KAT3 - Antenna tuned or not?

[Tedd Wong]

I am attempting to tune a Zero-Five Vertical with the KAT3.  How do I determine if the KAT3 has found a match?  I see the SWR on the K3 close to 1:1and full power out but my external SWR meter is still 5:1.  Thanks.


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[Ed Muns, W0YK]

> I am attempting to tune a Zero-Five Vertical with the KAT3.  
> How do I determine if the KAT3 has found a match?  I see the
> SWR on the K3 close to 1:1and full power out but my external
> SWR meter is still 5:1.  Thanks.

The external SWR meter is not affected by the KAT3 because it is between the
KAT3 and the non-resonant load.  The KAT3 has presented a 1:1 match to the
K3, but the antenna is still 5:1, and will radiate, or not, accordingly.

73,
Ed - W0YK

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[Tom Hammond-2]

Hi Ted:

>I am attempting to tune a Zero-Five Vertical with the KAT3.  How do
>I determine if the KAT3 has found a match?  I see the SWR on the K3
>close to 1:1and full power out but my external SWR meter is still 5:1.

Yes... and the SWR (AT THE POINT AT WHICH YOU'RE MEASURING IT) is going to
REMAIN 5:1 for a long time... hopefully... if it changes, then there's a
problem with your antenna.

The KAT3, while commonly referred to as an ATU (antenna tuning unit), which
is a misnomer, it does NOT "tune" then antenna... it attempts to provide a
match BETWEEN the antenna/feedline combination and the transmitter. Years
ago these units often were referred to as TRANSMATCHES, rather than ATUs
because transmatch was a better description of what they did.

The ATU/transmatch (take your pick) provides a 'match' (hopefully 1:1) between
the antenna/feedline combination (connected to its INPUT) and the transmitter
OUTPUT (connected to its OUTPUT. It does not however CHANGE the SWR ON THE
FEEDLINE, and this is where your other SWR meter (reading 5:1) is located in
the RF circuit... it IS between the antenna and the KAT3, right?

The ONLY 'change' in SWR created by the KAT3 occurs (and is measured) at the
INPUT to the transmitter PA, NOT on the feedline.. so the SWR presented by
the antenna/feedline combo (and present at the end of that coax, is still
whatever it was before the ATU was connected... complete with coax losses
and other characteristics which come with a somewhat mismatched antenna/
feedline on whatever frequency you are attempting to use the system.

The Radio (K3 in this case) 'sees' a low SWR because the 5:1 SWR is being
compensated for within the KAT3, so the radio thinks it's working into a
nice flat load.

I hope this helps 'splain thing s a bit better.  Normally, I'd have included
a diagram or two, but this reflector doesn't allow in-line graphics in
replies. I can, if you wish, send something directly to you however. Just ask.

73,

Tom Hammond   N0SS





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[John W2XS]

I have often thought about adding an additional BNC connector to my K2 and KAT2 to insert an external meter like the W1 in between the rig output and the antenna tuner input. A short jumper would be needed if the meter is disconnected. The "aux RF" is one BNC connection and another could be wired to the tuner's input.

The meter would then show the actual SWR that the rig sees after matching. I like the continuous display of SWR and power output but, as has been pointed out here, it does not make sense to monitor the SWR after the tuner.

I try and keep the coax cable as short as possible between the rig and the balun because of the high SWR on that line. Most of the time I use a male-to-male BNC adaptor between the rig's output BNC and the balun.

72,

John W2XS

KX1 (S/N 015 and S/N 925) w/KXPD1, KXAT1, KXB30
K2 (S/N 1116) w/KAT2, KSB2, K160RX, KIO2, KBT2, KNB2, KAF2, FDIMP
K3/100 (S/N TBD in Mar/Apr) w/KAT3, KBPF3, KUSB, KFL3A-200, 500, 2.7K, 6K
HexKey (S/N 113 )
DL1, BL1, BL2, N-gen, XG1, W1, BNC-MM

 

The external SWR meter is not affected by the KAT3 because it is between the
KAT3 and the non-resonant load.

[Julian, G4ILO]

Tom Hammond-2 wrote

Yes... and the SWR (AT THE POINT AT WHICH YOU'RE MEASURING IT) is going to
REMAIN 5:1 for a long time... hopefully... if it changes, then there's a
problem with your antenna.

And what's more, if the feeder is very long, it could result in significant signal losses. Take a look at the chart at http://www.g4ilo.com/mismatch_losses.html which shows the amount of loss at different frequencies for RG-58, RG-213 and open wire feeder. This is in addition to the loss normally expected because of the feeder length.

The Elecraft tuners have a great ability to match a wide range of loads (compared with the auto ATUs in other transceivers) but they can't do anything about this problem. If you have a non-resonant antenna and want to feed it with co-ax then the best place for the ATU is at the antenna feed point not the back of the radio. Built-in ATUs are really meant for matching resonant antennas that present a slightly too high SWR when used near the band edges.

[n6wg]

Hello Tedd
The problem is your external SWR meter is just that,
external.  The KAT3 provides a 1:1 match to the
K3, that is, between the KAT3 and the K3 TX.  Your
external unit is on the unmatched side of the KAT3
and, of course, sees no change.
Trust the KAT3 to get the job done, and set aside
the external unit.
Good luck and 73
Bob N6WG

----- Original Message -----
From: "Tedd Wong" <[hidden email]>
To: <[hidden email]>
Sent: Monday, January 28, 2008 10:51 PM
Subject: [Elecraft] KAT3 - Antenna tuned or not?


> I am attempting to tune a Zero-Five Vertical with the KAT3.  How do
I determine if the KAT3 has found a match?  I see the SWR on the K3
close to 1:1and full power out but my external SWR meter is still 5:1.
Thanks.

>
>
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> Elecraft web page: http://www.elecraft.com

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[Jerry Flanders]

Your external meter is intended to be used in a 50 ohm system,
right?  But in this situation your KAT3 internal tuner has
transformed the output so that you don't have 50 ohms at the KAT3's
output terminals (It has matched the load) and therefore not at the
external meter's input terminals.

So the external meter numbers are not valid in this case. Trust the
KAT3. Also - you will have a slight loss in the external meter in
this situation - I would remove it.

Jerry W4UK

At 01:51 AM 1/29/2008, Tedd Wong wrote:

>I am attempting to tune a Zero-Five Vertical with the KAT3.  How do
>I determine if the KAT3 has found a match?  I see the SWR on the K3
>close to 1:1and full power out but my external SWR meter is still 5:1.  Thanks.
>
>
>_______________________________________________
>Elecraft mailing list
>Post to: [hidden email]
>You must be a subscriber to post to the list.
>Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft
>
>Help: http://mailman.qth.net/subscribers.htm
>Elecraft web page: http://www.elecraft.com

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