Ron,

I just went through this scenario. With the help of Don Wilhelm I was able

accurately measure my power out on my KX1 and K3.

I first used a homebrew load with "free" resistors given away at a club

meeting. They only worked at low frequencies. At 20 meters the SWR to far

off to be of use!

I bought an Elecraft DL1 because it uses one of the correct types of

resistors for this application and it has a built in VDC test point!

The only thing to be wary of is that the DL1 test point is at the 25 ohm

point in the series of resistors!!!

Don's formula (and mine) differs from that found in the DL1 manual.

Elecraft:

P(in watts) = ((Volts * 1.414) +(.15))^2 / 50

Don:

P(in watts) = ((Volts) + (diode drop))^2 / 25

Jack:

P(in watts) = (((Volts) + (diode drop) * 2)) / (square root of 2)))^2 / 50

There are 3 points to be aware of.

1. Use the square root of 2 and not the 1.414 figure.

2. Measure your diode drop.

3. Combine the drop with the VDC before doing any other calculations.

4. If you do not use Don's formula, DIVIDE by the square root of 2.

The Schottky diode in my DL1 measures .330 mv.

A 1N34a (germanium diode) has a drop of about .3 volts. A Schottky's drop

is a little more but offers more linearity!

In any case, the VDC voltage must be divided by the square root of 2 to get

the RMS. In other words the VDC(0-Peak) is 1.414(approximately) times the

RMS voltage

If you measure the VDC at the 50 ohm point then my formula becomes:

P(in watts) = ((VDC + (diode drop)) / (square root of 2))^2 /50

After getting an accurate measurement of my KX1's power I found that the KX1

ATU was showing values that were too high. By adjusting C9 and R1 I was able

to get the KX1 and the DL1 to agree!

BTW, I also used the DL1 to calibrate my K3 at low power. Now the K3, my DL1

and my Versa Tuner V all agree!

-----Original Message-----

.....snip.....

I've now completed the construction of the basic KX1 and would like to have

a fairly reasonable measurement of the output power on 20M and 40M

I have a very decent dummy load but do not have a very accurate RF Power

meter. I do have a decent DMM and could measure the voltage drop across the

50 ohm dummy load - I'm not sure how accurate the DMM would be at 7 or 14

MHZ.

Is there a recommended method to measure the power output without an RF

power meter ?

Thanks in advance,

Ron, AC2C

.....snip....

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