Band Pass Filter

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BFIFM790

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Dec 19, 2002
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Im hoping someone with a technical background can help me in this field. Listening in the New York Metro area naturally brings intermod and front end overloading easily in open scanning modes. I see that Scannermaster has both the VHF band pass filter and the FM Notch Filter. Does anyone have suggestions on if any of these would be useful in a mobile scanning application where its a 396XT connected to a mobile antenna in the car?

Any insight would be appreciated

Thank you
 

ronhl

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Jun 1, 2003
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Live Free or Die St.
intermod issues

Im hoping someone with a technical background can help me in this field. Listening in the New York Metro area naturally brings intermod and front end overloading easily in open scanning modes. I see that Scannermaster has both the VHF band pass filter and the FM Notch Filter. Does anyone have suggestions on if any of these would be useful in a mobile scanning application where its a 396XT connected to a mobile antenna in the car?

Any insight would be appreciated

Thank you

I live in the city and such a strong RF environment i had so much intermod coming thru on VHF that made it very annoying to scan that band.
So on my base antenna main feed i have all 3 in series, 152,159 mhz Par notch filters along with a FM band notch and it made all the difference in the world. I can finally again enjoy the VHF Hi Band.
Also keep in mind front end rf overloading isnt good for our very sensitive receivers/scanners either. Because it will desense them and make them useless in capturing the weak distant signals. So yes, these filters are a must for the serious mobile or base listener...... if you did a search in these forums you will find allot of us are using them.
Hope this has helped

Ron
 

lmrtek

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Feb 11, 2009
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notch filters are very narrow and are used to attenuate a very narrow range of frequency without attenuating the intended frequencies.

Bandpass filters are usually designed to pass a wide range of frequency while attenuating everything outside that band width.

You can make your own notch filter with coax and a Tee connector

A open coaxial stub becomes a nitch filter
When shorted on the end, it becomes a bandpass filter

And it costs you a few cents worth of scrap coax.
 

prcguy

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So Cal - Richardson, TX - Tewksbury, MA
A coaxial stub is always a notch and never a band pass.

A 1/4 wave OPEN stub will notch frequencies which are 1/4 wavelength in cable minus the velocity factor of the cable and will also notch odd multiples of that frequency.

A 1/4 wave SHORTED stub will notch twice the frequency which is 1/4 wavelength minus the velocity factor of the cable and will also notch even multiples of that frequency.

A common lightning arrester for repeater sites is a 1/4 shorted stub which will not affect the desired frequency passing through but will otherwise short out the center conductor of the coax to ground.
prcguy

notch filters are very narrow and are used to attenuate a very narrow range of frequency without attenuating the intended frequencies.

Bandpass filters are usually designed to pass a wide range of frequency while attenuating everything outside that band width.

You can make your own notch filter with coax and a Tee connector

A open coaxial stub becomes a nitch filter
When shorted on the end, it becomes a bandpass filter

And it costs you a few cents worth of scrap coax.
 
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