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Low power draw, low power out?

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Nick Waterman

Low power draw, low power out?

K2 #5209, Set at 5W, TUNE, I'm drawing only 1.0A, and should expect 1.3
to 1.6. Similarly, set at 10W TUNE, I'm drawing 1.02A, not 1.8 to 2. I'm
pretty sure I'm not putting out the power I should be, and DL1+DMM also
implies I'm only putting out about 2-4W, not 5-10. This would be at
7100kHz during 40m TX alignment. Is there some way to calibrate the
power output using DL1 and my DMM, or have I built something wrong?

--
"Nosey" Nick Waterman, G7RZQ, building k2#5209.
#include <stddisclaimer> [hidden email]
Design simplicity: It was developed on a shoe-string budget.
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Don Wilhelm-3

RE: Low power draw, low power out?

Nick,

With both low power out and low current drawn, there is clearly not enough
energy being developed by one of the transmit stages.

If you have not already, build up the RF Probe that came with the K2 kit and
do the Transmitter Signal Tracing steps detailed in the Troubleshooting
Appendix of the K2 manual. Once you locate the stage where the RF Voltage
level is significantly lower than that which is expected, the problem will
be just before that stage.

Once you have localized the problem to one stage, we can help you localize
the component at fault.

73,
Don W3FPR

> -----Original Message-----
>
> K2 #5209, Set at 5W, TUNE, I'm drawing only 1.0A, and should expect 1.3
> to 1.6. Similarly, set at 10W TUNE, I'm drawing 1.02A, not 1.8 to 2. I'm
> pretty sure I'm not putting out the power I should be, and DL1+DMM also
> implies I'm only putting out about 2-4W, not 5-10. This would be at
> 7100kHz during 40m TX alignment. Is there some way to calibrate the
> power output using DL1 and my DMM, or have I built something wrong?
>

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Jim Campbell-7

Re: Low power draw, low power out?

Don and Nick,

Doesn't the K2 drop the power to 2 watts during tune? Or am I thinking
of a K2 with the ATU?
I know that I was bitten by this once - I thought something was wrong
with my K2 when I was
trying to tune it up with a new antenna and I had a power meter in
line. I had set the K2 to 5
watts and it was only putting out 2 watts in tune.

Jim
W4BQP

Don Wilhelm wrote:

>Nick,
>
>With both low power out and low current drawn, there is clearly not enough
>energy being developed by one of the transmit stages.
>
>If you have not already, build up the RF Probe that came with the K2 kit and
>do the Transmitter Signal Tracing steps detailed in the Troubleshooting
>Appendix of the K2 manual. Once you locate the stage where the RF Voltage
>level is significantly lower than that which is expected, the problem will
>be just before that stage.
>
>Once you have localized the problem to one stage, we can help you localize
>the component at fault.
>
>73,
>Don W3FPR
>
>
>
>>-----Original Message-----
>>
>>K2 #5209, Set at 5W, TUNE, I'm drawing only 1.0A, and should expect 1.3
>>to 1.6. Similarly, set at 10W TUNE, I'm drawing 1.02A, not 1.8 to 2. I'm
>>pretty sure I'm not putting out the power I should be, and DL1+DMM also
>>implies I'm only putting out about 2-4W, not 5-10. This would be at
>>7100kHz during 40m TX alignment. Is there some way to calibrate the
>>power output using DL1 and my DMM, or have I built something wrong?
>>
>>
>>
>
>
>
>
>
>

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Don Wilhelm-3

RE: Low power draw, low power out?

Jim,

Of course you are correct - Nick did not mention that he had the ATU
installed, and since it is a newly built K2, I ASSUMED it was not - shame on
me!!

If the ATU is installed, pressing TUNE and DISPLAY at the same time will
produce full power output.

