Terrible 800mhz reception

[bob-the-scanner-man]

I'm trying to use a Radioshack Pro-96 in my car and having terrible results. With the 800mhz rubber ducky I have a lot of dead areas and garbled traffic.

I figured that mounting an antenna on the car would make a difference but I'm still not having much luck. Right now I'm trying this antenna which advertises 2db of gain. Reception is much better but still not great. There are lots of areas where I should be receiving the control channels clearly but they still break up. Earlier I was about 3 miles from one of the tower sites and was still receiving garbled traffic and the control channel was cutting in and out.

So should I try some other kind of antenna instead or is there something else going on here? This is a simulcast system.

The scanner works great when I'm in my house, but I'd like to be able to take it with me when I'm in the car.

 

[mmckenna]

I'd say try a real whip. Usually those style antennas work fine at 800MHz, but there could be an issue with that particular one.

Also, make sure the center pin of the antenna is actually touching the center of the NMO mount. Some mounts and some antennas don't always work well.

Check your coax and connectors with a multimeter to rule out a short circuit in the connector/base and that you actually have continuity from the connector out to the NMO mount.

 

[bob-the-scanner-man]

Thanks for the response.

I checked everything out with a multimeter and everything seems fine. I didn't notice any shorts anywhere. The center pin of the antenna appears to be touching the center of the NMO mount.

What whip antenna would you recommend?

 

[mmckenna]

Basic 1/4 wave NMO. Should be about $10.00. Cheap, easy and works well. I'm using them on 50+ mobiles at work.

The loaded 3dB models work well also. Might cost a bit more.

The "transit" or low profile antennas like you have usually work pretty well since it's easy to fit a 1/4 wave inside the dome. I've got a couple of the Larsen versions on some garbage trucks at work and they're OK.
Makes me suspect there is an issue with your specific antenna.

 

[bob-the-scanner-man]

Makes me suspect there is an issue with your specific antenna.

That's what I'm leaning towards. The users for this system appear to have a mix of low-profile antennas like mine and whips.

 

[mmckenna]

The cheap 1/4 wave would be an easy test. You might even be able to try a little 3" length of wire and see if it improves.

 

[krokus]

What type of radio system are you trying to monitor? Is it a digital trunked system, which might be simulcast?

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[bob-the-scanner-man]

Is it a digital trunked system, which might be simulcast?

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That's what it is.

It's this system.

I've had issues with it in the past but then I set up my Pro-96 to only listen to the control channels for the two towers closest to me. This works great at my house but when I'm in the car the reception is spotty even though I'm not all that far from the tower sites.

 

[emtprt]

I would make sure that your coax cable is rated to cover the frequency range. Some NMO cables do not cover frequencies above 500 mhz.

 

[bob-the-scanner-man]

I would make sure that your coax cable is rated to cover the frequency range. Some NMO cables do not cover frequencies above 500 mhz.

I'm using an NMO lip mount on the corner of the hood of my car. It came with about 15ft of RG-58. I trimmed it down to about 5ft and put a BNC connector on it since that's all I needed to be able to reach my scanner.

I know RG-58 isn't the best coax for 800mhz but I figured that using it for such a short run would be alright.

 

[mmckenna]

RG-58 is just fine for 800MHz. Those 50+ mobiles I have on my 800MHz system at work are all using NMO mounts with RG-58, and many of them with 15 feet or more in some of the bus installs.

RG-58 compared to something like LMR-240 is a bit worse, but unlikely you'd be able to hear the difference with 5 feet of cable.

 

[JD21960]

Wow, my Pro96 is currently getting perfect reception with the pain in the *** Starcom21 700/800mhz statewide trunked system in Chicagoland. I even use a simple RCA digital TV antenna in the TRUNK of my car and it gets everything including individual 700Mhz freqs with the *extended freqs added thanks to ARC96 settings. RS800mhz ducky and any antenna works for me with the Pro96 while mobile. Before update U1.4 I had big trouble, garbled reception and problems when using U.1.3 long ago. I remember the re-banding of the 800 band happened and U1.4 came out. Fixed everything for me for trunked systems. IN fact my Pro96 gets this system far better than my new $500 WS1080. That scanner needs attenuation and a Yagi at home just to get consistent reception. Pro96 doesn't even need an antenna. I sit it there with no antenna and it gets 800mhz control channels fine. The big question nobody asked up there is WHAT firmware does your Pro96 have? U1.4 helped after rebanding here. Pressing #3 at the WELCOME screen shows you what DSP-APP: ?? you have. Anything under 1.4 makes me think that's your problem unless the Control channel -site is really far away and out of reception anyway.

 

[n5ims]

One thing to remember is that on a simulcast system, the simulcast distortion makes "all the right noises" to indicate that you have too little signal, when in actuality you have too much signal (well, strong signals from too many towers mixing together and ruining the signal for your scanner). If you can, use a very directional antenna to isolate your signals to be from only a single tower (it may not be the closest, but one where none of the other towers are in the same direction). Something that's pretty easy for a fixed location station, like a base, but pretty near impossible for a mobile station.

For a mobile station, you can try to somehow limit the amount of signal you're getting so only the very strong ones make it to your scanner. This could be by turning on your scanner's attenuator on that system's frequencies. It may be by using a very low gain antenna. It may be by doing something to block the signal from getting to your antenna (one trick I use is to hold the antenna in my hand to block much of the signal from reaching the antenna).

