Band Pass Filters

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stingray327

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Sounds like overload from other nearby out-of-band transmitters. You may need a band-pass filter for the air band only or a notch filter for the particular frequency that's causing the overload and desense. For example, I've got a pager transmitter nearby that kills my Pro-163 and HomePatrol1. With the notch-filter in line I don't have any more problems.

Scanners are such wide-band receivers that it's pretty easy for a nearby FM transmitter or pager site to completely swamp the front end and destroy your reception. A better antenna makes it worse - not better.

What does this filter looklike? I have same problem in car with mobile antenna and in house with outdoor base antenna.
 

ST-Bob

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Small box with BNC connectors on both sides. The tunable one is a bit larger with a tuning knob on one end of the box.
 

ST-Bob

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The FM trap which notches out the FM broadcast band just below the air band will eliminate some sources of interference. It's only about 2 inches long by 1 1/2 inches wide and 3/4 inches thick. However, it will not help with pager transmitters in the 158-162 MHz range. For that, you need a higher-end, narrower notch, bigger case filter. My tuneable notch filter is about 3" by 2" by 2.5" but that could easily be hidden under a seat or dashboard in a mobile installation.
 

ST-Bob

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FM and 0-30 MHz high-pass combined notch filter HPN-30118 Combined Notch Filter
Tunable notch filter(s): WAF-125 Tunable Notch Filter and Jim 96XI-1 Adjustable Notch Filter

Unfortunately, they're out of stock right now at ScannerMaster. Other scanner retailers may have them in stock, however. I, personally, have the WAF-125 tunable notch filter between my discone and splitter which feeds 2 or 3 scanners. It certainly solved my pager interference problem. I bought some in-line attenuators and between them and the adjustment knob I was able to make the adjustment to the filter to completely eliminate receiving the pager frequency even when 'trying' to tune it on the scanners. Removing the attenuators then restored the scanner(s) to normal operation WITHOUT the problem of locking up on paging tones and missing calls etc. that the desensitization caused before the filter was installed and adjusted.

This method solved my particular problem but yours may be different. You'll have to take your chances and pay your money, hoping you've guessed right about the source of your interference. Without a spectrum analyzer, you'll be shooting in the dark (as I was), but I knew from hearing the interference that mine was caused by the pager. If you know your problem is caused by a nearby FM station, then get the FM notch filter... Couldn't hurt.
 

rrbum

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Anyone recommend one that will keep noise out of the 2m band?


Sort of a vague question. You should provide more info such as if you are using a scanner to only listen or if you need something for a ham rig which could handle being transmitted through.
Being you posted in this forum I assume you need for a scanner or some sort of wideband receiver. There are bandpass filters which would allow only 144-148 Mhz through. There are also notch filters available which would knock down strong frequencies, such as nearby pagers, from getting into and mixing with the front-end of your radio, causing intermod or desense.
Maybe describe the sort of noise you intend to eliminate and I am sure people here could help you to make a wise choice and hopefully solve the issue.
 

Evgeni

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Sort of a vague question. You should provide more info such as if you are using a scanner to only listen or if you need something for a ham rig which could handle being transmitted through.
Being you posted in this forum I assume you need for a scanner or some sort of wideband receiver. There are bandpass filters which would allow only 144-148 Mhz through. There are also notch filters available which would knock down strong frequencies, such as nearby pagers, from getting into and mixing with the front-end of your radio, causing intermod or desense.
Maybe describe the sort of noise you intend to eliminate and I am sure people here could help you to make a wise choice and hopefully solve the issue.

VHF/UHF transciever.

Too much interference on VHF.
 

rrbum

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VHF/UHF transciever.

Too much interference on VHF.

Many possible causes. Still not enough information.

Mobile or base use?
Power supply if base?
Antenna being used?
Noise present at all times?

Could be any number of things. If you really want to address the problem details of exactly what you are experiencing will be needed.

What is SWR when you transmit on VHF? Can you receive any strong signals without the interference?

Describe a situation when the interference is an issue.
 
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