[Amps] More instability problems

[Zev Darack]

That sounds like a bad coax jumper.


On 4/12/13, N1BUG <paul at n1bug.com> wrote:
> On 04/12/2013 10:28 AM, Jim W7RY wrote:
>> Perhaps you have an antenna system problem?
>
> The problem is occurring with several different antennas. However,
> there is on thing I have not yet taken apart for inspection: an
> antenna switch.
>
> What makes me think oscillation is:
>
> Suppose I have the amp tuned for maximum output at 28 MHz. Indicated
> antenna SWR is low, output is 1500 watts.
>
> Now assume that for the following procedures I maintain RF drive at
> all times.
>
> Now I vary the amp loading slightly. As I decrease loading
> capacitance just a bit, I see a slow, gradual drop in output of
> maybe 50 watts, then all of a sudden a drop of at least 500 watts,
> and at that same instant, indicated SWR jumps up wildly. This is
> absolutely repeatable on several bands with different antennas.
>
> Once the sudden "jump" has occurred, returning the load cap to the
> previous setting does not return things to normal. Going well past
> the proper spot, toward higher capacitance, does at some point
> produce a sudden decrease in SWR and increase in output power.
>
> 73,
> Paul
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