Author Topic: NOAA Broadcast Bleeding Into My Scanner  (Read 2954 times)

RailfanJ-Ro22

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NOAA Broadcast Bleeding Into My Scanner
« on: February 27, 2012, 08:31:48 PM »
Every once in a while, my scanner will stop on a random CSX or NS frequency that I have programmed in and all I will hear is the National Weather Service broadcast. I have an old Radio Shack Pro 82 200 channel scanner. This especially happens on the east side of Indianapolis. I just wonder why this is occurring. Any help would be most welcome.
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CIOR

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #1 on: February 27, 2012, 08:47:12 PM »
Every once in a while, my scanner will stop on a random CSX or NS frequency that I have programmed in and all I will hear is the National Weather Service broadcast. I have an old Radio Shack Pro 82 200 channel scanner. This especially happens on the east side of Indianapolis. I just wonder why this is occurring. Any help would be most welcome.

Older scanners have this issue, especially when you are close to the transmitter.  Not really much you can do about it, that I'm aware.  Other than get a newer radio.  I never had this issue with the GRE400 and not had it with my Yaesu. Sensitivity is a big issue with older scanners.

RailfanJ-Ro22

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #2 on: February 27, 2012, 08:52:57 PM »
Oh ok. well I guess I'll just have to deal.  ;D
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shane_man15

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #3 on: February 27, 2012, 10:13:58 PM »
Actually, My radio did this a couple times yesterday.
My older scanner does it too, but it's really bad.
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CIND 2254

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #4 on: February 28, 2012, 12:32:01 AM »
I get that on my Yeasu when I'm going over the Shelbyville on Raymond Street in Indy.
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CIOR

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #5 on: February 28, 2012, 10:56:13 AM »
I get that on my Yeasu when I'm going over the Shelbyville on Raymond Street in Indy.

I didn't have it with my Yaesu FT7900, but I didn't have my FT250 on at all.  So I can't say.  My guess is the antenna is really close by and just kicks over onto anything it can.

CIND 2254

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #6 on: February 28, 2012, 01:41:18 PM »
I didn't have it with my Yaesu FT7900, but I didn't have my FT250 on at all.  So I can't say.  My guess is the antenna is really close by and just kicks over onto anything it can.
Yeah, once you get west of the bridge it quits.
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CSXIndyLine

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #7 on: February 28, 2012, 03:50:25 PM »
Every once in a while, my scanner will stop on a random CSX or NS frequency that I have programmed in and all I will hear is the National Weather Service broadcast. I have an old Radio Shack Pro 82 200 channel scanner. This especially happens on the east side of Indianapolis. I just wonder why this is occurring. Any help would be most welcome.
Mine always does that along 56th street, all the way out to Oaklandon.
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Caylorman

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #8 on: February 29, 2012, 10:33:46 AM »
The problem isn't so much sensitivity of the scanner as much as it is selectivity in this case.  Basically, the NWS transmitter is most likely overloading your radio's front end, and the fairly wide band filters aren't enough to knock down a close transmitter at that close of a frequency offset. 


If you were hearing both the RR and the NWS transmitter, you'd be having intermodulation distortion, which is usually fixed by throwing an attenuator on the antenna port. 

E.J.

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #9 on: February 29, 2012, 11:23:43 AM »
The problem isn't so much sensitivity of the scanner as much as it is selectivity in this case.  Basically, the NWS transmitter is most likely overloading your radio's front end, and the fairly wide band filters aren't enough to knock down a close transmitter at that close of a frequency offset. 


If you were hearing both the RR and the NWS transmitter, you'd be having intermodulation distortion, which is usually fixed by throwing an attenuator on the antenna port. 

E.J.

EJ, I'm going to put a disclaimer on your post... 
"RF Engineer"   ;D

Racecar52

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #10 on: February 29, 2012, 01:27:30 PM »
EJ, I'm going to put a disclaimer on your post... 
"RF Engineer"   ;D

that's what you get for asking those darn Purdue folks, lol  :P
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rrnut282

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #11 on: February 29, 2012, 05:43:50 PM »
OK, I'll bite.  Where do you find an antenna port attenuator that takes out NOAA?
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RailfanJ-Ro22

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #12 on: February 29, 2012, 06:01:22 PM »
The problem isn't so much sensitivity of the scanner as much as it is selectivity in this case.  Basically, the NWS transmitter is most likely overloading your radio's front end, and the fairly wide band filters aren't enough to knock down a close transmitter at that close of a frequency offset. 


If you were hearing both the RR and the NWS transmitter, you'd be having intermodulation distortion, which is usually fixed by throwing an attenuator on the antenna port. 

E.J.

Where can I get one of those and how does it work?
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Howard Pletcher

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #13 on: February 29, 2012, 09:43:34 PM »
Google "antenna attenuator" and you'll get lots of listings, including one listing for Radio Shack, although I couldn't actually find the part quickly. Sorting out what you actually needs gets more complicated.  I'd probably start with R and L Electronics (randl.com) in Hamilton, OH to be able to talk to some knowledgeable folks.

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Zenithfan

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #14 on: March 01, 2012, 02:02:00 AM »
Caylorman is correct.  It is a matter of selectivity,  not sensitiivity.  Selectivity is the ability to tune in a specific frequeny and reject the other frequencies around it.  (40 years of commercial and educational radio is probably more than enough, but I'm still at it.)
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indyspy

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #15 on: March 01, 2012, 09:33:50 AM »
The 158mhz pagers used to be bad about that too, but I think since the death of the pager, I quit hearing them so much.

