PRO 2055 ATTenuator logic

[dgoodson]

OK, another question for regarding this new (24 hour old) radio.

I have been disappointed with the sensitivity compared to my Uniden BC 895, so I started investigating, using distant NOAA weather stations as a benchmark.

I find that with ATT (or ATG) in all CAPS, my reception is noticably better (stronger); with ATT or ATG in lower case, my distant station go away entirely. This seems completely opposite what the manual leads me to expect (Page 66: ATT/ATG means attenuator = ON; att/atg means attenuator OFF.)

So is the manual wrong, or is there some other setting taking priority, or is this an indicator of something broken?

As for my Uniden, side by side, when I move the external antenna between the radios, is receiving my local NOAA station, plus 5 distant stations. My PRO 2055 is receiving the local station, but only 1 distant station and only when ATT is in all caps. When att is lower case, it receives only the local station. Even on my local NOAA station, quite powerful, when I set att to lower case I can begin to hear some "hash" while it is "full quietening" with ATT in all caps.

I am starting to think a trip to the return desk might be in order!

Opinions?

 

[ka3jjz]

No it isn't - rather it's time for you to understand a little more about your radios.

You are clearly experiencing what is commonly referred to as desense - the basic explanation is that the 2055 is being overloaded by some other station or stations, and as a result, turns down the sensitivity on all other frequencies in that range.

It's going to take some searching to identify the problem signal - one thing you didn't mention is if you are using an external antenna. If you are, take it off and revert to the little stick antenna. Rerun the same tests - if the attenuator works as advertised, whatever you are using is simply too much for the 2055 in that environment.

If the problem persists, it's time for a little detective work. What's around you - close by - that might be causing a problem? Is there a tower nearby? How about a TV or FM station - that can easily be the cause of the issue (I had that same problem years ago - I quite literally had an old MW antenna in my back yard - it caused horrendous problems. Solution? I got the xxxx out of there).

73s and GL...Mike

 

[pro92b]

This is a known issue with all recent GRE radios. VHF HI band overloads easily and reception is better with the attenuator on in many cases. Your attenuator is working exactly as it should. The dynamic range of the front end is less than it could be and the result is overload. This is a design issue and the only thing you might try to fix it is put an FM band reject filter in the antenna feed. If the overload is from signals outside the FM broadcast band that will not help.

http://www.notch-filter.com
http://www.parelectronics.com
Radio Shack FM Trap 15-577
Optoelectronics N100 notch filter

The cheapest filter is from Radio Shack but it may not work as well as the others.

 

[dgoodson]

Well I do understand desense, and that is probably the issue. This is my sixth scanner at the moment at this location, and one of three connected to my rather robust outside antenna... and its the only one that suffers the effect-- so if there is a design issue, that makes sense. I expected better!

I am able to monitor nearly 300 VHF frequencies, granted many sporadically, so I've nearly filled up the Uniden 895 and wanted to upgrade to something that would have 1) more capacity, 2) alpha tags and 3) DSQ detect... but I can't live with the desense. I'll give it a couple of more days, but right now I think this isn't for me.

 

[ka3jjz]

There are, of course, better scanners - all Unidens, but that's purely a biased judgement since that's all I run here :.>> The BC780, 785 and 796 all do those 3 things (only the 796 will be supported when rebanding occurs....) - and of course, the new mega channel BCD996 and BCT15 scanners.

It would be interesting to see how the new DMA (i.e. Dynamic Memory Architecture) radios - the 996 and the 15 - stack up in a high RF environment...but since this is the RS forum, I will leave that for someone else in the Uniden forum to comment <insert big xxxx eating grin here> 73s Mike

 

[pro92b]

It will take some work on your part to improve the performance of the PRO-2055. The Radio Shack FM filter is quite cheap and should be tried first. FM stations run 10-100 times as much power as public safety transmitters and can be a source of overload. If the desense is always present that suggests that a continuous broadcast is the main problem. The VHF HI bandpass filter in the 2055 passes 108-225 MHz and may not attenuate FM broadcast much. It is also possible that the NOAA weather station is a problem if it is really strong. You can set the radio to search 108-225 MHz and run it with no antenna to see if anything is received. Anything heard must be very strong to be picked up with no antenna. If the NOAA station is a possible problem, a coax stub filter might help at almost no cost. Otherwise PAR filters sells a weather band notch filter.