[Elecraft] What should the power output of the K2 be?

[John A. Ross [Ecraft]]

> -----Original Message-----
> From: Ron D'Eau Claire [mailto:rondec at easystreet.com] 
> Sent: Sunday, July 16, 2006 9:00 PM
> To: 'John A. Ross [Ecraft]'; Elecraft at mailman.qth.net
> Subject: RE: [Elecraft] What should the power output of the K2 be?

> Welcome to the K2-club John! I built mine in 2000. It's a FB rig. 

Ron

Thanks, you are right, it is a very nice rig indeed and fantastic fun to
build and work on.
 
> The specified output of the K2 is at least 10 watts CW. The 
> actual output varies with the band. It is a function of the 
> overall transmitter path gain.
> It tends to peak about 40 meters, where most K2's will make 
> 15 watts output, or very close to it. Up on 10 meters is 
> where the overall gain is lowest and many K2's just barely 
> make the specified 10 watts output.

> Since you're still getting familiar with your K2, here's a 
> couple of things to remember:
> 
> 1) The POWER control sets the "requested" power output. The 
> K2 monitors the actual power output and adjusts the 
> transmitter gain as needed for what you've requested. The 
> control allows you to "request" any power up to 15 watts, but 
> you can't get that much on all bands. 

OK, that makes sense now. I was not sure if the sample/control loop was
doing something wrong. You never know when firmware has a part in it ;-) 
 
> 2) Because the POWER control circuitry is monitoring the 
> power output to determine how much gain the transmitter 
> circuits should have, the accuracy of the output power 
> setting depends upon how accurately the K2 measures its 
> output. A basic QRP K2 uses a simple RF voltmeter to monitor 
> the output. It is highly-dependent upon an accurate, 
> non-reactive 50-ohm load for good accuracy. Any significant 
> SWR at the transmitter output will affect it, and the actual 
> power output. The (KAT2, etc.) ATU's use a bridge circuit 
> that is a little more accurate, but can still be thrown off 
> by reactive terminations. 

I had not installed the ATU yet, Po was dumped into a DL-600 then checked
again on a 2955B so I am pretty sure the loads were OK.
 
> 3) If you change the POWER control setting you have to 
> transmit before the new power level takes effect, since the 
> K2 must sense the output RF to tell how to adjust the 
> circuits. That means that you may notice that the output is 
> nearly zero when you hit the first dit or dah after turning the K2 on.
> It'll immediately jump up to whatever you have the control 
> set for. The same is in reverse when you turn the power down. 
> The first time you touch the key the power will still be up 
> at the old higher level until there's RF for the circuit to sense. 

OK, clear now.
 
> 3) The K2 is rated at 10 watts PEP on SSB, regardless of how 
> much it will produce. That's  because the distortion 
> increases above 10 watts PEP in SSB mode. CW doesn't need a 
> linear amp, so it's not an issue when you're pounding brass, 
> but don't exceed 10 watts PEP on SSB on any band. 
> 
> 4) The Bargraph power display is in peak power, so it'll show 
> flickers at the PEP peaks instead of the average power like 
> most inexpensive external meters. That cause confusion 
> sometimes when the opr notices that his external meter is 
> wiggling around at 3 or 4 watts while his K2 shows 10 watt 
> peaks on SSB. That's normal. The external meter is showing 
> the average output, not the peak. 

Cheers Ron

All best

John

 
> 
> Ron AC7AC
> 
> 
> 
> -----Original Message-----
> 
> Hi all
> 
> I have been having great fun with the K2 but I am wondering 
> what the output should be?
> 
> 10W or 15W?
> 
> The Po control seems to indicate 15W should be possible.
> 
> The PA alignment seems OK, or at least as per the manual, 
> Po/current seems to match at the levels stated. 
> 
> But occasionally the built in detector seems to read a little 
> higher than the Po is set to and the full scale setting of 15 
> only seems to yield 11w or so.
> 
> As this is the only one I have built so far I am curious.
> 
> Any guidance appreciated.
> 
> John
> 
> 
>