Attenuator on PSR800

[tilt404]

I remember someone told me about this a year ago but I couldn't find the post. I have a Uniden BCT15X and GRE PSR800. The Uniden will pick up the more distant VHF trunk system (100KMs +) away without any trouble. When I try on the GRE with the same Diamond X50A antenna which is outside on LMR400 about 100' up, I get nothing until I turn on the attenuator.

Its confusing to me since then I have to put in attenuation for things in the programming on a case to case basis yet that could change with me moving around in another location. I always thought of using attenuation locally when getting intermod or some other noise, but using it to get in a more distant station? Someone told me in the past I needed to use it, but then that didn't prove true over time as I changed settings in the GRE. I shut off AGC on the system I'm trying to get in but don't know if that would have an effect.

Even when I switch to my Comet Discone outside on the GRE, which is also on LMR400 and 100' up, I still have to put on the attenuator to get the more distant station and the discone has none of the gain the Diamond has.

I remember having this problem in the past, but then I never had to use the attenuator again on the GRE. My card recently corrupted so I had to start over in a way and I'm thinking I put something in differently that I shouldn't of maybe.

 

[dgmaley]

PSR-800

I don't think any police scanner was designed to be on an antenna 100' up. Those antennas will bring down a lot of RF. The design goal of a scanner front-end is broad bandwidth and good sensitivity. It's a tradeoff. It could be easily overloaded. A digital radio that is designed to properly operate with a tall antenna will have a name like Harris or Motorola on it and cost several times more.
There are scanners made for this kind of situation but not by GRE or Uniden. You need to look at AOR or ICOM and spend a few thousand. P25 is there but not trunking yet.
Dave...

 

[tilt404]

I use it for my ham radio also, the antenna that is. I don't get any RF noise on my scanner or ham radio. I've lived here for years and scanners have worked fine and this GRE was until yesterday when my memory card got corrupted. So was just trying to figure out why things changed. The antenna is on my balcony with good quality LMR400.

 

[Ed_Seedhouse]

Even when I switch to my Comet Discone outside on the GRE, which is also on LMR400 and 100' up, I still have to put on the attenuator to get the more distant station and the discone has none of the gain the Diamond has.

If you have to put on the attenuator to hear a signal then your scanner's front end is being overloaded by a strong signal, not necessarily the one you are trying to hear. If you can find where the overload is coming from and it is not too near to the frequencies you are listening to you can put in a notch filter for the frequency causing the problems. Otherwise you'll have to use a less sensitive antenna or get used to having the attenuation on. Well, that's what it's there for after all!

 

[tilt404]

Thanks Ed,

I just moved my equipment around here recently also, so not sure. Cell phone company just put an antenna farm on the roof of my apartment also recently. One of their antennas is just 20 feet or so from my Diamond on the balcony. My Uniden BCT15X does fine though. I guess the GRE is more sensitive. The Diamond X50a is 144/440 though and the cell antenna best I can tell says 860-924mhz on the bottom or it. But I usually have the GRE hooked to the discone I have so maybe it is that new cell antenna causing me some trouble here. Not noise but just causing some overload. I'll make some changes tonight and see how it goes. Thanks for getting the wheels spinning in my head.

 

[tilt404]

I went back into the EZ Scan software for the PSR800 and for that VHF system about 100kms away, I put in individual attenuator settings for just those systems and its working great now, nice and clear. Shut of global attenuation and put it on normal so just the ones I set to be attenuated are now and doesn't effect the other systems I'm scanning. So all is well now. Thanks for the help.

 

[dgmaley]

Thanks Ed,

I just moved my equipment around here recently also, so not sure. Cell phone company just put an antenna farm on the roof of my apartment also recently. One of their antennas is just 20 feet or so from my Diamond on the balcony. My Uniden BCT15X does fine though. I guess the GRE is more sensitive. The Diamond X50a is 144/440 though and the cell antenna best I can tell says 860-924mhz on the bottom or it. But I usually have the GRE hooked to the discone I have so maybe it is that new cell antenna causing me some trouble here. Not noise but just causing some overload. I'll make some changes tonight and see how it goes. Thanks for getting the wheels spinning in my head.

Yikes!
What do you mean 20 feet?
There's a RF exposure limit on that stuff. The transmitters feed each antenna about 35 watts at 800 MHz.
Dave..

 

[tilt404]

Yes you can see from the image. Stupid Telus cell phone company put 3 of their antennas on each corner of the roof of my apartment recently. They only had one antenna on the closest mast when I took this photo though. But you can see how close it is to my balcony and discone. My Diamond X50A is on the other side of the balcony about 17 feet from my discone to the right.

