Question about my KX2

[Paul Smith]

I have and love my KX2 serial number 855. Lately the ATU seems to be "turning loose of the setting" I usually can hit the tune button again and get it to tune. I use a doublet at 50 ft fed with 450 ohm line and a home brew balun/ Unun. I question the balun as when I ordered,  the wrong cores came and I wound the balun which was supposed to be a 9:1.

This may not be enough information but the manual has not offered me much as I have done some reading.

Any thoughts out there? Does it need to go to California to be looked into? This is my first ATU.

 Thanks in advance de Paul Smith N0NBD


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[David Shoaf]

Paul,  eliminate some of the variables to isolate the problem:

- Use a dummy load and step through the KX2 bands to be sure it can transmit directly into it.  Use the TUNE button to get that done.  Make sure the internal antenna tuner is set to BYP mode.

- Then, add in the transmission line with the dummy load terminating it.  Remove the hand-built balun to do this so you're testing the line only.

- Then, add in the balun and retest on all bands but connect it directly to the KX2 and terminate the other end with a dummy load.  This allows you to test it by itself.  It better read 1:9 or 9:1 depending on how it is connected.

- Lastly, add the transmission line and the balun together and then connect the dummy load to the output of it.  Be sure you're stepping through all the bands when you do this, too.

As you can see, isolating the items will help you determine where, if any, there's a problem.  It isn't appropriate to jump to conclusion - yet - there's a problem with the KX2.   Eliminate all that is known to work properly and you'll have your answer.

Cheers,

David

[Brian Hunt]

Most 9:1 designs are UNUNs - unbalanced to unbalanced. For feeding a window line fed doublet, you definitely want a BALUN - balanced to unbalanced. The doublet / window line is a balanced system. The output connector on the KX2 is unbalanced.

If you are using an UNUN in this setup you you may be getting RF on the KX2 case which, when you touch it, may cause the tuner to do what you are seeing.

The Elecraft BL2 is a great solution for this application since you can choose either 1:1 or 4:1 to see which one makes the ATU the happiest. Or you can roll your own but it needs to be a BALUN.

GL & 73,
Brian, K0DTJ
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[Paul Smith]

Ok Thanks for the things to check. I will do this in the morning.

Thanks

Paul Smith N0NBD


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________________________________
From: [hidden email] <[hidden email]> on behalf of David Shoaf <[hidden email]>
Sent: Wednesday, August 16, 2017 12:03 AM
To: [hidden email]
Subject: Re: [Elecraft] Question about my KX2

Paul,  eliminate some of the variables to isolate the problem:

- Use a dummy load and step through the KX2 bands to be sure it can transmit
directly into it.  Use the TUNE button to get that done.  Make sure the
internal antenna tuner is set to BYP mode.

- Then, add in the transmission line with the dummy load terminating it.
Remove the hand-built balun to do this so you're testing the line only.

- Then, add in the balun and retest on all bands but connect it directly to
the KX2 and terminate the other end with a dummy load.  This allows you to
test it by itself.  It better read 1:9 or 9:1 depending on how it is
connected.

- Lastly, add the transmission line and the balun together and then connect
the dummy load to the output of it.  Be sure you're stepping through all the
bands when you do this, too.

As you can see, isolating the items will help you determine where, if any,
there's a problem.  It isn't appropriate to jump to conclusion - yet -
there's a problem with the KX2.   Eliminate all that is known to work
properly and you'll have your answer.

Cheers,

David



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[Don Wilhelm]

Paul,

I suspect you have an antenna system problem rather than a KX2 problem.
Operate the KX2 into a dummy load as David Shoaf has suggested to verify
that it is working as expected.

The fact that your doublet is fed with "450 ohm" parallel transmission
line does not mean that you will be feeding 450 ohms.
The characteristic impedance of the feedline and the impedance to be
matched at the shack end depends NOT on the feedline characteristic
impedance, but the length of the feedline and the impedance presented at
the antenna.  That will change from band to band.  It can range from a
very low impedance to a high impedance.  There are a lot of variables
such as the length of your doublet, the length of the feedline, and the
frequency.

As has been said, most 9:1 transformers are Ununs (autotransformers) and
not a balun at all.

A proper balun would better be termed a common mode choke which will
minimize the common mode RF on the coax.  Place it at the junction of
the parallel feedline and the coax coming into the shack.  I would
suggest the Elecraft BL2 which is switchable between a 1:1 and a 4:1
configuration.  Use whichever setting gives the least "tuning activity"
to the ATU.

73,
Don W3FPR



On 8/15/2017 6:53 PM, Paul Smith wrote:
> I have and love my KX2 serial number 855. Lately the ATU seems to be "turning loose of the setting" I usually can hit the tune button again and get it to tune. I use a doublet at 50 ft fed with 450 ohm line and a home brew balun/ Unun. I question the balun as when I ordered,  the wrong cores came and I wound the balun which was supposed to be a 9:1.
>
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