Tedium @readtedium
The bizarre, unusually deep rabbit hole of DXing: bit.ly/2fQ90EA#radio#vintage
Sverre Holm, LA3ZA @LA3ZA
Even better low-pass filters for transmitters la3za.blogspot.com/2016/11/even-b… #hamr #hamradio #G3TMG #QEX
Phil Roland @N1DN
Check out the Maryland Slow Net and their CW Traffic Handling Course n1dn.blogspot.com/2016/11/maryla… #hamradio #NTS #telegraphy
Dave New, N8SBE says
I get QEX, and have read the Zolotarev filter design articles with interest.
I like the idea that they optimize the portion of the pass band that we are really interested in (the actual ham band of interest), instead of trying to create a strictly low pass filter, with a completely or near complete flat passband from the cutoff frequency down to zero Hertz (or as close to zero Hertz as you can go).
By doing so, and purposefully placing a zero at the 2nd harmonic, you end up with a design that gives you the biggest ‘bang for the buck’ — harmonic suppression that rolls off into the spectrum analyzer’s ‘weeds’ (greater than 80 dB), minimal component count, and relatively immune to component tolerance and temperature drift.
What is there to hate? Although it normally takes some fairly heavy math to calculate, the articles provide normative charts and tables that cover all the ham bands, so you can design a filter without a lot of heavy calculation.
Just the kind of fun thing to play with on your bench, using that cool Rigol spectrum analyzer with tracking generator that’s waiting under your holiday tree.