 

[tilt404]

They didn't have the cables hooked to it yet in that photo too but here is a closer shot of the cables hooked to the antenna closest to my discone.

 

[n5ims]

Imagine it this way. You're trying to get a drink from a garden hose that's turned on, but only partially so there's a good stream of water to drink from, but not so much that you get drenched. That was your signal without the cell phone antenna nearly on top of your antenna.

Now imagine that same garden hose with the same stream, but some fool put a fire hose, on full force pointing at the same direction of your garden hose and you try to take the same drink. You can't do it, there's just too much water flowing at you with too much pressure. This is what your scanner is dealing with now that the cell phone antenna is there. The attenuator is somewhat like placing a barrier in between the fire hose and your garden hose so most of the fire hose pressure is taken away and you can now drink (you'll probably get quite wet, but at least you can now drink).

 

[tilt404]

Drives me nuts how these companies just put these things wherever they want with no public hearing or warning. To tell the truth though, haven't noticed any difference so far. Just the trouble I was having dealt with getting in a VHF morotola system about 100kms from here I once did but haven't listened to much on the GRE. It was a bit weak on the Uniden. Comes in perfect now though but I understand what you said above. Some things might drastically change now. The main system I scan for my local FD/PD is in the same 800mhz band as the cell stuff but still comes in fine.

I don't know if they even turned these things on yet though. There's 9 of them on the roof of my building now. 3 on each of 3 corners.

 

[dgmaley]

I don't know if they even turned these things on yet though. There's 9 of them on the roof of my building now. 3 on each of 3 corners

Yep, that's a normal cell site. The top of your discone is very close to that antenna's pattern. I'm surprised no one talked to you. It might help moving your antennas down a couple of feet. RF exposure not normally a problem with these antennas over your head. Most of the RF goes straight out. There might also be a microwave dish on the roof. Make sure a exposure study is done for leakage. Otherwise put some Hershey bars around and see if they melt<grin>.
Dave..

 

[tilt404]

They look close but the mast the cell antenna is on is about 10 feet high I'm guessing, or 10 feet tall I should say, but then again the antenna is tall too. It looks like they are over my head also, but they are to the left of the end of the balcony, not right over head, but I know still close enough lol. I'm just glad they aren't over my unit, they are mounted over the unit next to mine but still close.

They left the middle mast empty on all of them. For future expansion I guess. My Diamond X50A is on the other end of the balcony, so I can't move the Comet discone much since I like to keep them about 10 feet apart. If RF starts getting bad though I will have to do something. So far though, so good. On a building just east of me 2 apartments over, is a massive tower on its roof with those huge microwave drum dishes on it. Hard to escape all this stuff going up these days for the sake of cell phone communication.

Strange thing though I searched the Industry Canada site for my location and still shows no application by Telus for any frequencies here. All the other sites around me are listed. Maybe it just takes time to show up. So many governments are asleep lately. It would be nice to know the power used and frequencies. Says 824-960Mhz on the bottom of that close up, but still not sure what is being used.

 

[Ed_Seedhouse]

The attenuator on the 800 attenuates all frequencies, and setting it on those two channels tells it to attenuate everything when it is receiving those channels only. So I presume the other frequencies are getting through the overloading, which suggests the signal that is causing it is narrow band. Likely an interaction within the receiver on just a few frequencies, as all receivers tend to have narrow bands where they don't perform well.

If the cell antenna aren't broadcasting currently I don't know why this would be so, unless there are other powerful signals nearby where you don't see them. You might try borrowing a field strength meter and checking to see if it is within the RF radiated power limits at your antennas. If it is you might be able to get the owners of the cell antenna to do something.

Have you tried lowering the antennas a few feet? It might reduce the signal from the cell enough to allow the GRE to remain at full sensitivity without losing you the other frequencies.

If your FD/PD is in the same band a filter on the cell phone frequencies become more difficult to do.

 

[tilt404]

I'm not sure about it attenuating everything. There's a global or normal setting. I have it set to normal which then tells the scanner to just attenuate the ones I set per site or frequency in the software. I can see it in the display how the A will show just when its scanning/passing those ones I set. I'm not using the button on the 800 at all, just doing it in the software.

The only time I've had some trouble with this sort of thing are the distant frequencies, like on the other side of the county about 100kms away. Only on the GRE at times. My Uniden has no problem or my ham radio. So I don't think its RF so much as just the GRE being more fussy than the others I have. Its also the only digital scanner I have too though, so that could be an issue? I can't expect it to act like my analog scanners can I?

