Understand. I did pick up the DL1, and check the readings. They were
along the lines of what I experienced with the MFJ. But I could not
read it at a higher power, as it is only a 20w dummy load. But it
jibed with what I was seeing. I will get further readings with it and
a voltmeter.
Dave Wilburn
K4DGW
K2/100 - S/N 5982
Don Wilhelm wrote:
Dave,
I cannot really give you a quick positive answer - the real answer is
"it all depends". To give a positive answer would require that you
operate into a dummy load which is 50 ohms non-reactive at all
frequencies in question. One can measure the dummy load with an antenna
analyzer - expect to see 50 + j0 at all frequencies of interest for
reliable and repeatable results.
I do not generally trust any wattmeter (including an uncalibrated Bird)
to provide any greater than 20% of full scale accuracy. If the full
scale reading is 100 watts, then the error can be as great as 20 watts
at any point on its scale. A properly calibrated KPA100 wattmeter can
do better than that.
I find that with a good 50 ohm dummy load and an 100 MHz oscilloscope
with a 10X probe (probe rated for 100 MHz), I can calibrate the KPA100
wattmeter to less than 5% accuracy on bands below 20 meters - at higher
frequencies, the 'scope and probe rolloff will indicate lower than
expected results. But I can state that once calibrated, the KPA100
power calibration can be trusted to greater accuracy than the
run-of-the-mill wattmeters.
Using a good 50 ohm non-reactive dummy load and measuring the RF voltage
across it:
At 4 watts, the Peak to Peak RF voltage will be 40 volts.
At 10 watts the p-p RF voltage will be 63.25 volts
At 40 watts, the p-p RF voltage will be 126.5 volts
At 100 watts, the p-p RF voltage will be 200 volts.
My dummy load is a heat-sinked Caddock MP9100-50.0-1% resistor rated at
100 watts with zero length leads that has been measured flat at 50 ohms
up to 60 MHz.
Up to the frequency limits of my oscilloscope, I trust my dummy load and
the peak to peak voltage measurement to provide more accurate power
measurement than any wattmeter available. I find that, after
calibrating with these tools, the typical KPA100 power indications are
within 5% of the actual power output.
I can also say that the TelePost LP-200 (and I assume the LP100) will
also produce power readings which are within 5% of the actual power
after proper calibration. I cannot make such statements about the
accuracy of the more common wattmeters which spec their accuracy as a
percentage of the full scale reading. A Bird with a 100 watt slug that
has been recently calibrated will have an accuracy of 5% of full scale,
which is a 5 watt error anywhere on the scale - so a recently calibrated
Bird with a 100 watt slug will indicate anywhere between 5 watts and 15
watts for an actual power of 10 watts. One can do better with a
precision 50 ohm load and a 100 MHz oscilloscope.
OK, that is my wattmeter rant for this month!!!
73,
Don W3FPR
David Wilburn wrote:
After trying unsuccessfully to get email to take data in tabs, I ended
up just putting the information on my website. Sorry for the trouble.
I was playing with an assortment of power meters, and noticed my K2
was reading lower than I expected. The closes things I had to a
gauge, was an IC-703+ that had just been to the shop, and repaired,
thus I felt it was likely to be putting out 10w.
When I compared a Bird 43 with an element I picked up on line, and one
that came with it, it read a bit low. But when I used an MFJ949e, it
was right on. Gotta run with what I have.
So I checked out the K2/100 at what it said was 10w/53w/111w (Full
Power). And I got the results, that are displayed here;
http://www.k4dgw.com/k2.html
The 10w settings seem a little bit more dispersed than I would have
thought. The 10m, 12m & 20m 53w settings seem a bit low. Then at
what the rig says is 111w/Full Power, the rig seems even lower.
Do I need to go back through and run the power calibration, or should
I start troubleshooting?
I have a KAT100, that was powered down, and the power was taken out of
the back of the K2/100.
_______________________________________________
Elecraft mailing list
Post to: [email protected]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
