I guess what's needed here to assist in this problem is to know a bit
more info. Oh yes, I don't like the idea of putting a tuner in the line
between the tranceiver and the amp input. Especially, if for some
reason, the amp has developed a "dynamic" input impedance change.
What bands? Does the SWR change with drive power? Does it happen in CW
or SSB mode on the SB-220? Have you tried it with a dummy load? What's
the results? Is the tuning on the SB-220 smooth or does the grid and or
plate current change suddenly?
The SB-220 does have a tuned input for each band. They are not
considered "user adjustable" but if I recall they can be tweeked for
enhanced performance within each band. I think they are slug tuned
coils in the bowels of the box.
I have a Tentec Centurion. It's somewhat of a circuit knock-off of the
SB-220. It has tuned inputs. On 160M and 80M the SWR will get as high
as 2:1 but it is clearly frequency dependant within the band. At band
edges, it's worse, in the middle of the band it's best. The SWR does
not change with drive or output power. The solid state Omni VI+ is very
happy driving this amp.
I suspect a bad coax jumper or a bad component in the input that is
changing with power i.e. heat thus causing the input tuning to change,
perhaps even go out of band since the SWR is reported to go to 5:1.
More clues would be helpful.
73
Bob K4TAX
Pete Smith wrote:
>
> At 07:49 AM 2/22/01 -0600, J. Setcer wrote:
> >
> >
> >If you cannot "correct" the problem you can "resolve" the problem by putting
> >a tuner between the radio and the Amp. Maybe this would even be about the
> >same as an "external tuned input", I'm not sure.
> >Maybe someone that knows will comment.
>
> This is all irrelevant anyhow, because the SB-220 has a tuned input.
>
> 73, Pete N4ZR
> Contesting is!
>
> The World Contest Station Database
> is waiting for your input at
> http://www.qsl.net/n4zr
>
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