I'll definitely try that if the yagi antenna doesn't help.

 

[jeremyzone]

I'd just go grab a RadioShack 800 MHz and hook it up directly to the scanner and see what happens. Does it still sound the same if you do that? Even when standing in the same spot as your antenna?

We need to figure out if it's the location or the antenna/cable.

 

[SevenMaryFour]

I'd just go grab a RadioShack 800 MHz and hook it up directly to the scanner and see what happens. Does it still sound the same if you do that? Even when standing in the same spot as your antenna?

We need to figure out if it's the location or the antenna/cable.

Tried exactly that, same result. The yagi antenna will arrive tomorrow, so I'll play with it some more this weekend.

 

[SevenMaryFour]

Update: mixed results with the cheap Yagi antenna. I placed it in the same location as the mag mount and connected it to the scanner with about 25 feet of RG-58. Signal was strong on all systems, including the county analog system, but the problem with interference (hissing and popping) remained on the county system.

However... after switching the antennas out a couple times, I noticed that the hissing and popping occasionally would go away and the audio would be nice and clear regardless of which antenna was installed. Looking at the RR Wiki, it appears that the Collin County Public Safety system has 4 control channels and 2 talk channels. One of those channels appears to be at the county courthouse and transmits at 30 watts. The other is on a tower east of town and transmits at 100 watts. I thought perhaps the weaker transmitter was a relay to the tower and the scanner was stopping on that before it scanned to the stronger signal from the tower, so I tried removing the weaker channel, but then I received no transmissions at all. The other possibility is there's something nearby transmitting near 851 mhz that's interfering, but I don't know what that would be.

As of this moment, I have the scanner back on the mag mount antenna with a 13 foot run of RG-174. The county analog system alternates between being strong and clear and barely readable, but everything else sounds good.

 

[bharvey2]

Does the Yagi require (or do you use) a 300 to 75ohm balun? I had much greater success with the balun than without. I suspect the coax braid was acting as part of the antenna and negating the directivity of the antenna. Mind you, I was experimenting primarily with a folded dipole and much less with a yagi.

 

[SevenMaryFour]

Does the Yagi require (or do you use) a 300 to 75ohm balun? I had much greater success with the balun than without. I suspect the coax braid was acting as part of the antenna and negating the directivity of the antenna. Mind you, I was experimenting primarily with a folded dipole and much less with a yagi.

No, the cable connects to the back of the antenna. No balun provided (and presumably not required). As I noted, it DID improve the signal strength, but the hissing and popping was the same.

 

[bharvey2]

Given your description, I'd have to agree with you that no balun is required. I have one setup with SDR dongles and a yagi (no balun) and reducing the gain of the dongles actually helped. Your mileage may vary though. Where I use the corner reflector, I've found that reception and decode rate is best with the antenna about 2 feet off the ground! I think solving this simulcast problem is as much witchcraft as it is RF theory

 

[scannermaster1]

Colln County reception and attenuation

I was in Collin County recently, in Frisco actually, and was using an outside antenna on the second story roof of a building and I could barely receive that Collin County analog trunking system. Reception was awful. Other trunked systems were doing well. I wouldn't be surprised if there's something wrong with that system. Is anyone having luck getting a good, clean, strong signal on it?

By the way you mentioned a 668 was good for attenuation. What is that? Are you using the scanner's attenuator or something external?

Thanks,

Rich Barnett

 

[sparklehorse]

Update: mixed results with the cheap Yagi antenna. I placed it in the same location as the mag mount and connected it to the scanner with about 25 feet of RG-58. Signal was strong on all systems, including the county analog system, but the problem with interference (hissing and popping) remained on the county system.

Did you try attaching the cheap Yagi with only the 3 or so feet of coax that came with it? I would experiment with that configuration first, and try rotating the Yagi in all directions. Also try it in a horizontal orientation as well as vertical. Also try moving the scanner/antenna combo to different rooms of your house. You'll likely get some clues from these types of adjustments. It is of course entirely possible the system has problems, as scannermaster1 suggested. That's where a little road trip might be helpful.

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[fredva]

I was looking at the info in the database and the separation of frequencies into different FCC licenses is a little confusing to me. But from what I can understand, this is a simulcast system. That means the same frequencies are used for broadcast on multiple towers.

It appears that this page has the bulk of the relevant system info: WPFD844 (COLLIN, COUNTY OF) FCC Callsign Details

There appear to be four main towers on the system: At Celina, McKinney, Farmersville, and Blue Ridge.

Did you only try pointing your yagi in one direction? If so, can you try pointing it at one or more of these other locations to see if that might help give you a more consistently clear signal?

 

[SevenMaryFour]

Quick thought: I was looking at the Plano/Allen/Wylie/Murphy transmitter map and realized I'm only about 1.5 miles from one of their towers, and it's almost directly between me and one of the county transmitters. The PAWM system uses 851.175, and one of the primary county channels is 851.225 Maybe the interference on the county system is bleed over when the PAWM system is active? That would explain why there are periods of clear reception and then periods of mostly static.

If so, any thoughts on how to correct for that?

 

[fredva]

Don't know if that's your problem, but if it is, the answer would be the same: Use the yagi to point to a different county transmitter.

Now that's just to determine the problem and solution for the county analog system. You may hurt your reception on the digital systems in the meantime.

 

[sparklehorse]

Quick thought: I was looking at the Plano/Allen/Wylie/Murphy transmitter map and realized I'm only about 1.5 miles from one of their towers, and it's almost directly between me and one of the county transmitters. The PAWM system uses 851.175, and one of the primary county channels is 851.225 Maybe the interference on the county system is bleed over when the PAWM system is active? That would explain why there are periods of clear reception and then periods of mostly static.

If so, any thoughts on how to correct for that?

You could be on to something there. You could easily be getting some bleed over from the P25 system when it's active. Do you have a second radio you could park on the P25 system in search mode? That way you could prove or disprove the theory pretty quickly.

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[SevenMaryFour]

Update: after some tinkering, I think I've found the best combination of location, antenna, and cable for my location. It's receiving the county system pretty well at the moment with the hissing and popping much less than what it was before.

Thanks to everyone on the thread for your help!

 

[fredva]

Glad it's working better.

If there's anything the rest of us can learn from your success, feel free to share if you get the time.