As I wanted to improve the reception of my kitchen radio, the old Grundig satellit 800, I thought adding an 1/9 Unun to her ‘short’ long wire which is about 9 meters by now, but must grow till 20 meters or more soon could be a good idea. So I look to the online shop of my favorite dealer just to discover that he has 1/1 1/2 1/4 and 1/6 but no 1/9 which looks good to me. And now, what to do? The other option was to make it by myself, why not.
Where did I got the information to make a 9/1 unun which works as it should. After searching the web for useful information, I found this German site owned by DG0SA. Information were clear, easy to understand and seems to be very accurate and most important reproducible . By the way he also sold all the material needed to make your own unun or balun at very reasonable prices.
What did I need to make my own 9/1 unun?
First I need a toroid. The one used by DG0SA has an AL value (nH/N²) of 640 and dimensions are 61 * 35.5 * 12.7 mms, these dimensions and value looks very close to an FT240/43 from amidon or from the one I bought from Wimo on line shop reference 40094.58 earlier. I will make a measurement to be sure that this toroid will be ok for building my unun (Yes, this toroid is ok as you will see later). The one I choose is the big one on the left of the picture. Using the mini ring core calculator (this program can be found in my LX2SM software page division under usefull tools) I found that the value of a 11 turns windings should be around 122uH, so lets do it and check it in the real world. You can see on my 5105N that the read is 125.8 uH not that bad. Ferrite core are mostly +-20% off the given value so again not that bad and I could go further with building.
I need also textile duct tape, Hopefully you don’t need a picture of that (If you ask friendly I will put a picture).You will find it just anywhere in your vicinity. Don’t underestimate the importance of this textile tape around the tore as it protect the coating of the tore from the wire, it also protect the wire if as I will do you use enameled copper wire. First choice is teflon insulated wire but I’m short of that... For big power, you really better use this teflon wire. I bought my wire here The coating of the wire is very very very resistant, so if you have an dremmel use it to remove the coating on the wire.
So as the explanation from DG0SA on the 1/9 unun are clear enough on how to wound, I wont explain it there, If I was able to make it I’m confident that you can 2.
More interesting is the question, Does it works? I take a picture of my finished 1/9 unun loaded with a 450 resistor at 1.8 and 30 MHz, and it’s really good. I made two pictures one at 30 MHz, SWR just a little over 1/1.2 and one at 1.8 MHz, SWR 1/1. As soon as I get my AA analyzer back, I will put a picture of the complete HF spectrum.
One thing is sure, the technic use by DG0SA to built this unun is really good.I’m sure he takes time to optimized the broadband of this balun, but if you still found the SWR to high on the high part of the spectrum, you could try to make a windings less without forgetting that the reactance will change and the SWR on the low part of the spectrum will change as well. I won’t do it, I wish the tore would be a little bigger to put 3 windings more on the tore as with 8 turns the reactance is about 673 each windings a little low for the low band. A 11 turns windings would have given about 1273 ohm of reactance and probably even better result on the very low band, medium and long wave. But there’s no room on this tore to do it if you want to use it also on TX as the wire as to be big enough.
About the power DG0SA give 800 watts as power rating (If teflon insulated cable is used), I don’t even know if it’s RMS or PEP power , I don’t check it as this one was for reception purpose only. I’ve seen this core used on 1/1 2 KW PEP balun and on a 1 KW PEP 1/4 balun. Your opinion or knowledge will be appreciate on that point. As usual you can E-mail me.
How does it cost?
The needed tore cost between 4 and 7€.
The duct tape cost less than 3€ for 5 meters (you need about 30 cms).
The wire cost was 7€ for 10 meters (you need about 1.5 meters).
You need an electrician box if mounted outside (price depending on your mounting choice).
And you need a PL or N Plug. Enjoy and replicate.