PSR-600 overload and desense

[mtitteri]

Hello,
I have heard mention of this issue on the board, but would like to know if anyone has ideas.

My new PSR-600 is unusable from 137-174mHz, due to full-scale overload across the entire band. The same problem happens on VHF-low, but I don't use those frequencies much.

I am using a discone about 18' high outdoors, but have the exact same issue using the supplied telescoping antenna.

I do understand overload and desense, but the surprising part is just how poorly the 600 compares with my Uniden 396, 996 and even an old Pro-95. All 3 of these radios receive fine with exactly the same antenna. ...no splitters or anything like that

If I use the attenuator across the band, the desense and overload goes down dramatically along with the signal. I don't expect any scanner in this price range to work miracles, but I am concerned that the Unidens, and even an older GRE do not have this issue.

This effectively makes my new scanner useless for scanning VHF.
Does anyone thing I may just have a bad or mis-aligned unit? I have always liked GRE products over the years and would much rather use the 600 than a 996. However side-by-side comparisons show the 600 is completely unable to deal with my environment.

Any suggestions or ideas are appreciated. I did check the CPU/DSP and found that they are current with the GRE site.

Thanks for your help.

 

[ka3jjz]

Mark, your problem is that these GRE scanners are too sensitive, and lack certain filtering to prevent signals from causing problems. It is possible, though it would take some homework, that you have a FM station or station(s) that is the cause of your issue. Some have noted quite an improvement by purchasing a FM filter from places like PAR electronics. Looking around your local FM band for stations that are really strong would be one way. Another possibility are pagers - which are notorious for running too much power, overdeviating and generally making a mess of the VHF hi band for scanners with poor selectivity. If you live within sight of a broadcast tower, that's an immediate red flag right there.

This isn't an alignment issue - it's a faulty design issue, frankly. Every manufacturer tends to take shortcuts to keep costs down, and sometimes this is the result. 73 Mike

 

[mikebennett]

Hello,
I have heard mention of this issue on the board, but would like to know if anyone has ideas.

My new PSR-600 is unusable from 137-174mHz, due to full-scale overload across the entire band. The same problem happens on VHF-low, but I don't use those frequencies much.

I am using a discone about 18' high outdoors, but have the exact same issue using the supplied telescoping antenna.

I do understand overload and desense, but the surprising part is just how poorly the 600 compares with my Uniden 396, 996 and even an old Pro-95. All 3 of these radios receive fine with exactly the same antenna. ...no splitters or anything like that

If I use the attenuator across the band, the desense and overload goes down dramatically along with the signal. I don't expect any scanner in this price range to work miracles, but I am concerned that the Unidens, and even an older GRE do not have this issue.

This effectively makes my new scanner useless for scanning VHF.
Does anyone thing I may just have a bad or mis-aligned unit? I have always liked GRE products over the years and would much rather use the 600 than a 996. However side-by-side comparisons show the 600 is completely unable to deal with my environment.

Any suggestions or ideas are appreciated. I did check the CPU/DSP and found that they are current with the GRE site.

Thanks for your help.

I don't think there is anything wrong with your radio. I have experienced the same problem with a 600 using an outside antenna which is about eighty feet up, across the entire VHF-HI and aircraft band. I attentuated all frequencies in this range and I am able to receive fairly well now. There is a certain area just West of my location that does the same thing in the same band in the car with a mobile antenna. Whenever I travel through that area I have a V folder programmed with the exact same frequency line-up, only the VHF- Hi stuff is attenuated. It seems to pick up fairly well then. It won't receive anything however if the attentuator is off. I had a similar problem with a Uniden BCT396 in this area. I never tried the attenuator because I thought it was an antenna issue at the time.

 

[ecps92]

I've found when mobile, using an 800 Mhz antenna reduces much of the VHF interference, including the cable leakage, yet I still maintain good VHF reception

I don't think there is anything wrong with your radio. I have experienced the same problem with a 600 using an outside antenna which is about eighty feet up, across the entire VHF-HI and aircraft band. I attentuated all frequencies in this range and I am able to receive fairly well now. There is a certain area just West of my location that does the same thing in the same band in the car with a mobile antenna. Whenever I travel through that area I have a V folder programmed with the exact same frequency line-up, only the VHF- Hi stuff is attenuated. It seems to pick up fairly well then. It won't receive anything however if the attentuator is off. I had a similar problem with a Uniden BCT396 in this area. I never tried the attenuator because I thought it was an antenna issue at the time.

 

[DaveIN]

Actually, I think the latest GRE radios were designed to be more sensitive on purpose. While the Uniden radios do well in my area with overloading, I like the current GRE radios for long distance and specialized band/antenna combination listening. As others have pointed out, the attenuation does help if your working with the transmitting frequency of interest is the problem, however if you are experiencing de-sense from an offending transmitter than a notch filter and antenna combination may be needed. These receivers are for general coverage usage, not designed specifically for one band as a ham transceiver or business band radio with filtering for the specific bandwidth.

