Wideband RF Preamp for 23cms

[Wolfie G8VAT]

I have forgotten almost everything I ever knew about RF, I think I must have forgotten it, unless I never knew it of course, and have forgotten that I never knew it.. I digress (I think).

I recently bought one of these wideband PreAmps with a view to using it for ATV on 23cms.. Cheap, cheerful and Chin.. erm, far eastern, It's actually a very tidy piece of work, laid out very logically inside the can.

Of course as this stands, it simply amplifies everything, wanted and unwanted so no actual benefit.. what I need to do is make it into a tuned amp to just amplify the 23cms band.
I thought maybe I could just add a bandpass filter at each side (or just on the input?). Could this be done by making a tuned line(s) cut into a copper clad PCB? The calculations for this just blew my mind, calculating electronics was always my nemesis, I prefer the hardware solutions where possible.

I thought I had better ask more knowledgable people before I tear my hair out with RF nonesense, and yes, you guessed it, thats YOU!

So, is there a simple solution to make this useful for 23cms or should i just give up and spend my/our holiday money?

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[g0mjw]

Look out for a surplus interdigital or post filter and use that at the input. Note you may end up with an oscillator, depending on how unconditionally stable or not the pre-amp is.

There is a design for an interdigital filter that is fairly easy to make if you can't find one surplus. You can also buy a new one but not cheaply.

Doug, VK3UM, now sadly missed, has a calculator http://www.vk3um.com/interdigital%20filter.html

You might also want to look here http://www.w1ghz.org/filter/Altoids_Tin_Filters.pdf

You can also do this on a PCB but performance won't be as good. Might be good enough though.

Mike

[g8gtz]

There are wiki pages dedicated to this topic - I've added in Mike's suggestions:

https://wiki.batc.tv/Filters

Always look on the wiki for this type of info - and a big plea to everyone, if you have any info that may be useful to anyone else, PLEASE put it on the wiki. That way we will build a knowledge base for the whole ATV community!

73 Noel - G8GTZ

[Wolfie G8VAT]

So, in the absence of an actual nod.. The pre filter simple idea is viable?

I can see the Altoids tin filters as a good candidate, one would fit nicely into my current project, which I may bore you all rigid with shortly.

I had imagined that one of those was a sledgehammer solution seing as my G8OZP pre amp simply has a short input lecher line to do the job.

But many thanks for the pointers guys, we'll be going shopping shortly, my wife may well be quizzing me about my sudden love of Altoids.

[Wolfie G8VAT]

Mmmm Altoids are quite nice as it turns out..


So, no one has still said that the pre filter will work as I expect?