QUESTION about TX CURRANT LIMIT, and absolute maximum output power

[WA2JJH]

I saw in one of the menus, something about setting a max TX CURRANT  draw.
Minimum was 3 AMPS. Maximum can be set for 5.02 amps max TX draw.
 
  Yes, I do see why many k2 portable users would want to have maximum  PA
eff. when using 5W CW. Battery life can provide many cw qso's.
 
  My concerns are different. I always use the K2 at maximum  output(15++W)
What is the maximum rf out can you get. The finals in that configuration  
should be able to
output almost 25W pep. True, you will no longer make commercial spec at 25W  
pep.
A good heat sink would be required too.
 
   Anybody push the envelope? I find the TX range on CW between  15 W and a
full power 100 W rig almost nil!
 
   On SSB, the range differential is more pronounced.
I have installed in the top cover, a single MRF-453 50 W PA. This was an  old
RF PA I had in my junk box.
   Results have been not too great. I can get 30-45 W pep. I used  a laptop
computer lithium battery for good batt life at 40W.
 
   However this single ended bipolar amp will not meet FCC spec  on spurs and
two-tone IMD.
 
    So, I must go back to my first idea. See if I can get  25W pep SSB out of
the k2's mil spec
final.
 
Any feedback welcome, tnx    de  MIKE   WA2JJH                                
                                                                             
                                                                             
                                                                             
                                                                             
                                                                             
                                                                             
       
 
 
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
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

[Ron D'Eau Claire-2]

WA2JJH wrote:
I find the TX range on CW between  15 W and a full power 100 W rig almost
nil!... See if I can get  25W pep SSB out of the k2's mil spec final.

--------------

You'll need to redesign the output filters as well. They assume a certain
collector impedance in the finals and that is a function of the power level
and the K2's filters were designed for 10 watts.  

The impedance issue also affects the IMD in the finals. That's why Elecraft
says not to exceed 10 watts PEP SSB even though running the power control up
for as much as it'll deliver on CW is okay. Linearity isn't as important in
CW. Lack of linearity will only affect the keying envelope somewhat.

The difference between 10 and 100 watts is 10 dB. That's 1.5 to 3 "S" units
on most receivers. The difference between 25 and 100 watts is 6 dB or 1 to 2
"S" units on most receivers.  

That's a big difference when signals are near the noise level or QRM is an
issue. Otherwise it's not needed, as the QRP and QRPp stations demonstrate
every day.

SSB suffers from lower signal to noise ratios compared to CW at any power
level, because the SSB signal occupies wider bandwidths. Narrower bandwidth
with a given power = better S/N ratio. That's why closing down the CW
filters helps pop a weak CW signal up out of the QRN. Since SSB needs 2+ kHz
bandwidth for intelligible audio, the only fix to a weak signal is more
power (and/or the use of some advanced filtering that doesn't restrict the
bandwidth further such as the KDSP2 offers). The basic K2 SSB filter is
already designed for a bandwidth of just over 2 kHz - the minimum for
intelligible audio - to gain the best possible S/N ratio our of the SSB
signal.  

Ron AC7AC  


_______________________________________________
Elecraft mailing list
Post to: [hidden email]
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