[Elecraft] K3 Low Pass Question

[Tom W8JI]

> It begs the question what we should do with the 1000s of LP filters out
> there.  Some are built very well, like my Drake, but I also have a couple
> made of "bent tin."  There was a QST article on them a few years ago 
> showing
> different construction styles and quite intriguing how costs could be
> reduced.

They are somewhat useful as low pass filters for some or many high power HF 
RF amplifiers, and with many older tube type or hybrid radios with 
pi-network outputs.

They are also useful for systems having active T/R switches like this one:

http://www.w8ji.com/johnson_tr_switch.htm

I looked back through some amplifier tests, and the worse case harmonic or 
spurious on the solid state ALS1300 above 30 MHz was a level less than -60.4 
dBc with a carrier level of 1200 watts.  That was one pip just out of 
analyzer noise that could have been a mixer product in the analyzer! HF rigs 
like the K3 look just as clean or cleaner.

Some harmonics in tube type amps are not nearly that well suppressed, and my 
data on older gear from the 1970's and earlier indicates they could result 
in a substantial improvement in VHF harmonic suppression from some 30-watt 
output transmitters. Those old 30-100 watt output transmitters exceed the 
absolute harmonic power levels produce by newer 1500 watt amps. :-)

I'd say save them in case you get an old boatanchor, because converting them 
to something else like an HF bandpass would only yield the sheet metal and 
connectors as recyclable.

Then of course nearly all low-band VHF TV transmitters are gone over here. 
There are none within range of me, even those that someone said were on. :-)

73 Tom