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Need some help understanding my MFJ 941E

Peter Walker

W9WDX Amateur Radio Club Member
Feb 23, 2011
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I got my MFJ 941E Antenna Tuner yesterday and was trying to figure out how to use it today. I understand how to connect it to the transmitter and the antenna to it. I understand that to use it for tuning the switch must be on Coax 1 which is where my antenna coax is connected. Per the instruction manual that came with it I put the Transmitter Matching on 5 and the Antenna Matching on 5. What I don't understand is what setting to put the Inductor Selector. I understand that setting A=Most Inductance(Resistance) and L=Least Inductance(Resistance) The instructions say to "Rotate the Inductor Selector control until maximum noise is obtained with the transceiver in the receiving mode." When I do that I don't see any change in the needle readings.

First question here is how do I know how much Inductance I need for the band I'm tuning on?
 

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This is what works for me...

1. Set the rig to the desired frequency.

2. Set the dials per the recommended settings in your manual. Remember - those setting are just "ball park" so they may change. I attached a set to this message.

3. Listen to the radio and turn the Transmitter Matching Dial until you hear the clearest signal.

4. Make sure you rig is set to CW because you will have to hold your key down to a solid signal to get your meter reading. You can't set your SWR using SSB. Now, drop your rig to about 10 watts or so and see how the SWR are...if they are high - play a little with the Transmitter Matching Dial to get the SWR down.

Now, if you can't get it down - try turning the Antenna Matching Dial to the next setting (below - or above) follow steps 3. and 4.

If that doesn't work - set the Antenna Matching Dial to the next setting above or below where you were set to begin with and follow step 4.

Once you are comfortable - turn up the Power and verify the SWR.

It sounds like a pain - but, trust me - after a few times it will be a piece of cake.

HINT: When you get a good SWR - record all the setting for that band so you can just change everything to those setting for that particular band when you move around.

Did I confuse ya yet?
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Thank you very much! (y) That helped 100%.
I will have to figure out how to generate a CW key because I don't have a keyer yet. I think I can do it from the hand mic on my radio. I do know how to adjust the output power because I was reading that in my radio manual the other day.
 
I have the Yaesu FT 897D and it allows you to use the hand mic as a keyer. I have been able to see what you posted about in action. I really appreciate your help and patience. After setting it all up I can only get the needles to read between infinity and 5.0. Given that I'm guessing the SWR's from Antenna are just naturally high. There is an adjustment up there that I can make to bring them down hopefully.

I'm on 28.000.00MHz which is bottom end of 10 Meters if I understand it correctly, and I have the Inductor set on L. I turn the Transmitter Match to 9 - 9.5 and that's where I get my clearest signal at the radio. I then turn the Antenna Match to 9 - 9.5 and the signal gets really quiet. 100% less background noise. I generate a Dash tone and get my reading. It swings to halfway between Infinity and 5.0.

Sound about right?

Update...I think I may have shot my own self in the foot by trying to adjust at the antenna. Now when I try to adjust via the tuner, I get High SWR warning on the screen. I know that can't be good. I'm too tired and frustrated now to get back on the roof to figure it out so its probably going to be a day or two, maybe a week before I can get back up there.
 
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Peter: I am a little confused by what you posted.(up and down on the roof)
The tuner does work for checking the tuning on the antenna but you must place the feed-line switching to By-Pass Coax 1 when checking the antenna....this removes the LC network from the circuit. This will give you the true condition of the antenna tuning.

Then when using the LC network the switch must be in the "Tuned" position...this engages the network back in the circuit to allow removing the reactance of the out of resonance antenna.

The tuner should only be in the "Tuned" position if your using the A99 on say 15m...Unless the 10m antenna is grossly out of resonance...lets say 2:1 the LC network of the tuner should not be required in the circuit...thus you would switch Coax 1 to By-Pass...

Hope that makes sense?
Peter also remember to keep the power set below 20 watts or less when tuning...never use the tuner with full power...that tuner will give you proper readings at that level....only once you get the proper SWR do you run full power...You may need to "touch" up the tuning at full power but that adjustment should be just a slight touch of the knobs to null out the mis-match.
I have done this 1000's of times so forgive me if I am not being clear.

