Re: [amsat-bb] K Band gear

["Murray Peterson VK2KGM" <vk2kgm@xxxxxxxxxxx>]

Hi Howard,
                    Thanks for putting the K band details on the web.

    The way I avoided running solder into the wave guide on some X band
waveguide filters I built is I heated the area of the guide breifly with the
smallest tip I had of a Oxy - Accetlyene welding kit but I did not use
accetlyene as this seems to contaminate the copper surface. I used LPG as
the fuel gas and didn't have any contamination problems even with a slightly
rich flame (just off neutral). The short duration intense heat meant that
the electronics grade resin core solder only flowed where you put the flame.
The rest of the waveguide stayed relatively cool so no unwanted tinning. In
my waveguide filters, I used a 1/64" (0.0156") slotting saw (in a milling
machine) and the inductive partitions with the coupling orifices (drilled
holes - round) are 0.015" brass shim. These are based on a design by G3JVL
published in the ARRL UHF/Microwave Experimenters Manual where he used an
exacto saw and 0.020" brass. The theory says the thinner the better and my
0.015" versions have an amasingly flat low loss band pass
and incredibly steep roll off at the edges of the bandpass. I could't belive
I could build a filter that was that good!

    I have seen comercial designs which simply use rods sweated into holes
drilled through the wave guide which appear to be a simpler construction
method. I am yet to try that idea but I know they are used in commercial
applications and they perform well.

regards,
Murray Peterson
VK2KGM

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