Antenna Tuner Range 1.8mHz to 30mHz

I have an MFJ antenna tuner and the range given is 1.8mHz to 30mHz, I would like to try 50mHz and assume it won't work at all or very poorly. Why is this the case, and is it just suck it and see if it works? It seems the range given almost seems arbitrary, covering the bands most used by amateurs.

Hi Mark,

There's a lot more to those little coils of wire and metal plates spaced apart than first seems.

You can go hell for leather and learn all there is to know about matching impedances but a little experimentation goes a long way. (Without all the fapping over numbers, smith charts and the like.)

My own homebrew ATU is a Pi-Match giving me all the impedances I'll ever likely to go to and with the addition of a common mode choke even handles my ladder line well. (None of the 4:1 stuff either.)
It originally matched 80m to 10m well, then I added a switched additional inductor to give a bit extra for 160m. For 6m I have to switch all the inductance right out (relying on the stray inductance through the switched line) and added a switched capacitor in series with the output variable to reduce that overall capacitance. Now it works well from 160m thru 6m.

There's loads of articles online for antenna tuning/matching circuitry and I've built a fair few of the different b*ggers in my quest to match my big long bit of electric lawn mower lead posing as a long doublet. 

There's even a fair few articles surrounding modification of commercial units to extend their range.

What model of MFJ do you have there?

If you want I can have a shifty for any mods but it's probably a typical T-Match circuit in which case a switched capacitor on the output might bring it into playing range. 

That of course is if you want to go down that path of 'modding' your matcher otherwise purchased options such as the MFJ902B gets good reviews for a manual tuner or else it's a look at the auto affairs such as the lovely SGC units. Loads of other stuff too if looking for purchased options such as the MFJ903 for 6m only and you could always build your own....but variable capacitors are getting more difficult to get hold of nowadays. 

Such an example here:-

https://www.qsl.net/v73ns/6m_tuner.html

Simple stuff really, until you delve into the mathematics!


Or, if you're not of a believer in 'matching' to squirt RF out of wires you could always go down the 'resonant route' which is what I did to start with recently finding myself luckily having access to 6m.

I built a 6m Delta Loop (pushed after Lynton's wonderful efforts with his 11m Delta) and was simple to make.

20 foot of wire will give you approx 6 foot 8 inches per side when folded as an equilateral triangle but will have the wrong impedance so then a length of 75 ohm coax will provide you a match to your 50 ohm coax. (I had mine 'pointy' side up fed at a bottom corner to give me low angle vertical polarisation.) You'll need 3 foot 2 inches length of it at 0.66 Velocity Factor for polyethylene coax or 3 foot 10 inches for 0.8 Velocity Factor with foam dielectric.

My effort had a 2:1 SWR range across the whole of the 6m band and bagged me my first 6m FT8 contacts across Europe. Easily fit into my loft space too.

If you have access to some external space the following is a typical antenna made from a length of coax for 6m which is reported to work well :-

https://www.youtube.com/watch?v=4h7UGNbWmsY

Whether you call it a 'flower pot', 'T2LT' etc. is up to you but it's essentially a "sleeved dipole" so that you can end feed it.

Of course a simple dipole would work wonders and for 6m you're looking at about 4 foot 8 inches of wire per element but worth making it a bit longer to start. It's easier to cut-off than it is to add-on.


I know, more of my 'waffle' but Amateur Radio does have some exciting opportunities whether you want to understand/comprehend, build yourself, or simply purchase a solution.

There'll probably be mention of me using imperial measurements, matching doesn't work or other things I can't probably think of right now, but each to their own. 

Enjoy your radio no matter what path you take, believe in, or otherwise. It's all fun stuff to be enjoyed.

(Flip do I love all this radio stuff!!!)


All the best,
Victor

A lot to digest there Victor, so there is more to my box of tricks than meets the eye. I bought the MFJ962D Versa Tuner III for a good price, total overkill for my power setting but wanted a roller inductor to squeeze the best performance out of my 10W. I easily get 1:1 every time now, far better than a rotary selector.

I would not trust my skills at modifying the tuner, so am probably better off building up a 6m antenna, far more within the scope of me being able to comfortably do. Perhaps I need you to set me some simple projects, so I can get up to scratch, I am sure getting to your level would be like chasing Alan's FT8 contacts.

Have you tried it on 6m.
Shouldn't go over 2 anyway witch is still ok to use.

Wow, nice bit of kit is that there MFJ926D Mark and should serve you well.  
(Apart from the obvious 6m shortcomings.)

I had to do a 'poor mans' inductor switching arrangement on my ATU to get a bit more finesse after finding roller inductors at ridiculous prices for corroded old relics.

Mark, don't praise me too highly as we never stop learning. (Hopefully!) 
A couple of my grandchildren were in the workshop with me recently exclaiming how 'clever' I was doing all the things I do. I turned to them and asked "How many fingers do I have? How many eyes? How many brains?" and after a little confusion with my grandson insisting we have eight fingers and two thumbs they gave me the answers of 10, 2 and 1. I then asked them how many they had and they agreed that they all had the same. I then explained that they had the same tools available to them as I have and all it takes is a little learning. The wonderful expression on their faces at that realisation was worth its weight in gold especially realising they could do almost anything if they simply put their mind to it. I think their appreciation of the education system we have went up by several points too.

You'll get there Mark and like everything else you won't be able to do everything at once. Bit by bit this sort of stuff will come as second nature as you travel along that radio interest path. It certainly has for me.

73
Victor

Well said Victor.
Radio is all about self learning.
I have been licensed since 1984 but I still learn things almost every day.