Re: Power supply adjustments



K3s are tested for -30 dBc or better 3rd-order IMD at 13.8 V at 100 W (ARRL method, 6 dB higher than your table). Average across all bands is typically -35 dBc. The one you measured may not be correctly biased, or not up to the latest rev. 

Further improvements have been made to both the 10 and 100 W modules in the K4. 


On Nov 7, 2019, at 11:50 AM, Rob Sherwood <rob@...> wrote:

This morning I decided to measure a K3 in respect to third-order IMD vs. power supply voltage as read on the K3 metering.  The pattern I measured was linear, the higher the voltage, the lower the third-order IMD.  At really low voltages the much higher odd-order products degrade significantly.  Test was on 20 meters, at a nominal 100 watts as per the K3 power setting.  Two equal tones were generated within the K3.  Note: at 14.8 volts on TX, the voltage on RX was 15.1 volts.  At 13.8 volts on TX, the voltage on RX was 14.0. The power supply was an Astron VS-35M, and the length of PowerPole cable was 16 inches.


Voltage                IMD in dBc   Note: Add 6 dB for PEP method

11.5                        -14.1 dBc

12.0                        -16.9 dBc

12.5                        -17.9 dBc

13.0                        -19.0 dBc

13.4                        -20.0 dBc

13.8                        -21.1 dBc

14.2                        -22.4 dBc

14.6                        -23.7 dBc

14.8                        -24.0 dBc


Rob, NC0B


From: [] On Behalf Of Dennis Ashworth
Sent: Thursday, November 07, 2019 11:28 AM
Subject: Re: [Elecraft-K3] Power supply adjustments


Are the supply voltage differences powering the K3 really material to IMD numbers? I’ve not seen data to answer the question either way ... just curious.

Dennis, K7FL

On Nov 7, 2019, at 10:22 AM, Michael Mickelson <mickelson@...> wrote:

Bob, thanks for that information.  I have two of the 30Amp Astron supplies and will make an adjustment to a higher setting.  The discussion on the effects of supply voltage on the K3/K3S tranSmitter performance has been very inStructive.


Thanks to all who contributed.  Mike  KD8DZ


On Wed, Nov 6, 2019 at 5:18 PM Bob McGraw - K4TAX <rmcgraw@...> wrote:

Why not get Alexa to adjust the voltage for you?   "Alexa, turn the
supply on and set the voltage for 14.5."

The supplies are usually in the category of the "set and forget" type.  
Thus the caution of "no user serviceable parts inside".

I adjusted one of mine this afternoon.  I put it on the desk, removed
the 4 screws holding then cover, plugged in the cord and turned the
supply on.   I picked up my light in one hand and my plastic adjustment
tool in the other {you do have and use a plastic adjustment tool don't
you?} and made the adjustment. Nowhere at any time did my hands or
fingers come close to any voltage.    I did put my Fluke DMV on the
output terminals first to monitor the voltage.  At 14.49 indicated,  I
stopped.   Turned the supply off, put the cover on and secured it with
the 4 screws.


Bob, K4TAX

On 11/6/2019 3:54 PM, Rick Bates, NK7I wrote:
> And for some stupid reason, when they could have put that pot on the
> underside of the circuit board (which ends up on the top) for simpler
> access, they didn't.  So you're reaching in around open hot high
> voltage OR turning it on/off a lot of times to get it set right.  Plan
> B could have been to put the pot on the edge or board flush with a
> hole for a plastic tool to access...
> I maintain that if the design engineers (of ANY field) EVER had to
> work on, fix, adjust their product, the design would be far different
> and techs would bless them instead of using 'adult language'
> curses...  ;-)
> I hold that Elecraft 'gets' this, their designs are modular and except
> cable routing and some panel connecting, is boringly simple.
> Rick NK7I
> On 11/6/2019 10:32 AM, Rob Sherwood wrote:
>> The Astron power supplies I own have an internal pot to set the
>> voltage. I would adjust it with nothing connected.  The can likely go
>> over 16 volts. I have 3 RS-35Ms, but have never used a 50. For some
>> reason removing the top covers are a pain.  Rob, NC0B


Michael Mickelson

J. Reid Anderson Professor of Physics and Astronomy, emeritus

Denison University

740-587-0687 H

740-644-1238 M


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