[Elecraft] Need to select a dummy load for K3 TX calibration...(advice?)

[Dick Dievendorff]

Jeff:  It all depends on the power level you want the load to handle.  Do
you want to acquire now a dummy load that will handle the output of a KW
amplifier in the future, or just the output of your K3?

If it's just the K3, then the MFJ-260C at $40 or so should be fine for 100W
for extended periods at the calibration frequencies from 3.7 - 52 MHz.

I burned up a much smaller MFJ unit that was an integrated PL-259 and a
cylindrical heat sink that could handle 100 watts for very very short
periods.  During K3 Utility development I stopped the Tx Gain calibration
code with a debugger with K3 key down for a bit too long and it Is No More.
I don't find that unit in MFJ's catalog now, though.

The Tx Gain calibration holds key down for a few seconds (maybe two to ten)
on each HF  band at 5 and 50 watts in quick succession.  

You might want to acquire a BNC to PL-259 adapter so that you can put your
50 ohm dummy load onto the XVTR OUT BNC connector for the milliwatt Tx Gain
calibration step.  That calibration really wants a 50 ohm load, although the
power requirement is very small.

For K3 Utility development when I run Tx Gain calibration over and over, I
keep a Elecraft DL-1 on the XVTR out connector and an AEA DL-1500 (which is
overkill) on the main rig ANT2 connector.


73 de Dick, K6KR



-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jeff Hall, W6EZY
Sent: Tuesday, February 23, 2010 10:14 AM
To: elecraft at mailman.qth.net
Subject: [Elecraft] Need to select a dummy load for K3 TX
calibration...(advice?)

Hello all,

I need help picking out a proper dummy load to use for calibrating my new
K3.  HRO is just up the road and they carry some of the less expensive MFJ
dummy loads -- would these be sufficient? Not looking to spend a lot of
money, but don't want to buy junk either.  What factors should I consider?
I'm assuming oil-cooled dummy loads are more robust, while air-cooled loads
are more compact, but you have to be more careful when operating or they can
burn up more easily.  The K3 manual says this is just a 5W test and I need a
load with low VSWR from 160 to 6.  What is considered "low" SWR? Anything
under 1:5?

If I can get by with the MFJ-260 for just $40, that sounds reasonable to me.

73 de Jeff, W6EZY
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