[Lowfer] New bench testing of PA output filter

Tue, 03 Sep 2002 17:53:11 -0400

Bill

Haven't done much bench testing of late. Any hint of the resonance "jump" was
eliminated in my case with RG-142 double shielded coax. I'm pretty well
convinced that it was rf getting back into the exciter.

A long time ago when I was running that 3 section 365 pF broadcast variable I
was able to arc between plates at resonance and that caused a noticable jump
(and nice blue light at night!). The stack of 500 volt silver micas and small
tuning range mica compression trimmer solved that problem.

I have also viewed the current waveform and found it to be an almost perfect
sine wave. Any harmonic content would be vanishingly small compared to the
fundamental. However, the antenna becomes a better radiator up higher in
frequency so a smaller harmonic current could possibly produce a bigger spurious
signal (as compared to the 185 kHz fundamental. I hope to get some time to set
up my calibrated e probe and receiver some distance from the antenna and get an
accurate measurement of the harmonic radiation.

Jay

Jay

Bill Ashlock wrote:

> John,
>
> >Retune the antenna?
>
> Sure enough did.... and often. When the Q is about 200 just a sneeeeez will
> throw the tuning way off. What is the efficiency with your filtered setup?
>
> Jay: I haven't seen our 'jump effect' lately (this is where the loop current
> jumps down to a lower value when the generator is carefully tuned through
> resonance). I suspended the loop simulator coil 6" above the bench with a
> string and this seems to have done the trick. Must have been some kind of
> electromechanical feedback. Has anyone else seen this weird effect?
>
> Bill
>
> >
> >----- Original Message -----
> >From: "Bill Ashlock" <[email protected]>
> >To: <[email protected]>
> >Sent: Tuesday, September 03, 2002 11:29
> >Subject: [Lowfer] New bench testing of PA output filter
> >
> >
> > > Mike and all TX loop enthusiasts,
> > >
> > > You may be interested in knowing that when I insert the 63uh-1.8n-63uh
> > > filter (IE: the Lyle filter) between my final and the loop stepdown
> > > transformer I loose at least 25% of the loop current for a constant 1W
> >of
> > > input power. I have tried different types of cores and
> >inductance/capacity
> > > ratios but the results are similar. Without the filter the total
> >efficiency
> > > is about 95% and those little MPS6602/52s run as cool as cucumbers. I
> >can't
> > > seem to make the Psice model agree with these results, however.
> > >
> > > Bill
> > >
> > > _________________________________________________________________
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