Cavity Filter

[RDowson]

Does anyone make cavity filters? I need one with a sharp notch to reduce a strong frequency in the middle of the air band that is causing overload problems with my scanner.
I’ve looked at a notch filter or a coax stub filter but they aren’t sharp enough to stop other nearby frequencies being wiped out so a cavity filter may be my only option.

 

[mastr]

Yes they do.

Cavity Filters

Sinclair Technologies

www.sinctech.com

 

[RDowson]

Yes they do.

Cavity Filters

Sinclair Technologies

www.sinctech.com

Thanks. Any idea how much they cost?

 

[jwt873]

Sinclair is commercial grade.. Not cheap for the hobbyist. Sinclair Technologies FP20107-1

What strong signal is in the middle of the air band? Is this an actual transmitter in your area (Like ATIS) or is it an image of some sort that might be attenuated without the use of a sharp filter?

 

[StoliRaz]

What frequency is yours on? I keep getting one lately at 125.000 on multiple scanners. It's probably interference from something in my house. I'm too lazy to seek it out so I just lock it out. Nothing on that frequency around me anyways

 

[mastr]

Thanks. Any idea how much they cost?

The example price above for the FP20107-1 is typical- BUT that is not an appropriate device for your need, it is exactly the opposite. The reject model is FR20107-1. Generally, the closer your "other nearby frequencies" are, the more costly the solution is going to be.

There are other makers, some probably cost less- Sinclair was just the first one I thought of.

 

[prcguy]

Here ya go, a 118-148MHz tunable notch cavity used for an ok price. Decibel Products Db4015-1 Notch Filter Free Tuning | eBay

 

[RDowson]

Sinclair is commercial grade.. Not cheap for the hobbyist. Sinclair Technologies FP20107-1

What strong signal is in the middle of the air band? Is this an actual transmitter in your area (Like ATIS) or is it an image of some sort that might be attenuated without the use of a sharp filter?

It’s VOLMET, so basically ATIS. It’s on 125.725

 

[RDowson]

What frequency is yours on? I keep getting one lately at 125.000 on multiple scanners. It's probably interference from something in my house. I'm too lazy to seek it out so I just lock it out. Nothing on that frequency around me anyways

125.725. Scottish VOLMET

 

[RDowson]

Here ya go, a 118-148MHz tunable notch cavity used for an ok price. Decibel Products Db4015-1 Notch Filter Free Tuning | eBay

Thanks. I’m in the UK so not ideal with shipping but I’ll keep looking for others.

 

[G7RUX]

You might like to try an O/C coax notch but with an odd multiple of quarter wavelengths length; you tune it so a harmonic of the notch falls on the troublesome signal, giving a somewhat narrower stop band. Worth a go.

 

[Ubbe]

It happens the same with a cavity, that it will notch at multiples, so be careful if it is kept in line when scanning other bands than VHF-Hi. The length of the coax between scanner and filter are also crucial. I think it has to be a 1/2 wave electronic length or multiples of it. It always helps to use a cheap VNA to sweep filters and their coax harness.

/Ubbe

 

[dcr_inc]

look at par electronics for a filter