Posted by
Jack on
Mar 17, 2009; 10:25pm
URL: http://elecraft.85.s1.nabble.com/KX1-Spring-Tune-Up-tp2494086p2494247.html
I have reformatted the text and corrected an error. Sorry for the
inconvenience.
Its spring and I am getting ready for some backpacking with my KX1 so I
thought I would take the time to tweak/tune/analyze/hot rod my baby.
The rig is fully loaded. 4 bands, ATU and the SMD CW TUNING AID.
I have several projects on the agenda.
1. Scope analysis
2. Dummy load construction with DVM RF measurement capabilities. Or
just buy the Elecraft dummy load!
3. Possible tweaking of the existing hardware.
4. Exploring the possibility of increasing the power output to a full
5 watts.
Just for the record, the KX1 is working FB on all bands and the readings on
the rig are all within specs!
Well, one thing at a time.
I have hooked up my scope to a dummy load consisting of six, 5 watt
Milwaukee 300 ohm sand resistors in parallel.
These resistors were given to attendees of a "hands on session" of my local
radio club. I was dubious about the resistor choice as I understand that
these are wire wound and that is not appropriate for a dummy load.
Sure enough, when comparing the SWR of the homemade dummy load, my MFJ-9895
and a BNC ½ watt 50 ohm terminator I found that the homemade load showed
different SWR readings at 80, 40, 30 and 20 meters. While the MFJ and BNC
terminator showed 1.0 SWR on the rig for all bands. The MFJ also showed the
1.0 on all four bands on its SWR meter.
Well, for convenience sake made I made my first scope connection on the
homemade dummy load at 3.550 MHz.
BATTERY NO LOAD = 12 VDC ON DVM.
CONNECTED TO KX1 11.9 VDC ON DVM
KX1 BAT FUNCTION = 11.7 VDC ON RECEIVE
SCOPE PPV RIG WATTS RIG SWR CALCULATED WATTS
32 2.9-3.0 1.1 2.559
I calculated the power out by this formula.
((32 x .3535) (32 x .3535)) / 49.2 ohms (Measured on my DVM)
11.312 x 11.312 = 127.961
127.961 / 49.2 = 2.6.00
My DVM and the scope both show the same frequency! The scope had been
calibrated when I bought it. The scope's self calibration function shows
the same measurements as when I bought it.
So, I have two questions for the group at this point!
1. Are my measurements consistent with what a KX1 would be likely
to put out?
2. Am I correct in thinking that the resistors in the homemade load
are not the best choice?
For what it is worth, I have found several articles on the web re: dummy
loads and also looked at the schematic for the Elecraft dummy load and all
indications are that sand style, rectangular, wire round resistors are
not appropriate!
It is true that my measurements confirm this, but as my construction
technique was rushed, I do not want to assume anything!
If my measurements pass the smell test I am going to trace the RF path of
the KX1 end to end in order to establish a baseline!
At that point, I will decide whether to try tweaking the KX1 or to continue
home brewing a dummy load with power metering capabilities like the Elecraft
dummy load!
Thanks in advance for all your expert advice/admonitions!
Jack, AE6GC, KX1 #1403, K3-100 #1433
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