Uniden vs GRE vs a 100 foot cell phone tower

Someone gave me a free PRO-106, and I decided to do a very thorough and scientific test, within the 30 seconds I had allotted for the task.

I work at a place that has a 100 foot cell phone tower adjacent to my parking spot. Obviously, it affects my 800MHz reception. I use my brand new 436HP connected to a rooftop antenna, and leave it locked onto my most distant 800 P25 system because it decoded P25 better at low signal levels than my XT's. It doesn't receive anything in the lot, even though it shows full signal. My 996's split off of the same antenna are lucky if they break squelch even a little. Unjacked the BNC off of the 436, and put it on the ugly old scratched and beaten up 106, and instant clear digital decode and reception.

Drove a few blocks from the tower, and the analog 800Mhz reception was similar to my 996's. Moral of the story, if you "base" or locate your scanner near cell towers often, or find you have a lot of full signal yet no reception areas, a GRE/Radio Shack/Whistlers Mother scanner might be the right choice for you.

Paul

Wow interesting ! I don't notice ANY of that with my 396 !

Anderegg said:

...Moral of the story, if you "base" or locate your scanner near cell towers often, or find you have a lot of full signal yet no reception areas, a GRE/Radio Shack/Whistlers Mother scanner might be the right choice for you.

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Or, perhaps, an 850-870 bandpass filter.

I lived near a cell tower for several years and it blocked all 800 MHz reception including my city's, county's, and state's trunked systems, using both GRE and Uniden scanners.

That's actually how I found this site because I had to rely on the live feeds. To this day when I drive within a half mile radius of it it still causes interference on these systems. That was the only tower which seemed to cause any problems, my luck.

A band pass filter would not have helped because that was the band I was trying to receive. I was looking forward to rebanding hoping that would help but moved away before it's completion.

Bandpass filters do very little when you can throw a rock and hit one of the cell antennas! If you are in the "beam" of one array, it's even worse than being under it. They are typically pointed slightly groundward, and some smaller towers/arrays can actually pump out more intense power than larger towers which can get away with height.

And my antenna system has a custom 851-869MHz bandpass system in place.


Paul

Anderegg said:

Bandpass filters do very little when you can throw a rock and hit one of the cell antennas!

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I suppose that depends. I live next door to a church. The church as 4 cell carriers on it's property. Putting just about any UHF/800 receiver or a scanner on an unprotected antenna here, the device immediately gets overloaded. An 850-870 MHz bandpass filter solves the problem. I'd say the cell site antennas are within 400 feet.

Anderegg said:

If you are in the "beam" of one array, it's even worse than being under it. They are typically pointed slightly groundward, and some smaller towers/arrays can actually pump out more intense power than larger towers which can get away with height...

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I frequently get called upon to hunt down interference sources and other coverage problems... situations that put me at a cell site with a need to be able to clearly receive 850-870 range signals. With a good quality filter, I have no difficulty making needed measurements in the presence of some pretty ferocious RF fields.

Anderegg said:

And my antenna system has a custom 851-869MHz bandpass system in place.

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What are you using, that works so poorly? Granted, when the cell site is putting out RF in the 850-870 band, there's not a whole lot to be done.

Im in between two count em two celltowers and the Uniden 436 and GRE 800 do fine.

Not sure about where you guys are located, but here in NJ so much of the mobile device activity is now using higher frequencies. It definitely can be a problem, but seeing a cell tower is not a definite radio disaster.

wa2sqq said:

Not sure about where you guys are located, but here in NJ so much of the mobile device activity is now using higher frequencies...

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This is why I suggested an 850-870 band pass filter. I've seen quite a bit of evidence that a 1.9 GHz cell site will overload a wideband receiver front end, even though it's well removed from the 800 MHz band the receiver is capable of hearing. The active front end device in the radio doesn't care what frequency it's seeing - if it's above it's IP3 rating, it'll go non-linear and create intermod where there was none.

Cell towers and wireless internet are probably why my PSR-500 is working flawlessly on p25 800 Mhz in some areas and my 396 goes silent. I visit the dog park downtown and the 396 is terrible there. A lot of missed calls and garble at 800 Mhz. There is a cell tower about 1/4 mile a way and a wireless internet provider on one of the taller buildings a few blocks away. I thought it was blocked by buildings. Been using the GRE there and it works perfectly.

I can always tell when a cell site is messing with my 800 reception. The signal strength bars on my Unidens will be full signal, and I will still get no attempts to stop on a talkgroup or receive at all. I was very surprised the little PRO-106 (big!) was receiving as if there was no cell tower adjacent to me. The main location I hang out at is within 1000 feet of two cell phone towers, and they affect both my local 800MHz as well as my distant 800MHz reception. I just purchased another PRO-106 on eBay because of this nice feature.

