On Wed,11/11/2015 5:48 AM, Herbert Schoenbohm wrote:
On 11/11/2015 8:11 AM, john@kk9a.com wrote:
Repeat after me --
SWR is NOT an indicator of antenna performance.
But it determines whether or not my very sensitive Alpha 87A will
trip off or a solid state amp will fold back.
Right. And the match of the antenna to the coax determines loss in the
line. But the matches that the original poster described were not
sufficient to generate much additional loss.
And several things that K6XX taught me -- First, the output devices
(tube or transistor) in ANY power amp must work into a matched load to
achieve minimum distortion. Tube amps can accomplish that match with
careful tuning, but solid state amps that lack an adjustable matching
network require an antenna tuner to achieve that match. In teaching me
this, Bob was not entirely altruistic -- we're close-in neighbors, so he
has a vested interest in my amp being clean. :)
Second, it's important to know whether your amplifier is "auto tune" or
"auto-recall" of previous settings on the same band. BIG difference.
I've never owned an Alpha, but I think that some models are auto-recall.
That means if you're using a different antenna, you've got to re-tune
the amp. My guess is that in addition to minimizing distortion, it will
also prevent the amp from tripping off or folding back.
73, Jim K9YC
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