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Durkin Tactical Franklin Armory
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Posted: 7/20/2010 6:46:34 AM EDT
I'm setting up my Hf station and built in essence a g5rv jr for 40-10 meter antenna. I used 300 ohm twinlead for the down line of approx.14ft. I'm thinking I need a "choke" balun for it to feed coax to the rig. I'm wondering if 8-10 turns of rg59 on a 4" pvc core would be enough. Any ideas or tips would help. The reason I want to use rg59 is I have gobs of it and want ot save my rg8 for the feeds to the radio. I'm studying for my extra and all this is starting to run together.
Link Posted: 7/20/2010 7:34:29 AM EDT
[#1]
Actually RG-59 is not bad from what I read.  Others do the same for the same reason.

If you use the "ugly balun", on the 4" pvc, use 18' - 20' of coax, which makes about 17 to 18 turns.  Do not bend the coax too sharply.  Hold the ends in place with ty-wraps through holes drilled in the pvc pipe and come off the balun at a tangent on each end so no sharp bends.

http://www.hamuniverse.com/balun.html

Drill a hole in the edge of the pvc to hang it with some cord (550 parachute cord makes great antenna rope) or by some other means.  Don't put that weight on the coax and connector.

You can also use 10 RCT-2 snap on ferrite beads for a choke balun.  These are listed under Chokes at hamcity.com or radiodan.com.  Many "1:1 baluns" are actually nothing more than a series of ferrite beads encased in pvc pipe.

AFM
Link Posted: 7/20/2010 7:42:37 AM EDT
[#2]
i wonder what effect the 75ohm cable will have on the output since most of whats used is only 50ohm. there are plenty of line loss charts on the web. hit up google and im sure you will find what your looking for.
Link Posted: 7/20/2010 8:58:11 AM EDT
[#3]
I made the ugly balun AFM mentioned. No complaints.
Link Posted: 7/20/2010 8:58:25 AM EDT
[#4]


I've never double-tapped since I joined and now it's happened to me twice in one day!
Link Posted: 7/20/2010 10:35:10 AM EDT
[#5]
Quoted:
i wonder what effect the 75ohm cable will have on the output since most of whats used is only 50ohm. there are plenty of line loss charts on the web. hit up google and im sure you will find what your looking for.


50 ohm output into 75 ohm coax... 1.5:1 SWR.

And if he has a tuner on the radio end, it will tune down.

If he uses a half wavelength of coax, it won't even hurt that much.
Link Posted: 7/20/2010 10:38:25 AM EDT
[#6]
Quoted:
I made the ugly balun AFM mentioned. No complaints.



I have the "Ugly Balun" 18 turns or so on 4" pcv, on my main antenna, a multiband dipole.

I have the snap on ferrite beads on coax I use for portable ops.  Leaving about 1/4" between beads allows some flexibility, and the coax can be coiled neatly with the beads on.  I have some little bands of large diameter heat shrink on each snap on bead, cut about 3/4" wide, to keep them clamped on the coax.  While they didn't seem prone to come loose, it was just a little added insurance against losing any.
Link Posted: 7/20/2010 11:09:00 AM EDT
[#7]
Thanks for the help. Yes I am running this into an MFJ 969 versa tuner II. Then into my ts-440sat. I didn't realize that I would need that many feet of coax. I might have enough rg8 to wrap on the core then transition to the tuner without adding more connectors. I'll have to make a bracket to secure it to the mast. Would a 8" stand-off be enough clearance to keep the mast from de-tuning it?
Link Posted: 7/20/2010 11:20:11 AM EDT
[#8]
I've used 2" PVC and about 12' of RG-8M and it still worked. Woudl it work better with more? most likely. But it was still usable. Made a psk contact on 20M from Nd to Belgium with that setup.
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