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K3 Hi SWR when sending CW

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Barry

K3 Hi SWR when sending CW

On 12m (only), despite the ATU bringing the SWR to 1.0 when I press the ATU TUNE button, it shows about 2.5:1 on the bar graph when I send CW. I am using a non-resonant antenna (fan dipole with wires for 40, 20 and 10), but it doesn't do this on the other bands for which I don't have a resonant antenna. Should this be a concern? WHy does the tuned SWR not agree with the bar graph?
Tnx,
Barry W2UP

vk4tux

Re: K3 Hi SWR when sending CW

Different pwr level. Do you have a 1:1 isolation balun in coax near
antenna feedpoint?

On 10/03/2012 09:58 PM, Barry wrote:

> On 12m (only), despite the ATU bringing the SWR to 1.0 when I press the ATU
> TUNE button, it shows about 2.5:1 on the bar graph when I send CW. I am
> using a non-resonant antenna (fan dipole with wires for 40, 20 and 10), but
> it doesn't do this on the other bands for which I don't have a resonant
> antenna. Should this be a concern? WHy does the tuned SWR not agree with
> the bar graph?
> Tnx,
> Barry W2UP
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K3-Hi-SWR-when-sending-CW-tp7563645.html
> Sent from the Elecraft mailing list archive at Nabble.com.
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Don Wilhelm-4

Re: K3 Hi SWR when sending CW

In reply to this post by Barry

Barry,

I don't know the answer in your particular case, but ....

Normally having a difference in SWR for tuning (low power) and operation
(higher power) is an indication that you have some faulty connection in
your antenna system - look for loose connectors, places where you might
have arc-over and things of that nature.

73,
Don W3FPR

On 10/3/2012 7:58 AM, Barry wrote:
> On 12m (only), despite the ATU bringing the SWR to 1.0 when I press the ATU
> TUNE button, it shows about 2.5:1 on the bar graph when I send CW. I am
> using a non-resonant antenna (fan dipole with wires for 40, 20 and 10), but
> it doesn't do this on the other bands for which I don't have a resonant
> antenna. Should this be a concern? WHy does the tuned SWR not agree with
> the bar graph?
>

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Barry

Re: K3 Hi SWR when sending CW

In reply to this post by vk4tux

No balun.

Don, no loose connection I can find. Simple setup and the high reading only happens on 12m and is consistent.

Vic Rosenthal

Re: K3 Hi SWR when sending CW

If you have a lot of common-mode current on the coax, this can upset SWR readings, and
will be worse the more power you run. If there is no balun and the feedline is a multiple
of 1/2 wl on 12m (the worst case for common-mode currents), then this is probably the reason.

On 10/3/2012 6:37 AM, Barry wrote:
> No balun.
>
> Don, no loose connection I can find. Simple setup and the high reading only
> happens on 12m and is consistent.

--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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Barry

Re: K3 Hi SWR when sending CW

Vic,

I think you're on to something. When I vary the power, below 85W, the SWR is 1:1. Above 85W, it starts creeping up with the power increase.

If I put some ferrites on the coax, but want to keep them indoors, is there a best location for them?

Tnx,
Barry W2UP

vk4tux

Re: K3 Hi SWR when sending CW

In reply to this post by Barry

No Balun ok, well do you think a 10 turn 8¨ diameter coax UB at the
feedpoint, may help reduce the shield radiation (which can mess your
indicated swr)?

On 10/03/2012 11:37 PM, Barry wrote:

> No balun.
>
> Don, no loose connection I can find. Simple setup and the high reading only
> happens on 12m and is consistent.
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K3-Hi-SWR-when-sending-CW-tp7563645p7563651.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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Vic Rosenthal

Re: K3 Hi SWR when sending CW

In reply to this post by Barry

I am not sure. But try it where it's convenient. Remember, for it to be effective at HF,
you must have a few turns around a ferrite -- I'd say 4 or 5 turns should be enough for
12m. Just clamping a ferrite bead on a cable doesn't do much.

On 10/3/2012 10:11 AM, Barry wrote:

> Vic,
>
> I think you're on to something. When I vary the power, below 85W, the SWR
> is 1:1. Above 85W, it starts creeping up with the power increase.
>
> If I put some ferrites on the coax, but want to keep them indoors, is there
> a best location for them?
>
> Tnx,
> Barry W2UP

--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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Geoffrey Mackenzie-Kennedy-3

Re: K3 Hi SWR when sending CW

Barry,

If the problem is not solved by Vic's suggestion to "choke" your feeder,
could you please let us know the length of the coax feeder (in feet or
metres) between your fan dipole's feedpoint and your K3. Also how long is
the part of the feeder which is indoors?

73,

Geoff
LX2AO

On October 03, 2012 at 10:02 PM, Vic K2VCO wrote:

>I am not sure. But try it where it's convenient. Remember, for it to be
>effective at HF,
> you must have a few turns around a ferrite -- I'd say 4 or 5 turns should
> be enough for
> 12m. Just clamping a ferrite bead on a cable doesn't do much.

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Barry

Re: K3 Hi SWR when sending CW

I set up a common mode choke with 3 turns of coax through 2 ferrites, similar to the figure 2 on p. 18 of this document: http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf
I placed it outside, near the feedpoint. it did not change anything.

Geoff, I have 20-25 ft of coax outside and about 15 feet inside.

Barry W2UP

Mike Reublin

Re: K3 Hi SWR when sending CW

Barry,

I doubt your choke has anywhere near the inductance needed to do the
job. I think a careful read of the paper you reference will show what
you need to do.

73, Mike NF4L

On 10/3/12 7:50 PM, Barry wrote:

> I set up a common mode choke with 3 turns of coax through 2 ferrites, similar
> to the figure 2 on p. 18 of this document:
> http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf
> I placed it outside, near the feedpoint. it did not change anything.
>
> Geoff, I have 20-25 ft of coax outside and about 15 feet inside.
>
> Barry W2UP
>
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K3-Hi-SWR-when-sending-CW-tp7563645p7563674.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
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Vic Rosenthal

Re: K3 Hi SWR when sending CW

In reply to this post by Barry

40 feet is close to one wavelength on 12 meters, so that would be a 'troublesome' length
(a multiple of 1/2 wl).

If the choke is at the feedpoint, the feedline can pick up RF radiated from the antenna.
Perhaps try it near the rig.

Alternatively, try adding a 10 foot piece of coax to the feedline. Or, as Ron suggested,
try attaching a 10' piece of wire to the ground terminal of your rig. The end of the wire
should not be connected to anything and may develop a high RF voltage in operation.

On 10/3/2012 4:50 PM, Barry wrote:
> I set up a common mode choke with 3 turns of coax through 2 ferrites, similar
> to the figure 2 on p. 18 of this document:
> http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf
> I placed it outside, near the feedpoint. it did not change anything.
>
> Geoff, I have 20-25 ft of coax outside and about 15 feet inside.
>
> Barry W2UP

--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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