Improving 850-860 mhz reception

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SevenMaryFour

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Hi, all. I wanted to get some feedback on my feed here: Collin County Law Enforcement

The digital channels sound great of course, but the analog county signal still has a lot of noise in it. I'm currently using this antenna with a cookie sheet as the ground plane and about 50 feet of RG-174 (SMA) cable. I'm only about 10 miles from the county's antenna farm, but I have a first-floor apartment and a couple medium size trees between me and them.

Considering my location restrictions, what would you recommend?

Do you think a discone antenna such as this is likely to improve the analog reception? http://www.amazon.com/Scanner-Amate...d=1430749223&sr=8-12&keywords=scanner+antenna

Would a higher grade cable be the answer?

Or do I just need to move? :)

Thanks in advance!
 

druhe

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Hi, all. I wanted to get some feedback on my feed here: Collin County Law Enforcement

The digital channels sound great of course, but the analog county signal still has a lot of noise in it. I'm currently using this antenna with a cookie sheet as the ground plane and about 50 feet of RG-174 (SMA) cable. I'm only about 10 miles from the county's antenna farm, but I have a first-floor apartment and a couple medium size trees between me and them.

Considering my location restrictions, what would you recommend?

Do you think a discone antenna such as this is likely to improve the analog reception? http://www.amazon.com/Scanner-Amate...d=1430749223&sr=8-12&keywords=scanner+antenna

Would a higher grade cable be the answer?

Or do I just need to move? :)

Thanks in advance!


What frequency range are you dealing with ? The antenna that you are using is designed for 800 mhz. If the frequencies you are having difficulty with are 450 or 155 mhz then another antenna may in order.
 

SevenMaryFour

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What frequency range are you dealing with ? The antenna that you are using is designed for 800 mhz. If the frequencies you are having difficulty with are 450 or 155 mhz then another antenna may in order.
850-860 mhz trunked systems. Specifically, the county repeater seems to broadcast the most on 851 mhz.
 

mmckenna

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and about 50 feet of RG-174 (SMA) cable

There is a big part of your problem.

RG-174 is REALLY lossy cable. 50 feet of that at 850MHz is resulting in you loosing 97% of your signal in feed line losses.
If you were to look at this from a transmitting standpoint, putting 100 watts into one end of the cable would result in only 3 watts coming out the other end. That's 15+dB of loss. The amount of signal loss is equal for transmitting or receiving, so you can see how much of your received signal you are losing.

Do you really need 50 feet of cable, or can you get away with something less?
If you really do need all that cable, then you need to upgrade to something with less loss.
 

SevenMaryFour

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There is a big part of your problem.

RG-174 is REALLY lossy cable. 50 feet of that at 850MHz is resulting in you loosing 97% of your signal in feed line losses.
If you were to look at this from a transmitting standpoint, putting 100 watts into one end of the cable would result in only 3 watts coming out the other end. That's 15+dB of loss. The amount of signal loss is equal for transmitting or receiving, so you can see how much of your received signal you are losing.

Do you really need 50 feet of cable, or can you get away with something less?
If you really do need all that cable, then you need to upgrade to something with less loss.
Wow, I didn't realize it lost that much. The only reason I'm using RG-174 is because there's about 15 feet attached to the antenna, and I have a 30 foot extension to reach my scanner.

If I cut that RG-174 down to a few inches, put on a new connector, and then ran RG-58 the rest of the way to the scanner, do you think that would be an improvement, or should I use a different antenna with RG-58 all the way?
 

mmckenna

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If you can install your own connectors and you are happy with that antenna, then that would be a good choice. Keeping the coaxial cable run as short as possible is important. RG-58 will still suffer from significant loss over those kinds of distances, but it won't be as bad as the RG-174.
You can play "chase the loss" all day long, there will always be something better. Get the best you can reasonably afford and keep the length as short as possible and signal will improve.
 

fredva

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Here is a line loss calculator: Coax Loss Calculator

RG-58 is a standard scanner cable, but there are other options that are just as good or better. Some other cable types that are popular are RG-6 tv cable with the appropriate adapters or connectors, and LMR-400. LMR-400 is low loss cable, but it is a little pricey and is thick and stiff. It's good for a straight line run and gradual bends, but not so great if you need to make sharp 90 degree turns.
 

sparklehorse

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LMR-400 is low loss cable, but it is a little pricey and is thick and stiff. It's good for a straight line run and gradual bends, but not so great if you need to make sharp 90 degree turns.

