Notch filter for the National Weater Service?

[wwhitby]

There's a nearby NWS transmitter on 162.4 that pretty much kills reception of the railroad frequencies when I use a base antenna. Does anyone know if there is a notch filter available that will block out the NWS frequencies without also blocking out the railroad frequencies?

Thanks,

Warren

 

[KC0QNB]

Yep MFC did a Google for VHF notch filter, and VHF notch cavity, good luck!
Google is a wonderful tool
Might want to check with a radio technician, they might be out of spec, maybe not I would look into it.

 

[brandon]

PAR electronics makes a 162 MHz filter
http://www.parelectronics.com/scanner.htm

 

[N3LLO]

I have one of the PAR electronics filters (well, 3 actually, 1 for WX, 2 for paging) and they work wonders for me.

 

[wwhitby]

How well do you receive railroad frequencies?

From the documentation that PAR and the other manuafacturer put on their website, it looks like their NWS notch filters are also filtering out a good chunk of the railroad frequencies, but not as much as the NWS frequencies. Unfortunately, that won't work for me, since I need to capture more distant transmissions on railroad frequencies.

Warren

 

[KC0QNB]

Warren I checked with par it can be done but not cheaply, minimum $800 and even then you will lose most of the railroad band, along with the NWR simply too close together, I do have an idea, don't know it it will work though, if you can use a yagi with a real high front to back ratio but if the rail road is between you and the NWR transmitter it won't work.
A real good radio with very tight selectivity, might help as well. But before I would spend any money, I would find a buddy with the rail road that happens to be a radio tech for the railroad, have him check the specs on the NWR transmitter, if the specs are out he can file a complaint with the fcc. Good Luck!

 

[zz0468]

Look on ebay for a vhf cavity filter. One cavity will do it. It's going to be about two feet long, and 4-8 inches in diameter. What you want can't be done in a small package. But VHF cavities can be had cheap. Even a pass cavity can be pressed into service as a notch, if you know what you're doing. But it's quite possible to notch out the weather transmitter without taking a significant hit in performance on the railroad frequencies. But, like I said, the filter will be LARGE!

Another possibility is to use a small yagi, like 3 elements, aim it AWAY from the weather transmitter, and take what you can get on the railroad stuff. A small yagi isn't so directional that you won't hear stuff off the sides and back. It'll work ok, but it might reduce the weather station enough that it's not so much of a problem.

A question that has to be asked... do you use a preamp? If so, lose it! I ask because I live in an area with multiple strong VHF weather transmitters, and lots of paging, and there is zero overload. I also use a unity gain antenna and no preamp.

 

[SAR923]

Warren, where is the NWS transmitter located? As you know, I'm on the other side of Prattville and never have a problem with the 162.400 transmissions knocking out my railroad reception. Do you get the same problem with other VHF frequencies or just the railroad band?

 

[ka3jjz]

Just thinking out loud here, and I'll probably be stepped on - but how about a coax stub? I'm stretching a bit from memory here, but I think they're got a very high Q - so you wouldn't lose nearly as much of the RR band using this approach.

73 Mike

 

[zz0468]

Just thinking out loud here, and I'll probably be stepped on - but how about a coax stub? I'm stretching a bit from memory here, but I think they're got a very high Q - so you wouldn't lose nearly as much of the RR band using this approach.

73 Mike

A coax stub is a great idea if you're trying to do something like notch out the FM broadcast band from an air band receiver, but the q just isn't high enough to work in this application. He's going to have to use a cavity notch filter.

 

[iMONITOR]

ScannerMaster has a great selection of filters:
http://www.scannermaster.com/Filters_s/39.htm

 

[zz0468]

ScannerMaster has a great selection of filters:
http://www.scannermaster.com/Filters_s/39.htm

None of those is likely to be useful for this particular problem. It takes a very high q device to be able to notch weather frequencies without excessive attenuation of rr frequencies. I doubt the notch filter shown even comes close.

 

[Cowthief]

Notch filter.

Hello.

This will work to a degree.
http://www.eagle-1st.com/prod/pr4/Filt400/body.htm
The trick is to tune up in frequency.
Will it cut the signal on RR frequencies? yes, but by adjusting the Peak and Frequency controls one can limit this.
Another thing is the quality of the radio.
A real commercial duty radio is going to do MUCH better than even a very expensive scanner.
The commercial radio will have a far better front end that only has to cope with one band.
A scanner is a very broad band receiver, so selectivity and sensitivity suffer.

 

[zz0468]

Hello.

This will work to a degree.
http://www.eagle-1st.com/prod/pr4/Filt400/body.htm
The trick is to tune up in frequency.
Will it cut the signal on RR frequencies? yes, but by adjusting the Peak and Frequency controls one can limit this.

That's not bad for a non-cavity type filter. Still, it'll leave a 1 MHz wide chunk of spectrum that's at least 10 db down. I like the other idea better... use a higher quality receiver.

 

[Josh]

What kind of radio are you using? Where I'm at, I had an iCom LMR radio work like crap when connected to a gain antenna on railroad band, and having received interference from NWS and a local PD.... my solution, use a different radio with better selectivity. The Motorola CDM1250 I have hooked up to the same antenna the icom was have given me zero problems in the many years I've had the antenna. Prior to the CDM was a GM300.... I've had good luck with Moto units not giving me any issues with intermod, even portables connected to decent-gain antennas.

-Josh

 

[kc9neq]

coax stub

i had similar problems with pager intermod mixing with the weather channel and local pd, while monitoring the railroad band. i took a recommendation for a coax stub from a person here on radio reference. the stub works great. i still get some intermod but not nearly as much as without using it.