Clandestine End Fed Antennas
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| Jul 30th 2012, 16:59 | |
0001216526H80Total Topics: 0 Total Posts: 0 |
The concept of an end fed antenna is Intriguing but from what I've read and heard "It ain't worth it". Still with a tuner away from your rig, the proper grounding and some degree of luck it might work. Now for the $64 question. What effect would coax, used to insulate the wire out of the shack, have on the antenna? Dan Clark WB4ARC |
| Jul 30th 2012, 19:17 | |
W1VTSuper Moderator Total Topics: 0 Total Posts: 0 |
Hi Dan, With a coax feed, instead of a long wire fed at the end, it would act as a grounded long wire fed the coax distance from ground. The shield of the coax would act as a wire to ground. The coax run itself would not only add loss to the system, but would act as an impedance transformer if the SWR weren't 1:1. Zack Lau W1VT ARRL Senior Lab Engineer |
| Jul 30th 2012, 22:37 | |
0001216526H80Total Topics: 0 Total Posts: 0 |
Thanks Zack. Plan B now goes into effect. PVC pipe with scrap RG58 center conductor and shield shorted, installed to take the antenna out of the shack. The PVC pipe will have an end cap with a hole with a bolt and a nut to connect to the long wire. I'll have to do the exposure test and warn the family not to go near the egress while I'm operating. It's a small price to pay for a lot of fun. Thanks again. Dan Clark WB4ARC |
| Dec 4th 2012, 02:22 | |
NC8VTotal Topics: 0 Total Posts: 0 |
Just a thought... If you're thinking of using RG-58 as your end fed wire, to take advantage of it's greater surface are (the shield) could you just short the shield and center conductor together at one or both ends, and feed it as a random-length wire via a transmatch? Alternatively, if you're putting the wires inside the PVC pipe already, you might consider a "sleeve dipole": it's centerfed, with the center conductor serving as one leg, the coax running from end-to-middle surrounded by a conducting sleeve serving as the other leg. Electrically it's a regular hald-wave dipole, but physically the feedline "comes out" of one of the elements. I made one using RG-8X as the feed, and sliding the shield scavenged from RG-8 as the sleeve. Remove all but about an inch of shield from the center-conductor leg, and peel back the shield over the coax jacket and tin it. Then bunch up the RG-8 shield (like scrunching a finger puzzle to get your fingers out) and slide it over the feedline/coax. You could also slide the whole coax through and cut off the shield for the bare leg once you got enough through--that's what you'd do if the coax connector was already soldered on one end of the feedline, for example--and solder the larger diameter shield (now covering the jacketed part of the coax feedline) to the turned-back bit of RG-8X. Smooth out the new braid-shield, and affix it at the "far end" from the center of the dipole with sealing goo of your choice and a bit of electrical tape to cover the goo. Anchor the far end of the center conductor-only leg suitably, and place/raise/hang the antenna as you choose. There will be some considerable common-mode currents induced on the shield of the feedline from the endpoint of the RG-8 braid, so you'll need a common-mode choke at that point. On the suspenders-and-belt principle, I formed a coil of multiple turns of the RG-8X feedline, put a string of ferrite split-core toroids on for good measure. Mine was foe a proof-of-concept--I hung it outdoors "naked" (not inside PVC) and eventually the exposed braid corroded from getting rained on; water was wicked doen the feedline from the center feed-connection site, etc. But due to tower restrictions (XYL's not neighborhood's!) and our "re-landscaping" project, I ca |
| Dec 4th 2012, 02:34 | |
NC8VTotal Topics: 0 Total Posts: 0 |
Sorry, spiteful smartphone. Due to tower restrictions (XYL's not neighborhood's), and a "relanscaping" project, I have to feed from along the back or side of our property near the detached garage that houses my shacck. This thing frequently outperformed my End-Fed Zepp on 40/15, being positioned more favorably around the compass. There are some good QST articles on people making these as Verticals, but I wanted to try doing one for horizontal mounting. Now that I've proved the concept, I'll have to make a more durable version to hang some raw winter day--maybe goo the centerpoint and varnish/seal the whole RG-8 shield-leg to protect them from the elements? Good luck on your antenna farm. As an antenna designer told my radio club last week, "The best antenna is the one that works for your station and your QTH." Ted Morris, NC8V (ex-WB8VNV) Cincinnati, OH |
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