Hi guys;
First of all, I must say that I was quite amused after reading articles
concerning the MFJ equipment and finding out about the inconsistency of Quality
Control in their construction practices.
A few months ago I got a near new MFJ-949E tuner and opened the box and
installed it per usual and nver gave checking the innerds a second thought.
However, recently I have been plagued with RFI on 40 meters. Trying everything
I could think of to include the following:
1 Replacing the RG-8X feedline with RG-214
2 adding a 12 turn 4.5 inch diameter common mode choke within the same
feedline
3 re-checking and establishing good ground connections and RF connections
4 Tightening all ground rod grounding clamps
5 Tightening all ground connections to the tuner
Nothing worked or at least seemed to work so I began checking the tuner and
here's what I found:
First of all checking the tuner and controls for RF using a fluorescent light
tube the following controls showed the presence of RF
a Transmitter tuning capacitor control
b Inductor 12 position selector switch
c Antenna tuning capacitor control
Checking these controls, I found that the nut securing the controls were very
loose and they were then tightened. The fluorescent tube was again used to
check for RF and all was fine with the exception of the antenna tuning
capacitor control, nothing seemed to fix it.
I then discovered that the 12 position tapped inductor had several turns
shorted together either by way of solder connections or the taps themselves
were actually touching other taps. This was all cleaned up and the spacing on
the tapped inductor checked for proper clearance between turns and again the
fluorescent tube was used to check for RF and still the Antenna tuning
capacitor shows the presence of RF.
I am currently only running 100 watts of power from a recently overhauled
IC-735 transceiver thanks to Scott Malcolm in the state of Washington.
Does anyone have any idea as to where I may further look for the RF problem. I
can tune my 90 foot tall inv-L anywhere on 160 down to a 1.0:1 match although I
rarely use the tuner from 1800 to 1865 as the resonance there is an average of
1.5:1 or less. Above 1865 I use the tuner.
On 10 -80 meters, I switch out a 4 turn 4.5 inch diameter loading coil that is
spaced with .5" turns between the turns. I can tune anywhere I desire and
obtain a 1.0:1 match in doing so.
If I were to remove the common mode choke coil on the new feedline would this
make any difference at all?
Would I be better off to use a toroid core and wrap afew turns on it to
eliminate RF currents on the coax? I would think that the silver plated qual
shiel coax would elleviate most of that, but maybe I am not thinking as I
should. Can anyone offer any suggestions to these issues?
Thanks in advance
73s de K0CKDennis
Dennis G. Peterson
326 East Jefferson Street
Apt 2
York, SC 29745
803-389-9366
Read my story below by clicking the URL:
http://www.yananow.net/Mentors/DennisD.htm
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