[Elecraft] IMD and supply voltage

[frank]

On Thu, 29 Oct 2015 07:43:24 -0700
Wayne Burdick <n6kr at elecraft.com> wrote:


> The K3 and K3S, like our other radios, are very popular for Field Day and other applications where a battery might be used. So we provide two ways for you to monitor the supply voltage:
> 
> 1. The CONFIG:BAT MIN menu entry. This sets the voltage at which you will periodically see a BAT LOW warning on the display. 
> 
> 2. Voltage display: Tap DISP and rotate VFO B until you see XX.X VDC. You can also display current drain and PA temperature this way.
> 

Verifying the obvious is sometimes helpful.  Of course the battery voltage is going to drop when you are pulling enough current to power a 100 watt transceiver.

I was hoping for a more pro-active suggestion to the IMD problem.

My old Drake, tube type, mobile did not have an IMD problem even when run off less than 12 volts.  it had a switching supply delivering 700 volts at 200ma to the finals.  Today we use switching supplies to deliver 12 volts to finals that are not capable of delivering a clean signal at 12 volts.

This is state of the art?

Just because everyone else is building radios that produce dirty signals, does that justify doing the same?

Also, you did not answer my questions.  Maybe I should ask them one at a time.

I
> 
> On Oct 29, 2015, at 8:09 AM, frank <frank at k5dkz.com> wrote:
> 
> > This subject keeps cropping up.  Is this a serious issue ?
> > 
> > I have heard that IMD improves by 10db with a one volt increase in supply voltage.  Is this really the case or just a measurement error?  10db is a large difference.  One volt is a small variation.
> > 
> > What is the minimum acceptable IMD?  How linear does the amp need to be?  If 36db is better than 26db is 100db even better or just overkill?
> > 
> > Are other solid state amplifier products similarly effected?
> > 
> > What is the IMD performance of the K3S at 10 watts over a supply voltage variation from 11 volts to 14.7 volts?  I ask because I believe those ten watts are generated by Dmos devices as well.  Do these devices only misbehave with varying supply voltage at higher (100w) power levels and lower supply voltages?
> > 
> > Should I wait to purchase a K3S until this issue is resolved?  (Assuming this is a valid issue)
> > 
> > Back in the good old days we used to solve problems.  Today we don't have problems, just issues.  
> > 
> > -- 
> > Frank - K5DKZ
> > KX3 - 7550
> > PX3 - 1143
> > KXPA100 - 1566
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-- 
Frank - K5DKZ
KX3 - 7550
PX3 - 1143
KXPA100 - 1566