The AM Forum

Hi Everyone,

I decided to put up a 134 foot inverted L and build my own 9:1 UnUn to match the antenna. Using a 450 ohm resistor has a Terminator, I ran the circuit through my spectrum analyzer and the results were less than expected. I was hoping the swr at the transformer would be a little flatter, such as 1.8 MHz to 35 MHz, that was not the case. My question is should I be using a different mix then the T200-2 core?  Perhaps a 43 mix. Should I decrease or increase the number of triflier turns around the core? I've included three pictures one of the 9 to 1 UnUn, and two of the spectrum analyzer results. Any comments would be appreciated.

73 de Gary,KF9CM

Nice build. If that's a 4 in. box and #12 wire looks good for 300 watts or so matched. 

1.) Do you really need 9:1?  And is #10 or 12 wire large enough?
Try modeling 4:1, and 6:1 into the wire antenna.  And as for the antenna Try changing the wire length. a DL secret is that a matching circuit (tuner) is required anyway. The Unun just gets you in the ball park.

The steep incline on 10 leads me to believe that internal wiring lengths might be straying with capacity somewhat chaotically. Some baluns, so maybe ununs too actually have compensating caps at higher freqs.

lesser ratios might be simpler construction and results might surprise you.
I'm finding complex impedances all over the place in trying to do same with a Windom.  Results vary drastically from even middle to band edges, let alone from band to band.  One solution works great for 80/40 but 20's dirt.
One works for 80/20 but 40's dirt, etc. 

TNX for the reply Rick,

I think the solution to making the Windom work, (from the research I found), you will need a Guanella (Current) BALUN because the single core BALUN won't cut it.
I found an excellent site that that has some good data and construction on Guanella (Current) BALUNs.

http://www.kn9b.us/guanella-balun  (http://www.kn9b.us/guanella-balun)

I might take my inverted L down and put up a Windom

73 de Gary,KF9CM

Are you talking about a true Windom with single wire feed off center?  If so, either it or the Inverted L will require a good ground or radial system.  Can you do that?

Hi Jim,

Yes I have a good radial system. It's not a true Windom with single wire feeder. It's 130 ft wire split 65%/35% and fed with coax through a 4:1 BALUN.

Gary

  Yo'


      I think your right, It's the mix.. I always thought LF/HF cores
were Yellow. At least Amidons are..   Please let us know.

GL

/Dan

Mine is a true Windom which I finally got working on 80, 40 and 20 but with an L net match.
All three wire elements, short, long and feed line, are critical, height above ground..  Just about everything. Going to put the results and MMANA calcs. on my Previous Windom thread.  The measuring, cutting, reconnecting and number of trials is not for the faint hearted.  Burndy solderless connectors are very handy, to say the least.

Another thing I found was minimum capacitance in an L net should ideally be zero, not some 30pf or so found in a real variable and misc. wiring.

I'll release a set of impedances and SWR (vs. 200 ohms ) matching values found. Used 200 ohms because a lot of literature mentions that value if using coax feed like yours, Gary.  I may do that but the single wire feed is working fine.  Don't be scared by all the advice and broken dreams out there including having to have huge ground fields, but of course some is required.  I'm pretty sure the 300 ft. Of buried AC line to the house is doing its share along with my connected to neutral piddling ground system.

Another neat thing is that the far field lobes are smoothed and nowhere near as sharp as imagined particularly on 40 and 20 but with peaks of 6 or 7 dbi.   80's field of course is just a big nearly circular blob.  Because of true Windom's open wire feed vertical component, 40 and 20 have surprisingly low radiation angles for those not so narrow lobes too.

One thing I did learn; feeding any Marconi or derived system on anything more than a single freq. is closer to " art" than science.  ...and an arcane art at that.  ;D

Is it an Inverted-L or a Windom? What bands are you hoping to cover?

43 or 61 mix is what you want.

My understanding is that iron powder cores are higher Q than ferrite.  Since you want a wide bandwidth, a lower Q would be more desirable, i.e. Ferrite.

Consider Ferrite vs iron powder saturation at power and other characteristics such as freq.

'9CM, tnx fer the guanella link.  Neat stuff.

And all, -it's a fun subject

Well I went ahead and built a Guanella (Current) BALUN and I like the results a lot better. The pattern is a lot smother.

Gary