Winding an Un-Un

[A.Z.]

The resistors are fine.  Carbon or metal film type axial resistors have a spiral stripe that becomes inductive up in the GHz (and even then, for fairly low R values, up to say 200-300 ohms; above which, lead capacitance dominates instead).

The stray wiring is not however!  Trim that tight and short between core and connector(s).

Tim

ok for the resistors, but the wiring is screwed, it is like having a bunch of random inductors connected to the unun

[Squarewave]

Yes that appears to be what the problem was/is......but it was a little learning curve as I wanted to make my own and make one for a friend. Thanks everyone so far with your help and input on this one.

[A.Z.]

Yes that appears to be what the problem was/is......but it was a little learning curve as I wanted to make my own and make one for a friend. Thanks everyone so far with your help and input on this one.

Come on, you can't leave us in a limbo ! Keep us updated about your progress, please !!

[Squarewave]

Post 23

Much better throughout. I'll do it again with the enamelled wire later and see what happens!

[A.Z.]

Post 23

Much better throughout. I'll do it again with the enamelled wire later and see what happens!

thanks, keep us updated, please; then, if you want, please, take time to read this and reason a bit

https://cromwell-intl.com/radio/9-1-unun/

HTH

[Squarewave]

Thanks, will read that.

This is another FT140-43, with the enamelled wire, the arrangement isn't too tidy, as the wire is too thick really. For this size core, I really need a lighter gauge, but the results are very good.
The large croc clip is grounding the ground end of the winding to the coax socket ground.

[A.Z.]

much better now, you're on the right path

a suggestion; since a "random" endfed will have common mode even if used with a counterpoise, consider the idea of adding a choke to the coax feeder

http://www.karinya.net/g3txq/chokes/

as for the random antenna see here

https://udel.edu/~mm/ham/randomWire/

a good lenght is 25.6m (83ft) with the feedpoint at 9m (29.5ft) from ground and a counterpoise going down to ground (but not connected to it), optionally you may add some (insulated wire, as for the counterpoise and the antenna, #10 stranded, insulated will do) radials laying on ground and connected to the bottom of the counterpoise, if possible route the coax away from the antenna and place the choke at some distance or where the coax reaches ground, also, if possible, ground the coax braid right before entering the building/shack

HTH

[Squarewave]

Yes, I made a choke on FT240-31 with 17 turns of coax on it. I've had RF burn before, don't want that again 

[A.Z.]

Yes, I made a choke on FT240-31 with 17 turns of coax on it. I've had RF burn before, don't want that again 

In my experience, 17 turns of coax over a #43 toroid will serve you well over the whole HF band, then, in some conditions we may need to add a second choke for the "top bands" (160 and 80) wound on a #61; by the way, when it comes to unbalanced antennas like the endfed ones you will NEED a good counterpoise system AND a good choking system, otherwise your coax braid will work as part of the radiating system, and not only you'll risk RF burns, but your antenna will radiate in a SUB optimal way

[joeqsmith]

I pulled out one of my old ARRL handbooks and saw they show a un-un 9:1 taking a much different approach.  They don't have a lot of information on it so I thought I would toss something together.   I pulled out a couple of TDK HF70 cores and wrapped some silver plated solid core Teflon insulation wire on it.   I didn't have a decent 450 ohm load so stuck a couple of 1ks together.  Their performance is poor beyond 110MHz. 

After putting it together, swept it from 20M-200M.  It's not real flat.   

[T3sl4co1l]

For higher bandwidth, try a matched delay or Guanella type (the type shown above is Ruthroff).

This is constructed by wiring transmission lines in parallel at one end, and series at the other.  That is, consider a TL as a common mode choke.  By arranging some series-parallel combination on one end of a set of TLs, and a different series-parallel combination on the other, you can get any rational ratio you like (though going beyond quite small values of p, q (for ratio p/q) is rather bothersome).

By considering the CM voltages on each TL segment, and connecting them appropriately in each S/P stack, the number of turns for each TL on a common core can be determined.

For example, for a 9:1, you'd use 3 TLs in parallel on one side, wired in series on the other side.  Use Zo = 150 ohms, so the parallel combo presents 50 ohms to the source, and the series combo presents 450 ohms to the load.  The bandwidth is limited only by the TL width (i.e., breakup into higher TE/M modes) and how tightly you can arrange the parallel/series connections.  Only real delay is added, which as usual manifests as leakage inductance at LF, but does not incur the roll-off at HF that the mismatched delays of the Ruthroff design has.

Tim

[joeqsmith]

Used a surface mount part for the load.  It's 420 ohms but at least it's well behaved.   Wound something similar to what was shown but on a much smaller core (Fair-Rite T75).    Decent in the 3-30MHz. 