And my antenna system has a band-pass filter custom made by RCBI.

Paul

And GRE has the reputation for getting overloaded.

I'm seeing a bunch of references to a "bandpass" filter which is exactly the opposite of what you want if you're getting cell interference. You need a bandstop filter if you want to block 850-870MHz. A bandpass filter in that range would only allow cell frequencies through to the scanner, and attenuate everything you actually want to hear.

Perhaps that is why so many of you are having reception issues?

jonwienke said:

I'm seeing a bunch of references to a "bandpass" filter which is exactly the opposite of what you want if you're getting cell interference.

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Not necessarily. It depends on what the specific problem is, and what the user's requirements are.

jonwienke said:

You need a bandstop filter if you want to block 850-870MHz. A bandpass filter in that range would only allow cell frequencies through to the scanner, and attenuate everything you actually want to hear.

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The 850-870 range is typically where public safety 800 MHz systems operate. A and B band cellular is on 870-896, so a bandpass filter on 850-870 would be effective in many cases. The sticking point there would go back to Nextel and their IDEN system, which operated on 850-870, as well as 900 MHz spectrum. Well, IDEN is gone, but Sprint is still operating within the 850-870 range. Most of the country has rebanded, giving that situation at least a snowballs chance of being manageable.

jonwienke said:

Perhaps that is why so many of you are having reception issues?

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Perhaps, but for those running filters and still having problems, perhaps a better understanding of the filters are in order. There are a lot of filter designs that have tight skirts and good performance across their specified part of the band... an 850-870 filter, for example, that has 1 db loss at 869, and 60 db loss at 871. But further out, it may be wide open to whatever else is out there. A band stop filter may stop a wx transmitter, or the cellular band, but could be wide open at 1.9 GHz, letting in an overloading signal that you don't even hear that's crunching the snot out of your scanner front end, and all you know is that it works like crap.

Specifying and buying a filter without having used a spectrum analyzer on the problem is a game if dice.

cell

uniden should put a cell tower on their roof so they can beta test.

k2ool said:

uniden should put a cell tower on their roof so they can beta test.

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They can do all the testing they need with a couple of signal generators and a power splitter/combiner.

Anderegg said:

And my antenna system has a band-pass filter custom made by RCBI.

Paul

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Who is RCBI? Can you provide a link? Since I only listen to 851 - 860 while mobile exclusively, I'm looking for a filter (notch?) that filters out EVERYTHING else. Tower interference is a chronic problem for my 996T.

I am very interested in this thread....I can see a cell tower from my house and I have 800MHz reception problems at home due to the tower. I have a several BCT-15s and a HP-1 hooked to a rooftop antenna and cannot receive distant 800 systems hardly at all. Many times they will have trouble with my local system even though I have good signal on the S-meter for all of the systems. Even my BCT-396XT portable has issues as soon as I walk within visual sight of the tower...the signal gets scratchy or goes away all together. I can also tell with the 996XT in my car....as soon as I drive into my neighborhood reception goes to crap...again it's due to the tower!

I have been frustrated to the point that I'm just ready to move away (which is not an option right now) and I sure would like my live audio feeds to sound better on a consistent basis. So is a bandpass filter what I need to try and can anyone recommend one to get?

Brandon

RCBI is a company that mainly sells items on eBay along side their main operations.

http://stores.ebay.com/rcbi?_trksid=p2047675.l2563

The cell interference at full signal on a Uniden can be "heard" by pressing hold on the system when you are not getting any talkgroup reception. You may hear the control channel broken or garbled, and this is a sure sign it is being "covered" by the cell tower RF.

I have used a multicoupler from Stridsberg with a built in bandpass for 800, as well as a notch filter added by RCBI, but to be perfectly honest, I really don't think they do anything. I've never had the ability to bypass them, but the reception is so poor in cell areas that it 's hard to conceive that they actually perform any meaningful function.

Paul

I am beginning to experiment with using my FunCube dongle or RTL stick for monitoring the CC via Unitrunker, then controlling one of my scanners as the voice channel with Unitrunker following the control channel. The advantage is that with SDRSharp or SDR Radio, you can control the bandwidth of the CC and maybe knock out some of the crud on adjacent frequencies above or below.
On some difficult to monitor trunk sites here in Los Angeles using my 536HP, 996XT, or WS-1080, I have found that monitoring the CC via Unitrunker, then using one of the scanners to follow the voice channel sometimes seems to work better.
I'm finding that combining the power of SDR filtering with these scanners is providing some benefit in tough-to-deal trunking scenarios.
Steve AA6IO