[Elecraft] K3/100 and the PSU

[Jan Erik Holm]

As a good engineer I should have stated what I measure
with, sorry.

Normal 2-tone test, and a HP 8591E spectrum analyzer.

Normally I like to do it with speech, i e fully
modulate the radio and look at the sample 5 kHz
on each side. That is IMO better then a 2-tone test
since it will tell you more.

And by the way, I did NOT say 2 dB, read below.

As an anecdote you can look at this:
http://sk3w.se/sm2ekm/view_photo.php?set_albumName=SM2EKM-pictures&id=FT_1000D
http://sk3w.se/sm2ekm/view_photo.php?set_albumName=SM2EKM-pictures&id=KWM_2

We can see that the Collins KWM-2 is ca 10 dB better
on adjacent channel compared to Yaesu FT-1000D.
The FT-1000D is one of the best modern things around
when it´s up to TX IMD. Anything else I have measured
is worse then the FT-1000D.
Receivers has been getting better but not transmitters
that is the bottom line.

/ Jim SM2EKM
-----------------------------
m.j.willis at rl.ac.uk wrote:
> I am sure PSU regulation affects all other 12V radios in exactly the same way. The only reason Elecraft users will see it more is because they are more discerning. 
> 
> How do you measure IMDs? 2dB is a worthwhile improvement.
> 
> It would be interesting to try a better supply cable and also to see if the 20A cutout has any effect.
> 
> Mike
> 
> Jan Erik Holm wrote:
>> Yes I´m beginning to think that K3 is more sensitive to PS
>> then other radios, right now it looks that way.
>> Then this should be in the manual!!!
>> What happens is if I have a bad signal on the bands I will
>> together with Elecraft get a bad reputation. I will of course
>> tell everyone what I´m running and do have it operating
>> exactly according to the manual.
>>
>> If this PS deal is the case with the K3 I quite understand
>> and it´s no problem to me what so ever but it should be
>> in the operating manual. Every user of a K3 should not
>> need to be a super engineer and have to figure out things
>> like this them self.
>>
>> This morning I increased PS voltage to 14.6V (14.2) under load,
>> I was at 13.9V (13.5 load) before, I could see a "slight"
>> improvement in IMD (1-2 dB). I am using the supplied high
>> performance cable from Elecraft and IMO it does not have
>> enough Cu area. Next But if Elecraft supplies it and it´s
>> not good enough, what can I say?
>>
>> / Jim SM2EKM
>> ------------------
>> AD6XY wrote:
>>> Everyone knows it is important for the K3/100 to receive a solid DC
>>> supply.
>>>
>>> If the supply drops significantly when high current is drawn several
>>> effects
>>> may occur:
>>>
>>> 1 - The Transmitted signal becomes wider than it should be
>>> 2 - The power control loop is upset leading to unstable output power
>>> 3 - In severe cases the radio might shut down, or engage sulk mode.
>>>
>>> Of course this does not apply to us, we are all experienced constructors
>>> and
>>> never make mistakes when wiring up our shacks. Like many people I run my
>>> K3
>>> from a 13.8V DC supply that also supplies other items, in my case XV
>>> transverters, an LP100, an LDG ATU etc. This supply is very good (tnx
>>> BNOS,
>>> 1980s) and only varies by a few 10s of mV between no and full load.
>>> Originally when installing my K3/10 I used the supplied DC cable via a
>>> powerpole distribution board with an appropriate fuse. In fact this
>>> particular board had two fuses, one 30A one at the input and one at the
>>> output plus around 1 metre of thick cable to the supply. This worked
>>> fine. 
>>>
>>> Later I upgraded to the 100W KPA3, and of course changed the fuse in the
>>> distribution board. The DC voltage drop according to the K3 at 20A was
>>> over
>>> a volt, much no doubt due to the fuses and extra connections through the
>>> distribution board. A 1 volt drop is not a problem for the K3 but will
>>> cause
>>> more IMDs on SSB. 
>>>
>>> I now connect the K3 directly to the PSU with as short a DC cable as is
>>> practical. It would be even better to use voltage sensing so the supply
>>> is
>>> regulated at the K3 end of the cable.
>>>
>>> Mike