Re: Power supply adjustments

Rob Sherwood
 

Ok, it isn't a straight line, but what I was trying to imply was it consistently improved with higher voltage.
It didn't plateau and then get worse.
Approximately a 10 dB difference from 10.5 to 14.8 volts, and approximately 3 d difference between 13.8 and 14.8 volts.
Rob, NC0B

-----Original Message-----
From: Elecraft-K3@groups.io [mailto:Elecraft-K3@groups.io] On Behalf Of Joe Subich, W4TV
Sent: Thursday, November 07, 2019 1:50 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] Power supply adjustments

On 2019-11-07 2:50 PM, Rob Sherwood wrote:

The pattern I measured was linear, the higher the voltage, the lower
> the third-order IMD.

Given the rate of change, I would not call the slope linear.

There is a terrible 2.8 dB worsening of IMD when the voltage drops from
12.0 to 11.5 volts. In addition, you change from 0.5V steps below 13.0
V to 0.4V steps above which hides an improvement in dB/V between 13.0
and 14.6V (1.0, 1.1, 1.3, 1.3 dB/0.4V). The improvement "flattens out"
again above 14.6V (only 0.3 dB/.02V).

It does make one wonder if the K3/K3S could achieve -36 dB/PEP at
50-60 W with a 14.5V supply <G> (particularly if the LPA were set up
for better IMD at that level).

73,

... Joe, W4TV


On 2019-11-07 2:50 PM, Rob Sherwood 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

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