Re: K3 increasing SWR with increasing Power

Mel Farrer, K6KBE <farrermesa@...>

Please  remember that SWR is a reflection of all of the energy going to the antenna.  In the past, I have seen incorrect bias on the finals causing an increase in the harmonic content of the signal.  I usually look for harmonic output along with everything else.  Harmonics can really screw up the SWR reading.

Mel, K6KBE

On Tue, Sep 28, 2021 at 9:49 AM Paul G4KZY <paul.g4kzy@...> wrote:
Hi Holger,

The RF voltage when transmitting is on the anodes of the diodes (junctions with R44 and R35).  You need a n oscilloscope to measure here. The small DC voltage on the anodes of the diodes comes via R34 and the secondary of T3. and I think the low voltage here shows that T3 is connected OK. 

The DC voltage when transmitting comes up on the diode cathodes (junctions with R46 and R38).  With a low VSWR you expect the voltage on D36 cathode / R46 to increase (forward power) but the voltage on D37 cathode / R38 to stay close to 0V (reflected power), or at least low compared to D36 cathode voltage.  If you see the voltage on D37 cathode significantly rising when transmitting into a dummy load, try to put a (temporary) short across C230 to see if this improves the situation.

73,  Paul

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