I couldn't resist to open the filters (low pass and balun) I recently bought at the radiorally. The balun is not really a filter, or is it? It filters common mode radiation from the coax though.
Not really anything special. A FT240 ferrite ring wound the classic way with 50 Ohm teflon coax. Made something similair myself in the past. And I think I proved that it worked. Choice of ferrite is important just like the number of windings. The ON7FU filter/choke is well made.
The military low pass filter, or is it a pass band filter, was more difficult to open. I didn't trust this filter because something was rattling inside like something was loose and not right. The casing can not be opened with screws. It looked like a solid iron box but somehow I opened it without damaging the filter.
I really don't know exactly how they made this casing. I estimate that the filter is made around 1950-1960. The loose part was just a piece of solder. It looks like the backside was soldered to the filter compartiments. Not shure how I'm going to close it again, have to think about it.
Interesting little filter Bas, but they really did not want anyone to open it once built. Not that unusual in milspec type modules like this though.
ReplyDeleteMy first thoughts on how to refit the lid was to use low temperature solder paste and a blowtorch. With some suitable flux it should go together ok without affecting the other joints