Topband: Several questions:

[Terry Conboy]

Dennis,

You didn't say how the RFI affects you.  Where does it appear?

It sounds like your vertical antenna is very close to the shack.  Maybe 
40 feet or less?  If so, you are definitely in the near field and 
everything conductive will couple to your antenna.

The presence of RF on the tuning capacitors in the 949E isn't too 
surprising, since they are floating from ground.  They may use an 
insulated coupler or just depend on the insulated knob to keep you from 
getting RF burns.  (The MFJ manual online doesn't have any interior photos.)

If your choke coil in the feedline presents a reasonable reactance, 
replacing it with a ferrite choke may not make much difference.  Adding 
a second choke at the TX end might change the flow of currents - but you 
may not know if it would get better or worse without experimenting.  
Adding a good connection to ground from the coax shield roughly midway 
between the chokes can also help prevent common mode current flow on the 
coax shield, if that is indeed the problem.

Glad to hear you performed the "final QC" on your fine MFJ product.  
Their low prices apparently depend on QC taking place after the sale!

Good luck,
Terry N6RY

On 2009-07-25 2:27 PM, Dennis Peterson wrote:
> 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?
>
>