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KAT500 TUNER WOES

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David Inger-2

KAT500 TUNER WOES

I have a fairly early KAT500 tuner (#275). I am using it to tune several
antennas. Recently it has stopped finding acceptable matches to a
ladderline-fed 110 ft. dipole. This problem is only on 40-meters. The SWR
anywhere in that band is around 8:1. The tuner works great on all other
bands (well, not so much on 160, but that's the antenna's problem). I also
have a 43-ft vertical and the tuner matches fine on that antenna. I
replaced all intervening coax jumpers and even the 1:1 current balun at the
transition of the ladderline to the coax in the shack. None of the above
help.

Interestingly, when I bypass the KAT500 and enable the internal tuner in the
K3, everything works fine, including matching 40-meters. I have also done a
reset using the KAT500 utility program; still no help.

Before, I tear into things or stop bothering the good people at Elecraft, I
wonder if any in the group has any suggestions.

73 de K6SBA

David in Santa Barbara, CA

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Don Wilhelm-4

Re: KAT500 TUNER WOES

David,

What have you changed on that antenna system since it last "worked"?
The length of the antenna is only part of the story, because the length
of the feedline is also an important parameter. If you changed the
feedline, that can make the difference between working and not working.
The length consideration should be the feedline length plus 1/2 of the
antenna length. If that comes close to a 1/2 wavelength, the antenna
will be hard to feed since it represents a high impedance to the tuner.
Likewise, if the feedline plus half antenna is an odd multiple of 1/4
wavelength, it will present a very low impedance to the tuner which can
be difficult to match.

Adding (or subtracting) a bit of feedline - add or subtract 1/8
wavelength at the problem frequency - can make all the difference
between obtaining a match or not.

73,
Don W3FPR

On 5/19/2014 9:26 PM, David Inger wrote:

> I have a fairly early KAT500 tuner (#275). I am using it to tune several
> antennas. Recently it has stopped finding acceptable matches to a
> ladderline-fed 110 ft. dipole. This problem is only on 40-meters. The SWR
> anywhere in that band is around 8:1. The tuner works great on all other
> bands (well, not so much on 160, but that's the antenna's problem). I also
> have a 43-ft vertical and the tuner matches fine on that antenna. I
> replaced all intervening coax jumpers and even the 1:1 current balun at the
> transition of the ladderline to the coax in the shack. None of the above
> help.
>
>
>
> Interestingly, when I bypass the KAT500 and enable the internal tuner in the
> K3, everything works fine, including matching 40-meters. I have also done a
> reset using the KAT500 utility program; still no help.
>
>

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Nr4c

Re: KAT500 TUNER WOES

In reply to this post by David Inger-2

Have you tried a dummy load with tuner on 40m?

Have you used an analyzer on the antenna?

Sent from my iPhone
...nr4c. bill

> On May 19, 2014, at 9:26 PM, "David Inger" <[hidden email]> wrote:
>
> I have a fairly early KAT500 tuner (#275). I am using it to tune several
> antennas. Recently it has stopped finding acceptable matches to a
> ladderline-fed 110 ft. dipole. This problem is only on 40-meters. The SWR
> anywhere in that band is around 8:1. The tuner works great on all other
> bands (well, not so much on 160, but that's the antenna's problem). I also
> have a 43-ft vertical and the tuner matches fine on that antenna. I
> replaced all intervening coax jumpers and even the 1:1 current balun at the
> transition of the ladderline to the coax in the shack. None of the above
> help.
>
>
>
> Interestingly, when I bypass the KAT500 and enable the internal tuner in the
> K3, everything works fine, including matching 40-meters. I have also done a
> reset using the KAT500 utility program; still no help.
>
>
>
> Before, I tear into things or stop bothering the good people at Elecraft, I
> wonder if any in the group has any suggestions.
>
>
>
> 73 de K6SBA
>
> David in Santa Barbara, CA
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

Elecraft mailing list

Re: KAT500 TUNER WOES

In reply to this post by Don Wilhelm-4

Also, consider making sure you have the latest firmware updates. I have
also experienced the situation where the K3 internal tuner will tune my
200' ladder-line fed doublet but the KAT500 will not. I'm hoping that
subsequent updates will improve the KAT500's algorithms.
73, Doug -- K0DXV

On 5/19/2014 8:50 PM, Don Wilhelm wrote:

> David,
>
> What have you changed on that antenna system since it last "worked"?
> The length of the antenna is only part of the story, because the
> length of the feedline is also an important parameter. If you changed
> the feedline, that can make the difference between working and not
> working.
> The length consideration should be the feedline length plus 1/2 of the
> antenna length. If that comes close to a 1/2 wavelength, the antenna
> will be hard to feed since it represents a high impedance to the
> tuner. Likewise, if the feedline plus half antenna is an odd multiple
> of 1/4 wavelength, it will present a very low impedance to the tuner
> which can be difficult to match.
>
> Adding (or subtracting) a bit of feedline - add or subtract 1/8
> wavelength at the problem frequency - can make all the difference
> between obtaining a match or not.
>
> 73,
> Don W3FPR
>
> On 5/19/2014 9:26 PM, David Inger wrote:
>> I have a fairly early KAT500 tuner (#275). I am using it to tune
>> several
>> antennas. Recently it has stopped finding acceptable matches to a
>> ladderline-fed 110 ft. dipole. This problem is only on 40-meters.
>> The SWR
>> anywhere in that band is around 8:1. The tuner works great on all other
>> bands (well, not so much on 160, but that's the antenna's problem).
>> I also
>> have a 43-ft vertical and the tuner matches fine on that antenna. I
>> replaced all intervening coax jumpers and even the 1:1 current balun
>> at the
>> transition of the ladderline to the coax in the shack. None of the
>> above
>> help.
>>
>>
>> Interestingly, when I bypass the KAT500 and enable the internal tuner
>> in the
>> K3, everything works fine, including matching 40-meters. I have also
>> done a
>> reset using the KAT500 utility program; still no help.
>>
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

ke9uw

Re: KAT500 TUNER WOES

In reply to this post by David Inger-2

Sometimes when the weather changes, the match changes. There was a thread like this awhile back and it was noted that the different residual capacitances and inductances when using the KAT500 versus the ATU in the K3 makes a difference in being able to find a match with certain loads. It was also pointed out by Elecraft that the tuner values in the K3 ATU and the KAT500 are the same.
Changing the length of the feedline sounds like a plan.

Chuck, KE9UW