[CW] My low pass filter works

[Hans Brakob]

Did you ever have one of those days that you thought maybe you ought to check to see if your Novice license was still valid?






Couple years ago K0CKB gifted me a modern Yaesu FTdx-5000 radio which includes all those new WARC bands, and even 6 meters.






Well I finally got curious to see what lay behind that "50" band-button, and having no antenna, I cut and bent and soldered up a bunch of copper water pipe into a reasonable facsimile of a 6-meter J-Pole last week.






Put it up in the air, ran some fresh coax to the shack, and hooked it to a vacant connector on my antenna switch box.






Mashed in the "50" button on the rig, tuned around, and the band seemed empty.  Checked the SWR at 50.010 --- infinity.  Checked SWR at the top of the band and spots between --- infinity at all those spots too!  Checked all my construction dimensions, ohmed out the new coax, tried several adjustments to the J-pole feed point looking for a match.  NOTHING.






So this evening I borrowed an antenna analyzer from N0AT.






Unhooked the coax from the switch box, attached the analyzer, fired it up, and found a nice 1:1 match at 52.873 mHz, and under 2.5:1 across the band.






WTF!?!?






Hooked the coax back to the switch box and checked the SWR at the radio.  Infinite mismatch across the band.






WTF!?!?






Clambering around under the desk looking for a bad patch cord (or something), I came face to face with......






.....the low pass filter (50 mHz cutoff) that I installed way-back-when to protect TV channel 2 in the neighborhood.  On the input line to my antenna switch box!






Sunnuvagun!  See the subject line.






de Hans, K(n)0HB
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