Dear Peter,
I have had similar problems in constructing PAs.
First: One reason for the ringing might be the transistors. Put a capacitor
2n7/ 3kV ceramic from
drain to source at each PA-transistor. This is likeliy if the pa is operated with an quiescent current.
sec.: If You dont have any quiescent current at all, than there is no damping resistor at the transformer for the winding that is not driven . Any winding of a transformer that carries no current will ring. This effect has been never described in amateur radio . The only thing You can do against is adding an quiescent current or using an topology where all windings carry allways a current, that is only two windings, pri and sec.
More upon request.
Hans-Albrecht Haffa
DK 8 ND
CBA, ++49-(0)7161 - 87847
[email protected] schrieb am 07.01.04 16:04:23:
dj9dw schrieb:
> Hello group,
> as I can't get in contact with David, G0MRF, I want to spread out my problem
> here.
> The TX works fine except the outputtransformer T2. There is heavy ringing at
> abt 1 MHz. Now I figured, the inductance seems to be abt 300uH from drain to
> drain. That shure is far too much.
> Could it be that David has changed the toroid - type to one with higher u so
> that 10 turns primary has to be reduced?
> Your help is very welcom, I am stuck.
>
> Regards, dj9dw, Peter.
Hi Peter,
pse see
http://www.qsl.net/dj8wx/My%20second%20transmitter.htm
if T2 is not pressed p.e. between two ceramic pieces
it should be coold by a fan or else it vibrates on subharmonics of the
transmitted QRG.
btw. how did you find out a "ringing" at abt 1MHz ?
best regards
Uwe/dj8wx
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