FW: FW: [Elecraft] Kit arrived...

[Don Wilhelm]

Brett,

In TUNE, the power control loop is not as tight in the firmware portion 
of the loop as compared with normal keying.  The reason for that is to 
allow those using a manual tuner with their K2 to be able to adjust it 
without the power jumping quickly all over the place.

I am glad to hear that you had good results with the direct connections 
- that seems to verify that there is reactance (or other cause of a 
non-50 ohm purely resistive) condition somewhere in your setup - whether 
it is the coax, the external wattmeter or the dummy load itself we may 
never know, but you can check each one easily at the frequencies of 
interest with an antenna analyzer.  You may be able to borrow an AA to 
make those measurements if you do not have one.

You may find some frequency dependency between 1N5711 diodes (I have 
occasionally noticed that), but I do not consider it a problem because 
the power indication and control point are not more than a few tenths of 
a watt off at any point if all is normal.  Considering that most 
wattmeter specs are in the range of 5% to 20% OF THE FULL SCALE READING, 
the diode detector in the K2 is actually more accurate than most if the 
  load is 50 ohms resistive at the frequency of operation (measuring 
with an ohmmeter is not suficient, resistance at DC is not likely to be 
equal to the resistance at RF).

On your wattmeter accuracy, consider that even 5% of the 20 watt scale 
can result in an error of 1 watt at any power level - and even the Bird 
wattmeter is only that good immediately after calibration - you must 
expect such errors in your measuring equipment (check the spec sheet and 
  verify the measurement by independent means if you really want 
accuracy).  The Diode Detector is actually more accurate than most 
wattmeters, but it must be used with a known good non-reactive load.


73,
Don W3FPR

Brett gazdzinski wrote:
>  
> At lunch I did some more tests.
> I made a dummy load using 4 200 ohm 2 watt resistors, measured
> the resistance at 50 ohms, and plugged that right into the watt meter.
> The other end of the wattmeter plugged into the K2 antenna jack
> using adaptors.
> 
> I did the tx setup per the book, and now have at least 10 
> watts out on all bands, but it does roll off on the 
> higher bands. 10 meters might be below 10 watts, I don't
> remember. 80 and 40 meters do about 13 or 14 watts.
> 
> What the 'tune' button seems to do is measure the rf out
> per a set power (2 watts), display it, and when out of the tune mode,
> corrects the power so its right.
> You can really see it work on 80 and 40 meters, set the
> power knob to 2 watts, hi the tune button and the meters read 3 watts.
> Exit the tune mode with the power still set at 2 watts
> and hit the cw key and I get 2 watts out on the bar graph 
> and my meter.
> 
> 
> This works a treat on 80, 40, and 30 meters, the power output
> matches the knob set point and the bar graph very closely 
> AFTER you do the tune setup, at least up past 10 or 12 watts.
> 
> Above about 30 meters, the bar graph and the tune position start
> showing more power then the 3 watt meters I have do, I have some
> diwa little thing, a Kenwood average/pep meter, and the heathkit
> antenna tuner meter. All read the same.
> 
> The higher you go above 30 meters, the more the rig says its doing
> more power out then my meters do.
> 
> The RF sense circuit is after all the stages, its at the 
> antenna output basically..
> 
> I checked all the components in the rf output sense circuit and
> they are the correct values and measure correctly.
> I did not mess with the diode (D9 1N5711), nor can I verify
> its number without unsoldering it.
> 
> Maybe I should order a few 1N5711 diodes and see if there is
> any difference in how they act.
> 
> This sure is a fun rig to trouble shoot and play with, although
> I am still not over fond of computers in HF gear...
> 
> Brett
> N2DTS