The videos on YouTube were all running CW at various frequencies. No pulse
modes.
73
Jim ab3cv
On Oct 29, 2016, at 11:37 PM, jeff millar <wa1hco@wa1hco.net> wrote:
Hi Jim...
IIRC, the amplifier in those video are using a pulse mode with limited duty
cycle. The transistors have a high enough voltage rating to with infinite
VSWR with a phase that causes open circuit voltages, but they don't have
the thermal capability to handle the equivalent of short circuit
impedance...thus the limits on duty cycle.
If the spec mentions 20 ms pulses, then the VSWR trip should respond in
less than 20 msec.
jeff, wa1hco
On Wed, Oct 26, 2016 at 7:17 AM, Jim Miller <jim@jtmiller.com> wrote:
> From several Youtube videos it appears that the LDMOS FETs.are quite
> capable of withstanding opens and shorts indefinitely. If true then
> agonizing over VSWR and the need for a tuner for the typical case of 3:1 or
> less would seem to be unwarranted at least for the FETs.
>
> The next question would be what about other components in the finals and
> lowpass filters and how would they react to continuous 3:1? Coils,
> capacitors, etc.
>
> How would the power supply to the FET output stage be affected? Would the
> excess voltage or current at the amp LPF output cause the signal to degrade
> due to starvation of either?
>
> 73
>
> jim ab3cv
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