I have to do more testing here and compared one scanner to another. I've made changes here recently also, and like I mentioned earlier here I think, my memory card got corrupted so I lost my settings and it worked fine before. So I'm trying to find how I had things set before.

It might be better for me to swap places for the antennas.. Move the discone more away from the cell antennas, and diamond closer since the diamond is a 144/440 antenna where the discone is 25mhz-1.3ghz. The Diamond X50A runs to a Diamond CX210A ( Diamond CX-210A Antenna Switch CX210 ) switch where I have it connected to the Uniden and my ham radio transceiver. That makes me think now too since that switch is rated for 0-1000Mhz yet the antenna hooked to it is just 144/440mhz. Might be better for me to put the switch with the Comet discone for a better match.

Sorry, thinking (writing) out loud... I have no trouble with the PD/FD here though which is a P25 800Mhz system. Still comes in fine on the GRE. Even just on a small Larson 800Mhz antenna I put on the GRE sometimes inside here. At least I see now how to get that more distant system in with the Att. Its in the 140mhz range. I'll try to swap the Diamond X50A and Comet DS-150S discone places with each other this week before winter starts to come on. The GRE is on the Comet which is in the photo closest to the cell antennas. Moving it 12 feet or so down the other side of the balcony might help.

 

[danw5211]

Attenuator on 800 Mhz

Could the cellular antenna panels act as a passive reflector to the discone due to the close proximity? Similar to a full length mirror reflecting light. Just my thoughts.
That's a whole lot of radiated power to be placed on an apartment roof. Even if only 5% is reflected. 35 Watt Microwave oven over head.

 

[NDRADIONUT]

For VHF u need to notch out the 88-108 FM band with an expensive filter or a cheap "T" trap....

 

[tilt404]

There's was pretty good documentary made about this stuff I've been going through here with the cell antennas.

Full Signal

Its a few years old now, but shows even worse cases than what I have above me. Shows how these cell companies prey on residential buildings since they can get away with paying off the building owners more easily. I worry more about the group of cell antennas mounted on the west side of my roof since there is an identical apartment as mine west of me only about 6 or 7 car lengths away. The west group of cell antennas on our roof point downward slightly right into the side of that apartment into all their units.

Anyway, I don't mean to keep ranting about it all. I found I couldn't swap positions of my two antennas on the balcony due to my cables being cut to length. The discone would be too low to my railing. I'm quite happy now though with how things are set up. I'm able to get the stations I wanted to now just by changing some settings. I see so many roofs here with many antennas of different types, all side by side. At least I'm below this one. I'll still look into moving it over a bit in the future. I'm taking this day by day now since I think it will take some time to learn what consequences these newly installed cell antennas will have on other electronics here and my health.

Below is a photo taken this morning of how it sits now. Hard to see the far left cell antenna but glad they aren't using the middle mast so far.

 

[Ed_Seedhouse]

I'm not sure about it attenuating everything. There's a global or normal setting. I have it set to normal which then tells the scanner to just attenuate the ones I set per site or frequency in the software. I can see it in the display how the A will show just when its scanning/passing those ones I set. I'm not using the button on the 800 at all, just doing it in the software.

The attenuator on a scanner is either on or off, globally. If you turn it on for one channel it is attenuating all the signals that come into the radio, not just the channel you are on. Then when it moves to another frequency the attenuation is turned off again.

A broadband attenuator is easy to do and low cost. Easy to turn off and on as well.

A notch filter for R.F. is expensive and requires separate resistance and capacitance for each channel. But they have no way of knowing which channels you will be listening to in advance. It would be crazy to design a radio with a notch filter at every possible frequency the radio can receive. The thing would cost a million bucks and you certainly wouldn't be carrying it around with you. Of course you could implement it digitally with a lot more efficiency but that would require a lot more computing power than you are going to find in a cheap radio. And by "cheap" I mean under several thousand bucks.

 

[Halfpint]

The attenuator on a scanner is either on or off, globally. If you turn it on for one channel it is attenuating all the signals that come into the radio, not just the channel you are on. Then when it moves to another frequency the attenuation is turned off again.

Actually you *can* set the attenuation for individual freqs/channels on the PS-800. The `Global' setting can be turned on/off seperately just so one *can* individually attenuate freqs/channels when needed. (Read The Fine Manual! [It might take a couple readings if you are reading the included manual or it might be slightly quicker if one uses the EZScanDG program's Help function.{In the software look under the `General Tab' menu item in HELP. It's down near the end of the page under "Attenuation Settings".} Either way it actually is there.])