A question for the folks who know scanner repair.

[Benzman66]

I have a Pro-96. Recently started doing a strange thing. On the frequency 462.950 which is a standard med frequency used in many areas for dispatch, my scanner is constantly sticking on it because of a "weak something".

Now, it isn't a transmit signal because all my other scanners are not picking it up. I am really not sure what it is. It seems like interference and no matter how much you turn the squelch down, it will not leave the channel unless you press scan. Then when it scans again and a call comes thru on that channel, it will stick again with a faint squelch sound afterwards. It received calls ok though on every other channel as well as this one too.

It seems more like static and sometimes you can hear a faint hum in the background when they do talk on the freq.. When you turn the ATT on, it eliminates the situation all together.and scans and receives normally.

I have been in the business for many years repairing electronics and this has me really stumped. I have thoroughly checked all settings (FM), etc,and no results.To save time and a lot of questions;

1. I do know about programming and the operations of scanners, so I am not a newbie..
2. There is no problem with the local transmitting system in Pittsburgh on this frequency, nor anywhere else nearby.
3. It is not happening with any other scanners of mine or my friends scanners.
4. No electrical interference.
5. No 'birdie'.
6. Antenna connector as well as solder post from antenna to board are perfect!

I also tried moving the freq to another bank but the problem still happens. Could it be a RF coil issue or chip problem? The scanner is a 1.5 CPU and has the latest downloads. Oh, by the way, I even re initialized it and redid the downloads thinking that may solve the issue, nope.

Thought I would bounce this off some of the techies on here. Maybe you can come up with something.

 

[SCPD]

adjust the squelch ?

 

[zz0468]

Just sounds like a spurious response, to me. The fact that the attenuator affects it indicates that something in the outside world is a factor, but it's likely that internal spurs are also playing a part. Those spurs could be caused by an overload condition on the front end, or they could be an artifact of a noisy synthesizer.

Things as simple as a loose shield cover could alter the synthesizers spectral purity (which, in a scanner is none too good to start with), and cause it to receive all sorts of weird stuff.

Without knowing exactly what the mechanism is that's causing it, I couldn't begin to offer suggestions for a fix.

 

[DickH]

...Thought I would bounce this off some of the techies on here. Maybe you can come up with something.

Remove the antenna. If you still get the interference, it's internally generated (a birdie).

 

[GrayJeep]

It could also be a new piece of gear in the house/next door/ across the street/ on the nearest tower could be giving this off as a spurious emission. Or your cable TV cable could be leaking.

For things like this the CTCSS tone squelch is great if the desired signal has it.

 

[Benzman66]

Nope, definitely not a birdie, but took the antenna off anyhow.

And it happens anywhere I have the scanner. Car, home, on the street walking, etc, and only in this scanner.

Never thought about spurs, but maybe? The strange thing is that it only does this on the one frequency (462.950). I wish I could describe the sound better. It is almost like a faint squelch/static, but when it stops on there for a transmission and they are done talking, no matter whether you turn the squelch up or down, it does not move nor change the sound, but soon as you hit ATT, it definitely changes things and goes to regular squelch where you can turn it up or down and the squelch works normally. Another thing is it just doesn't stop on the channel and do this, it is just when it stops for a transmission that it freezes up.

 

[gmclam]

You say this does not happen on other scanners, but does it happen on another PRO-96? Different model scanners have different birdie and image frequencies. It could be an external spurious signal on an image frequency, which is not an image on the other scanners you are trying.

I wonder if the signal is very short in duration; enough to keep the 'resume scan delay' triggered, but not enough that it would break the squelch so you could hear it. Have you looked at the "signal present" signal to the CPU on a scope? Do you see anything there during this condition? Perhaps this signal does not fully 'negate' after a signal goes away. That would keep the CPU there thinking there is a signal.

 

[radioman2001]

If the noise goes away when you remove the antenna, the problem is external to the radio. If the noise is still there when you remove the antenna it's internal to the radio. Now some of the things I have found to cause interference: clock radios, microwave ovens, computers in cars, even an incandescent light bulb. I can always tell when a GM product is near me, 46.14 unsquelchs and you hear a buzzing sound. You might even have that one of your other scanners is causing the problem, had that too. When I had 2 scanners next to one another, I would actually receive transmissions on both at the same time even though one was VHF and the other was Low Band. You might try, if the problem is external, walking around with the radio on the offending channel and see where the problem becomes most noticeable. If you have an attenuator, put that on and walk around and do the same. I have found that a lot of household appliances cause problems. We even had to replace a clock radio because it was taking out one of our channels 1/4 mi away.

