ARRL

NC8V

Joined: Sat, Apr 4th 1998, 00:00 Roles: N/A Moderates: N/A

Latest Topics

Topic Created Posts Views Last Activity
Shortened 160M Loop: inductor placement Jul 22nd 2012, 00:08 3 1,145 on 4/12/12

Latest Posts

Topic Author Posted On
Shortened 160M Loop: inductor placement NC8V on 4/12/12
Somehow, I forgot that the "loading coils" would look different on other bands! ("D'oh!"). Thanks for remindIng me, and for strengthening the argument for using some more conventional techniques.

Ted Morris, NC8V
Clandestine End Fed Antennas WB4ARC on 4/12/12
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
Clandestine End Fed Antennas WB4ARC on 4/12/12
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
Shortened 160M Loop: inductor placement NC8V on 22/7/12
I am pondering over the use of loading coils to "shorten" two legs of a 160M horizontal full-wave loop, to make it fit my property. I would use ladder line to my transmission line matcher (Handbook design) at the operating position. Also, I am most interested in a particular part of the band, so a narrow "resonant" bandwidth at 160 is acceptable. I could use help on calculating the inductor value needed to "lengthen" two parallel physically short legs, and on determining the "best" place in those legs to place the inductors. I have done some extensive reading of 'net-accessible resources, but pointers to valued resources are always welcome. Tnx!

Back to Top