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Custom 5W Notch filter? For a VXR-1000V repeater.

k1jak

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Sorry if this is in the wrong forum area, as this is for a Part 90 radio setup for our volunteer fire department.

Any idea on a source for a custom 5W Notch filter? For a VXR-1000V repeater.
I would like the filter only to allow 151.37MHz.

The primary 110W radio will be set up on adjacent channels, such as 153.7925MHz thus the need for filters.

Thanks in advance.
K1JAK
73
 

k1jak

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I believe you are looking for a preselector. What are the adjacent channels? Most preselectors have a 2MHz bandpass and don't get full rejection until 5MHz offset. An example of a Telewave VHF preselector https://www.telewave.com/wp-content/uploads/2016/07/TWDS-2015.pdf
This radio will be fixed on 151.37MHz. I need to filter out adjacent channels, such as 153.7925MHz.

It looks like the Telewave may allow too much in the 1514 seems to allow 150-160 MHz, unless I am misunderstanding the document. (I am brand new to filters).
 

mmckenna

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VXR-1000V is a mobile vehicle repeater, he is just using it inband connected to his radio (i'm assuming).

Ah, right. Extender….

Yeah, as noted above, Pyramid sells suitable devices for this. Absolutely needed in that sort of application. There are specific mobile 'flat pack' duplexers that will do what you need. Good ones are in the $250-300 range. Avoid the Cheap Chineses ones.
 

k1jak

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ramal121

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In band filtering is tricky in the VHF space. Considerations include a bandpass filter for the VXR, a notch filter for the mobile radio, frequency separation between the two, and distance of antennas. I would not try and piece meal something that may or may not work and have to go back with additional items to try. Go all in and get it right the first time.

Back to Pyramid here's a little read on the subject...
 

k1jak

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In band filtering is tricky in the VHF space. Considerations include a bandpass filter for the VXR, a notch filter for the mobile radio, frequency separation between the two, and distance of antennas. I would not try and piece meal something that may or may not work and have to go back with additional items to try. Go all in and get it right the first time.

Back to Pyramid here's a little read on the subject...
I don't have a lot of choice in frequency selection. Much of it is defined by the state and country. The repeater frequency was assigned by the FCC a decade ago.

Thanks for the article. I will share it with the person I am working with on this ( he is a better ham and knows a lot more about radios than I) .

Thanks again -K1JAK
 

ramal121

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I hear ya. Once or twice we snagged a frequency from the old press corp pool which was up in the 173's. Worked great. But you are a slave to whoever passes out the channels and they don't quite understand.

Your saving grace maybe is using that pole that puts the antenna up tens of feet. I have only used the real estate that's on the body of the rig.
 

kf8yk

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Trying to run a 100 W mobile that close to your extender frequency is going to require some expensive RF filtering, you would probably need a notch filter or two tuned to the extender freq. on the 100 W mobile and some tight bandpass filters on the extender.

A better solution would be to move the extender to 173 MHz. The FCC set aside six 173 MHz freqs for this exact use case: https://docs.fcc.gov/public/attachments/FCC-15-103A1.pdf Even with the 20 MHz of separation a 173 extender freq. provides you'll probably still need some filtering like the Pyramid preselector.

Coordinating a 5 W mobile only license is really not difficult or expensive & you'll have a much greater chance of making this work without spending thousands of dollars on filters.
 
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