[Elecraft] K2 power output level fluctuation

[Johnny Siu]

Hello George,
With due respect to Don's valuable advice, you could also consider KXPA100 stand alone linear amplifier.  Then you have the flexibility of using the linear with other non-elecraft radios.
If you do not need full 100w, Hardrock HR50 linear amplifier is another one very value for money.  This one also let you have the joy of kit building Welcome to HobbyPCB Store 

73
Johnny VR2XMC
  
|   |
|   |   |   |   |   |
| Welcome to HobbyPCB StoreHobbyPCB is your source for innovative amateur radio products. We design and manufacturer the HARDROCK-50 HF Power Amp with integrated antenna tuner (ATU). |
|  |
| 查看於 www.hobbypcb.com | Yahoo 預覽 |
|  |
|   |

       寄件人︰ Don Wilhelm <w3fpr at embarqmail.com>
 收件人︰ George Kuehn <imjustgeorge at comcast.net>; elecraft at mailman.qth.net 
 傳送日期︰ 2015年04月24日 (週五) 10:21 AM
 主題︰ Re: [Elecraft] K2 power output level fluctuation
   
George,

That is a relatively small change in power output.  I do not think you 
will have a problem with it in normal operation.
Keep in mind that the K2 power control resets after a band change or a 
change in the requested power setting - the output starts out low and 
then increases to the requested setting.  That is done purposefully to 
prevent overshoot.

The initial increase you see is likely a result of starting out at a 
lower power level and then increasing.  It takes a couple dit times to 
come up to the requested power.

I have no suggestions on the homebrew amplifier other than to say that 
if you include a closed loop power control as is done in the KPA100, you 
may find it easier to simply add the real KPA100 - the KPA100 wattmeter 
circuit is scaled for high power operation and eliminates the scaling 
for low power operation - all that is controlled by the KPA100 
firmware.  I doubt your homebrew amplifier can achieve that level of 
integration with the K2 at a price less than the KPA100.

73,
Don W3FPR

On 4/23/2015 8:43 PM, George Kuehn wrote:
> I know from the forum that a K2 will show a power increase over a given setting if left in tune for an extended time as a consequence of the final transistors heating up.  That makes sense from what I’m seeing here.  The effect is greater at higher power settings although not proportionally higher as my set level increases.  I’m just wondering if the amount of shift I’m seeing is normal.
>
> Here’s what I’m seeing:  With my K2 operating into a zero SWR 80 watt (nominal) dummy, the observed increase both on the K2 display as well as on my computer monitored W2 wattmeter tends to be 1.5 watts or less over a ten second period.  The initial increase happens quite quickly and then slows.  It is difficult to confirm, as I don’t want to leave the rig in tune for an extended period, but it seems like the system stabilizes or at least increases very slowly once it passes the initial increase. Operating CW at 12-15 wpm into the dummy, the power output fluctuates but doesn’t exhibit a tendency to rise more than noted above, given a 50/50% sending/receiving behavior.
>
> My observations were made at 7.100 MHz with power settings at 2, 5 and 10 watts.  The K2 was connected by short length coax leads through the 200 watt W2 Wattmeter  Directional Coupler into a dummy consisting of a set of 4 series-parallel 50 ohm Caddock MP820 thick film non-inductive resistors mounted on a fan-cooled heatsink (nominal 80 watt rating) that shows zero SWR from 160 meters through 24 MHz and 1.1 SWR thereafter though 6 meters as measured with an MFJ 259B Antenna Analyzer.  The resistors remain cool to the touch even after extensive testing.
>
> So, do I need to be concerned about the power increase behavior I’m seeing?
>
> I do wish to operate digital modes such as PSK31, Hellschreiber, and similar modes where the duty cycle is higher than casual CW or SSB phone.  Assuming normal power level control in the K2, is there a power level setting recommended to protect the final in this type of operation?
>
> In the future, I plan to homebrew a linear amplifier to give me PEP output in the 80 to 100 watt range primarily for SSB.  I was hoping not to have to create gain control back into the K2 from the amp as is done in the K2/100 setup.  Any recommendations from those who run a homebrew linear?
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to vr2xmc at yahoo.com.hk