73,
Don W3FPR

> -----Original Message-----
>
> Don and Nick,
>
> Doesn't the K2 drop the power to 2 watts during tune? Or am I thinking
> of a K2 with the ATU?
> I know that I was bitten by this once - I thought something was wrong
> with my K2 when I was
> trying to tune it up with a new antenna and I had a power meter in
> line. I had set the K2 to 5
> watts and it was only putting out 2 watts in tune.
>
> Jim
> W4BQP
>
> Don Wilhelm wrote:
>
> >Nick,
> >
> >With both low power out and low current drawn, there is clearly
> not enough
> >energy being developed by one of the transmit stages.
> >
> >If you have not already, build up the RF Probe that came with
> the K2 kit and
> >do the Transmitter Signal Tracing steps detailed in the Troubleshooting
> >Appendix of the K2 manual. Once you locate the stage where the
> RF Voltage
> >level is significantly lower than that which is expected, the
> problem will
> >be just before that stage.
> >
> >Once you have localized the problem to one stage, we can help
> you localize
> >the component at fault.
> >
> >73,
> >Don W3FPR
> >
> >
> >
> >>-----Original Message-----
> >>
> >>K2 #5209, Set at 5W, TUNE, I'm drawing only 1.0A, and should expect 1.3
> >>to 1.6. Similarly, set at 10W TUNE, I'm drawing 1.02A, not 1.8 to 2. I'm
> >>pretty sure I'm not putting out the power I should be, and DL1+DMM also
> >>implies I'm only putting out about 2-4W, not 5-10. This would be at
> >>7100kHz during 40m TX alignment. Is there some way to calibrate the
> >>power output using DL1 and my DMM, or have I built something wrong?
> >>
> >>
> >>
> >
> >
> >
> >
> >
> >
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Nick Waterman

Re: Low power draw, low power out?

In reply to this post by Don Wilhelm-3

Don Wilhelm wrote:
> With both low power out and low current drawn, there is clearly not enough
> energy being developed by one of the transmit stages.

That's what I figured... or something confusing the power meter into
thinking it's kicking out far more than it really is (EG set to 5W, it
pretends it's producing about 7W, but is actually producing about 1W
according to DL1+DMM)

> If you have not already, build up the RF Probe that came with the K2 kit and

done

> do the Transmitter Signal Tracing steps detailed in the Troubleshooting
> Appendix of the K2 manual.

That seems to involve testing RX first, because of the shared circuitry,
which unfortunately seems to require 0.14V from a signal generator, and
my only signal generator is the Elecraft XG1, producing 50uV. :-(

Is it possible/sensible to test the shared circuits the other way
'round, whilst transmitting into DL1?

--
"Nosey" Nick Waterman, G7RZQ, k2 #5209.
#include <stddisclaimer> [hidden email]
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Don Wilhelm-3

RE: Low power draw, low power out?

Nick,

Read that paragraph with the undertanding that the most important shared
circuits are the PLL Reference oscillator, the VCO, and the BFO stages - and
they are also measured with the RF Probe even for receiver testing - the VCO
and BFO should also be tested for correct frequency using CAL FCTR. Yes,
the Bandpass filters, T/R switch, and Low Pass Filters are also shared, but
they will be tested with a signal 'the other way 'round' during the steps
indicated under Transmit Signal Tracing.

73,
Don W3FPR

> -----Original Message-----

> > do the Transmitter Signal Tracing steps detailed in the Troubleshooting
> > Appendix of the K2 manual.
>
> That seems to involve testing RX first, because of the shared circuitry,
> which unfortunately seems to require 0.14V from a signal generator, and
> my only signal generator is the Elecraft XG1, producing 50uV. :-(
>
> Is it possible/sensible to test the shared circuits the other way
> 'round, whilst transmitting into DL1?
>
>

Nick Waterman

Re: Low power draw, low power out?

In reply to this post by Don Wilhelm-3

Don Wilhelm wrote:
> With both low power out and low current drawn, there is clearly not enough
> energy being developed by one of the transmit stages.

OK, this is kinda annoying, and kinda good news.

[...]
> Once you have localized the problem to one stage, we can help you localize
> the component at fault.

Right, I've sussed it. the "component at fault" was the one between the
K2 and the DL1. I was using a stupidly long bit of antique co-ax. Seemed
like a good idea at the time - it was all I had, no other connectors, no
other patch leads, and I didn't fancy my chances of successfully
removing the connector from one end and making a 2m patch lead out of my
25m lead. :-/

I've now obtained a newer, nicer, cleaner, 2m lead, and I get the
expected 5W or 10W at the other end (slightly more actually, but not
enough to worry about).

