> Having an issue with a homemade GS35B operationon 15 and
> 17 m. When
> keyed, the power seems to hesitate before going up to 1.5
> KW
> output. CW is a mess on these bands due to this
> situation. On RTTY
> the power hesitation is so short that it doesn't present a
> problem. Amp. seems to be okay to about 1200 W, but the
> hesitation
> returns above this level. Other bands, 10, 20, 40, 80,
> 160 work okay.
That's a big tip-off of what is happening.
That effect is almost always caused by the electrical length
of cables and networks and what they appear like to a sensor
or detector someplace upstream towards the transmitter.
Worse case is when a network/ line combination comes out an
odd 1/4 wl long to a point that is high impedance when idle
or at the instant of activation.
Consider a 1/4 wl line with an open at the far end. Say it
is connected to a tube cathode and the tube is biased off.
At the moment of excitation you'd have very low voltage
available at the exciter end of that 1/4 wl line because
that point would look nearly like a short. If you had an
electronic bias or fault protection circuit looking at that
point, it would see very low voltage and be slow responding.
It doesn't have to be a transmission line, it can be a
network with suitable phase delay. A minimum Q network can
look like a phase delay of around 90 degrees, so it
approximates the characteristics of a 90-degree transmission
line with a surge Z0 equal to the surge impedance of the L/C
combination at the operating frequency. Open the far end by
having a tube in cutoff or an open relay, and an electrical
1/4 wl away you have a dead short (except for some small
resistance caused by component losses).
Almost anytime you have a band-sensitive start delay, it is
rooted in this problem.
If you are using active bias you need two or more sensors
that are analog "or'ed" at different points in the system,
and you should never set quiescent bias into low level
non-linear regions. That,. along with a response time faster
than envelope rise, will cure any problems.
73 Tom
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