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:[email protected]
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