Doesn't quite qualify for the "stupid mistakes" thread, but another
"stupid question that's not stupid unless you fail to answer it"...
Please educate me...

I can understand why the power at the DL1 end was low, but why was the
current drawn on the supply at the K2 end so low? If the dodgy old co-ax
had any sort of resistive loss, I'd imagine the K2 would still be trying
just as hard to pump out 5W or 10W, drawing just as much supply juice?

Is my dodgy cable more shorted, or more open than it should be, or is
this some other effect?

Thanks in advance, and hopefully you get a chance to scoff at me after I
scoffed at you for pointing out ohm's law as applied to human bodies and
different mains voltages ;-)

--
"Nosey" Nick Waterman, G7RZQ, k2 #5209.
#include <stddisclaimer> [hidden email]
It is ten o'clock; do you know where your processes are?
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Don Wilhelm-3

RE: Low power draw, low power out?

Nick,

In your original probelm description, you did not state how much power the
K2 display was indicating - and I would tend to believe it indicated that
the power was near the requested power value.

Of course, the actual power was not that high, but since the base K2 uses an
RF probe type detector to determine the power output level, it only responds
to the RF Voltage present, not the actual power. If the effective impedance
at the K2 end of the cable was high, the RF voltage would also be high
there, resulting in a lower actual power output than the K2 micropressor
thinks is present.

Bottom line, the RF probe detector can only report the power output properly
when the load resistance is known (and athe K2 assumes that is 50 ohms)- in
your case, because of the bad coax, the actual load resistance was unknown,
and the K2s calculation of output power would be invalid.

Hopefully that helps with your understanding of what was happening. I would
believe that your cable could have had high resistance connections (likely
corroded), but almost anything could have been possible since the electrical
characteristics of transmission lines is not straightforward at RF because
it depends on the frequency and the electrical length - recall that a
shorted transmission line will look like an open circuit at the end opposite
the short when it is a quarter wavelength (or multiple) long (and look like
a short at the near end at a frequency where it is a half wavelength long),
and in between it will appear electrically as an inductor or a capacitor.

73,
Don W3FPR

> -----Original Message-----
>
> Doesn't quite qualify for the "stupid mistakes" thread, but another
> "stupid question that's not stupid unless you fail to answer it"...
> Please educate me...
>
> I can understand why the power at the DL1 end was low, but why was the
> current drawn on the supply at the K2 end so low? If the dodgy old co-ax
> had any sort of resistive loss, I'd imagine the K2 would still be trying
> just as hard to pump out 5W or 10W, drawing just as much supply juice?
>
> Is my dodgy cable more shorted, or more open than it should be, or is
> this some other effect?
>
> Thanks in advance, and hopefully you get a chance to scoff at me after I
> scoffed at you for pointing out ohm's law as applied to human bodies and
> different mains voltages ;-)
>
> --
> "Nosey" Nick Waterman, G7RZQ, k2 #5209.
> #include <stddisclaimer> [hidden email]
> It is ten o'clock; do you know where your processes are?
>

Nick Waterman

Re: Low power draw, low power out?

Don Wilhelm wrote:
> In your original probelm description, you did not state how much power the
> K2 display was indicating - and I would tend to believe it indicated that
> the power was near the requested power value.

Think it was indicating HIGH actually. If I remember right, set at 5W,
it was indicating 7W, and I was measuring 1.1W.

I'll admit I'm not 100% sure, I didn't make enough notes. I could
reproduce it tonight if you like? I've not stripped and buried the ropey
old bit to make earth radials yet!

> recall that a
> shorted transmission line will look like an open circuit at the end opposite
> the short when it is a quarter wavelength (or multiple) long (and look like
> a short at the near end at a frequency where it is a half wavelength long),

Very true. I guess I could theoretically locate a fault by making
measurements at various frequencies, plotting graphs, and spotting mins
and maxes :-)

The old ropey bit was allegedly used for 10base2 networking in the past,
so SHOULD have been 50ohm, but what would be the expected behaviour if
it was actually 75ohm cable, and how could I prove if it was? It's not
as simple as measuring resistance of it, is it?

--
"Nosey" Nick Waterman, G7RZQ, K2 #5209.
#include <stddisclaimer> [hidden email]
Don't throw your computer out the window. Throw Windows out of your
computer.
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