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Old 08-04-2011, 9:21 PM
  Amateur Radio Operator
Amateur Radio
Join Date: Jul 2011
Location: Pekin, Illinois
Posts: 8
Question Problems with the Pro-433

I always get weird looks when I ask about this certain problem I have been having, I am very sure I am not the only one having this problem. On VHF and Lower Military Air frequencies I get these weird noises, I will try to describe them. Its a data noise with NOAA weather radio going in the background and other voices mixed in. Now, the thing that is weird is it only happens with external antennas, the antenna that came with it is fine, I never get it, or have ever noticed it. I hear it with the Mobile Antenna, my base outside antenna and one that I used before. Does anyone know how a 162.475Mhz frequency can be mixed in with all of this on a different frequency? Is there a way to fix it?? BTW - I do have 3 of these radios and they all do it. I provide a feed and its pretty annoying when it happens.

Any help would be appreciated,
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Old 08-05-2011, 3:25 AM
Join Date: Oct 2007
Posts: 5,230

I took the liberty of looking up your ham callsign to figure out where you live in relation to the local NOAA transmitter. Sure enough, you live just 1.9 miles from the WXJ-71 transmitter on 162.475 MHz. That transmitter is putting out 1000 watts and is located on the top of the WTVP-TV tower, which is at the intersection of Cole St/Cole Hollows Rd and Shelby Ln/W Muller Rd, a few hundred feet to the south of 474. The tower is almost 600' high according to the FCC records.

Being close to THAT much power at that height, it's no wonder your scanners are getting overloaded when connected to an external antenna!

What you need is a notch filter that will attenuate the offending signal on 162.475 MHz. PAR Electronics makes just such a notch filter for the NOAA frequencies, the VHFSYM162HT model. The filter will attenuate the signal by -35 dB, which should be plenty to get rid of the intermod that is overloading your scanner's front end.

PAR Electronics | Scanner Filters

VHF SYM 162HT Specifications and Plot | PAR Electronics

PAR 162-HT Scanner Intermod Filter

Here is the location of the radio tower: 40.628917, -89.570111 - Google Maps

Details about the NOAA transmitter: National Weather Service, Lincoln IL -- NOAA Weather Radio Station WXJ-71 (Peoria, IL)

FCC data for the WTVP-TV tower: TV Query Results -- Video Division (FCC) USA
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Old 08-05-2011, 3:43 AM
Join Date: Oct 2007
Posts: 5,230

After posting I re-read your post and realized that you might be picking up very strong signals on frequencies other than the NOAA transmitter. You're probably picking up the TV signal as well from that WTVP tower. That would explain the "data" sound from the digital TV signal they're putting out.

You might have to use two or more notch filters and cascade them to get rid of the offending signals. You'll need to figure out what frequencies/bands you're getting this intermod from. We already know the 162.475 MHz is a problem because you can clearly hear it bleeding through, and we suspect the TV frequencies are an issue also.

According to WTVP's license, they are transmitting on Channel 46 which is 662-668 MHz. If that's the only channel they transmit on, then you could probably solve your intermod with a notch filter centered on 665 MHz. That filter combined with the 162.500 MHz filter should solve your issues.

Single Channel TV Filters | PAR Electronics
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pro433, troubleshooting

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