There's one simulcast digital system where the closes tower is about 1 mile to my northeast. There are also close towers to the north and east, with further ones at various locations from my north to my east so isolation is pretty difficult. By accident, I happened on an unexpected solution that fixed my problem. After trying several things that didn't work, I got frustrated and quit for the day. The next day, I turned on my scanner and the system worked great, clear copy with no choppiness or other interference. Checking on how things were hooked up so I could figure out what magic fixed my reception I discovered that I had left the jumper to the scanner disconnected to my multi-coupler. I connected it as normal and the issues returned. Unplugged, things worked just fine. In my situation the solution was simply to have the antenna not connected to the scanner (although the 5' jumper remained).

 

[bob-the-scanner-man]

DSP-APP is 1.4. I just upgraded it a few months ago.

One thing to remember is that on a simulcast system, the simulcast distortion makes "all the right noises" to indicate that you have too little signal, when in actuality you have too much signal (well, strong signals from too many towers mixing together and ruining the signal for your scanner). If you can, use a very directional antenna to isolate your signals to be from only a single tower (it may not be the closest, but one where none of the other towers are in the same direction). Something that's pretty easy for a fixed location station, like a base, but pretty near impossible for a mobile station.

For a mobile station, you can try to somehow limit the amount of signal you're getting so only the very strong ones make it to your scanner. This could be by turning on your scanner's attenuator on that system's frequencies. It may be by using a very low gain antenna. It may be by doing something to block the signal from getting to your antenna (one trick I use is to hold the antenna in my hand to block much of the signal from reaching the antenna).

There's one simulcast digital system where the closes tower is about 1 mile to my northeast. There are also close towers to the north and east, with further ones at various locations from my north to my east so isolation is pretty difficult. By accident, I happened on an unexpected solution that fixed my problem. After trying several things that didn't work, I got frustrated and quit for the day. The next day, I turned on my scanner and the system worked great, clear copy with no choppiness or other interference. Checking on how things were hooked up so I could figure out what magic fixed my reception I discovered that I had left the jumper to the scanner disconnected to my multi-coupler. I connected it as normal and the issues returned. Unplugged, things worked just fine. In my situation the solution was simply to have the antenna not connected to the scanner (although the 5' jumper remained).

I thought this might be the issue too but in the past when I used the stock rubber ducky that came with the scanner I still had trouble hearing the system in the car. That's part of the reason I went to the NMO antenna. I figured something with some gain mounted outside of the car would help my reception.

My reception is definitely improved but I still have a lot of areas in my commute where everything just cuts out. The other day I was about 2 miles from one of the tower sites and didn't hear a peep on its control channel. That leads me to believe the scanner is getting overloaded but if I turn on attenuation I still don't get anything and then I don't pick anything up the locations where I did before.

Thanks everyone for the ideas. I'll keep tinkering with it.

 

[bob-the-scanner-man]

Did some more testing on my commute today.

To me it really seems like I'm not getting enough of a signal rather than too much of one. The antenna I'm using is rated at 2dBi of gain rather than dBd which, if I'm reading things correctly, isn't much of an improvement over a 1/4 wave antenna.

Once or twice I pulled over in the areas where I was having the most trouble receiving traffic and found that either all of the control channels were silent or they were breaking up. Enabling attenuation only caused the choppy signals to go away completely and I received no traffic at all, broken up or otherwise. I then tried disconnecting from the external antenna and trying the rubber duckie or even just a short piece of coax. This also gave me silence on the control channels.

From what I've seen it looks like most of the users of this system are using this antenna or one very similar to it.

So I'm thinking I might try an antenna with similar gain and see if that helps any.

 

[W8RMH]

I would try something with a little more gain like a trilinear design such as the Laird Technologies AB8065CT.

 

[N5XTC]

I'm trying to use a Radioshack Pro-96 in my car and having terrible results. With the 800mhz rubber ducky I have a lot of dead areas and garbled traffic.

I figured that mounting an antenna on the car would make a difference but I'm still not having much luck. Right now I'm trying this antenna which advertises 2db of gain. Reception is much better but still not great. There are lots of areas where I should be receiving the control channels clearly but they still break up. Earlier I was about 3 miles from one of the tower sites and was still receiving garbled traffic and the control channel was cutting in and out.

So should I try some other kind of antenna instead or is there something else going on here? This is a simulcast system.

The scanner works great when I'm in my house, but I'd like to be able to take it with me when I'm in the car.

definitely an external scanner antenna will help. easy fix.

 

[mmckenna]

From what I've seen it looks like most of the users of this system are using this antenna or one very similar to it.

So I'm thinking I might try an antenna with similar gain and see if that helps any.

I think that's probably your answer. If that is what the local agencies are using to access the system, then that's probably what you need too.

I'd agree with your troubleshooting conclusions, sounds like not enough signal.

 

[trentbob]

... welcome to the world of LSM...

 

[bob-the-scanner-man]

Just wanted to give everyone an update on this.

It seems like my problem was actually two-fold. I definitely wasn't getting enough of a signal but it appears that out of the two Pro-96s I have the one I was using in the car is "deaf" compared to the one I had been using in the house.

Even after trying out a 3dB antenna similar to the ones the users of this system use I still had trouble getting reception. So I tried a side by side comparison of both scanners. Turns out the one in the car could barely pick up anything on the control channels while my other one could hear them just fine in the areas where I had been losing reception. Using that scanner I had clear reception of the system all over the county.

So it looks like the solution is going to be to use my "deaf" scanner in the house where I get a good signal anyway and use the other one in the car.

The "deaf" scanner has CPU 1.5 while the other one has CPU 1.4. Not sure if it's a Simulcast issue or what, but the 1.5 CPU scanner definitely had issues when mobile while the 1.4 CPU one did not.