[Elecraft] 14.9V to KX1?

[ab4cz at comcast.net]

Martin & Chris,

I think you're giving too little thought to the quality of your power supplies.  True, if you're lost in the desert and have no alternative, any power supply that works is good enough ... but you paid nearly a kilobuck for a K2 with accessories and now you're betting your signal will sound good with a $3.00 wall wart.  If your voltage is dropping from 14.9 volts to under 13 Volts when you key the transmitter you probably have hum.  Everybody gives you a "9" for tone, but do you know what your signal REALLY sounds like?  I've heard Cubans get "9" for tone, and they don't have an electrolytic capacitor anywhere on the island!  I just did the experiment ... looked in my JUNK box and found a 14V unregulated wall wart.  Ran the K2 at 5W and got about 15% 120 Hz modulation on the CW waveform.  Changed to one of my switcher bricks and had zero perceptible hum modulation.  It's your signal.  Kinda like the "swing" in days of old, people will be able to recognize your signal on the air by the hum.  To be fair, I think my wall wart is wimpier than yours, as my voltage regulation was worse than you mention ... but you will still have hum.  And I'm not promoting switchers, just a REGULATED power supply.  Remember, regulation stabilizes the voltage AND REMOVES RIPPLE.

Even if it seems to sound OK, don't you want the best signal your Elecraft rig is capable of?  The power supply is often the last thing people think of in designing an electronic system, but it's the only part of the system that touches EVERY circuit ... Your keyed waveform is dependent on power supply dynamic regulation.  Even though the PLL runs off a local regulator, every regulator has a Vin / Vout regulation specification.  They're not perfect; if the input changes, the output also changes.  I know I don't want my callsign associated with a signal that hums, chirps, or drifts.

Sorry if I seem a little passionate about this, but there's places to be cheap and places not to be cheap.  It doesn't cost that much to get a decent regulated power supply, even if you have to add a regulator to the output of your wall wart.  

For those of you wanting to build some kind of power supply, you may want to look at the Far Circuits catalog.  They sell printed circuit boards for QST and ARRL Handbook projects so you can build a decent regulated power supply on a nice quality circuit board.  There are a BUNCH of different regulated power supply boards available, several in the $5 price range.  Download a copy of the FAR catalog at http://www.farcircuits.net/FAR_CKTS.pdf.  I've bought a number of project boards from FAR over the years and have been completely satisfied with the quality of the boards.  You have to determine which project board is suitable for your purposes, but the stuff is out there.  Or, do a Google search on "electronic kits".  There are a number of kit suppliers out there (Ramsey, Rainbow, and others).  Nearly any kit supplier has some kind of regulated power supply kit.  Build a decent regulated power supply and be confident that your rig is performing at it's peak potential.

Oops, just fell off my soap box.  Ouch.

73,

jim


 -------------- Original message ----------------------
From: Martin Gillen <martingillen at yahoo.co.uk>
> Hi, Chris.
> 
> > Ah, good catch Tom - it drops to under 13V under Tx
> load.
> > I'll look for something else.
> 
> 13V is still well within the specified range.  As long
> as that
> 13V is developing enough RF does it matter that its 2V
> below the
> RX voltage?
> 
> If it were dropping to 7V on transmit I'd be more
> worried :)
> 
> - Martin.
> 
> 
> 		
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