GRE scanners receiving images?

[Jay911]

Hey all,

I and at least one other person in my area just found that our GRE scanners are receiving images in the 796 MHz area, of frequencies in the 866 MHz band. Specifically, an EDACS control channel on 866.1000 was being duplicated on 796.5000. The scanner could not decode the EDACS control channel on 796.5 and could not send CC Dump data through the PC/IF to software, so I am pretty convinced that it's an image. That, plus, there are no systems in operation in this part of Canada yet on 700 MHz, so it is definitely not a "real" transmission.

I checked with three different scanners myself, and the other fellow checked with two. I had a PSR-500, a PSR-800, and a Uniden BCD396XT. The other fellow had a PSR-500 and "another scanner" (he didn't specify). I could consistently hear the image on both my GRE scanners and not on the Uniden; the other guy could hear the image on his GRE and not on the other scanner.

Is this likely to be (or be related to) the already-mentioned (in the thread http://forums.radioreference.com/radio-shack-scanners/212385-info-missing-796-806-mhz-pro-106-a.html) "intermod problem" that keeps 796.9-to-806 out of the more recent GRE scanners?

 

[rgchristy]

Hi, I'm getting the same thing for Philadelphia, PA and Delaware State.

Rich C

 

[rdale]

All scanners have some sort of images somewhere, it just depends on the strength and the construction of the radio how much you'll notice it.

 

[KE4RWS]

Don't ask GRE . . .

I was wondering why my year-and-a-half old PSR-600 had that region blocked out when literature everywhere insists it covers this range. Even when I asked GRE via email why this range was blocked out when all their literature say's it does, they just emailed me an attachment of the same literature I already had where it say's it IS covered when it actually is NOT.

Funny even the manufacturer didn't bother answering my question. I would have been happy to hear the REAL reason, but to merely send literature that states it is covered when it isn't, and then to not even bother answering my original question, kinda told me one hand doesn't know what the other is doing in some of these offices.:roll:

 

[brianearlspilner]

Reminds me of this thread that I posted over a year ago:
http://forums.radioreference.com/gr...cussion/186006-police-793-184375-p25-3f3.html

 

[ecps92]

Have you updated your FIRMWARE?

I was wondering why my year-and-a-half old PSR-600 had that region blocked out when literature everywhere insists it covers this range. Even when I asked GRE via email why this range was blocked out when all their literature say's it does, they just emailed me an attachment of the same literature I already had where it say's it IS covered when it actually is NOT.

Funny even the manufacturer didn't bother answering my question. I would have been happy to hear the REAL reason, but to merely send literature that states it is covered when it isn't, and then to not even bother answering my original question, kinda told me one hand doesn't know what the other is doing in some of these offices.:roll:

 

[jackj]

A cheap and dirty way to extend coverage up into high UHF and microwave frequencies is to do something called block conversion. You take a block of frequencies you are interested in and mix them down to a lower frequency range that your radio already covers. The advantage of using this method is cost, the disadvantage is performance. Let's say that your radio receives 140 to 170 Mhz and you want to receive 800 to 830 Mhz. You add a simple, wide-band front end and mixer with a local oscillator that runs at 940 Mhz. This results in a frequency output of 140 to 170 Mhz with an input range of 800 to 830 Mhz. The drawback to using this method is that your front end is wide enough to drive a truck through and the image frequencies of 1080 to 1110 Mhz are not reduced by much.

There isn't anything you can do to improve your radio's image rejection, that was determined at the drafting table.

Disclaimer: The above frequencies have little or no relation to the real world. They were picked to illustrate the principle and not how your radio was designed.

 

[eorange]

I was wondering why my year-and-a-half old PSR-600 had that region blocked out when literature everywhere insists it covers this range.

As ecps92 said, a firmware update a while ago whacked some portions of the 700 MHz range. Your 600 probably came with that firmware rev level or later.

 

[KE4RWS]

Firmware

Have you updated your FIRMWARE?

Valid question Yes, I have updated the firmware with every release since originally purchased new in late 2009. However, I admit I never checked the referenced coverage when I orignally purchased my PSR-600 for at least the first two updates so it's at least possible the original firmware it shipped with may have covered this frequency range.

Clearly it's not a real issue with me, as I'm not aware of anything in that range to really listen to anyway. Its more a principle issue that GRE say's it DOES cover this range when it doesn't while not even offering the possible explanation of blockage due to newer firmware

 

[Jay911]

I was just made aware again of this thread linked from a newer topic someone else had posted. I see that nobody ever answered my original question in here (and there was tons of "help" that, while accurate for the things the "helpers" were talking about, has absolutely nothing to do with the true situation).

The truth of the matter is, yes, GRE radios have consistent problems receiving images of 800 MHz frequencies in the 796-806 portion of the GRE's receiver. There appears to be no solution, as GRE's response has been to remove the ability for their scanners to be tuned to that part of the band.

If you have a GRE radio that will tune to a frequency between 796 and 806, there is a greater than 99% chance that what you hear there will be images (duplicates) of things being broadcast in the 851 to 869 portion of the radio spectrum.

 

[BigC801]

My 106 gets images from 851+ and from 771-775.

 

[GTR8000]

Jay,

My PSR-410 covers from 791 to 797, and I pick up images from 851 to 862 all the time on the upper 700 MHz frequencies.

What I'm picking up right now, very strong and clear signals, but no decoding:

851.250 CC on 791.550

852.7375 CC on 792.350

860.9625 CC on 794.740

So this image problem is not just limited to 796-806, it plagues the entire upper 700 MHz band on GRE scanners.

Just like you, I checked those frequencies with my Uniden using the same antenna and heard absolutely nothing, as expected.

 

[GTR8000]

I sent a support ticket to GRE about the missing frequencies, just for the heck of it, and this was their official response (with regard to the missing 797-806...clearly the issue plagues even more frequencies):

700 MHz Spectrum coverage

The 310/410 have a rather noticeable gap in coverage between 797 MHz and 806 MHz. Is there any reason these frequencies have been omitted?

Unfortunately we had to remove these frequencies due to a regulatory compliance issue. Any traffic on these frequencies will be found with much stronger signals on conventional or trunked repeater output frequencies 30 MHz down, and simplex operation is not permitted in this part of the band (in fact, Motorola's own subscriber radios cannot be programmed to receive the frequencies in this range).

I know you want full coverage, and I wish I had a better answer for you, but hopefully you'll understand. We really don't have much choice in the matter.

Best regards,
GRE Support Team