 

[Patch42]

It is possible, though it would take some homework, that you have a FM station or station(s) that is the cause of your issue.

You can use the FCC database to find FM stations that are close by and could be causing problems.

Toward the bottom of the form on the page linked above there's a place to enter your lat/long. If you do so, the resulting search data will include distance to the transmitter. It also includes transmit power. If you enter a radius of 50km on the search form you should get every FM transmitter that might be causing you problems.

 

[ratboy]

On my Pro-197, I have several transmitters causing issues, but the worst offender seems to be a nearby FM station at 99.9MHZ. Also, there is a TV audio problem and a couple of pagers that don't help much at all. I finally got one of the PAR FM filters, and it solved much of the issues I had, but if I put the 197 on the Scantenna, it overloads on VHF to the point everything under 400MHZ is unusable, and on the discone, the TV audio causes a lot of problems, but it's tolerable. It will be nice when they finally go digital and this signal goes away. I'm pretty disapointed in the 197's VHF performance, even on the factory whip, and the PAR filter, I have to lock out a lot of VHF objects, as the scanner won't pass them over even attenuated..

 

[n4jri]

Actually, I think the latest GRE radios were designed to be more sensitive on purpose. While the Uniden radios do well in my area with overloading, I like the current GRE radios for long distance and specialized band/antenna combination listening. As others have pointed out, the attenuation does help if your working with the transmitting frequency of interest is the problem, however if you are experiencing de-sense from an offending transmitter than a notch filter and antenna combination may be needed. These receivers are for general coverage usage, not designed specifically for one band as a ham transceiver or business band radio with filtering for the specific bandwidth.

I agree. At least GRE gives us the OPTION of sensitivity. You can reduce that sensitivity either by using the attenuator (either globally or for individual objects) or by changing your antenna configuration. I never use an external antenna with my 500's and I don't use the supplied stock antenna, either. Like ecps92, I use the 800 duckie and that serves me pretty well even in rural areas. Yes, a VHF duck would make my radio virtually explode in the city.

And take it from me, I've had it both ways. My first PSR-500 was fairly deaf on VHF-hi, and although it worked very well in cities and suburbs, it failed me in outlying areas. I had no option to INCREASE sensitivity in a way that would work well with a handheld. (inline preams are such a pain...) When I got a more sensitive unit I knew immediately that I wouldn't trade it for the world.

With my current 500's I can reduce sensitivity if it gets to be too much, but still have the ability to work well in outlying areas. I get great recepion with 800 duck antennas inside my pickup truck where one radio sits in a cup holder and the other is clipped to an air vent.

Now there are some cities where the intermod alleys are pretty bad--but that stuff affects professional equipment as well--particularly if it isn't using CTCSS or DCS. I don't see this scanner as being that much worse than the tightly-tuned Motorolas we used on the rescue squad 20-some years ago.

73/Allen (N4JRI)

 

[ka3jjz]

Here's an interesting question - has anyone gotten a service manual or schematic, particularly of the IF and RF sections? It would be informative to see whether there's a high pass filter (something that cuts off everything below a certain freq range, and passes anything above it) or similar in there - if it's highest cutoff would be around 92 mhz or so (which is, I think, the highest FM frequency range in China) then that would answer a great many questions about why FM overloading is such an issue with these radios 73 Mike

 

[wmbio]

These are $4.99, from RS... 75-OHM COAX FM TRAP 15-577C ...get 1 or 2, they work well in series if your overload is high.
Wmbio

 

[pro92b]

Here's an interesting question - has anyone gotten a service manual or schematic, particularly of the IF and RF sections? It would be informative to see whether there's a high pass filter (something that cuts off everything below a certain freq range, and passes anything above it) or similar in there - if it's highest cutoff would be around 92 mhz or so (which is, I think, the highest FM frequency range in China) then that would answer a great many questions about why FM overloading is such an issue with these radios 73 Mike

Every GRE triple conversion scanner going all the way back to the PRO-2004 uses switchable front end filters for the various bands. Most af the filters are bandpass types with the possible exception of the one for 800 MHz and up. The VHF-HI filter passes the range 108-174 typically so it passes both the civil air band and VHF-HI band frequencies. These filters are not brick-wall and the attenuation outside the passband gradually becomes greater the farther you move from the cutoff frequency. With FM broadcast being right below the air band, the bandpass filter attenuation is poor that close to the cutoff frequency. That allows FM broadcast to affect reception well into the VHF-HI band by causing overload.

