Par VHFSYM152HT Scanner Intermod Filter

[iMONITOR]

I use my Uniden BCT15X strictly for aircraft, both VHF Civilian/Commercial & UHF Military monitoring. As usual I added a Par VHF-FM notch filter to reduce interference from strong FM broadcasting stations.

Recently I also added a Par VHFSYM152HT intermod filter. I don't know if pagers are still the problem they used to be for me at least. I grew up in N-W Detroit 1950-1982 before moving out. Pagers were a really big interference problem in the 70's +. Now I'm in Macomb, MI about 34 miles N-E of Detroit and I doubt pager interferance is as bad. But being a dedicated Airband scanner I figure it couldn't hurt. Anyone using this notch filter?

The Par VHFSYM152HT is scanner intermod filter that has a notch band of 152 to 153 MHz and a useful passband of 0 to 1 GHz. The notch band covers the offensive pagers in this range. The notch depth is up to >38 dB. Typically, PAR symmetrical filters have a 3dB bandwidth of ± 1.5% or roughly 2.25 MHz for VHF HI filters. Designed for receive-only, scanner use. BNC female input and BNC male output. Size: 4 x 2 x 0.75 inches. Made in the U.S.A.
[source]:

PAR VHFSYM152HT Scanner Intermod Filter

www.universal-radio.com

 

[ko6jw_2]

Intermod is the mixing of two or more frequencies the result of which interferes with the frequency you want to receive. In theory, a notch filter could eliminate or attenuate one of the offending channels and reduce or eliminate the intermod. The notch in the PAR filter assumes that the interference is in a narrow frequency range. This may be erroneous. Example, one of our county fire frequencies has an intermod made up of another county fire frequency and a NWS station. Because the interfering frequency has the same PL on the output it blasts through. The PAR filter would do nothing in this case because the interfering signal and the desired signal are both in the notch and the other component is outside the notch.

Do you actually have intermod issues? If not, you don't need the filter and it will have an insertion loss.

 

[prcguy]

There are still some big paging type transmitters in the 152-153MHz range that transmit endless data. Not sure who uses it but I've seen it interfere with nearby VHF repeaters on local mountain tops. I have a couple of PAR pager filters and next time I visit a Govt repeater site that may be getting interference I will try the PAR filter on the repeaters receiver input.

 

[iMONITOR]

Intermod is the mixing of two or more frequencies the result of which interferes with the frequency you want to receive. In theory, a notch filter could eliminate or attenuate one of the offending channels and reduce or eliminate the intermod. The notch in the PAR filter assumes that the interference is in a narrow frequency range. This may be erroneous. Example, one of our county fire frequencies has an intermod made up of another county fire frequency and a NWS station. Because the interfering frequency has the same PL on the output it blasts through. The PAR filter would do nothing in this case because the interfering signal and the desired signal are both in the notch and the other component is outside the notch.

Do you actually have intermod issues? If not, you don't need the filter and it will have an insertion loss.

The filter has two adjustments that allow you to fine tune it to the offending frequency within the range is designed for. I haven't noticed any intermod issues in particular. I guess I should scan the range and see what shows up. In any event insertion loss is not an issue as I have an excellent signal in the aircraft band with the BCT15X!

 

[iMONITOR]

There are still some big paging type transmitters in the 152-153MHz range that transmit endless data. Not sure who uses it but I've seen it interfere with nearby VHF repeaters on local mountain tops. I have a couple of PAR pager filters and next time I visit a Govt repeater site that may be getting interference I will try the PAR filter on the repeaters receiver input.

Thanks Mike, I'd be interest to hear how it worked for you.

 

[2IR473]

I use the Par 152 mHz notch filter. I live two air miles from a hospital that has paging transmitters on the roof. These pager transmissions with mix with my county’s VHF analog fire dispatch, and will wreak havoc with the front end of my scanners. The Par filter works very well, filtering out 100% of the intermod.

 

[db_gain]

Yep, was gonna mention hospitals within 10 miles will likely have some pagers blasting away with some high efficiency antennas.