In any case, you will find what you need on this page
http://www.grove-ent.com/preselectorstuners.html

You probably want.
PAR 162-HT Scanner Intermod FilterFTR162DS

They used to have a really nice adjusible scanner intermod filter. I had one but I sold it though when I junked my scanners a long while back. They no longer offer it it seems.

Note that there are two types of filters.
One will knockout a certain frequency range, the other will only let a certain range pass.

Last I looked at the PAR-162 and PAR-158 the notch was wide enough to slightly atenuate some rail frequencies at the lower end of the PAR-158 and upper end for for the PAR-162. But since it's on the very edge, it will be neglible if any. But it was one reason I got the adjustible one they don't offer. I could put the dial at 157mhz to knock that out, and still knock the pagers down to where they did not come in on the scanner.

AVOID the preamps on that page if your having intermod. It will make it worse.

Also most of these are for receive only radios, keying a transceiver will blow most of these filters to hell. (Smoke, melting stuff, not good)

As for the Yaesus, thats the trade off for having 2meter/440mhz dual types. The RX circuitry is more susecptible to intermod as the RX has to be able to handle the two bands. My single band FT-1900 and FT-2600 never intermod, even in downtown Chicago. (thats the worst RF spot I have ever seen)
« Last Edit: March 01, 2012, 09:48:44 AM by indyspy »
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Caylorman

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #16 on: March 01, 2012, 10:24:43 AM »
EJ, I'm going to put a disclaimer on your post... 
"RF Engineer"   ;D

4.5 years at Purdue and 10 years in the industry, I knew this stuff would come in handy some day......  :)

Caylorman

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #17 on: March 01, 2012, 10:46:48 AM »
OK, I'll bite.  Where do you find an antenna port attenuator that takes out NOAA?

One that takes out NOAA specifically? You can't.  If you don't want technical explanation, skip the next two paragraphs...

Again, it really depends on what you are trying to do and what is going on in the radio.  If all you are getting is NOAA bleed-thru while scanning the RR band, then you'd want either a bandpass filter for the RR band (if you don't plan on listening to anything else) or a notch filter for the NOAA band (if you want to listening to stuff besides RR).  The specs for the 162 MHz notch didn't open up for me, but I'd guess that given that it's only $70, it's probably only about 30dB of filtering and will still eat up the high end of the RR band.  YMMV

If you're getting both RR and NOAA transmissions at the same time on a frequency, you are having intermod problems.  The NOAA channel is getting into a front-end amplifier, causing compression and generating spurs that are making it into the audio filter passband.  The best fix a new amp in the radio....though who want's to pay for that?  A notch or BP filter would do the job also, if you happen to have one or want to spend the money.  The cheapest solution is to put an attenuator on the antenna port, bringing the NOAA signal level down (along with everything else, of course) to a level below compression of your amplifer.

In short:

Hearing one unwanted transmission - filter it
hearing one wanted and one unwanted transmission - attenuate it.

indyspy

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #18 on: March 01, 2012, 11:06:36 AM »
All very true, but it will help quite a bit.

I have used the adjustible version of the PAR162 thats no longer offered, it was -30DB. It was enough to stop the intermod of any 162 or 158 signal depending on where it was. I could set the adjustment for 157mhz or 163mhz and it would be enough to eliminate any of the pager or NWS from getting into the scanner.

Even with the 162, you will gain more then you will loose. And with exception of the INRD yard on 161.535 and the CSX Dispatch on 161.520 there isn't a lot near the top end of the band.

HOWEVER, for the price. You might as well do as he said and get a better radio.

One that takes out NOAA specifically? You can't.  If you don't want technical explanation, skip the next two paragraphs...

The specs for the 162 MHz notch didn't open up for me, but I'd guess that given that it's only $70, it's probably only about 30dB of filtering and will still eat up the high end of the RR band.  YMMV
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torgy1962

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #19 on: March 01, 2012, 12:04:35 PM »
This whole thread is quite interesting and informative. I'm glad to see that there is still some hardware knowledge out there!

Myself, I haven't turned on my RR scanners in years. My Regency HX 1500 still worked quite well the last time, although it is a relatively gigantic beast.

sataraid1

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #20 on: March 01, 2012, 03:28:08 PM »
I've never priced attenuators, but I do know that when you reach the price level of a quality notch filter, you're to the point where it's cheaper to just buy a clean used commercial radio that's purpose-built for the band you want to listen to. Especially handhelds.

torgy1962

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #21 on: March 01, 2012, 03:33:07 PM »
it's cheaper to just buy a clean used commercial radio that's purpose-built for the band you want to listen to. Especially handhelds.

That's exactly what I did for another of my hobbies, watching Great Lakes freighters. I purchased an Icom marine handheld that works great, plus it's waterproof.

bosworthj

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NOAA Maps
« Reply #22 on: March 03, 2012, 04:46:29 PM »
The weather service has a pretty comprehensive series of maps for their transmitters.   

Relatively speaking, they use a hughamonguluss amount of power, 1000 watts usually, as compared to the average 40-50 watt power of a locomotive radio.

Their frequencies are between 162.4 and 162.55, which is just a megahertz from the railroad band at 160-161.55.  If you are close to their towers, you will get your radio front end overloaded.  Or you get plusses and minuses of two or more frequencies intermodulating in your receiver.  I agree with the previous poster about the pagers, which were located just below the RR band.  Good riddance to them!

Here's the NOAA link.

http://www.nws.noaa.gov/nwr/nwrbro.htm
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indyspy

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Re: NOAA Broadcast Bleeding Into My Scanner
« Reply #23 on: March 04, 2012, 11:01:29 PM »
The tower is located along Post Road between Brookville Road and Washington St
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