K2 KPA100 transmit test: fail

[Brian - N5BCN]

Hi All,

During the course of testing my recently built KPA100, I'm experiencing odd results on the cw transmit tests.  All tests, resistance, and voltage checks up until this point have been normal.

When transmitting cw into a 100 watt dummy load, things appear normal when transmitting in QRP mode (below 11 watts).  The strength of the cw signal on a separate receiver increases in strength as does the current draw up until the 11 watt level.

When the K2 Power level hits 11 watts, the high power relay clicks but the signal strength actually drops.  At 20 watts, the signal strength on the separate receiver is quieter than at 10 watts.  However, the current steadily increases and did not drop after the high power relay kicked in.

My approx current draw measurements at key down for various power levels (measured by my power supply's meter):

5 W    ~ 2 A
10 W  ~ 3 A
15 W  ~ 7 A
25 W  ~ 8 A
50 W  ~ 11 A
100 W ~16-17 A

My current draw during tune at less than 11 W is 343 mA (I have a number of option modules, fixed audio output mod, and Z10000 output buffer).

My current draw during tune at 11 W plus the fan on low is 545 mA.

I set the bias current so the current draw during tune at 11 W plus fan on low is about 950 mA, although it rises pretty quickly to above 1000 mA during tune.

As always, many thanks for your thoughts and suggestions.

73

N5BCN - Brian

[g3ymc]

I don't think you can conclude anything by monitoring the transmitter
with a separate nearby receiver. Have you tried measuring the power
output with a power meter or even an SWR meter? Your current readings
look just like what would be expected, and I suspect there is nothing
whatsoever wrong with your K2. Put a power meter or swr meter in series
with the dummy load and tell us what that says.

73 Dave G3YMC

On 6 May 2011 at 22:17, Brian - N5BCN wrote:

> When transmitting cw into a 100 watt dummy load, things appear normal
> when transmitting in QRP mode (below 11 watts).  The strength of the cw
> signal on a separate receiver increases in strength as does the current
> draw up until the 11 watt level.
>
> When the K2 Power level hits 11 watts, the high power relay clicks but
> the signal strength actually drops.  At 20 watts, the signal strength on
> the separate receiver is quieter than at 10 watts.  However, the current
> steadily increases and did not drop after the high power relay kicked
> in.
>
> My approx current draw measurements at key down for various power levels
> (measured by my power supply's meter):
>
> 5 W    ~ 2 A
> 10 W  ~ 3 A
> 15 W  ~ 7 A
> 25 W  ~ 8 A
> 50 W  ~ 11 A
> 100 W ~16-17 A
>

http://www.davesergeant.com

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[ac0h]

There's nothing wrong with the currents you're getting.

What does your Watt/SWR meter say when you change power?
Forget about how "loud" it sounds on the receiver. The econd receivers
AGC could be clamping down to make the signal sound the same. I'll
bet the S meter on the second receiver is going up.

To do transmitter testing you need a watt meter.


On Fri, 6 May 2011 22:17:56 -0700 (PDT)
Brian - N5BCN <[hidden email]> wrote:

> Hi All,
>
> During the course of testing my recently built KPA100, I'm
> experiencing odd results on the cw transmit tests.  All tests,
> resistance, and voltage checks up until this point have been normal.
>
> When transmitting cw into a 100 watt dummy load, things appear normal
> when transmitting in QRP mode (below 11 watts).  The strength of the
> cw signal on a separate receiver increases in strength as does the
> current draw up until the 11 watt level.
>
> When the K2 Power level hits 11 watts, the high power relay clicks
> but the signal strength actually drops.  At 20 watts, the signal
> strength on the separate receiver is quieter than at 10 watts.
> However, the current steadily increases and did not drop after the
> high power relay kicked in.
>
> My approx current draw measurements at key down for various power
> levels (measured by my power supply's meter):
>
> 5 W    ~ 2 A
> 10 W  ~ 3 A
> 15 W  ~ 7 A
> 25 W  ~ 8 A
> 50 W  ~ 11 A
> 100 W ~16-17 A
>
> My current draw during tune at less than 11 W is 343 mA (I have a
> number of option modules, fixed audio output mod, and Z10000 output
> buffer).
>
> My current draw during tune at 11 W plus the fan on low is 545 mA.
>
> I set the bias current so the current draw during tune at 11 W plus
> fan on low is about 950 mA, although it rises pretty quickly to above
> 1000 mA during tune.
>
> As always, many thanks for your thoughts and suggestions.
>
> 73
>
> N5BCN - Brian
>
> -----
> K2 #6800 KPA100/KAT100-2, KSB2, KAT2, KIO2, K160RX, KNB2, KAF2,
> LP-PAN/K2 w/ Pre-amp, SignaLink USB --
> View this message in context:
> http://elecraft.365791.n2.nabble.com/K2-KPA100-transmit-test-fail-tp6339548p6339548.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list Home:
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--
R. Kevin Stover
AC0H
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[Brian - N5BCN]

