BCDx96XT: Uniden 996XT Squelch

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RF-Burns

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Does anyone know if there is a squelch pot or some sort of adjustment inside the 996XT? The scanner shows full scale signals even when the reception is very lousy. I would like to adjust it if there is a way.

Motoman55
 

Boatanchor

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Unless your radio is faulty, you appear to have a bad noise floor/interference problem.
What band are you listening too? VHF maybe?
Are you using an external antenna, or an internal antenna near a computer or TV?

Holding on a conventional channel, if you turn the squelch right down and then switch to AM, do you hear any pulse or loud static/crackle type noise?

The 'S' meter on the Uniden scanners only operates when the analogue squelch opens.
On digital channels, the analogue squelch still operates and a full scale 'S' meter can be displayed without any digital audio being produced. Or, if the digital channel you are listening to is weak, you can have a full scale 'S' meter reading (caused by the noise/interference) but high digital error rate and poor or garbled digital audio from the system you are trying to monitor.

For the squelch to open and the 'S' meter to register anything, you must have carrier/noise/interference on the channel strong enough to open the analogue squelch.

You could also try the IFX (IF exchange) function too.

The best idea is to manually tune to a frequency on the band you are monitoring, then switch to AM, turn the squelch right down to zero and find out what the noise floor is.

On a handheld scanner, you can walk around the home, holding the scanner near to various appliances. You will be surprised how RF noisy a DVD player or even a non-operating microwave can be.

Lowering the noise floor (broadband noise level), or putting it another way, improving the Signal to Noise ratio, is critical to obtaining low digital error rates and noise free analogue reception.
 
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RF-Burns

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Thank you for a quick reply,

I use a Antenna Specialist MON33 Mobile Antenna with a magnet in my attic on a cookie sheet due to my HOA.

Yes, it happens on VHF. I do have a tv and a PC in the same room but the results are the same with the TV and PC unplugged. I did switch the 996 into AM Mode with the squelch open and there was no excess noise floor.
The only Digital stuff around here is 800 Trunking and that operates normal. I can program my XTS2500 VHF P25 radio on a 2 meter frequency and try to see what happens on conventional P25 VHF vs Analog.

Let me try that in over the weekend and I will keep you updated.
 
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FeedForward

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I think what you may have is the equivalent of a long wire antenna. Or, it could be that the shield of the coax is picking up noise from around the house. You could try a small jumper from the center connector of the BNC to the center of the coax and note the results. One more possibility is that you have a strong FM radio or TV station close by. I have one about 2 miles away and I've had to shield everything with ferrite beads to prevent high signal level on the shields of the coax. Don't forget the power supply for the radio. Try plugging it in on another outlet and be sure florescent lights and dimmers are off for the test. The charger for my cell phone makes a racket in my AM radios around the house - one more thing to check. Everything runs on wall transformers these days.

FF
 

RF-Burns

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I would doubt I am getting any long wire affect. The antenna is directly above me and only has 14 foot of coax. I do have a NOAA Weather transmitter about two miles from my house. That could be it. I will put a choke inline on the power cord and coax feed.

No problems on P25 Conventional, that works as it should

I think what you may have is the equivalent of a long wire antenna. Or, it could be that the shield of the coax is picking up noise from around the house. You could try a small jumper from the center connector of the BNC to the center of the coax and note the results. One more possibility is that you have a strong FM radio or TV station close by. I have one about 2 miles away and I've had to shield everything with ferrite beads to prevent high signal level on the shields of the coax. Don't forget the power supply for the radio. Try plugging it in on another outlet and be sure florescent lights and dimmers are off for the test. The charger for my cell phone makes a racket in my AM radios around the house - one more thing to check. Everything runs on wall transformers these days.

FF
 

jonwienke

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NOAA transmits about 1000 watts in the 160 MHz band. So if you have one nearby, you're going to have trouble receiving VHF transmissions without a notch filter in your antenna line set to reject the frequency the NOAA transmitter is using.
 

RF-Burns

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NWS does have 1K Transmitters but not nearly all of them are 1k. The majority are 500 and some even down to 250.
 

FeedForward

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If you suspect local interference from the NOAA, a simple way to check for front end overload is to fashion a simple attenuator using a couple of resistors, just for a quick test.
 
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