Re: Power supply adjustments

Rob Sherwood
 

In general with factory supplied power cables, particularly very long Icom cables, the voltage drop in the cable is 0.5 volts, if not significantly more. I cut my Icom cables in half, which also removes the fuses and fuse holders and their associated poor connection issues.

My Astron power supplies are over voltage and over current protected. An Icom PS-125 or PS-126 doesn't have any fuses in the short power lead, so I feel comfortable removing the fuses. My TS-890S runs on an Astron RS-35M with a shortened cable with no fuses.

In any case, as asked for, here is some more data all taken at 13.8 volts in transmit mode as read by the K3 LCD.
Also the PA in this K3 is Rev C.

Wattage 3rd order IMD
100 watts -21.1 dBc
75 watts -27.8 dBc
50 watts -33.7 dBc
35 watts -36.7 dBc
12 watts -23.4 dBc
10 watts -29.2 dBc

Note at 12 watts and below the driver is providing the RF output. The PA is out of the circuit.

Rob, NC0B

-----Original Message-----
From: Elecraft-K3@groups.io [mailto:Elecraft-K3@groups.io] On Behalf Of Bill K9YEQ
Sent: Thursday, November 07, 2019 2:56 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] Power supply adjustments

That is significant. I checked my voltage at the K3S and need to make some changes real soon. I generally only run < 30 watts into my KPA1500, but need to improve voltage at the radio for those few times I run barefoot at 60+ watts.

73,
Bill
K9YEQ

https://wrj-tech.com/

-----Original Message-----
From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> On Behalf Of Rob Sherwood
Sent: Thursday, November 7, 2019 3:54 PM
To: 'Elecraft-K3@groups.io' <Elecraft-K3@groups.io>
Subject: Re: [Elecraft-K3] Power supply adjustments

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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