New Balanced Antenna Tuner at NE1S

[NE1S]

Or...

"How I Spent my Thanksgiving Vacation" 

Here's a pic of what I ended up with. Think link-coupled tuner, without the link. Instead, the center of the main (in this case, only) coil is grounded, and the hot conductor from the coax gets tapped up one side of center. Thanks to Pete W1VZR for this idea. It works slick, and avoids the complexity of adding the link coil. The air variable on the left can be inserted in series with this connection if necessary to improve the match, be rearranging a few clips. According to Pete, the entire coil is shorted end-to-end on the higher bands, but I haven't tried that yet.

The neon bulb test indicates good balance between both sides of the feedline for every band, and both antennas, I've attempted to tune. It'll even load the 80M dipole on 160M, although I'd only do this as a temporary measure if the 160M dipole came down.

The coil is a 50" length of 3/16" copper tubing wound on a temporary form of 4" PVC pipe, then allowed to expand to just under 5" in diameter. I then drilled out a piece of plexiglass and threaded it through. Paul KB1IAW helped me make the supporting frame around the coil from scraps of Corian-like material, which was microwave-tested and passed for RF loss. The base is a large piece of the same stuff.

The micas on the right are switched in for 160M.

-Larry/NE1S

[Steve - WB3HUZ]

Nice! Your system is just an autotransformer instead of the usual. It works the same when transforming impedances. I've seen this arrangement in some old handbooks. I think N2IDU built one back in the early 90s.

Happy Thanksgiving!

[WA1GFZ]

Larry,
I have a hunk of corian sitting on my service meter outside since about '87 and still looks good. When I built my kitchen I had a few hunks left over pressed into pot holder service and cutting board service. They go through the dishwasher a couple times a week.
Material has not changed color in 20 years. The only break down Ive ever seen is a friend uses a hunk on the hitchen stove near the burners that turned tan after a while. Cool stuff to work with.
Sure wish I could find someone to sell me raw materials for the new place. Custom made is out of site now. Nice job on the tuner.
That was Bob N1KW's method of doing a tuner.  

[Todd, KA1KAQ]

Nice! Now I wanna build one too!

"Mr Larry's Winter Tuna Project" , anyone can play. There's even a larger roller inductor with thick copper strap (strap) lurking in the basement.

[N3DRB The Derb]

yeah, thats a cool tuna. After I get my current project done,  some thing like that is next, with rf ammeters in the feeders. Same as it ever was. You gots to have fire in yo wire.

good enuff in 1923, good enuff for me.

[NE1S]

Hey, thanks for the comments, guys.

Maybe this weekend I'll put it in its intended home: off the bench and hanging upside down from the floor joists. I'm gonna need some help with that, though - that counter-top stuff is HEAVY.

-'1S

[WA1GFZ]

My long counter is 12 feet long 3/4 inches thick. It was like hauling a slab of aluminum.

[Vortex Joe - N3IBX]

Larry,
       I love the pic of that "dish" you have as an avatar. It came straight from SW Craft magazine in the early-mid 30's (I have the issue and can't remember which one it is offhand)

She was definitely one of the better looking ones. Some were obviously just "Gal Fridays" and others had some looks and maybe even some brains.

What the hell, any girl who'll take a gander at, and "strap on the cans" to listen to a homebrew "Dorele" with a pair of 30's in it is beautiful in my book!

[WU2D]

Larry,

What I want to know is  - did you use that thing on your TNT in the 1929 QSO Party?

I made a small version of this just for 160M after talking about it with Pete W1VZR. I see no negatives with it as built on a board. Why deal with the link? The power gets transferred!

However, if you were to put it in metal enclosure and were depending on it for harmonic supression and TVI reduction in a tight neighborhood I would say go with the link! The link idea can also allow a Faraday shield which would provide further protection.

Mike WU2D

[WA1GFZ]

A link may provide more common mode rejection

[Steve - WB3HUZ]

Lots of good info here.

http://www.cebik.com/link/link0.html

[NE1S]

I changed my avatar (going thru a mid-life crisis?) and in the future no one will know what the heck Joe IBX was talking about in his post  (sorry Joe!).

-'1S

[k3zrf]

Larry,

That is one MA-HA antenna tuner.

I haven't heard you using it (tuner) on the air yet.

Keep warm by the rig.

