From: Chris Wilson <dead.fets@gmail.com>
Date: Sat, 15 Apr 2017 13:32:20 +0100
Message-ID: <272136023.20170415133220@gmail.com>
To: rsgb_lf_group@blacksheep.org
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Subject: LF: Poor aerial connection affecting gate waveforms??
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Status: RO

Hello LF'ers,

      A very happy Easter to everyone!

      I  have  a  tech  question  tthat I am sure you more experienced
      operators  can answer. yesterday I mowed the lawn and found some
      of  my temporary earth leads connecting a square of ground wires
      with  2  diaganols  to  8  foot  ground  posts had been eaten by
      rabbits  and  were  disconnected.  i re-made them and today will
      finish  them  by  blting  soldered  eyelt tags to the pists with
      stainless  bolts  and  covering them well with Galvafroid paint.
      When  I  finished  I  had  a  meal and started the night's TX on
      137.550  as  normal.  I  saw a very poor gate and drain waveform
      from  my  W1VD  style amp, the previous night they looked normal
      9and  OK to me...). I assumed it was to do with my fiddling with
      the  grounds.  My  Scopematch box also showed a slight impedance
      mismatch  and  a  slight  resonance mismatch. I attended to both
      with  the tapped matching coil outside and the variometer in the
      loading  coil, but the waveforms on gate and drain remained very
      spiky.  I risked running and signal reports seemed OK, if not as
      good as the night before, using WSPR2 and OPERA.

      This  morning i investigated properly and put my 500W dummy load
      after the LPF bank in the shack and the gate and drain waveforms
      were  back  to  normal. I then put it outside after the matching
      transformer,  and  although  there was an impedance mismatch the
      gates  and  drains wave forms were still fine. So i moved to the
      loading  coil.  This  has  had  reapirs  to the lead to vertical
      section  of  the aerial, where it goes up from the coils housing
      in  a  big  wheelie bin to where the ladder line vertical secion
      goes  up  to  meet the horizontal loop top hat. it has two "choc
      bloc"  screw  connectors joing a new piece of wire where the old
      one  shorted out and burnt the insulation. They LOOKED fine, but
      i  decided  to  remove  them  and  properly solder in the repair
      section and use adhesive lined shrink tube to seal the joints.

      Hey, gates and drains now back to normal. I had also noticed the
      Scopemeter  was  showing a peak og 13.6V when the gate and drain
      waveforms  were  spiky, and now that was back to the normal 12.4
      or so volts.

      Finally.my  question.  Why  would  a  poor  or  high  resistance
      connection  on  the  vertical  section of the antenna affect the
      gate  waveforms? I think I can see why the drains were affected,
      but  why  the  gates, and why the higher volts on the Scopematch
      traces?    Thanks,  I  like  to try and find out WHY things have
      happened,   even   after   fixing  them,  so  I  appreciate  any
      instruction  here.  I  attach links to the normal gate and drain
      waveforms  and a second link to how they were last night. Amp is
      voltage mode Class D.

      Normal:  http://www.gatesgarth.com/normal.jpg

      Last night : http://www.gatesgarth.com/spiky.jpg

-- 
Best regards,
 Chris                          mailto:dead_fets@gmail.com