K2 power out increase with higher SWR

[Gary D Krause]

I've noticed that with my K2 the power increases with highter swr.  While
adjusting the tuner as the swr goes up the power increases and sometimes
doubles and when going down the power goes down.  Just last night, I was
running 5 watts and switched to another antenna. I forgot to tune the antenna
before transmitting and the transmit power went from 5 to 10 watts because, of
the higher swr.  I've noticed this before.  Is this normal?  It seems to make
more sense for the opposite to happen.

Gary, N7HTS



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[Thom LaCosta]

On Wed, 1 Aug 2007, Gary D Krause wrote:

> I've noticed that with my K2 the power increases with highter swr.  While
> adjusting the tuner as the swr goes up the power increases and sometimes
> doubles and when going down the power goes down.  Just last night, I was
> running 5 watts and switched to another antenna. I forgot to tune the antenna
> before transmitting and the transmit power went from 5 to 10 watts because,
> of the higher swr.  I've noticed this before.  Is this normal?  It seems to
> make more sense for the opposite to happen.
>

Simply another example of mojo.  The K2, realizing that since you have more loss
with higher swr, it craftily ups the power to compensate for the loss.

Rumor has it that the K3 has hidden "appendages", that reach out and trim/add to
the antenna should it detect a mismatch.

Elecraft has denied production of the "Bad" K3 which can inflict pain and other
torture on lids you may encounter.

May the Mojo be with you.

Thom - k3hrn,EIEIO
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[Don Ehrlich]

It is a normal indication but ... the power is not actually increasing.  The
power display is only accurate when feeding a tuned ( 50 ohm resistive )
load.  The untuned antenna is causing the reading to be in error.

Don  K7FJ


> I've noticed that with my K2 the power increases with highter swr.  While
> adjusting the tuner as the swr goes up the power increases and sometimes
> doubles and when going down the power goes down.  Just last night, I was
> running 5 watts and switched to another antenna. I forgot to tune the
> antenna before transmitting and the transmit power went from 5 to 10 watts
> because, of the higher swr.  I've noticed this before.  Is this normal?
> It seems to make more sense for the opposite to happen.
>
> Gary, N7HTS

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[Don Wilhelm-3]

Gary,

If you are talking of the basic K2 without the KAT2, KAT100 or KPA100,
then the answer is that may be normal.  The basic K2 measures the RF
voltage across the antenna jack, and reports the 'power' by computing as
though the load were 50 ohms resistive.  If the complex impedance
produced by the antenna is higher than 50 ohms, the RF voltage will be
higher - you will only observe that during a TUNE - during normal
operation, the K2 will level its power to produce the amount of RF
voltage that is indicated by the power requested control - again
computed as though the load were 50 ohms resistive.

With the KAT2, KPA100, and KAT100, there is a true wattmeter in the
circuit that is used - if it is properly balanced and calibrated, you
should not notice this increase in power with a higher SWR.

73,
Don W3FPR

Gary D Krause wrote:
> I've noticed that with my K2 the power increases with highter swr.  
> While adjusting the tuner as the swr goes up the power increases and
> sometimes doubles and when going down the power goes down.  Just last
> night, I was running 5 watts and switched to another antenna. I forgot
> to tune the antenna before transmitting and the transmit power went from
> 5 to 10 watts because, of the higher swr.  I've noticed this before.  Is
> this normal?  It seems to make more sense for the opposite to happen.
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[Julian, G4ILO]

On 8/1/07, Thom LaCosta <[hidden email]> wrote:
>
> Elecraft has denied production of the "Bad" K3 which can inflict pain and other
> torture on lids you may encounter.

But is it true the firmware has got so much intelligence it can insert
comments of its own into CW and data mode contacts?
--
Julian, G4ILO K2 s/n: 392  K3 s/n: ???
G4ILO's Shack: www.g4ilo.com
Ham-Directory: www.ham-directory.com
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[Thom LaCosta]

On Wed, 1 Aug 2007, Julian G4ILO wrote:

> On 8/1/07, Thom LaCosta <[hidden email]> wrote:
>>
>> Elecraft has denied production of the "Bad" K3 which can inflict pain and other
>> torture on lids you may encounter.
>
> But is it true the firmware has got so much intelligence it can insert
> comments of its own into CW and data mode contacts?

