Pro-96 overload

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N9AZZ

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Hello

I had not hooked up my Pro-96 to an outside antenna until recently. When I did I noticed that reception was down on VHF. Since the radio with the rubber duck works very well I was a bit puzzled. I wondered about the attenuator so I hit the ATT button and the VHF station that was very noisy came in full quieting. I played with it bit more, finding stations that were at the squelch level and found that when the ATT was enabled they were readable. Of course this isn't acceptable since the unit is carried almost every day, and to have to go through and disable/enable the attenuator would be a pain.

I live in a rural area, and intermod is a non issue. but I figured something was getting in to the front end. I switched to a emergency antenna I have in the attic with lousy feed line and the attenuator worked as it is supposed to.

I decided to try and find the problem, so I started searching different slices of spectrum. While searching the AM aircraft band I heard music. It was all up and down the band. I figured out which radio station it was, a local FM transmitting on 103.5 located approximately 3 miles away from my house.

I figured that I would try and reduce the level of the FM station, so I decided to try a tuned stub. I attached the antenna connector to one side of a BNC "T" connector. I attached the male end of the "T" on the scanner, and cut a piece of RG-58 coax cable with a length of one quarter wave length of the FM stations frequency.

234 / 103.5 = 2.2608
converting that to inches 2.2608 * 12 = 27.13

Also the cable was left open on the end (not shorted).

This completely notched the FM station from the front end of my radio. The scanner receives as it should on VHF, and the attenuator also works as it should, reducing the received signal, not enhancing it.

This might not work if you are bombarded with different signals, but I would think that if FM radio stations are your problem you should be able to reduce the interference with this method.

I called a friend who has a Pro-97 and asked him to check his on an external antenna. While mobile in Springfield IL he experienced the same problem. When he heard VHF stations weaker than he thought he should, he hit the ATT button and they also came in much better. I don't know if his was FM radio overload or not, but it seems that the Radio Shack portables are prone to this interference when they are on a base or mobile antenna.

Hope this helps someone.


Flip N9AZZ
 

N1BHH

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I worked for a short time for WMVY on Martha's Vineyard and built and installed about 150 traps. Back then, people had one or two huge antennas on 5-20 foot towers on the roof to get good solid Boston and Providence TV reception. Many of the homes we visited we had to put traps in line. Most had a distribution amp for as many as 4 TV's in their large homes.

We had a message on the station play rotation (station was automated, except for news) that told residents if they had problems watching TV to call and we would come out and check it out. We would get there and watch for the tell-tale herring bone pattern on the TV. We would then call the station by phone and have them switch the 3,000 watt transmitter off for about 5-10 seconds to be sure it wasn't us causing the TVI.

We did install traps in nearly 75% of those homes we got called from, the other 25% had traps for 75 Megahertz installed, for the interference they received from the airports Radio Navigation beacon. That got into more TV's than people thought it did. What I remember the most is going to the home of Carly Simon, but she used the name Hart, because the mailbox had the last name of her then husband on it. She was cordial, asked if we wanted apple juice or lemonade and we took the lemonade, which she made just a few minutes before we arrived.

That was a treat. Here I was, the voice of the Carly Simon sweeper that said, "Here's The Island's favorite voice, Carly Simon!" before every play of her songs and putting in a trap for her.
 

hypersight

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Thanks for posting this info N9AZZ.
I also get overload from a radio station when my pro96 is connected to a base antenna.
I just want to clarify - that piece RG58 coax you cut off, did you attach it to the other side of the T connector?
 

N9AZZ

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Yes, the feed line comes in on one female side, the RG-58 is on the other female side and the male goes to the radio. It works pretty well.

Flip N9AZZ
 

hemi

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Nortumberland county Ontario
Iam pulling my hair out. I sold my uniden to get a pro 96, love it, but i can't have a outside antenna at all because the whole scanner just gets wiped by interference.
 

hypersight

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N9AZZ said:
Yes, the feed line comes in on one female side, the RG-58 is on the other female side and the male goes to the radio. It works pretty well.

Flip N9AZZ
Thanks again. I will try it this weekend.
 

N9AZZ

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hemi said:
Iam pulling my hair out. I sold my uniden to get a pro 96, love it, but i can't have a outside antenna at all because the whole scanner just gets wiped by interference.
Well the main thing is to find out what signal is overloading you, I went to AM aircraft and searched until I was able to hear it. I then matched it up with the correct station and frequency. I would assume that it could be any close by VHF transmitter if the interference came and went, but if it was like the situation here, it was there all the time, so that points to FM or TV in the VHF band.

Good luck

Flip N9AZZ
 
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