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Date: Sat, 23 Dec 2017 16:35:57 +0100
From: DK7FC <selberdenken@posteo.de>
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Subject: Re: LF: TXing 2200m WSPR
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Hi Paul,

So at least there is an improvement.
Does the blue core become warm during operation?
How does the drain-voltage look like?

73, Stefan

Am 23.12.2017 14:13, schrieb N1BUG:
> Hi Stefan,
>
>> The C on the gate is not a good idea i think. Better try a 10...22 Ohm
>> resitor or a ferrite bead in front of the gate.
>
> I removed the C on the gate and added a 15 ohm resistor in front of 
> the gate (in series with RF input to the gate). No change in performance.
>
>> Is the bias voltage stable? It may be worth to spend 1000 uF parallel to
>> the Z diode. And a normal diode in front of the z diode, i.e. into the
>> yellow wire...
>
> I didn't have any 1000 uF but I put 470 uF in parallel to the Z diode, 
> added a 1N4007 in series at the end of the yellow wire. No change in 
> performance.
>
> At this point I became curious about the 1 uF C bypassing the +V lead 
> of the blue core to ground. It seemed strange to have it bypassed with 
> 1 uF there, then a series choke, then 2200 uF bypass. I could not find 
> any published circuits like that.
>
> As a test (not having any idea what I was doing!) I removed the 1 uF 
> bypass. The amp went completely crazy.
>
> So I decided to try some more C in parallel to the 1 uF. All I have 
> are electrolytic caps, but I tried 10 uF. Stable output increased from 
> 12W to 16W.
>
> What about even more C? I removed the 10 uF and put 100 uF in parallel 
> to the 1 uF. No change from the 10 uF.
>
> It still does very strange things if I try to adjust bias for more 
> than 16W.
>
> I don't know what this experiment tells me...
>
>> The blue core, maybe it saturates at higher power? Could be worth to try
>> 2 more turns and better use abt 0.5 mm wire for higher power.
>
> I will try that next if I find some suitable wire here. I also thought 
> about trying a 10 turn bifilar winding instead of the trifilar. Again 
> I have no idea what I am doing, but the worst that can happen is 
> another dead FET. :) I have more.
>
>> But the design is not good for > 30 W or so. Don't expect to much from
>> an IRF530 at 13.8 V.
>
> I would be happy if I could get 25W stable from this amp. I can get 
> 25W but it is not stable at that level.
>
> 73,
> Paul N1BUG
>