[NE1S]

Yo Dave,

Well, I'm fairly active, but mostly weekend mornings on 75M, and evenings on 160M. On 160M, I can usually be found on the Gray Hair Net (1945 Tuesdays at 8:00PM), and on the new AWA net on 1900 Mondays at 8:00PM. I also am a regular check-in to the AWA 75M AM net on 3837 at 4:00PM Sundays, although I'll miss this weekend 'cuz I'll be playing in an AWA CW "contest" instead. I use the new tuna mostly on 75M and 40M, mostly because out of convenience (long story). But it will easily load either the 160M and 75M dipoles (open-wire line-fed) on 160M.

My other tuna (in the 1st-floor shack) is a balanced pi-net with a toroidal balun on the input. I have coax running from the cellar shack to the 1st floor shack, so I can select either antenna tuner from the cellar shack. The open-wire line on both antennas has battery clips at the ends to clip onto the feed-throughs to enter the house, so I can swap both antennas between the tunas, too. Right now I have the 160M dipole running into the upstairs shack, and the 75M dipole going to the new tuna in the cellar shack. But to swap them around takes less than a minute.

Probably way more than you wanted to know!

[k4kyv]

That autotransformer idea will work just as well as a fixed link if you don't ground the frame of the main split stator tuning capacitor.  Grounding both the midtap of the coil and the capacitor frame can lead to high circulating currents and loss of efficiency.  If the layout is symmetrical, it should remain balanced.  Usually on  my balanced tuners I don't ground the coil or capacitor.

The problem with grounding any part of the tuned circuit is that it may make the feedline try to act like a Marconi antenna.  That common mode current will make the feeders more unbalanced than with nothing grounded.  The  balance in open wire tuned feeders is inherent to the antenna.  You can't force-balance a feedline.

If your setup results in unbalanced current in the feeders, try inserting a choke  balun in the line between transmitter and tuner.  A neon lamp should show a cold spot on the coil right at the midtap.

[N3DRB The Derb]

I may ditch the pair of matchboxes idea and build something like this instead. I think I could still handle a project like this.

The price of copper is really going nutz. makes buying coil stock a real pain.

[Steve - WB3HUZ]

Probably cheaper to snag one of those nice edge-wise wound types from a BC TX than to buy wire or tubing and wind your own.

[Vortex Joe - N3IBX]

I changed my avatar (going thru a mid-life crisis?) and in the future no one will know what the heck Joe IBX was talking about in his post  (sorry Joe!).

-'1S

Larry,
        At least you and I will know what a "dish" that girl was...............

[k4kyv]

The price of copper is really going nutz. makes buying coil stock a real pain.

Luckily I have a lifetime supply of copper tubing from some kind of high powered rf transformers I picked up for almost nothing at Young Engineering in Salem MA back in the 70's.  Must have purchased a half dozen of the things for just a few bucks.

Looks like copper products are going the way of 2A3's, 300B's, 845's, UTC LS transformers and HV electrolytic capacitors.

And gov't officials have the gall to tell us that inflation is "under control".  What a bunch of BS!

[NE1S]

I changed my avatar (going thru a mid-life crisis?) and in the future no one will know what the heck Joe IBX was talking about in his post  (sorry Joe!).

-'1S

Larry,
        At least you and I will know what a "dish" that girl was...............

Hey, Joe, I'll tell you what - you can have her, she's all yours 

-'1S

[NE1S]

That autotransformer idea will work just as well as a fixed link if you don't ground the frame of the main split stator tuning capacitor.  Grounding both the midtap of the coil and the capacitor frame can lead to high circulating currents and loss of efficiency.  If the layout is symmetrical, it should remain balanced.  Usually on  my balanced tuners I don't ground the coil or capacitor.

The problem with grounding any part of the tuned circuit is that it may make the feedline try to act like a Marconi antenna.  That common mode current will make the feeders more unbalanced than with nothing grounded.  The  balance in open wire tuned feeders is inherent to the antenna.  You can't force-balance a feedline.

If your setup results in unbalanced current in the feeders, try inserting a choke  balun in the line between transmitter and tuner.  A neon lamp should show a cold spot on the coil right at the midtap.

Hi Don,

I float the frame/rotor of the capacitor - I knew better than to ground it, with the center-tap of the coil already grounded.

I'll check to see if the center of the coil lights a neon - I haven't done that yet - good suggestion.

On all bands I've tried, with either antenna, the brightness of a neon looks equal on each side of the feedline. That speaks well to the balance of the magnitude of the voltage at that point, but gives no information about the phase relationship - correct?

-'1S