PSR500 Birdie Problem on EDACS (Problem)

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stlouisx50

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I finally figured out my EDACS Issue. The frequencies were programed in the correct order and the scanner was tracking them fine, but there is a strong birdie on one of the EDACS frequencies, it keeps the scanner from resuming the tracking function and locks on the specific channel. Using the A works sometimes but depending on signal strength of the EDACS transmission, the birdie is stronger than that of the transmission and almost totally distorts the real signal.

Is there anything that can fix this major problem?
 

DickH

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Is there anything that can fix this major problem?
If you are using a base antenna, probably not.
If you use the antenna on the scanner, move it around and you may get lucky and find a spot in your house where it's not as strong. At that freq. there should be nulls every 3-1/4 inches.
 

stlouisx50

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It seems as if there is an open carrier and moving the scanner a bit helps here a tad , however there is still the sound of 2 mics covering each other due to the strong open carrier or birdie.... I think birdie because while traveling I still notice the strong signal/birdie.
 

DickH

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It seems as if there is an open carrier and moving the scanner a bit helps here a tad , however there is still the sound of 2 mics covering each other due to the strong open carrier or birdie.... I think birdie because while traveling I still notice the strong signal/birdie.
1) If you have another scanner, see if it also gets the signal. If it doesn't it's probably a birdie (a signal generated inside your scanner).
2) Remove the antenna. If it is still strong, then it's likely a birdie.

What are the I.F. freqs.? Some manuals list them. There may be 3 and the highest might vary depending on the band.
 

stlouisx50

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It is a birdie for sure. I undid the antenna and I still get a 3-4 bar strength. The frequency I am reporting is 857.0875. I talked to GRECOM support and they said either to use an external antenna otherwise there is not much that I can do.
 

Mike_G_D

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"Birdie"

Yeah, that's a problem! I tested it on my 500 and same deal. I did note that it seems to be a bit impedance dependent. In other words, characteristic impedance that the antenna presents to the radio's RF amp has a definite effect on the self-quieter's apparent level. In the RF engineering arena that's what a "birdie" is technically called: "self-quieter". All radio receivers have them but with good internal shielding and layout plus paying attention to the receiver's internal frequency plan you can keep them to a minimum at least in the band you are designing for. Unfortunately for receivers designed for a very wide frequency range this is very difficult especially when you have a low price point to hit; internal shielding costs money which a typical scanner manufacturer might forgo in order to remain cost competitive.

Anyway, getting back to the antenna impedance effect - I am not sure which antenna you are using but if you are using the one that came with the radio (I am assuming it is a PSR-500 as opposed to a PSR-600) then that is worst case. That antenna most likely presents a pretty bad load at 857MHz to the receiver's RF amp. I noted that the "birdie" was strongest with no antenna (worst mismatch), slightly less strong with the stock ducky (really bad but slightly better mismatch than no antenna) and weakest with my Radio Shack 800MHz ducky (best of the three apparently in terms of antenna characteristic impedance at 857MHz. The best result I got was from using the 20dB attenuator. This seems to confirm my suspicions that this is an impedance dependent self-quieter. Possibly the RF amp or (depending on the interstage coupling characteristics, port-to-port impedance isolation, etc.) some succeeding stage is going into oscillation when a non-ideal load is present at the antenna port. In such a case, putting a resistive attenuation "pad" in line can often cure or greatly reduce the severity of the problem. I noticed that when I kicked in the attenuator the self-quieter went away completely when no antenna was present. Unfortunately, with the stock antenna attached kicking the attenuator in helped but not completely - not sure why this should be; possibly there is a radiating component to this self-quieter that is still picked up by the antenna (in which case as GRE said, using an external antenna may help). A resistive pad of 20dB should provide more than enough impedance isolation port-to-port. It depends on the internal design and component layout so I really can't speculate further. Using the Radio Shack 800MHz duck with the attenuator kicked in was almost as good as attenuator + no antenna though I still needed to increase the squelch a bit.

So, I would suggest experimenting with different antennas - try the Radio Shack 800MHz ducky as that seems to work well overall on 800MHz. Also, if you are in a strong signal area use the attenuator.You'll probably still have to raise the squelch more than normal but it's better than nothing. If you use it alot in the car then try a mobile whip with a good impedance at 857MHz and see if that helps. If you can find a 6dB to 10dB external 50 ohm pad with BNC connectors (try Mini-Circuits) you could try putting one of those in line between the antenna and the radio to see if that helps - it might be a little mechanically unwieldy but it might help and wouldn't be as lossy as the internal 20dB attenuator. Otherwise, there isn't much else you can do. I really sympathize!

One other thing to try - in the super expert settings of the radio there is an EDACS disconnect tone setting or settings that may help in keeping the radio from hanging on the problem frequency after a transmission ends. I can't help you much here so you should try and find someone more familiar with EDACS disconnect tone settings to help you adjust these. I am having a similar problem on a Motorola system I monitor (though it seems more like external interference in my case rather than an internal self-quieter) and have been playing with the Motorola disconnect tone settings - so far to no avail but I'm running blind as I do not have sufficient knowledge of the finer points of Motorola trunking protocols to intelligently drive these. If you could work this out it wouldn't get rid of the "birdie" but at least (in theory) it might keep the scanner from hanging on the frequency after the transmission ends (you'd still get the interference during transmission though which will vary depending on the strength of the desired signal relative to the strength of the self-quieter).

