[Elecraft] K3 pwr out on digimodes

[hb9ari]

Dave,

I followed the problem you described on the group and this is the reason
i do some measurements around the power output because i was a little 
bit anxious!

At the beginning, my only 2 "ham" references were my MiniVNA output
(calibrated at my office at -2.04 dBm , 7.040MHz with 50 Ohms load) and
a 25W MCE/Weinschel bi-directional attenuator (calibrated as 50.1 Ohms and
29.83 dB attenuation) These 2 "references" have permitted to "verify" 
the "coupling"
factor of my LP-100A RF Sensor as 29.12 db for the 29.1 dB used by Larry!!
The LP-100A is now my 3rd "ham" reference instrument.
I also do some peak/average power ratio measurements for different digi 
modes and
results were ok between 0 db (FSK) and 15 dB (EasyPAL during digital 
picture transmission)
(the 2 extremes "tested" with software running in my PC).
After that, i do also power output measurements with and without ALC 
(with a lot of caution!)
for the K3 and.found something like ~ 1dB more power without ALC (ONLY 
for TESTING!)
With ALC ON, i measured  a mean error < +/- 0.1 dB between 1W and 12W and
< 0.45 dB between 13W and 20W. (may be due to the activation of the PA?)
During all these measurements, i have my "old" TDS 220 scope (1Gs/s 
100MHz BW) connected
at my -30dB "dummy load" output for monitoring in case of distortion 
and/or oscillation but
all was ok and i'm very satisfied with these results.The measured P-P 
values divided by 2*SQR(2)
gave me a good confirmation for the RMS value.
One more (and last precision...), all measurements were done with a 
sinus audio single tone, except
for peak/average ratio measurements done with some available digi modes.

73 QRO fr Rudolf, HB9ARI


Dave G4AON wrote:
> Rudolf, the problem is not one associated with the accuracy of the K3
> meter, but one of the ALC being fairly "slack" with the end result that
> a fluctuating audio input from speech or from a sound card on many data
> modes results in widely varying power, unfortunately often exceeding the
> level set by the power control. An oscilloscope or peak reading
> Wattmeter, such as the LP-100, will catch and display the peaks far
> better than can be read from the K3 meter.
>
> I hope Elecraft continue their efforts to fix this irritating problem,
> as not only does it make the use of some digital modes tedious, but
> running a linear on SSB results in power levels which often exceed the
> legal power limit - even when being very careful to set the drive level
> (UK power limit 400W, using an Acom 1000 which does not use ALC feedback).
>
> 73 Dave, G4AON
> K3/100 #80
> -------------
> <SNIP>
>
> I've done some measurements some time ago with my K3 #1212 and i had the
> following values:
>
> K3 power set to 20W, f=7.040MHz 25W 50 Ohms dummy load MCE/Weinschel
> LP-100A Wattmeter
> mode USB 1 kHz sine audio at rear line-input, level adjusted to have the
> desired ALC bar configuration
> <SNIP>
> Rudolf, HB9ARI
>
> _______________________________________________
> Elecraft mailing list
> Post to: Elecraft at mailman.qth.net
> 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
>
>