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K2 Frequency Shift On 80 Metres

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Ray G3XLG

K2 Frequency Shift On 80 Metres

Hi Elecrafters

I have recently bought a second-hand K2 with the KSB2 SSB module, the KPA100
100 watt amplifier & the KAT100-1 antenna tuner. Everything appears fine
running either QRP or 90+ watts on all bands except 80 metres. I am using an
off centre fed dipole (133') and the KAT100-1 antenna tuner to match.

Running in excess of 10 watts or so on 80 metres however when I switch the
microphone, the tuning apparently shifts to another frequency on the band.
The shift may be a few Hz or even a few 100Hz. The receiver is then on that
new frequency. Reducing power back to a QRP level, the transmitter &
receiver behave normally.

I guess there's something wrong with the 80 metre sections of the KPA100
and/or the KAT100-1.

Any clues of what I should check please?

73

Ray, G3XLG

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Ray G3XLG

Don Wilhelm-4

Re: K2 Frequency Shift On 80 Metres

Ray,

Before you do anything desperate, try the same thing into a dummy load.
If it does not happen with the dummy load, you can conclude that it is
RF getting into the K2 somehow.

Off-center fed antennas are notorious for creating RF in the shack
unless you take drastic steps to suppress it. The proper place to do
that is within the antenna system - maybe adding a balun at a point
outside the house where the feedline changes from balanced to unbalanced.

73,
Don W3FPR

On 5/2/2011 5:21 PM, Ray Spreadbury wrote:

> Hi Elecrafters
>
> I have recently bought a second-hand K2 with the KSB2 SSB module, the KPA100
> 100 watt amplifier& the KAT100-1 antenna tuner. Everything appears fine
> running either QRP or 90+ watts on all bands except 80 metres. I am using an
> off centre fed dipole (133') and the KAT100-1 antenna tuner to match.
>
> Running in excess of 10 watts or so on 80 metres however when I switch the
> microphone, the tuning apparently shifts to another frequency on the band.
> The shift may be a few Hz or even a few 100Hz. The receiver is then on that
> new frequency. Reducing power back to a QRP level, the transmitter&
> receiver behave normally.
>
> I guess there's something wrong with the 80 metre sections of the KPA100
> and/or the KAT100-1.
>
> Any clues of what I should check please?
>
> 73
>
> Ray, G3XLG
>
>
>
> ______________________________________________________________
> 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
>

Ray G3XLG

FW: K2 Frequency Shift On 80 Metres

In reply to this post by Ray G3XLG

-----Original Message-----
From: Ray Spreadbury [mailto:[hidden email]]
Sent: 03 May 2011 10:25
To: '[hidden email]'
Cc: '[hidden email]'
Subject: RE: [Elecraft] K2 Frequency Shift On 80 Metres

Hi Don & Dave

Thanks for the advice re RF in the shack.
I tried it with a dummy load on 80 metres & the problem disappeared (!!!!),
so good call both of you -I wasn't looking forward to trying to find a
problem in the rig & ordering replacement parts from Elecraft in USA!

The antenna is currently fed with RG213 cable and there is a 4:1 balun at
the feed point so as the impedance at the dipole is supposed to be about 300
ohms I thought it would be a reasonable match for the 50ohms cable?

Anyway the antenna was OK until yesterday, when I raised it a bit, but
obviously changed something to now cause the rf in the shack.

I might put up a balanced feeder to the OCFD or have a dedicated 80 metre
dipole instead, what do you think or do you have other suggestions ?

73 & many thanks
Ray, G3XLG

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: 02 May 2011 23:08
To: Ray Spreadbury
Cc: [hidden email]
Subject: Re: [Elecraft] K2 Frequency Shift On 80 Metres

Ray,

Before you do anything desperate, try the same thing into a dummy load.
If it does not happen with the dummy load, you can conclude that it is
RF getting into the K2 somehow.

Off-center fed antennas are notorious for creating RF in the shack
unless you take drastic steps to suppress it. The proper place to do
that is within the antenna system - maybe adding a balun at a point
outside the house where the feedline changes from balanced to unbalanced.

73,
Don W3FPR

On 5/2/2011 5:21 PM, Ray Spreadbury wrote:
> Hi Elecrafters
>
> I have recently bought a second-hand K2 with the KSB2 SSB module, the
KPA100
> 100 watt amplifier& the KAT100-1 antenna tuner. Everything appears fine
> running either QRP or 90+ watts on all bands except 80 metres. I am using
an
> off centre fed dipole (133') and the KAT100-1 antenna tuner to match.
>
> Running in excess of 10 watts or so on 80 metres however when I switch the
> microphone, the tuning apparently shifts to another frequency on the band.
> The shift may be a few Hz or even a few 100Hz. The receiver is then on
that

> new frequency. Reducing power back to a QRP level, the transmitter&
> receiver behave normally.
>
> I guess there's something wrong with the 80 metre sections of the KPA100
> and/or the KAT100-1.
>
> Any clues of what I should check please?
>
> 73
>
> Ray, G3XLG
>
>
>
> ______________________________________________________________
> 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
>

Ray G3XLG

AC7AC

Re: FW: K2 Frequency Shift On 80 Metres

CONTENTS DELETED

The author has deleted this message.