I've often wished that manufacturers consider a "detune" feature for the receiver which would allow one to shift the internal local oscillator slightly in tandem with the rest of the receive chain's frequency plan to allow one to shift a problem self-quieter to another non-used frequency. Unfortunately, that would take some planning as you need to maintain center slot for all of the internal IF filters and interstage coupling components. Also, such a feature would likely complicate FCC acceptance testing. But it would be nice!

Good luck!

-Mike
 
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hoser147

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Not to through a kink into anyones theory, but last week I moved my 600 from the front of the house to the back and was getting reception with no antenna at all. The closest tower is about 12mi. Hoser
 

Mike_G_D

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no antenna reception; birdie 2

Hoser,

If by what you wrote you are speculating that the carrier on 857.0875MHz on the PSR-500 is external I am afraid the answer is a definite "no". Three observations confirm this:

1) An external signal would not get weaker with the antenna attached vs. no antenna (unless we are talking about such a severely mismatched antenna that the nearly infinite impedance of no antenna is better than the antenna itself - even the stock ducky is not that bad at 857MHz!).

2) It would be highly unlikely (though, admittedly, not completely impossible) that the gentleman in St. Louis and I, here in Southern California would both be getting a strong carrier with no modulation on the same frequency.

and finally, and most definitively,

3) I just checked using an ICOM communications receiver and verified that 857.0875 is clean - except when I bring the PSR-500 up close to the ICOM's antenna! This absolutely verifies that the scanner is internally generating the 857.0875 signal!

Now, your PSR-600 MIGHT be different as, if I understand it correctly since I do not own a 600, the 600 has a metal enclosure plus, possibly a different internal component layout on the PCB so it may not have the same self-quieter characteristics as the handheld 500.

-Mike
 

hoser147

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No by no means was I comparing anything, I just found it strange I took it back there to work on the front room came back to the front to get an antenna and heard it as I was going back, so I sat and checked it out sure enuff, only one Edacs system programed and couldnt tell ya what freq it was on. It was just an observation...............Hoser
 

spooney

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I finally figured out my EDACS Issue. The frequencies were programed in the correct order and the scanner was tracking them fine, but there is a strong birdie on one of the EDACS frequencies, it keeps the scanner from resuming the tracking function and locks on the specific channel. Using the A works sometimes but depending on signal strength of the EDACS transmission, the birdie is stronger than that of the transmission and almost totally distorts the real signal.

Is there anything that can fix this major problem?
and the problem is always present everywhere you go with your scanner or just in a specific room or location?
 

Mike_G_D

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Birdie 3

Spooney,

I have verified that what StLouisx50 is experiencing is, in fact, an internally generated self-quieter, aka "birdie" at least in the current design of the PSR-500 (see my two posts above) using my own PSR-500 as a test unit. Since I don't own a PSR-600, I cannot comment on whether or not it, too, experiences this issue.

-Mike
 

stlouisx50

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Yes is anywhere you take it. Anywhere from inches to miles. So its not an area issue. GRE People confirmed the issue on that frequency when I emailed them. GRE also suggested the EDACS END Tone setting, but this just caused the system to sound like Priority was selected (cutting in and out) on the transmission.
 

Mike_G_D

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Son Of Birdie

stlouisx50,

Unfortunately that's all I can suggest. I'd use the RS 800MHz antenna if you aren't already and leave the attenuator on if at all possible. That seems to bring the level of the internally generated self-quieter down to reasonably "squelchable" levels. I really don't understand end tone settings very well so I can only guess as to what you are experiencing regarding the behavior of the EDACS endtone. I imagine one problem would be that if the desired signal falls in level below that of the self-quieter during a transmission then the end tone detector may miss the end tone...meaning that it might still hang on the undesired carrier? The cutting out might be because the end tone settings are set too severely (you need to ask someone else about this - I'm ignorant here) so as to cause the receiver to interpret the end of transmission too quickly or some such.

I still think if you try a better antenna with a better match at 857MHz and use the attenuator and, maybe, play with the end tone settings somewhat, that you should be able to get around the problem at least when in a strong signal area. In a weak signal area you may be out of luck if you can't use the attenuator. If this is really really important to you I would suggest trying an external resistive attenuation "pad" with a smaller attenuation than what the built in attenuator has. I would go with something between 6dB and 10dB. Try Mini-Circuits and go for a BNC-BNC pad. This might isolate the impedance mismatch enough to lower the self-quieter to a manageable level while still giving you enough desired signal level. Unfortunately, it will be a little mechanically less desireable but there you go. The site is at

http://www.minicircuits.com/products/attenuators_coax_fixed.html.

The model HAT-6+ is the one you would try for 6dB and you will see others going on up in attenuation from there.

Short of this - going to another scanner model is all I can suggest. If your primarily mobile the 600 might work but you should test it out if possible. Otherwise - Uniden?

I would also suggest that you try the state specific site for your area and see what others are doing in your area and how they may have dealt with this problem.

-Mike
 
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