Aptos will not confirm...but I heard they looking for female K3 ops to
participate in the DOM Look Ahead tests.  Rumor has it that once those tests are
finished, the production "Reach out and touch" module will be offered.


Thom - k3hrn,EIEIO
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[Brett gazdzinski-2]

 
If you tune the antenna tuner each way, you should
see the power go both up and down from say 5 watts.

If I tune the heathkit antenna tuners roller inductor
 (before adding the built in tuner to the K2), one way
would increase the K2 power display, the other way would lower it.

Since the K2 only reads voltage, a higher power would be higher
voltage, not a good thing for the caps and other parts in the output
section....


Brett
N2DTS

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Gary D Krause
> Sent: Wednesday, August 01, 2007 11:57 AM
> To: Elecraft
> Subject: [Elecraft] K2 power out increase with higher SWR
>
> I've noticed that with my K2 the power increases with highter
> swr.  While
> adjusting the tuner as the swr goes up the power increases
> and sometimes
> doubles and when going down the power goes down.  Just last
> night, I was
> running 5 watts and switched to another antenna. I forgot to
> tune the antenna
> before transmitting and the transmit power went from 5 to 10
> watts because, of
> the higher swr.  I've noticed this before.  Is this normal?  
> It seems to make
> more sense for the opposite to happen.
>
> Gary, N7HTS
>
>
>
> _______________________________________________
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>
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> Elecraft web page: http://www.elecraft.com
>

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[Gary D Krause]

Oh, well that explains it then.  I forgot about the Mojo.  That's a pretty
cool idea compensating for the loss in power like that.  I wonder how much
power I could get out of it if I used my body as an antenna?  The K2 is full
of surprises. :-)

Gary, N7HTS

>
> Simply another example of mojo.  The K2, realizing that since you have more
>loss with higher swr, it craftily ups the power to compensate for the loss.
>
> Rumor has it that the K3 has hidden "appendages", that reach out and
>trim/add to the antenna should it detect a mismatch.
>
> Elecraft has denied production of the "Bad" K3 which can inflict pain and
>other torture on lids you may encounter.
>
> May the Mojo be with you.
>
> Thom - k3hrn,EIEIO
> Email, Internet, Electronic Information Officer
>
> www.baltimorehon.com/                    Home of the Baltimore Lexicon
> www.tlchost.net/hosting/                 Web Hosting as low as 3.49/month

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[David Woolley (E.L)]

Gary D Krause wrote:
> I've
> noticed that with my K2 the power increases with highter swr.  While
> adjusting the tuner as the swr goes up the power increases and sometimes
> doubles and when going down the power goes down.  Just last night, I was
...
> watts because, of the higher swr.  I've noticed this before.  Is this
> normal?  It seems to make more sense for the opposite to happen.

Even if true power were being measured, I think you would be making the
mistake of assuming that the output impedance of the PA is 50 ohms.
Whilst my RF engineering knowledge isn't good enough, and I don't have
SPICE tools, to work out the value in this case, it is almost certainly
not true here.  In general PAs are not operated according to the maximum
power transfer theorem, even though many simple text books may claim so.

Also, SWR is a rather crude measure.  It's a simple mathematical
transformation of the ratio of forward and reverse power flows into a
measure that was probably only directly meaningful with very old methods
of measuring it.  As a figure of merit, the straight ratio would be just
as good.

Neither really tell you what the threat to your PA is, because they
ignore phase, because it is difficult to measure.  In particular, the
same SWR value with different phases might cause both increases and
decreases in net forward power.  Also the same SWR with different phases
could result in either voltage or current breakdown.

Incidentally, for most combined SWR power meters, the power measurement
is forward power, which exceeds the net forward power by the value of
the reverse power.  As a result, they overestimate transmitted power
when the SWR is not 1:1.  I don't know if the KAT2 firmware applies this
correction.


--
David Woolley
Emails are not formal business letters, whatever businesses may want.
RFC1855 says there should be an address here, but, in a world of spam,
that is no longer good advice, as archive address hiding may not work.
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