Hi all,

Thanks for the tips.  I might have taken the instructions too literally and not taken into account the receiver attenuating the signal.  However, I did confirm that AGC is turned off on the receiving radio, so that can be ruled out.

What is hard for me to understand is that the signal is loud and clear at 10 Watts, but drops off significantly at 11 Watts when the high power relay kicks in.  In my mind, there shouldn't be that much of a difference from 10 to 11 watts, one way or the other, to kick in any attenuating circuits or AGC.

Measuring the actual power will be my next step:

I'm relying on using a DL1 and taking the voltage measurements and converting it into power.  Now this has me worried that I'm using the wrong formula since I've seen at least two floating around on the reflector.  Here's what I'm using:

Power (Watts) = (2x((DC Volts + 0.15)^2))/50

Or: add 0.15 to the measured voltage, squaring the sum, multiplying the result by 2, and then dividing the final product by 50

Can you all verify that this is the correct Power formula for the DL1?

I'm using the DL1 up until about 25 watts, then I'm switching over to a 100 Watt dummy load.

73

N5BCN - Brian

[AC7AC]

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[Brian - N5BCN]

Hi all,

Here's the results of my power measurements:

Requested/Measured Power

5 W   -->  5.81 W
10 W --> 11.06 W
11 W --> 11.93 W
20 W --> 18.22 W
30 W --> 30.25 W

Looks pretty good to me.

The take away lesson is not to rely on a separate receiver to judge signal strength.

It's still a mystery to me why there is such a drop off in heard signal strength going from 10 to 11 W, but the wattmeter doesn't lie.

Thanks to all that helped out and putting my mind at ease!  Now on to testing on the rest of the bands.....

73

N5BCN - Brian

[Guy, K2AV]

What is most likely to have fooled you is that if you are transmitting
into a dummy load, then what you are hearing in an antenna-less nearby
second receiver is miscellaneous leakage from the K2 case.  This could
easily change when the termination of the low power stage changes its
termination from the dummy load to the input of the 100 watt stage.

Glad the direct measurement is FB.  Enjoy.   73, Guy.

On Sat, May 7, 2011 at 1:48 PM, Brian - N5BCN <[hidden email]> wrote:

> Hi all,
>
> Here's the results of my power measurements:
>
> Requested/Measured Power
>
> 5 W   -->  5.81 W
> 10 W --> 11.06 W
> 11 W --> 11.93 W
> 20 W --> 18.22 W
> 30 W --> 30.25 W
>
> Looks pretty good to me.
>
> The take away lesson is not to rely on a separate receiver to judge signal
> strength.
>
> It's still a mystery to me why there is such a drop off in heard signal
> strength going from 10 to 11 W, but the wattmeter doesn't lie.
>
> Thanks to all that helped out and putting my mind at ease!  Now on to
> testing on the rest of the bands.....
>
> 73
>
> N5BCN - Brian
>
> -----
> K2 #6800 KPA100/KAT100-2, KSB2, KAT2, KIO2, K160RX, KNB2, KAF2, LP-PAN/K2 w/ Pre-amp, SignaLink USB
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-KPA100-transmit-test-fail-tp6339548p6340510.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> 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
>

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