[AMPS] reply on connectors and VHF

[John T. M. Lyles]

Yikes, Larry Sez:

>The best solution is no connectors at all. For HF use there is little
>reason to do so. Short pigtails with spade lugs can be weatherproofed
>easily and the connection is capable of John Lyles power levels.

Now! I don't know about 18 kV of RF on spade lugs, unless you put 
some pretty good goop around the whole thing......



on another seemingly endless topic:

>Class C amplifiers biased amplifiers, like class C biased
>oscillators, are cut off when there is no drive. Since the tube is cut
>off, it won't oscillate.
>
>Drive the tube, and it will turn the oscillator on.
>The proper way to test a PA for stability is to bias it into
>conduction, and load it with all possible phase angles and
>impedances on the input and output that it will see in operation.
>I'd bet money your PA would have oscillated like a champ if it was
>tested that way.
>
>There is no such thing as an oscillator that requires excitation on a
>harmonic related frequency to start it, that won't start on it's on
>when the amplifying device isn't cut off.
>
>73, Tom W8JI

Actually the standard test I ran was to shock the amplifier either 
with the power switch, or but pulsing bias into conduction. Of course 
that proved the frequency of the parasite, when things were tuned 
properly to set it up. And when that filter was installed. It was not 
evident in this test, when the filter was removed, or when the 
operating freq of the PA was shifted. One might say, the phase angles 
and impedances made the difference.

The second paragraph above states the same thing that I did.

The oscillation was there when the PA was conducting, when driven ON 
by the driver stage. However, being a class C transmitter, it was 
never intended to sit in conduction until driven. However, the real 
fact is that it ONLY drove the oscillation when the second harmonic 
was very close to a parasite freq. The parasite could be seen with a 
GDO or network analyzer, but it was not started until there was 
harmonic energy very close by. If the rig was tuned away from this, 
it was stable, the F2 (second harmonic) was normal, etc.

Once I spent hours explaining to an experienced RF oscillator 
designer (RF heating business, big oscillators) that RF amplifiers 
can oscillate while also amplifying on the desired frequency. This 
engineer couldn't believe it was possible, and never agreed to the 
possibility. I didn't sweat it, as I had a whole career to learn 
about things like this, with an open mind.

John
K5PRO



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