The PRO-2004 and PRO-2006 had RF stages with high dynamic range and could handle the FM overload issue better than today's scanners. Starting with the PRO-2035 (the replacement for the PRO-2006) things took a turn for the worse and the dynamic range was much inferior to the older models.

Uniden scanners have slightly better dynamic range than the current GRE models, but not by much. They make up for it by using two bandpass filters, 108-137 and 137-174 where GRE uses just one. That way Uniden can reject FM broadcast better when tuned to VHF-HI frequencies.

All the radios made for the US market are designed for a 108 MHz FM band cutoff. If China has a 92 MHz upper limit, that has no bearing on the scanners sold here.

 

[smason]

The PRO-2004 and PRO-2006 had RF stages with high dynamic range and could handle the FM overload issue better than today's scanners. Starting with the PRO-2035 (the replacement for the PRO-2006) things took a turn for the worse and the dynamic range was much inferior to the older models.

Now *that* makes sense!

I would disagree with those that say that the 500/600 is more sensitive, as I've compared my 600 to the 2004 2005 and they seem almost equal particularly on VHF (144-156), yet the 2004 2006 are much more bulletproof as far as desense, overload and intermod.

 

[pro92b]

Now *that* makes sense!

I would disagree with those that say that the 500/600 is more sensitive, as I've compared my 600 to the 2004 2005 and they seem almost equal particularly on VHF (144-156), yet the 2004 2006 are much more bulletproof as far as desense, overload and intermod.

My measurements support what you are saying. In fact GRE radios tend to be less sensitive than Uniden radios. The amount of difference varies somewhat by band and model and in some cases the difference is negligible.

 

[DaveIN]

My measurements support what you are saying. In fact GRE radios tend to be less sensitive than Uniden radios. The amount of difference varies somewhat by band and model and in some cases the difference is negligible.

Not sure how your taking your measurements, but in comparison with PSR550 vs. BCD396T or PSR600 vs. BCD996T using the same antenna type, I am able to get a better signal on the GRE radios. My GRE radios will de-sense with higher gain beam antennas, while the Unden equivalents appear to be OK, so YMMV. My Uniden radios are low in the serial number range so it is possible improvements have been made in subsequent production runs.

 

[pro92b]

Not sure how your taking your measurements, but in comparison with PSR550 vs. BCD396T or PSR600 vs. BCD996T using the same antenna type, I am able to get a better signal on the GRE radios. My GRE radios will de-sense with higher gain beam antennas, while the Unden equivalents appear to be OK, so YMMV. My Uniden radios are low in the serial number range so it is possible improvements have been made in subsequent production runs.

My measurements are using a signal generator on the test bench. That is the only way to isolate raw sensitivity and compare scanners under identical conditions. There is no way to duplicate those conditions by connecting the radios to an antenna and comparing reception. Other factors like dynamic range, front end filtering, IF selectivity and even the amount of grounded metal in a hand held will skew the results.

There is also variation in performance among scanners of the same model given a large enough production population. For example, the PRO-97 is specified to have a sensitivity of 0.5uV typical and 2uV at the worst in the 137-225 MHz range. This is from the service manual. Most units will be around 0.5uV, but if one measures near 2uV, it will still pass the production test and be shipped.

In real world conditions there will always be cases where one brand beats the other and lots of conflicting reports can be found on these forums. It isn't my intention to get into one of those arguments - I'm just reporting what I measured. I do hope GRE sees this thread and if they plan to continue producing scanners with poor dynamic range, I hope they consider splitting the 108-174 front end filter into two filters as Uniden has done. Otherwise they will always be at a competitive disadvantage with Uniden for VHF-HI band performance.

 

[wwhitby]

I don't have a PSR-600, but I do have the PSR-500 and I use it mobile. Even with a quarter wave antenna or a cell phone antenna, I get a lot of desense on VHF when I get close to the nearby major city where I work. Unfortunately, 95% of frequencies used around here are VHF. Using PL/DPL/NAC does help, but i'm constantly adjusting the squelch upward because of the scanner stopping on VHF frequencies that don't use PL/DPL/NAC. Its almost useless on the railroad frequencies due to overload from a nearby NWS transmitter. However, it does work really well on UHF trunked and conventional and MHz trunked systems. It is also great when I get away from bigger cities and their concentration of transmitters.

I've tried selectively using the attenuator, but like you found out, it also attenuates the frequency enough so that you can no longer receive it. To listen to the railroad frequencies, I stopped using my PSR-500 and just use my ham 2M mobile radio.

When my PSR-500 went back to GRE for repair, I used my old PRO-96 in the car in its place. I was amazed at the difference between the two. The PRO-96 actually worked better. I wish GRE would have have kept the same kind of reception capabilites of the PRO-96.

