Balun help

[WA1GFZ]

Tom,
I'm looking at a 160 meter ant for the other QTH and Frank's antenna double size gives a higher input Z than a 75 meter dipole on 160. I'm torn between 2X Frank's and and a FAN dipole 130 feet long.  Hanging vertical legs off the ends will bring the ant closer to the house which has a double internal aliminum layer under the sheetrock. I would like to keep the antenna as high as possible. Also the neighbors are close.

[k4kyv]

My method for putting antennas in trees is to avoid anything like pulleys or springs.  They were always more trouble than they were worth.  I prefer to use a daisy chain of johnnyballs for end insulators, and #8  or #10 copperweld for wire.  From my experience, the tree limb will break before the antenna, and the antenna will actually immobilise the tree limbs to a certain extent.

One problem I had with a dipole was the open wire feedline.  At first I used EF Johnson ceramic spreaders spaced several feet apart.  Whipping around in the wind repeatedly and consistently caused every other spreader to break.  I finally replaced all the ceramic spreaders with home-made ones, using 1/2" plexiglass rods.  That took care of the problem until I put up the tower and replaced the natural antenna support system altogether.  Shortly afterwards, a wind storm took down the entire tree.

[flintstone mop]

Since ladder lne has been re-popularized, there are numerous ways to bring it into the house and then you can avoid the lossy balun.
There are a few companies that sell a device that installs in the sash type window, enabling you to bring the ladder line into the shack.

And then you can bring it in through vinyl siding through an outside wall and hang your tuner on the wall near your shack and run coax to the tuner from the transmitter/receiver. Weaving it around the duct work and around the joists, flourescent lights, etc, in the basement can bring a lot of extra noise into your receive.
Good luck

Fred

[N3DRB The Derb]

you cant really weave it at all, or it's no longer balanced feedline. 

[K1JJ]

I did a rather extensive study of Frank's antenna system 2 years ago and recommended moving the balun from the output of the tuner to the input for less loss as I recall.  The study included other incremental changes and their losses, which order to procede, all by antenna and transmission line simulations:

http://amfone.net/Amforum/index.php?topic=9181.0

Interesting study, Tom.  I missed that a coupla years back.

Is this a conventional FOLDED dipole, but using a 1/4 wave flat top? Looking at Frank's  diagram I thought that the opposite point from the feedline was open like linear loading- but evidently it is closed with a jumper across the insulator? I wonder how your study would come out if the opposite end was open....   Oughta model it to see.

*** Whoops -  I see this whole subject was finally beat to death in that old thread. The opposite end is open and the specs look pretty good now.

T

[WA1GFZ]

Johnson spreaders work best with a center support. I have a run that has been in use since '83. I had to tighten the tie wires a couple times.

[kc2ifr]

Well.......here goes...
My antenna is a 165 ft. dipole. No room for anything bigger. I feed it with home made balanced line....number 10 solid copper wire......and tune it with a home brew LINK COUPLED tuner. Works on all bands 10 thru 160.
Cant get any simpler for a compromise  antenna that has to cover all the bands. You dont have complicate a simple problem.
No stinking baluns

Bill

[Mike/W8BAC]

Hi Johnathan,

My lot is just about identical to yours and I'm only about 12 miles away from you. I use a W7FG doublet at 40 feet and a Johnson kilowatt tuner.

If your interested in seeing how it's put together, stop by this weekend and have a look. Drop me an email w8bac at comcast.net. You can see more at www.w8bac.com.

Mike

[W2PHL]

I had a 75m dipole fed with the brown plastic window line. It seemed to perform OK and tuned easily on all bands (except 160m) THe only problem was RFI up the wahzoo, even at low power. When the antenna fell, I put it back up and fed it with coax. I also used a coax common mode choke. The RFI problem does not exist anymore. I can use my SB-220 now and watch TV at the same time. The TV antenna is about 20ft from the dipole. Just my two cents worth.

[WA1GFZ]

My open wire line is just outside the livingroom about 8 feet away from the TV. Legal limit on 160 and the family doesn't know I'm on.

