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K2 Transmit Test

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pagoglia

K2 Transmit Test

I ran a transmit test today on my recently built (serial 7059) K2/100, with SSB adaptor, KAT 100 antenna tuner and elecraft balun. For the station antenna, I have an 80 meter dipole with each leg currently cut to 66 feet. The center of the dipole is not quite 40 feet high. The two ends are inverted downward and are each 10 feet off the ground. All three points of the antenna are anchored in trees.

The antenna is fed to the shack with 165 feet of The Wireman 'window' ladder line

I used my microphone to call a CQ on 40 meters, and the KAT 100 lit up like a Holiday Tree. SWR all the way to the red zone. I tried this at various power settings up to 100 watts, and only transmitted long enough to see how many lights I got. Always to the end of the scale. I used a separate SWR meter and was getting readings of 7:1.

I switched to a 300 watt dummy load from the 80 meter dipole, and the SWR reading on the KAT 100 was perfect. Just one light lit up.

I also did a continuity check between the two lines on the ladder line to verify I did not have a short. OK there.

Any suggestions? Is it possible that all I need to do at this point is trim the antenna? Or do I have something internal going on?

73 de WN2K
Paul Agoglia

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Don Wilhelm-4

Re: K2 Transmit Test

Paul,

Did you set the menu ATU parameter to AUTO and then do a TUNE before
trying to transmit?
If you did, you should have heard relays clack while the KAT100 found a
match, then the SWR indicators should have settled to less than 1.5.

If you followed that procedure, then yes, you can conclude that the
feedpoint impedance of the antenna is beyond the matching range of the
KAT100.

Remember that the KAT100 is not an "automatic tuner" that will initiate
a TUNE when it detects a high SWR - the operator must do a TUNE into the
antenna for each band, and then afterwards, those settings will be
remembered by the KAT100, and restored when you return to that band. As
long as you do not change the antenna, those settings should be good,
but first, you must do a TUNE on each band to allow the KAT100 to find a
match for that band/antenna.

73,
Don W3FPR

On 5/4/2011 7:49 PM, Paul Agoglia wrote:

> I ran a transmit test today on my recently built (serial 7059) K2/100, with SSB adaptor, KAT 100 antenna tuner and elecraft balun. For the station antenna, I have an 80 meter dipole with each leg currently cut to 66 feet. The center of the dipole is not quite 40 feet high. The two ends are inverted downward and are each 10 feet off the ground. All three points of the antenna are anchored in trees.
>
> The antenna is fed to the shack with 165 feet of The Wireman 'window' ladder line
>
> I used my microphone to call a CQ on 40 meters, and the KAT 100 lit up like a Holiday Tree. SWR all the way to the red zone. I tried this at various power settings up to 100 watts, and only transmitted long enough to see how many lights I got. Always to the end of the scale. I used a separate SWR meter and was getting readings of 7:1.
>
> I switched to a 300 watt dummy load from the 80 meter dipole, and the SWR reading on the KAT 100 was perfect. Just one light lit up.
>
> I also did a continuity check between the two lines on the ladder line to verify I did not have a short. OK there.
>
> Any suggestions? Is it possible that all I need to do at this point is trim the antenna? Or do I have something internal going on?
>
> 73 de WN2K
> Paul Agoglia
>
> ______________________________________________________________
> 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
>

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Tony Estep

Re: K2 Transmit Test

In reply to this post by pagoglia

Paul, you can use an 80 meter dipole on 40 as you describe. Many have done
it with success. However, you may have to fool with it to get it to work,
since the antenna is being fed at a very high impedance point.

I assume the balun you're talking about is 4:1. To start, I'd suggest
grounding the cold side of the balun to a counterpoise consisting of at
least 3 wires 33 feet long strung out in various directions, out the window
and lying on the ground if possible. Another helpful measure is to insert an
RF isolator (like those available from Radioworks.com). It goes between the
balun and the tuner. This is just a 1:1 choke balun which kills off any RF
current flowing on the outside of your coax.

I'd bet that these two modifications will bring things under control. If
not, you may have to try different lengths of feedline, but save that for a
last resort.

good luck,
Tony KT0NY

On Wed, May 4, 2011 at 6:49 PM, Paul Agoglia <[hidden email]> wrote:

> I ran a transmit test today ....
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Don Wilhelm-4

Re: K2 Transmit Test

Tony and all,

Those "counterpoise" wires should not just be dangled on the ground.
They will carry RF current, and the RF voltage at the ends can be quite
high. Treat them just like an antenna radiating element - keep them
clear of possible contact for humans and pets, and use insulators on the
ends just as you would on an antenna radiator.

Be safe for yourself and your family and guests.

73,
Don W3FPR

On 5/4/2011 8:09 PM, Tony Estep wrote:

> Paul, you can use an 80 meter dipole on 40 as you describe. Many have done
> it with success. However, you may have to fool with it to get it to work,
> since the antenna is being fed at a very high impedance point.
>
> I assume the balun you're talking about is 4:1. To start, I'd suggest
> grounding the cold side of the balun to a counterpoise consisting of at
> least 3 wires 33 feet long strung out in various directions, out the window
> and lying on the ground if possible. Another helpful measure is to insert an
> RF isolator (like those available from Radioworks.com). It goes between the
> balun and the tuner. This is just a 1:1 choke balun which kills off any RF
> current flowing on the outside of your coax.
>
> I'd bet that these two modifications will bring things under control. If
> not, you may have to try different lengths of feedline, but save that for a
> last resort.
>
> good luck,
> Tony KT0NY
>
>
> On Wed, May 4, 2011 at 6:49 PM, Paul Agoglia<[hidden email]> wrote:
>
>> I ran a transmit test today ....
> ______________________________________________________________
> 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
>

Don Wilhelm-4

Re: K2 Transmit Test

In reply to this post by pagoglia

Paul,

In addition to the points in my last post, a check of the feedpoint
impedance (with an antenna analyzer) at the end of the parallel line
would be informative. If you have an 80 meter radiator and a feedline
that is close to a half wavelength on 40 meters (34 feet or some
multiple of that length), the feedpoint impedance will be very high.
You might do well to try adding a 15 foot length of parallel feedline.

I would advocate that a 1:1 balun will usually serve you better than a
4:1. It is not the characteristic impedance of the balanced line that
is to be matched, but the actual feedpoint impedance of the feedline at
the point where the balun is inserted - it all depends on the electrical
feedline length and the electrical length of the radiator.

An 80 meter radiator used on 40 meters is "two halfwaves in phase" which
has a high feedpoint impedance at the antenna feedpoint, one must use a
balanced feedline that has an electrical length of 1/4 wavelength or an
odd multiple thereof to bring the feedpoint impedance down to a
reasonable level.

73,
Don W3FPR

On 5/4/2011 7:49 PM, Paul Agoglia wrote: