How to recognize signal overload?

[chas0039]

I am getting as lot or distortion on digital signals, and I assume it is due to multipath distortions from multiple antennas. I am not clear on when attenuation might be needed and I am not positive on how I would recognize signal overload form a signal that is too strong, a problem I have read about.

So, how do I know if I should be using the attenuation features?

Thanks

 

[mdulrich]

Try it and see if it makes it better.

Mike

 

[kruser]

Try it and see if it makes it better.

Mike

That pretty much says it all. The best thing to do is turn the attenuator on and see if it makes things worse or better then you go from there.
If turning in on does help, then you need to try and determine if it is helping by reducing out of band signals that can cause desense of the receiver or if it is helping by reducing the signal from one of the other towers in the system when the system is a simulcast system.

You won't hurt anything by trying it!

 

[chas0039]

I don't mind trying things, I do so all the time with HF, but it would be helpful if I could know just what I would be hearing that would be helped? Any ideas?

 

[kruser]

I don't mind trying things, I do so all the time with HF, but it would be helpful if I could know just what I would be hearing that would be helped? Any ideas?

In the simplest terms, you may not hear any change other than a better signal.
Try it and see if the "distortion on digital signals" gets better or worse.

That was your initial complaint so try the attenuator function and see if the distortion clears up or not.

What type of scanner are you using anyway?

Also, an FM Trap may help as it does for many by eliminating signal overload from commercial FM broadcasters. That is a known problem that affects the GRE made radios more than the others. This includes the RadioShack scanners as their digital scanners are made by GRE and are almost identical clones of their GRE brothers.

 

[kruser]

Also, on the GRE made radios at least, a signal strength meter that always shows a full or near full strength signal even when tuned to a frequency with no signal can be an indication of signal overload. In this case, it is usually caused by out of band signals and is where an FM trap may help.
Picking up signals that are not really on the frequency the scanner is tuned too may also be an indication of signal overload.
Hearing hints of an FM broadcast station in the static when you open the squelch is another indicator.
There is really no one method though to answer your question as there can be many causes all with a different symptom or outcome.
Experimentation is usually the best method.
You could also start a thread in the forum for your state and list the system you are having issues with.
The users in your states forum have likely experienced the same problem as you and may offer an easy fix or solution. Make sure you list the system you are having issues with as well as a general idea of your location as that can help those that may be able to offer better help.

 

[chas0039]

Thanks, I have a GRE 800 in the Twin Cities and the local experts say multipath problems are a big problem here. I am getting signals where the voice warbles and wavers and generally sounds like Donald Duck with marbles in his mouth. Often, this is only one side of the transmission, and on a long transmission, it sometimes clears up.

Thanks for the ideas as to what to look for. That gives me a great start.

 

[puzzleriddle]

AntennaSearch - Search for Cell Towers, Cell Reception, Hidden Antennas and more.

 

[kb2vxa]

Chas, your problem isn't overload, it's the codec losing signal lock thus failing to decode the digital signal. If the experts say it's multipath I believe them, with analog it causes dead spots and "picket fencing" with mobiles, with digital the distortion totally disrupts the decoding process.

If you're receiving multiple towers simultaneously the attenuator MAY eliminate the more distant one(s) or it may not but you have nothing to lose by trying. Then multipath is commonly caused by reflections, either way the attenuator MIGHT work. If not next step is a beam antenna, the higher the gain the greater the rejection so bear that in mind if push comes to shove.

Something else came to mind, usually the codec settings can be adjusted in a little known part of the programming menu. Default settings usually work but not always so check the manual, you just may clarify the butter.

 

[chas0039]

Chas, your problem isn't overload, it's the codec losing signal lock thus failing to decode the digital signal. If the experts say it's multipath I believe them, ...

I am not clear, is the codec problem due to multipath or something else? The "experts" here are commenting on their problems and have not heard my radio. My GRE 800 has nothing on this so if it is a codec problem, is their a source you can point me to for help?

Thanks for the feedback.

 

[kb2vxa]

You say the voice sounds like Donald Duck, that tells me you're listening to digital which tells me the firmware codec (COmpression / DECompression) not properly locking onto the data stream is making it sound that way. If the radio system loses lock it sounds like that to everybody on it and instead of the expected "you're coming in garbled" they'll say "you went digital" which really makes no sense because it's digital in the first place.

"The "experts" here are commenting on their problems and have not heard my radio."
<giggle> I'm no expert either and I haven't heard YOUR radio but your description sounds exactly like what I have heard. Since digital is an all or nothing proposition a weak signal below the capture threshold will drop out entirely about the only thing I can think of that would disrupt the data stream above the threshold would be multipath.

"My GRE 800 has nothing on this so if it is a codec problem, is their a source you can point me to for help?"
Unfortunately no, using instructions in the manual I have adjusted the codec in my BC796D but I know absolutely nothing about GRE. If your manual says nothing (it really should if it has that feature) you may find a more comprehensive one on line, if not perhaps your GRE has no way of adjusting it. That only eliminates one avenue of approach, mine, but the RR experts posted above have valid suggestions you can try.

If at first you don't succeed try a bigger hammer. If all else fails dynamite is sure to work.

 

[chas0039]

Thanks for all the help guys. Just one more reason I HATE all the switch to digital in this country, the all or nothing mess, both in radio and television. The day that I lose analog on the 20 meter band is the day I sell everything.

I know it can't happen, but I also know someone somewhere in the government is thinking about it.

 

[kb2vxa]

What makes you think you can sell analog equipment to a digital world? Well, you'll have some really cool looking doorstops. Oh and hey, what makes you say someone in the government is thinking? When was the last time THAT happened?

"I know it can't happen..."
OH YEAH? Frank Zappa - It Can´t Happen Here 1966 - YouTube

 

[ab3a]

I think modern scanners with a CODEC should have a tuning display option so that you can spot distortion issues and see what the channel looks like when it's squelched.

It is entirely possible that something is radiating a signal in the background and your CODEC can't deal with it. But like everyone else here, I'm just making stuff up. We don't have any way of knowing.

 

[chas0039]

What makes you think you can sell analog equipment to a digital world? Well, you'll have some really cool looking doorstops. Oh and hey, what makes you say someone in the government is thinking? When was the last time THAT happened?

"I know it can't happen..."
OH YEAH? Frank Zappa - It Can´t Happen Here 1966 - YouTube

Good point about my mistake to imply "thinking" in the government. As to selling off my analog stuff, I'll do so at the first hint. I'll have plenty of time to unload, as short wave is a global hobby. Besides, the airwaves will always be there. If I am analog and someone else is analog, we can always talk.