Strange Scanner Pick-Up

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Twister_2

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For as long as I can remember, I have been picking up NOAA Weather Radio on 163.250 MHz. It is the same thing that I hear on 162.55 MHz at the same time. Is it a simulcast? If so, why? I don't think that it is bleeding over because this is THE only channel I can hear it on besides 162.55 MHz and the tower is about 3 miles away "as the signal travels" (not as the bird flies :lol:). Also, does anyone else pick it up in and around the Harrisburg, PA area?
 

N9JIG

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163.250 is usually a voice paging freq at hospitals. I think you are getting some sort of image due to the proximity to the tower.
 

Twister_2

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163.250 is usually a voice paging freq at hospitals. I think you are getting some sort of image due to the proximity to the tower.
I could understand that because when the weather radio is not talking (Silent) I can hear a radio station in the background....97.3 The river. One time I heard Led Zeppelin!
 

kb2vxa

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"I have been picking up NOAA Weather Radio on 163.250 MHz. It is the same thing that I hear on 162.55 MHz at the same time.
I can hear a radio station in the background....97.3 The river."

Since you are hearing two signals at once it is a mixing product commonly called intermodulation, intermod. Since the two are continuous broadcasts this spurious product is most noticeable but I'll bet that FM station causes others intermittently so you'll notice them too somewhere down the line. Since the weaker weather station signal isn't likely to cause problems we'll tackle it from the stronger FM side. You can effectively eliminate it with an FM bandstop filter available from Tin Lee Electronics, check out part number CR7-FMU-40 which "according to my calculations" is exactly what you need.

Here's where you start, contact information is at the top of the page, technical data at the bottom.

http://www.tinlee.com/Graph_ALL_FM_filters.php?active=2

I sincerely reccomend this company over all others for SO many reasons, the number ONE being is they work with you every step of the way from inquiries to delivery and by that I mean when you get it in your hands. Hey, I got a follow up call to ask if I was satisfied with the product! They'll customize the product to your specifications too, talk to them. Hey bro, it ain't Radio Shack, this is WORD.
 
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spooney

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I get the same kind of thing going on with my GRE 500 & 600 , but not on my Unidens. It must be something in the circuitry in my case I would think.
 

Twister_2

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"I have been picking up NOAA Weather Radio on 163.250 MHz. It is the same thing that I hear on 162.55 MHz at the same time.
I can hear a radio station in the background....97.3 The river."

Since you are hearing two signals at once it is a mixing product commonly called intermodulation, intermod. Since the two are continuous broadcasts this spurious product is most noticeable but I'll bet that FM station causes others intermittently so you'll notice them too somewhere down the line. Since the weaker weather station signal isn't likely to cause problems we'll tackle it from the stronger FM side. You can effectively eliminate it with an FM bandstop filter available from Tin Lee Electronics, check out part number CR7-FMU-40 which "according to my calculations" is exactly what you need.

Here's where you start, contact information is at the top of the page, technical data at the bottom.

http://www.tinlee.com/Graph_ALL_FM_filters.php?active=2

I sincerely reccomend this company over all others for SO many reasons, the number ONE being is they work with you every step of the way from inquiries to delivery and by that I mean when you get it in your hands. Hey, I got a follow up call to ask if I was satisfied with the product! They'll customize the product to your specifications too, talk to them. Hey bro, it ain't Radio Shack, this is WORD.
Would this go on the TX or RX...if TX...would it be The FM music radio station?
 

kb2vxa

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"Would this go on the TX or RX"

Twister, what the heck are you talking about?

I have already answered your question "would it be The FM music radio station?"

"...we'll tackle it from the stronger FM side."
 

Zack08

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I live in Lebanon and the -55 machine is still so strong that I can take the antenna off most of my radios and still hear it. With it being that strong at my distance, it's no surprise that you're hearing it on "other" frequencies in Harrisburg.

I have a strong feeling that the WRVV 97.3 interference is actually getting picked up on the audio side of the weather transmitter. I can hear it, too, and it sounds much clearer and more consistent than any intermod I've ever heard. The weather transmitter is at the WVIA site, and I think the WRVV transmitter may be there, too, so its a good possibility that its getting picked up in poorly routed audio cabling.
 

kb2vxa

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Well Rat you just may have hit on something. The coordinates of all licensed fixed transmitters except Amateur are listed in the FCC database so you can match them up with a little detective work. While very unlikely it is possible the broadcast RF is getting into the WX transmitter's audio chain, I know of an FM station (one of those grass burners) that clobbers the courtroom recorder/PA in a municipal building across the street. Like I said it's unlikely, how FM can be so demodulated is beyond me unless it has an unwanted AM component and that's unlikely with transmitter specs and FCC requirements being what they are.

There's another and highly suspect possibility, the intermod may be being generated at the transmitting site itself. Improper bonding and corroded tower joints are notorious "nonlinear devices" and such devices are essential for mixing and detecting radio signals in receiver circuitry. An unintentional mixer diode is created much like the classic point contact semiconductor "crystal detector" by corrosion, particularly between dissimilar metals and when strong RF is applied mixing products (intermod) are produced and radiated by the metallic structure acting as an antenna.

A friend who is a radio tech for the New Jersey Turnpike Authority uncovered the source of severe interference at one of the tower sites, intermod produced just as I described above. It radiated for miles clobbering other systems as well but careful welding of critical tower parts and electrical bonding of others effectively "jumpered over" the problem areas thus eliminating the intermod.

Now I may be way off base with this but there's one way to find out, an RF survey may be in order. You may wander around with a portable receiver checking it out from several locations, just stay off private property. This is done on site professionally with a spectrum analyzer among other things so you guys may be just a bit out of your league here, but maybe those responsible for transmitters at the site would be interested in the possibility of spectral purity issues you may have found with your impromptu "site survey" which could cause problems with the FCC for them. Those sites ARE inspected by the FCC from time to time and NOVs and NALs are indeed the bane of the industry.

Hey, if you get an I don't care attitude you can always cop an attitude of your own; it's not my license and not my money so foo foo 2U2 boo. (;->)
 

Big_Ears

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No, but the fixed links from the WX station to the transmitter sites operate on the 410-411 MHz spectrum.
 
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