Posted by
Don Nesbitt on
Jun 22, 2004; 3:21pm
URL: http://elecraft.85.s1.nabble.com/Dumb-dummy-load-question-tp368028p368038.html
Hi Eric - if the 10W 50 ohm resistor is NOT a "non-inductive" resistor (and
if you got it at RS it is a pretty sure bet that it is a wire-wound - and -
they are not "non-inductive - but - being wire-wound - are very
inductive!!), then you are having problems because it is NOT presenting a
pure (or reasonably pure) 50 ohm load to your KX1 even though the resistor
reads 50 ohms at DC (as read by your DMM). At RF frequencies, it will
exhibit "reactance" in addition to the "resistance" and this will make it
look like something other than a resistive dummy load to the KX1. It will
look more like a pretty poor antenna with very high SWR and the readings
that you get on the KX1 in the calibrate position will be incorrect - VERY
incorrect!!
Most likely this is what you are experiencing and there is nothing wrong
with the rig as evidenced by the fact that when you run it into an SWR close
to 1:1 it seems to read correctly!
Bottom line - see if you can get your $ back at RS and get an actual dummy
load that is close to purely resistive at RF. Have fun es 73 --don n4hh
K2/100/KAT100/etc/etc/#2028 and KX1/etc #243
----- Original Message -----
From: "Eric Ward" <
[hidden email]>
To: <
[hidden email]>
Sent: Tuesday, June 22, 2004 9:32 AM
Subject: [Elecraft] Dumb(?) dummy load question
In an attempt to save pennies, I got a 10W 50 ohm resistor ($1.79 for two)
at the Shack and soldered it to a male BNC--I figured this would make a
serviceable QRP dummy load. The resistor checked out at 50.0 ohm on my DMM.
When I hooked this to my KX1 and went through the ATU alignment procedure
(nulling C9, etc), I only get an apparent out put of about 0.3W (according
to the display on the radio). Ditto when I tune my G5RV--I get to 1:1.1,
but with only 0.3W. (This antenna/feedline system is tunable by my LDG Z100
to 1:1; see below.)
I had previously gone through the ATU alignment using, instead of a dummy
load, the G5RV routed through the external match (the LDG Z100) tuned for
that frequency. I figured that would be pretty close to 50 ohm, since it
achieves an apparent 1:1 on that freq with my Icom 706 rig.
When I use the tuned G5RV as a "dummy load" and go through alignment, I get
what appear to me more reasonable values--i.e. when I subsequently tune the
same antenna with the KX1 ATU, I get 4.3W and SWR of 1:1.6.
So something funky is going on and I cannot figure it out. Is there some
bloody obvious reason why the 10W resistor is not a good dummy load? Is
something else wrong with my rig, which otherwise is nominal in all
respects? (BTW, I have R4 maxed out clockwise.) I do not have a wattmeter,
so I cannot independently check output with and without the ATU installed,
but the rig is transmitting on 40 and 20m.
Thanks for any ideas...
73,
Eric
N0HHS
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