Re: Low loss receive filter for 23cm
Hello Neil and other readers.
If you're willing to engage in a bit of precision metal work (which I do like doing!), I can recommend the solid copper-and-brass interdigital filter that was first described in the 'QST' magazine for March 1968 - yes, nearly 50 years ago! That article focuses more on such filters for 432 MHz, but does include dimensions for one for 1296 MHz.
I have one here and, in acknowledgement of your 'problems' possibly being as far away as 600 MHz, I have today measured its performance down that far - insertion loss across a broad range of frequency - and the results of my testing were:MHz I.L. (dB)
1309 0.2 (the minimum)
The pattern further above 1300 MHz is very much a mirror image of the above measurements. The return loss looking into each port (with the other port terminated) is very good.
I trust that these data may be of assistance - possibly to initiate another project!
If you have difficulty accessing the original article (which must have been copied many times over the years), do get back to me and I should be able to scan and post somewhere Ed's hand-drawn design notes (which are essentially the same as the article), thus avoiding violation of QST's copyright.
And I could post an image or two of the completed filter.
--Doug Friend, VK4OE.
p.s. I was fortunate a decade or more ago to have been given the precisely-cut elements for this filter by the (now) late Eddie Penikis VK1VP. Ed had an inspiring ability to work precisely in everything that he set his hands to do - all I had to do was to build the housing, which I did in solid brass. As you'll see, it works wonderfully well!
p.p.s. I immediately also thought of the nice off-the-shelf
filter made by a German fellow and recommended by the Kuhne
company for use with their 28 MHz to 1296 MHz transverters.
However, not having one here to test, I can't vouch for it having
similar broadband performance to the 'old' design over the same
frequency range shown above.
On 26/09/2016 08:25, Neil neil@... [ukmicrowaves] wrote: