K3: Now I've heard everything

[n7ws]

Having just acquired an RFSpace SDR-IQ I thought I'd take a look at the K3's transmit IMD, particularly with respect to input voltage and output power.

So I engaged the 2-tone generator, connected a dummy load and proceeded to take a look at the output spectrum.

I haven't gotten very far with this because 1) the IMD is apparently temperature sensitive and drifts, becoming a moving target and 2) I can hear the two tones acoustically emanating from the PA. The level is somewhat proportional to RF power and goes away completely when the power is reduced to the point where the PA drops out.

Can anyone else confirm or deny that their PA talks back to them?

Wes  N7WS





     
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[Kok Chen]

On Jul 12, 2010, at 7/12    10:25 AM, Wes Stewart wrote:

> I haven't gotten very far with this because 1) the IMD is apparently  
> temperature sensitive and drifts, becoming a moving target

For what its worth, when I ran close-spaced IMD measurements (*very*  
closed spaced -- the BPSK31 idle tone :-), I did not notice much  
drifting in IMD values once I got the "ALC" meter up to 4 to 5 bars.  
The transmit IMD will vary a little (I saw 2 dB) depending on the  
input drive, even while maintaining a constant 5 bars on the "ALC"  
meter.   But the reading was stable as long as I kept the drive stable.

Also, are you systematically tapping the signal from the dummy load?  
If you are just using a short pickup wire on the antenna port of the  
SQR-IQ, you could be seeing other artifacts.  I had used Elecraft's  
directional coupler kit (no one should be without one :-) plus oodles  
of attenuation to directly feed the measurement receiver.

73
Chen, W7AY

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[Joe Subich, W4TV-4]

 > Can anyone else confirm or deny that their PA talks back to them?

Does not do it here.  I've made the same tests using the SDR-IQ
with the directional coupler from my LP-100 and additional
attenuation for the input to the SDR-IQ.  IMD was stable as long
as the power level was stable (Keep ALC at 5 bars and adjust power
with the power control) and not particularly temperature sensitive
although I did not push long key down times.

I also made measurements of transmit image (+/- 30 KHz) using the
FM filter for transmit in SSB and CW (no measurable image within
the range of the SDR-IQ) using the same test set-up.

The only thing I found necessary was to keep the SDR-IQ and K3
separated (could not leave the SDR-IQ set on the top of the K3)
and use good quality cable between the SDR-IQ and directional
coupler to limit any direct pick-up.

73,

    ... Joe, W4TV

On 7/12/2010 1:25 PM, Wes Stewart wrote:

> Having just acquired an RFSpace SDR-IQ I thought I'd take a look at
> the K3's transmit IMD, particularly with respect to input voltage and
> output power.
>
> So I engaged the 2-tone generator, connected a dummy load and
> proceeded to take a look at the output spectrum.
>
> I haven't gotten very far with this because 1) the IMD is apparently
> temperature sensitive and drifts, becoming a moving target and 2) I
> can hear the two tones acoustically emanating from the PA. The level
> is somewhat proportional to RF power and goes away completely when
> the power is reduced to the point where the PA drops out.
>
> Can anyone else confirm or deny that their PA talks back to them?
>
> Wes  N7WS
>
>
>
>
>
>
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[n7ws]

Thanks Joe and Chen,

I'm using a series of power and stepped attenuators to couple the K3 to the SDR-IQ.  The input attenuator is underrated a bit so I've been necessarily limiting transmit time at the higher levels.  When time permits, I'll drag in a directional couple from storage and use it.

Chen does your K3 PA talk back?

Wes

--- On Mon, 7/12/10, Joe Subich, W4TV <[hidden email]> wrote:

 > Can anyone else confirm or deny that their PA talks back to them?

Does not do it here.  I've made the same tests
 using the SDR-IQ
with the directional coupler from my LP-100 and additional
attenuation for the input to the SDR-IQ.  IMD was stable as long
as the power level was stable (Keep ALC at 5 bars and adjust power
with the power control) and not particularly temperature sensitive
although I did not push long key down times.

I also made measurements of transmit image (+/- 30 KHz) using the
FM filter for transmit in SSB and CW (no measurable image within
the range of the SDR-IQ) using the same test set-up.

The only thing I found necessary was to keep the SDR-IQ and K3
separated (could not leave the SDR-IQ set on the top of the K3)
and use good quality cable between the SDR-IQ and directional
coupler to limit any direct pick-up.

73,

    ... Joe, W4TV



--- On Mon, 7/12/10, Kok Chen <[hidden email]>
 wrote:

For
what its worth, when I ran close-spaced IMD measurements (*very* closed
spaced -- the BPSK31 idle tone :-), I did not notice much drifting in
IMD values once I got the "ALC" meter up to 4 to 5 bars.  The transmit
IMD will vary a little (I saw 2 dB) depending on the input drive, even
while maintaining a constant 5 bars on the "ALC" meter.   But the
reading was stable as long as I kept the drive stable.

Also, are
you systematically tapping the signal from the dummy load?  If you are
just using a short pickup wire on the antenna port of the SQR-IQ, you
could be seeing other artifacts.  I had used Elecraft's directional
coupler kit (no one should be without one :-) plus oodles of attenuation
 to directly feed the measurement receiver.

73
Chen, W7AY





     
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[Kok Chen]

On Jul 14, 2010, at 10:31 AM, Wes Stewart wrote:

> Chen does your K3 PA talk back?

Nothing that I can hear over my tinnitus, Wes.

73
Chen, W7AY

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[Joe Planisky]

Hi Wes,

Meant to reply earlier but got distracted.

Yes, my PA definitely "sings" with the 2-tone generator on.  Like  
yours it's somewhat dependent on power level.  Unlike yours, I can  
hear mine down to about 2.0w (albeit at a reduced level when the PA  
drops out.)

73
--
Joe KB8AP

On Jul 12, 2010, at 10:25 AM, Wes Stewart wrote:

> ...I can hear the two tones acoustically emanating from the PA. The  
> level is somewhat proportional to RF power and goes away completely  
> when the power is reduced to the point where the PA drops out.
>
> Can anyone else confirm or deny that their PA talks back to them?
>
> Wes  N7WS

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[n7ws]

Hi Joe,

One more question, do you have the K3STFNR installed?

Wes

--- On Wed, 7/14/10, Joe Planisky <[hidden email]> wrote:

Hi Wes,

Meant to reply earlier but got distracted.

Yes, my PA definitely "sings" with the 2-tone generator on.  Like yours it's somewhat dependent on power level.  Unlike yours, I can hear mine down to about 2.0w (albeit at a reduced level when the PA drops out.)

73
--
Joe KB8AP





     
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