I really like the features of PSR-500, but it really irritates me that its almost useless on VHF when you're in a big city. Kind of like buying a new car, but finding out that only half of the cylinders work. For $500, I really expected better

Warren

 

[ratboy]

I had my 96 out today with me in the car, with my PSR-500, and had them both searching railband, and the 96 crushed the 500, not even close. The place I was listening at is close to an FM station, and a pager tower, and the 500 had a lot of problems. I put an FM trap on the 500, and it helped a lot, but the 96 was still a lot better. The trap didn't seem to do much at all on the 96 though, I could use one of my 2M ducks on the 96 and it did ok, but the 500 was usable with the stock antenna only. .

My Yaesu VX-170 was light years better than the 96 with just a short VHF antenna on it, and fantastic with the full size 2M whip on it. I could hear distant locos clearly on it that the 96 either didn't hear at all, or were very weak, and yard handhelds could be heard OK on the Yaesu that the 96 didn't hear at all. The 500 heard little except the dispaticher and close by trains, and was generally quite deaf , compared to the Yaesu. Using the ATT did nothing to help on the 500 at all.

At home, the 500 does an ok railband job, on the stock antenna, and on VHF in general, the 96 is just slightly better.

It's really too bad that GRE dropped the ball on VHF with these newer radios, so close..

 

[SOFA_KING]

I'll put my $0.02 in on this topic. GRE did drop the ball on the VHF and 800 RX overload issue (dynamic range problem). What a shame for such a feature packed line of scanners! But some of the statements here are out of whack! Allow me to clarify:

The "selectivity" of the new GRE line is OUTSTANDING. Bleedover rejection on adjacent channels is better than any scanner I have ever owned...and I have had many. The scanner IS very "selective".

"Attenuation" does next to nothing to solve this front end overload issue. Why the heck would you put your antenna at 85' and then attenuate the signal? That is funny. The correct solution to solve this problem is front-end filtering. Get an FM Broadcast filter, and get notch filters for "in-band" overload issues. The FM filter fixes almost all my problems even in the city. I know some cities, like NYC, are an RF nightmare, so almost all radio equipment has some level of degradation. Scanners get wiped! BUT REDUCING THE RECEIVER'S SIGNAL INPUT ON DESIRED FREQUENCIES IS NOT THE ANSWER. I want to to HEAR the weak signals, than you.

The term "very sensitive" is not the issue here. It is dynamic range and front end filtering. From what I have measured with my signal generator, my PRO-197 is fairly sensitive. Not as good as some other scanners I have, but good enough. I would pay GRE more money for a scanner with top shelf sensitivity AND overload rejection, but who else would want to spend that amount of cash? If you would pay a bit more, they would make it that way. But all we hear is the whining about how overpriced these things are. Get real! :roll:

"Images" are a problem with almost all modern scanners I have had. My Uniden scanners are real bad at image rejection. I think this GRE is a bit better. Sure I would love NO IMAGES, but there is the cash factor again.

And the statements like "you will never have everything you want in one scanner" are the biggest cop-out I have heard in my life. Maybe if you think that way, you make it your reality. Why "rollover" and let the scanner company give you a half-@$$3d product when you could DEMAND a complete package from them? Get active! Speak up for what you want! As the person paying those companies and keeping them in business, you have a lot of power with your money and your voice. Tell them what you want, and choose your battles carefully. From my own conversations with GRE, I can tell you they DO listen. The more people who give them constructive feedback, the better the feature set and quality of their products! Make it happen!

Finally, use your head about all of this. If you don't like the product, don't keep buying it. I found Uniden kept leaving me wanting more, so I HAD TO buy the "next scanner" to get some feature I wanted. This is by design! They were "spoon feeding" me features one model line at a time. This p!$$3d me off big time. I'm not so inclined to buy Uniden again. GRE did it better in many key areas. But I made it clear to these companies that I will not continue to buy scanners IF they don't "just do it already". Get the product right or I'm not spending money. This is your last chance!

Rant over ~

Phil

 

[rankin39]

The problems with the GRE include TV channels 2-6 in addition to the FM broadcast band. We need somebody to make an outboard filter that will block 53-108 MHz. Par and other companies make excellent filters for particular frequencies, but not for this entire range.

Bob, WoNXN

 

[ratboy]

My friend just bought a Pro-106, and he is having major problems with both TV and FM stations overloading it. He lives near where several TV transmitters are, and an FM station is nearby too. He likes the 106 a lot, but the overload/Intermod issue is making the radio useless for everything below 400MHZ. I let him borrow my PAR FM filter yesterday for testing, and it helps VHF, but not very much. It does clean up 460 MHZ nicely though, so he will order one as soon as he can. I would like to see a filter that would kill everything from 108MHZ on down, as low band is something most people around here don't even bother programming in anymore. I think this would solve almost all the problems.

But how big would it be?