Ham Radio Outlet carries a sort of generic version of LMR-400 Ultraflex:

http://www.hamradio.com/detail.cfm?pid=H0-012002

It's affordable, comes with PL-259 connectors on both ends, and it's pretty darn flexible too. I just installed a new discone at my house using a 50' run of that coax and I'm really liking it. Get yourself that discone, which is PL-259, or an 800 specific antenna and an adapter or two, and you should see a marked improvement in your reception. You may also want to get a little 1' jumper coax that's more flexible to connect to the back of your scanner if you find the 25400 puts too much stress on it. That coax is flexible for what it is, but it's over 3/8 inch diameter, so it just depends on your set up whether you need a jumper or not.

Ham Radio Outlet has a store in Plano - just head over there, they'll help you out.

G
 

SevenMaryFour

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Thanks, all. I'm going to try some new cable and in a shorter length and see how that works. Based on that Coax Calculator, I bet that will help a LOT.
 

SevenMaryFour

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I rearranged things to reduce the cable length to 13 feet of RG-174 (the cable attached to the mag mount base) and there's definitely some improvement, but there's also still a good amount of hissing and popping. I did some quick reading on ground planes; mine is about 8" in diameter, and it appears I should have one closer to 28"x28". Would that likely help with the hissing and popping?
 

mmckenna

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Probably not as much. On 800MHz, you don't need a big ground plane. Usually 1/4 wave in radius is sufficient.

Since it sounds like you are using this antenna indoors, it could be the construction of your home is causing issues. Any sort of metal in the construction can block signals, that could be aluminum window screens, electrical wiring, metal lath, siding, etc.
Try the antenna outdoors, see if it improves.

Hissing/popping could be localized electromagnetic interference. WiFi routers, cell phones, poorly shielded electronics, etc. Try moving the antenna around to different locations and see if it improves.
 

SevenMaryFour

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I have it sitting on a table on my patio. There is a high tension power line that runs in the street median about 150 feet away, but in a previous thread, I was advised that probably wouldn't interfere with 800 mhz. What do you think?

There's also what I think is a cell tower less than a mile away and direct line-of-sight.
 

SevenMaryFour

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Unfortunately, no. I'm streaming 3 or 4 different systems with signals from all directions. Is it possible to splice in a directional antenna to point at one system and use my current non-directional antenna for the others, or would that cause issues?
 

mmckenna

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Cell tower at one mile won't be an issue. Power lines won't be an issue either.

Getting the antenna up higher would be the next likely choice. Down low near the ground there are a lot of obstructions. Getting the antenna higher up above those obstruction will help.
 

mmckenna

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Oh, and looking at your first post again, a Discone antenna isn't going to help.
The only thing discones are good for is their wide bandwidth. Other than that, they don't have any useful gain. The antenna you are using, keeping all things the same, is probably going to outperform the discone.

I've got a $1800 commercial discone at one of my sites. I use it mainly for monitoring, and it really doesn't do that good a job. Where it shines is that in an emergency I can swap it in place of the main antennas for any of our other VHF or 800MHz systems. Other than that, performance is mediocre. A dedicated antenna with some gain will work better.
 

sparklehorse

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Wow, I finally listened to your feed. You're getting a lot of weird noise and distortion on that analog system. What radio are you using for that feed? Have you tried just a normal back-of-set antenna for that? Like the one that came with your scanner, but collapsed to one segment. Or better yet a RS 800 antenna, or a Laird 800? If that site is just 10 miles away I doubt you really need an external antenna.

.
 

prplehz

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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.
 
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