 

[Big_Ears]

It also could be a 2nd, 3rd or 4th order harmonic which is eminating from some electronic device which contains an electronic oscillator circuit. Sometimes digital alarm clocks are guilty of transmitting alot of carrier noise.

 

[randyK]

My Pro-96 does this also, thank goodness the county I monitor runs a dpl code on the frequency which silences it. My Psr500 also does it. It doesn't matter where you are, so I think it is something internal to the radios.
Randy

 

[gewecke]

It also could be a 2nd, 3rd or 4th order harmonic which is eminating from some electronic device which contains an electronic oscillator circuit. Sometimes digital alarm clocks are guilty of transmitting alot of carrier noise.

This is likely. Try shutting off other nearby equipment one at a time,to eliminate the possibility of a strong i.f. signal. Some older radios have very strong I.F.sections cabable of interference from several feet away.
N9ZAS.

 

[Benzman66]

You say this does not happen on other scanners, but does it happen on another PRO-96? Different model scanners have different birdie and image frequencies. It could be an external spurious signal on an image frequency, which is not an image on the other scanners you are trying.

I wonder if the signal is very short in duration; enough to keep the 'resume scan delay' triggered, but not enough that it would break the squelch so you could hear it. Have you looked at the "signal present" signal to the CPU on a scope? Do you see anything there during this condition? Perhaps this signal does not fully 'negate' after a signal goes away. That would keep the CPU there thinking there is a signal.

I tried my friends 96 and it does not do it, so the problem definitely is with mine.

I don't keep any of my channels on delay. I have not thrown it on a scope yet but the reason it is staying on the channel is due to the interference after the transmission and again, no matter if you turn the squelch up or down, or wherever the scanner may be at the time, it does not change things. Unless you press the scan button, it will stay on that with the noise, but once you hit scan, it won't stop on that channel until there is a transmission and then the whole thing start over. I wish I could describe the sound better. Think of it like what a normal CB sounds while monitoring with the squelch open.

 

[gmclam]

I wish I could describe the sound better. Think of it like what a normal CB sounds while monitoring with the squelch open.

Do you have the channel programmed as FM (or AM)?

Take a look at the "signal present" signal to the CPU. It sounds like it is not negating (pulling up or down) as it should when the signal goes away.

 

[Benzman66]

Set to FM, signal present shows constantly thru the static.

 

[DickH]

Nope, definitely not a birdie, but took the antenna off anyhow.

... and what happened when you took off the antenna???

My Pro-96 does this also, thank goodness the county I monitor runs a dpl code on the frequency which silences it. My Psr500 also does it. It doesn't matter where you are, so I think it is something internal to the radios.
Randy

Since Randy is in Central NJ and you are in Pittsburgh, that pretty much proves it is not an external signal, unless it is a rare coincidence.

 

[Benzman66]

... and what happened when you took off the antenna???



Since Randy is in Central NJ and you are in Pittsburgh, that pretty much proves it is not an external signal, unless it is a rare coincidence.

The scanner scans normally without stopping on any channels when the antenna is off.

I am wondering if it is a flaw in the 1.5 CPU models? My friends has a 1.4 CPU and it does not do it.

Too bad it isn't a different frequency as I would just remove it or lock it out, but it is our citys main EMS dispatch freq, and they have no other mirror.

I can set it to ATT, which eliminates the interference, but than in turn, pretty much silences the transmissions on the channel.

 

[N8IAA]

I am wondering if it is a flaw in the 1.5 CPU models? My friends has a 1.4 CPU and it does not do it.

Download the 1.4 from Radio Shack and reflash your radio. Might be the way to take care of it.
Larry
Edit: My bad, that is the DSP version. Sorry.
Larry

 

[DickH]

The scanner scans normally without stopping on any channels when the antenna is off. ...

When it is stopped on the freq. and you are hearing the noise, THEN take off the antenna.

But the whole subject might be moot if you use their PL tone of 100.0. Wouldn't that take care of your problem?

 

[Benzman66]

When it is stopped on the freq. and you are hearing the noise, THEN take off the antenna.

But the whole subject might be moot if you use their PL tone of 100.0. Wouldn't that take care of your problem?

DickH,
When it makes the sound and I take the antenna off, it quits the sound and resumes scanning. When I put the antenna back on, there are no issues til a transmission comes over that channel and then it starts all over again.

I tried the CTCSS 100.0 PL, stops the noise, but that cuts out all reception on that channel.

 

[SCPD]

gmclam I see that you have customized scanners, can a pro 95 be changed in anyway, I just came in procession of one,I have trouble remembering, some things about scanners , also what are or is a upgrade for a pro95 thank you