Re: Dirty Transmitters

David Bunte

Bob -

I am not posting this to the list, as I don't think it will add anything of value... but I was surprised to see K9VUJ talk about up to 35 watts drive power to his KPA500. Your numbers are FAR more like mine. I have never bothered to adjust the digital display and the bar graph on my KPA500 as you described... so thanks for the reminder that I can do that.

I appreciate many of your posts. I do not have a technical background (my career was on the microphone side of Public Radio). After 62 years of hamming, and at age 76 I am glad I can still learn.

73 de Dave - K9FN

On Wed, Nov 6, 2019 at 8:49 AM Bob McGraw - K4TAX <rmcgraw@...> wrote:

I find that my KPA500 {s/n 3519} drives to 500 watts output on all bands with 19 to 23 watts.   I find that driving power of over 25 watts will push my KPA500 to over 500 watts.   All measurements were made with my Bird 43 into a 50.5 ohm resistive load.  {Please do not use an antenna for this measurement even if the SWR is 1:1.}  

The LED bargraph and the LCD display were correctly calibrated using the Menu / Edit and PWR ADJ feature of the KPA500.    The PWR ADJ feature DOES NOT affect the output of the amplifier.  It only affects the displayed or indicated values of both the LED display and the LCD display.  The FAULT power function is also affected by the PWR ADJ setting.

Based on earlier discussions, some amps may require more power to attain 500 watts output.


Bob, K4TAX

On 11/6/2019 7:09 AM, dalej via Groups.Io wrote:
Also if you have the KPA500 you only need around 30 watts to drive it and that is in the good area for IMD from 12 volt amps.  That’s were I run mine, maybe a little more 35 watts driving the KPA.  That also helps with the amp draw from a power supply.  

Dale k9vuj

On 06, Nov 2019, at 6:45, Bob McGraw - K4TAX <rmcgraw@...> wrote:

This has been stated and confirmed several times.  

A suggestion:   If you have a power supply with good regulation, no load to rated load, and you use power leads with very low resistance between the power supply and radio, you can run the power supply at 14.5 volts.  This will certainly improve the transmit IMD. 

Power leads should be of minimum length required, use #10 AWG wire, crimp on the correct terminals required for each end.   If in doubt crimp and solder terminals.  AND do connect the radio power cable direct to the power supply.  DO NOT use a DC power distribution strip.  Every connection adds resistance and results in voltage drop.  


Bob, K4TAX

On 11/5/2019 3:40 PM, Steve wrote:
I remember a comment from Elecraft saying that the K3 will transmit a cleaner signal with voltage around 13.8 to 14 volts.   I don't remember the exact comment.

Join to automatically receive all group messages.