Guy, K2AV

Re: FW: K2 Frequency Shift On 80 Metres

In reply to this post by Ray G3XLG

A dipole can have a center impedance anywhere between 50 and 90 ohms,
depending on height above ground. Off-center feed impedances are
subject to wild variation depending on height. A guaranteed 300 ohm
feed at a certain offset is simply a myth.

Further, with off-center feed the issues with the feedline shield are
exacerbated, and switching short end to shield and long end to shield
connections make the antenna behave quite differently. This MIGHT
improve your feedline current problem, just depending on the
particulars.

If that were not enough, baluns which can behave with 50 ohm feed Z
and near resistive impedance become ineffective to the point of
invisible when confronted with largely reactive impedances in the 500
ohm plus range.

To be blunt, your setup is practically guaranteed to have high current
on the feedline. You would never get me to bet real money that it did
NOT. Sucker bet.

If you want to have a "hanging" network off center feed to multiband,
use a stepdown transformer THAT HAS NO CONNECTION between the high and
low side (isolation transformer) and use balanced feedline to the
ground. Use a second isolation transformer to go over to coax.
Unfortunately, nobody makes those, and they have to be fabricated at
home.

73, Guy.

On Tue, May 3, 2011 at 1:26 PM, Ray Spreadbury <[hidden email]> wrote:

> The antenna is currently fed with RG213 cable and there is a 4:1 balun at
> the feed point so as the impedance at the dipole is supposed to be about 300
> ohms I thought it would be a reasonable match for the 50ohms cable?
>
> Anyway the antenna was OK until yesterday, when I raised it a bit, but
> obviously changed something to now cause the rf in the shack.
______________________________________________________________
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Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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Fred Townsend

Re: FW: K2 Frequency Shift On 80 Metres

In reply to this post by Ray G3XLG

One minor point. If your feed point impeadance is really 300 ohms (folded
dipole) then you should be using a 6:1 balun.

73, Fred, AE6QL

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Ray Spreadbury
Sent: Tuesday, May 03, 2011 10:26 AM
To: [hidden email]
Subject: [Elecraft] FW: K2 Frequency Shift On 80 Metres

-----Original Message-----
From: Ray Spreadbury [mailto:[hidden email]]
Sent: 03 May 2011 10:25
To: '[hidden email]'
Cc: '[hidden email]'
Subject: RE: [Elecraft] K2 Frequency Shift On 80 Metres

Hi Don & Dave

Thanks for the advice re RF in the shack.
I tried it with a dummy load on 80 metres & the problem disappeared (!!!!),
so good call both of you -I wasn't looking forward to trying to find a
problem in the rig & ordering replacement parts from Elecraft in USA!

The antenna is currently fed with RG213 cable and there is a 4:1 balun at
the feed point so as the impedance at the dipole is supposed to be about 300
ohms I thought it would be a reasonable match for the 50ohms cable?

Anyway the antenna was OK until yesterday, when I raised it a bit, but
obviously changed something to now cause the rf in the shack.

I might put up a balanced feeder to the OCFD or have a dedicated 80 metre
dipole instead, what do you think or do you have other suggestions ?

73 & many thanks
Ray, G3XLG

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: 02 May 2011 23:08
To: Ray Spreadbury
Cc: [hidden email]
Subject: Re: [Elecraft] K2 Frequency Shift On 80 Metres

Ray,

Before you do anything desperate, try the same thing into a dummy load.
If it does not happen with the dummy load, you can conclude that it is RF
getting into the K2 somehow.

Off-center fed antennas are notorious for creating RF in the shack unless
you take drastic steps to suppress it. The proper place to do that is
within the antenna system - maybe adding a balun at a point outside the
house where the feedline changes from balanced to unbalanced.

73,
Don W3FPR

On 5/2/2011 5:21 PM, Ray Spreadbury wrote:
> Hi Elecrafters
>
> I have recently bought a second-hand K2 with the KSB2 SSB module, the
KPA100
> 100 watt amplifier& the KAT100-1 antenna tuner. Everything appears
> fine running either QRP or 90+ watts on all bands except 80 metres. I
> am using
an
> off centre fed dipole (133') and the KAT100-1 antenna tuner to match.
>
> Running in excess of 10 watts or so on 80 metres however when I switch
> the microphone, the tuning apparently shifts to another frequency on the
band.
> The shift may be a few Hz or even a few 100Hz. The receiver is then on
that

> new frequency. Reducing power back to a QRP level, the transmitter&
> receiver behave normally.
>
> I guess there's something wrong with the 80 metre sections of the
> KPA100 and/or the KAT100-1.
>
> Any clues of what I should check please?
>
> 73
>
> Ray, G3XLG
>
>
>
> ______________________________________________________________
> 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
>

______________________________________________________________
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

______________________________________________________________
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