[K3ZS]

When I first put up my window line fed 135 ft doublet, I also had a lot of RFI.   I did some testing, I had an old voltage mode low power balun, using that the received RFI went away.   Did some measurments and found out that the so-called current balun in the commercial T-tuner was very poor on 40M and 80M, and nonexistent on 160M.  I bought a hefty balun from DX Engineering (again, no interest in the company) and it cured all the RFI problems.    The measurements also confirmed good balance.    I think that all the bad publicity here on baluns is due to the fact that most of the ferrite baluns available from most places on the internet and in tuners are mostly crap and don't work very well.    You can tell if a balun is heating up by transmitting 1KW into it for a while and seeing if the SWR changes (assuming the tuner was tuner for a match), especially on 160M with a short antenna.   Do that with a tuner with a built-in balun and you will see why baluns get a bad rep.

[K1JJ]

Hi Bob,

Yes, DX Engr uses Tom/ W8JI, to design some of their stuff. They have some really good products there. I would have confidence in their high power baluns.

I agree that ferrite baluns have gotten a bad rap cuz of the W2AU smoke-baluns and possibly from the MFJ history of blown-out baluns in some of their under-rated tuners.

In addition, most ferrite baluns are prone to EMP saturation from nearby lightning strikes too. One bad pulse and they are permanantly saturated. I suppose you could see the damage by a bad SWR if it was a true ferrite transformer. Bad beads over the coax might not show up at all.

Bottom line is, for a simple dipole, a coax balun using turns carefully wound on a PVC form is probably the most strapping way to go.

BTW, how is the DX Engr balun constructed? Does it use ferrite and is it a true transformer with wire turns or simple beads over coax sealed in a tube?

Later -

T

[WA1GFZ]

They explode if they take too much pulse power.

[k4kyv]

Anyone remember the air-core baluns made by B&W?  They were made as a pair of coils that looked like regular open-air Miniductor  stock, but were actually two bifillar wound, 150Ω parallel transmission lines, each wound into a solenoidal coil.  At one end, the transmission lines were wired in parallel, while at the other end they were wired in series, to give a 4:1 match.  A pair of these coils would match the 300Ω balanced transmission line feeding a folded dipole to the 75Ω unbalanced output from a pi-network or the balanced output from a low-Z link output.  A set of these  coils feeding 300-ohm TV ribbon to a folded dipole (usually also made from 300Ω TV ribbon) would be broadbanded enough to cover the entire 80/75m band and handle 150 watts or so of power.  They were designed to work 80-10m.

[K3ZS]

Don, I believe Heathkit had one like that also.     Tom, the DX Eng. baluns are heavy and large and expensive.  They are true ferrite core transfomers, they have a version made for use after tuners.    This type uses high voltage insulated wire in the windings.    My 1:4 tuner type balun is rated for 50 to 200 ohms and 5 KW continuous power.   You probably have to derate the power in actual use since it would not be anywhere near 50 to 200 ohms in actual use.  They suggest using a 1:1 for use on the output of tuners figuring you would just as likely see a lower impedance on the output, depending on your feedline length and band.   I still plan on making your version of a balanced tuner for 160M.

[Mike/W8BAC]

T Said,

In addition, most ferrite baluns are prone to EMP saturation from nearby lightning strikes too. One bad pulse and they are permanantly saturated.

This is really interesting Tom. What is permanent saturation? Please explain this if you will. Always something to learn here. Thanks

Mike

[K1JJ]

Bob, 

That sounds like a very nice toroidal transformer.  I've made  some myself that were wound on 2" toroids using Teflon wire. They were designed for 6M and worked great with little added swr.

Mike: There's not a lot on the web about lightning EMP core saturation damage. But, any ferrite core can be damaged by severe oversaturation. As far as actual effects,  I don't know if it's the heat generated that physically splits the ferrite into bits or a permanent magnetic direction sets in the atoms ... or some other type of physical damage.  But either way, the permabilty gets wasted from what it was originally.

I'm sure someone here will know the inner scientific details... :-)

T

[Mike/W8BAC]

Thanks Tom

My first (only) guess was magnetism. That is an interesting subject. Maybe Stu will chime in.

Mike