Posted by
Don Wilhelm-4 on
Jan 30, 2008; 12:31am
URL: http://elecraft.85.s1.nabble.com/K1-KAT1-SWR-Adjustment-tp460470p460474.html
Carl,
:-) Don't worry about it - it does work.
Actually the KAT1 (and other Elecraft tuners) do a comparison of the
forward and reflected power in the microprocessor in the tuner. It is
the main K2 microprocessor that displays the SWR.
The way I read that statement in the manual the tuner determines that
the match is sufficiently low (and that will always be less than 1.2:1)
- it may be mush less, and usually is. But that is a way of explaining
that a match of 1.2:1 *is* a good match. Many hams get all bent out of
shape if the match is anything greater than 1.0:1 (you have likely heard
them on the air and in private discussions). It becomes a game of "My
SWR is better than your SWR!", and the discussion goes on and on. In
reality the loss from a 1.5:1 or even a 2:1 SWR is not that great at HF
- when you get up to VHF and UHF, it becomes much more significant. I
don't try to prune my antennas any more than is necessary, and I am
happy with 1.5 or less with no greater than 2.0:1 at the band edges - I
don't normally use a tuner, and that works out just fine for me - the
transceiver loads just fine.
Bottom line is that the approximate setting (for those who do not have
the capability to set the SWR accurately) is good enough for the tuner
to do its job.
73,
Don W3FPR
Strode, Carl R wrote:
> If the KAT1 merely tunes for the lowest voltage as developed at TP1, then does the KAT1 really use the <1.2:1 criteria to initiate an attempt at finding a good match?
>
> Page #11 of the Rev. C KAT1 manual says:
>
> "If the match is already very good (< 1.2:1), the tuner's L and C settings will not be changed."
>
>
> Without adjustment of R2, how does the KAT1 know the difference between a good match and a bad match?
>
> Of course, once the tuning process is started, the lowest voltage at TP-1 indicates the best match (assuming C9 was adjusted with a valid load).
>
> Geez - my feeble brain is suffering from SWR overload.
>
> Carl Strode
> WA7CS
>
>
[hidden email]
>
> -----Original Message-----
> From:
[hidden email] [mailto:
[hidden email]] On Behalf Of Don Wilhelm
> Sent: Tuesday, January 29, 2008 1:09 PM
> To: '
[hidden email]'
> Subject: Re: [Elecraft] K1 KAT1 SWR Adjustment
>
> Carl,
>
> Yes, I may have been the one to suggest those resistors for a dummy load
> - if you used the 50 ohm ones, they should be flat up to 200 MHz or more depending on your physical implementation - short leads and such.
>
> Yes, adjust R2 to indicate the correct SWR - no smoke will happen - but do that as the last step.
> The C9 adjustment must be done first, and once that is correct, do not touch it again or you will have to do everything all over.
>
> If you want to use your 25 ohm and 100 ohm resistors to indicate a better setting for C9, then connect them alternately (use *short* leads) to the antenna jack - you are looking for the SWR indication to be the
> *same* for both (ignore the actual SWR amount, just adjust C9 slightly until they both read the same). After that, go back to the 50 ohm load and set the trimmer resistor for forward power, and lastly use either your 25 or 100 ohm load and set the SWR = 2.0, then call it done. On the KAT2 and KAT1, it is not uncommon for the final adjustment of the reflected trimmer resistor to be quite different than the setting for the FWD trimmer - it just happens to be that way. As I indicated in my previous note, the actual SWR means nothing to the tuner itself, it merrily searches for the minimum SWR - and minimum SWR is a better indication of correct tuning than any actual SWR value.
>
> 73,
> Don W3FPR
>
>
>
>
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