Toroidal Balun vs. Choke Balun

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W2XR:
Guys,

I made the plunge and changed out the RG-213 coaxial choke input balun last night before 75/80M bandwarming activities; it was replaced by a toroidal 1:1 current balun that is rated at 5 KW CW/10 KW PEP. Although the original coaxial choke balun worked well, the toroidal balun allowed me to maintain a unity VSWR all the way down to 3.6 Mhz, and I noticed less RF in the shack, indicating better isolation between the xmtr output and the input to the balanced L-network antenna tuner, and possibly less open wire feedline radiation due to better balance  conditions. The RF  in the shack was never a problem, but this was a nice benefit just the same.

With the coaxial choke balun, the VSWR would gracefully rise to 1.4:1 at 3.6 Mhz., although this was of course,  an acceptable mismatch.

With this balun change, the W2XR homebrew antenna tuner now covers the entire frequency range of 1.8 to 30 Mhz..

Thanks for all of the input!!!!

Best 73,

Bruce

The input L and output C settings did not vary much at all when the new toroidal current balun was installed.

WA1GFZ:
Bruce,
What antenna and feed line are you using? Also what are your L and C values in the tuner. My 160 meter dipole is now a Vee with shorter feed line and 62 feet of 450 on a 250 foot Vee is a problem length for my tuner. I think I have to make the feed line shorter. I lost about 50 feet when the tree yanked it down. Still have to drop 2 trees before I can put it back up.
I'm doing a 1:2 step up transformer with CT of the secondary grounded. Coax balun also has a problem. When the feed line was 110 feet I had no problems.
Odd thing is the KW match box works on 75 m. fc

W2XR:
Hi Frank,

The antenna is a 1/2 wave dipole cut for the 75M band up 45 feet and fed with 600 ohm open wire feeders. The overall length of the antenna is 122 feet.

The balanced L-network I'm using to tune this antenna consists of two high-power 22 uH roller inductors synchronized by a 3/4" wide cogged timing belt, and the output shunt C is a 1000 pf @ 14 Kv vaccum variable. The balun I described in the previous post is a toroidal  1:1 50 ohm current device and is located directly at the input to the network; it is rated at 5 KW CW, 10 KW PEP.

The network is located about 20 feet away from the xmtr, and is fed with RG-213. PITA to retune, now that we'll probably be QSYing frequently with the new 75M frequency privileges. I do have turns counters on the L and C, so this will makes resettability easy, but I have to walk across the basement to do this.

I built the entire assembly on a 32" X 28" piece of 3/4" thk MDF (large footprint necessitated by the large size of the components utilized in the design, and component spacing to maintain high Q) and there are no metallic housing components, etc.; this was done to maintain the Q of the tuner to as high as possible. Everything is right out in the open.

Hope this helps!

Would have like to worked you last night; I was on 3725 and later 3715 with WA2PJP and KA1KAQ for quite some time, until about 2:15 AM EST.

73,

Bruce

WA1GFZ:
cool,
I also have a pair of 22 UH HP inductors with bread slicers. On 1945 I use 22 uH and about 225 uf.  My antenna is 125 foot on a leg Vee at 60 degrees with 62 feet of #10 spaced 4 inches(about 400 ohms). All I have is 250 uf max or 350 uf max depending on padder. Maybe I need more C? What is the inductance when you are tuned up on 75. I should be about double that on 160.
My old set up was 110 foot feed line and 250 foot dipole. It tuned up a lot easier.
I think the optimum feed line length would be 55 feet. 
I crapped out at 1:00 and never got above 3685.

W2XR:
Frank,

For operation on 75/80M, which is the only band I currently operate on HF, the roller inductors are set for approx. mid-position, so this is about  10-12 uH.

The output shunt C is set for around 500 pf.

The length of the 600 ohm open wire feedline feeding the 1/2 wave flat-top is 66 feet, or a little more than 1/4 wavelength on 75/80M.

Hope this helps!

73,

Bruce

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