Topband: A little assistance needed with an attempt at a T antenna

[Ashton Lee]

I don't believe that the off center top loading will have a huge effect if you feed it as a T, vs a symmetric  T

Theory would say that a ground fed T against even  3-4 radials will have a lower DX angle. The price you pay is the ground losses of a vertical (not due to the modest ground radial system, but true of all vertically polarized antennae). Let me hazard the guess that you will be down about 1-2 S-units versus an ideal monopole vertical. That's not bad given that you don't have 160 acres and a 135 foot tower. An amp puts you right back in the game.

Basically it would be nice if you set it up so as to be able to switch from one feed to the other to test, since your existing antenna did OK. But I suspect you will like it slightly more as a vertically fed T.

You might pick up a bit of efficiency by using a full length, or even over 1/4 wl inverted L since the longer antenna should have more radiation resistance. 127-135 feet of wire, roughly.

A bigger deal will be to work out a receiving antenna set up. I've had terrific luck with the Wellbrook loop which will easily fit into your set up. Because your transmitting antenna will be non-ressonant you shouldn't need to worry about having the receiving antenna close to it. If you do go with a resonant L you may pick up noise off that.

KQ0C
Ash

On Jan 4, 2013, at 6:56 AM, Mike Armstrong <armstrmj at aol.com> wrote:

> 
> Hey guys and gals,
> I have a question: I have an OCFD that is about 130 feet long, end to end.  It is Off Center Fed at a current node for 15 meters, which is the band it was designed for.  Ends up that it tunes easy on just about any band, albeit with open wire feeders and a tuner.  It works very well for 10, 15, 17 and 20, since the major lobes are directed where I want them.  Although anecdotal, what I can say is that I rarely have to make a second call to any station I want to work on those bands..... which was a very real surprise considering its simplicity.  it is 40 feet high, which is not great, but it is as good as I can do.  I have actually tuned it to 160 during a contest last year and ended up working (and thank you guys, CONFIRMING) a total of 9 countries....... Japan, Australia and Chile included..... Which REALLY blew my mind.  But I digress...... Suffice it to say that for the higher bands, I am very happy with it.
> 
> I want to try to use it as a T antenna and lay out some radials.  I do have a limited space situation, from a 160 point of view, with the typical postage stamp lot.  I got the OCFD as long as it is by placing a good portion of the antenna in my Mother-in-Law's property and terminating the far end in one of her palm trees.  I needed to say that because some folks might wonder how I put a long antenna on a postage stamp lot..... I didn't..... It is 2 postage stamps side by side.  However I can't go crazy and lay antennas everywhere on her land.  So...... After all the preliminaries, I want to try the T, but it definitely struck me that the antenna, being OCFD as much as it is, is definitely NOT balanced side to side.  Would this have a negative impact on a T?  Would it be better to call it an inverted L and just forget the short side, including that side of the transmission line?  I am thinking that the latter is probably the way to go, but if a T would work in such a strange c
> onfiguration, I would prefer to use the extra wire rather than having it sit idle.... LOL. 
> 
> Anyway, thanks for taking the time to read this tome..... Any response would be welcome, especially if anyone has actually done something similar with an OCFD that is so "unbalanced."  Ay anecdotal data concerning performance is welcome, as well...... If you are still using it, because it is a decent performer on 160, that matters because you guys are so willing to alter antennas if they aren't doing EXACTLY what you want them to...... He he he.
> 
> Mike AB7ZU
> 
> Kuhi no ka lima, hele no ka maka
> _______________________________________________
> Stew Perry Topband Distance Challenge coming on December 29th.
>