[joeqsmith]

Using the same T75 material.   Changed the load to two 1206 909ohm resistors.   Wound a new transformer using five turns of 22AWG TFE insulation, silver coated wire.  This is a little larger diameter.   

I should be clear I have no use for this device.  It's purely for adding to the discussion and was made from materials I had on-hand.  I'm sure there are better core choices and obviously this core is far too small to handle much power.

Notice the twisted core.  This was also a six turns but was a total waste of time. 

[joeqsmith]

LiteVNA calibrated for lower range and swept from 3-30MHz.  Touchstone attached for comparison.

[joeqsmith]

Looks like I missed the picture of the last one. 

[T3sl4co1l]

Should be as good as you're going to get with that arrangement.

How 'bout the Guanella design?

Tim

[A.Z.]

Should be as good as you're going to get with that arrangement.

How 'bout the Guanella design?

Tim

a guanella for a 9:1 UnUn ?!?

[cdev]

A picture tells a thousand words,(old proverb) it really is true with so many things in electronics.

 

Should be this one, for anyone curious.
https://www.fair-rite.com/product/toroids-5943002701/

So that's what, about 4cm turn length?  And it's three windings stacked to make an autoformer?  So the overall electrical length is 4cm * 5t * 3 = 60cm, or 1/4 wave about 125MHz, less velocity factor (twisted pair probably 80% so 100MHz).

Shouldn't be too bad.

LF limit is, let's see, AL = 0.8 so 5t is 20uH, somewhat less at ~MHz; into 50 ohms that's 0.4MHz cutoff.  So say 4x above that should be okay, which seems to be the case here.  Maybe more if you're putting a lot of power into it (watts?) because the core material is a bit lossy by some MHz.

Photo of the build?

Tim

That is the design that I use for ununs but I try to twist the three wires together they work better if I do that, my first and second ununs which I used for years just had the windings wound semi randomly around the core (nine, more than on the web page) When I twisted the three wires together first it improved a bit. Mine use from nine to 12 turns. Its connected to around a 50 foot wire. around 35 feet above the ground. I am probably goping to put a vertical of some kind up soon. Maybe 43 feet.

[cdev]

Do this if your un-un has a decent counterpoise or ground at the un-un or at the antenna (and its fed by coax) Otherwise the shield is the ground. hat could be a very noisy ground. Mine is. Its truly horrible. I suspect one of the local power poles, maybe . Putting a ton of chokes on the coax helps a bit but not enough.

much better now, you're on the right path

a suggestion; since a "random" endfed will have common mode even if used with a counterpoise, consider the idea of adding a choke to the coax feeder

http://www.karinya.net/g3txq/chokes/

as for the random antenna see here

https://udel.edu/~mm/ham/randomWire/

a good lenght is 25.6m (83ft) with the feedpoint at 9m (29.5ft) from ground and a counterpoise going down to ground (but not connected to it), optionally you may add some (insulated wire, as for the counterpoise and the antenna, #10 stranded, insulated will do) radials laying on ground and connected to the bottom of the counterpoise, if possible route the coax away from the antenna and place the choke at some distance or where the coax reaches ground, also, if possible, ground the coax braid right before entering the building/shack

HTH

[joeqsmith]

Should be as good as you're going to get with that arrangement.

How 'bout the Guanella design?

Tim

Easy enough to make a small 9:1 BALUN.   

Looking at his early papers, I guess my common mode transformers would be considered a Guanella design as well.   I would expect them to be prior art but maybe they didn't have Google patents back then...

[joeqsmith]

Mounted to a test board, used surface mount for the load and sweeping from 20MHz to 200MHz.  Again, just what cores I have on-hand and I'm sure it could be improved. 

I am interested in seeing how this 1:9 UNUN is constructed.   Post a few pictures of it along with test results.

[joeqsmith]

9:1 UnUn made from 4X HT70 TDK cores, 22AWG Teflon silver plated, 9 turns each. 

[metrologist]

Oh, I just wanted to play too. I named this file 25t balun and I remember I was trying to match my SDR I or Q input. No fancy VNA measurement this time.

[A.Z.]

Oh, I just wanted to play too. I named this file 25t balun and I remember I was trying to match my SDR I or Q input. No fancy VNA measurement this time.

Well, if you have fun winding impedance transformers, you may like this reference

http://www.introni.it/pdf/Amidon%20-%20Transmission%20Line%20Transformers%20Handbook.pdf

[joeqsmith]

After taking the time to build them, it seems appropriate to put a little power through them.   Not being a radio hobbyist, I'm not really setup for it.   I don't have any sort of load so I made up an array of 16 X 2W 470ohm Ohmite parts.   I started out at 3MHz using a small home made amplifier.   I don't have an in-line Watt meter but the supply was running about 40W.  Load required fan cooling.   My childhood VSWR meter seems to show something decent.