The "High" warning light can and will come on most of the time when you first engage the tuner and apply carrier...but watching the SWR meter on the rig(or tuner) it should go off when you get near the proper setting.
This is why you remember your setting for each band...this reduces the time the rig will see the "High" mis-match...
Hope I helped...
All the Best
BJ

One more note...Make sure the rigs "internal " tuner is set to "OFF"(OUT) when making adjustments...if it is not it will cause you to get some very strange readings...
 
Peter: I am a little confused by what you posted.(up and down on the roof)...

I went up on the roof to turn the tuning rings that the antenna has. I just got things out of whack. It was getting late, dark, and the wind was picking up. That on top of a very long day, I just didn't have the will power for another trip. I will go back up and try to reset everything tomorrow weather permitting but they are calling for showers the next two days and my work schedule is full, so it may be a while. :(
 
i would first tune the antenna to the band you will work the most "without" the mfj tuner inline.(28000 should easily tune on a antron)
trying to tune the antenna with the tuner inline will only make it harder to do .
this of course is my opinion and i could be wrong ,but thats how i would do it .just makes better sense to me .
good luck
 
'fnkycoldmedina' has it right, first set up the antenna without the tuner, for where you will be using it the most. That can change over time, so don't put away that ladder permanently!
The 'original' instructions were basically the right way to do it, adjust the inductor for the loudest noise, then the two capacitors for 'loudness' too (on the 'S' meter). That gives you a 'ball-park' starting point. Then at low power, adjust for maximum output on a watt meter, or lowest reading on an SWR meter. It will become easier the more you become familiar with things. The settings given in the manual are only very 'approximate', what you might see if you've got an antenna system that's fairly 'close' to right to start with, and shouldn't be thought of as the settings you will end up with. They make a fair starting point though.
Since you are using an antenna that's 'adjustable', has it's own impedance matching device built into it, by using another tuner to 'move' that antenna off of it's resonant point to another means that the tuner is going to have to compensate for the antenna's built-in 'tuner'. That's going to make for some interesting results sometimes. In particular circumstances, the two 'tuners' will combine and result in a really 'nice' result. In other circumstances/instances, it'll probably be impossible to get that antenna system to tune where you want it to go. You win some and lose some, you know?
Using two or more impedance matching devices isn't exactly the 'best' idea in the world. The odds of them 'playing well' together just isn't very likely, one trying to compensate for the other get's very aggravating.
The more you 'fiddle' with it the more accustomed you get to twiddling knobs, and seeing what happens. A very good idea is to keep notes of the various settings that result in a 'good' results! There are various ways of keeping those notes, use the one easiest for you. [How about marking the tuner's settings on it's face, or in a list, or cutting a slot in an index card that'll fit over a knob's shaft and slide that card behind the knob, lots of ways. The numbers around the dials don't relate to any particular values, they are 'logging' scales. It's a pretty good idea to take the 'lid' off and see where the minimum/maximums are for each capacitor and inductor, which end of that scale is the most and least. One reason for that is that you want to use the least amount of inductance/coil as is required.

You'll also find that there will be more than one place where you can get a 'good' match with things. If you compare those 'places'/settings, you'll see that there is one of them that's just a bit 'better' than the rest. That's the one you want to use! The differences won't necessarily be 'huge', but there will be a difference.
If there are differences in those 'good' settings from time to time, it means that there's a change in the antenna system. That's a nice 'tip-off' about changes, so keep it in mind.
There are a lot of things that tuner can tell you, you'll pick them up over time.
Have fun!
- 'Doc
 
As a general rule, the lower the frequency, the more inductance you'll need. Adjusting the controls for maximum noise is a good way to start, and you don't really have to use the S-meter if your ears can hear the background noise rise to a peak and fall back off as you tune across part of the spectrum. (No, you don't need an actual signal from another station; just the background hiss.)
 

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