43 ft antenna question

[gcgrotz]

For several years I ran a 43 ft vertical in a small backyard. I had over 1000' of wire in about 70 radials of varying length. It worked great; a real pileup buster on 40 with 600 watts and was pretty good on 75 to Europe with the loading coil switched in.

So here's the question: if a 43 ft vertical works well as a non-resonant antenna, how about a dipole of 86 ft with a 4:1 balun or 450 ohm open wire? Has anybody done this or heard of it?
Any EZNEC experts care to model it?

 

[LtDoc]

I figure it ought to work as well as your vertical, sort of. Different polarization so you'd probably hear different stations better than on that vertical. One variable that wasn't specified was the doublet's height above ground. That can make a difference too.
Have I ever used an 83 foot doublet? No, I haven't so no direct experience. Did I model it? Nope, I'm too lazy.
- 'Doc

 

[mtindor]

I ran a 110' Vee fed with about 40' of ladderline, which then ran into a 1:1 current balun and on to my LDG autotuner. Easily tuned up on all amateur bands between [and including] 6m and 40m. On 80m it was tunable on the CW but I could not get the LDG to tune 75m phone. Of course, if I had experimented with ladderline length it would have made a difference.

If you intend on using your dipole as an all band antenna (80-10 for instance), I think should at least make sure it's 88'. I'm thinking that's the magic minimal number. And, important if you are using it as an all band antenna, you should use a 1:1 current balun rather than a 4:1. The feedpoint impedences are going to vary greatly depending upon the band being tuned, but overall the 1:1 current balun will give better results. The guys who know (W5DXP, W8JI, G3TXQ, etc) all agree on the 1:1 current balun. Definitely don't use a voltage balun.

You'll likely have to fiddle with ladderline length adding/subtracting a little bit if you can't get it to tune where you want to on 80m.

Here is a good writeup -- scroll down to the "D. Can we do better?" section...

http://www.karinya.net/g3txq/g5rv/

Another interesting read:

http://www.w5dxp.com/notuner.htm

And another...

http://www.w8ji.com/g5rv_facts.htm


Mike

 

[gcgrotz]

Thanks, I was just curious. I'm afraid no horizontal wire will work as well as that vertical did. My problem is the back yard is flat, but about 15' lower than the front yard, but the front yard has the high voltage power line across it. It looks like the home-brew carolina windom gets the call, it has been assembled with a new BalunDesigns balun and new RG8x to the line isolator. At least until I can try out a horizontal loop after the leaves fall.

BTW, I used the BalunDesigns 1:1 special for the vertical and have to say that he makes a quality product and answered some email questions promptly.

 

[mtindor]

Thanks, I was just curious. I'm afraid no horizontal wire will work as well as that vertical did.

You're right, for the most part. With 70 radials / 1000 ft of radial system your 43-foot vertical was an efficient low-angle radiator, great for working DX. If you can get a dipole up in the air at least a half wavelength, it'll do pretty good for DX as well. The problem is, and this is especially true for 80/160m, most people can't get their dipoles up 1/2w in the air. Heck, I'd say that even for 40m most people cannot. We're talking 270/135/67 ft in the air.

So if you compare your vertical to a dipole at suboptimum height, the vertical is going to be a better DX antenna. I have no doubt you're vertical was especially good on 40m long haul DX.

How high are you able to get your dipole?

My current wire is an Alpha Delta DX-LB Plus (a 40/80/160 wire, shortened with coils, along with parallel wires for 10m and 20m). It's up about 37'. At this height, and in the V config, it does pretty good on 10-20m for DX -- within the antenna's limited gain and it's omnidirectionality. On 40m it does great stateside and over into Western Europe but would do a much better if I could get it up about 66' and horizontal. On 80m and 160m it's pretty much a cloudwarmer. I'm lucky to get into the next state on 160m, and I can only really cover the East Coast on 80m.

Given the height limitations of the wire antenna, I'd surely gain a lot if I had a vertical with an efficient ground system for 40-160m. But, we all make do with what we have.

Mike

 

[zz0468]

Right up my alley...

I currently run a dipole with 43 foot legs, and open wire feed. I can offer a few observations. My configuration is an inverted vee with the apex at about 25'. the ends are about 10'. It's fed with about 25' of home made open wire line of undetermined impedance and using ceramic insulators for spacing. The open wire is fed by an SGC autotuner, with the ground lug attached to one side of the open wire line, not ground. The tuner itself is isolated from ground except that the coax from the rig to the auto tuner is grounded normally where it enters the shack.

NEC modeling shows it to be close to omni-directional with no lobes on 160 meters and 80 meters. Gain is a bit less than unity, but the pattern is clean. In the higher bands, the pattern gets increasingly complex with several deep nulls above the horizon. It also becomes slightly directional, as one would expect of a shallow vee configuration.

Operational results are quite satisfying. It loads up on all bands from 160-10 meters. Reports on the lower frequencies are particularly satisfying, and include questions such as what amplifier am I running. I run a 746PRO barefoot. I'm not a big DX'er, at least not on HF, but I can consistently work South America, Asia, Australia, and all of North America on all bands.

I've built several versions of this antenna at several locations, and all performed quite well, considering they were only 25' or so at the apex. Hope that answers some of your questions. I've found the antenna to be easy to build, easy to tune, and I have no complaints about performance. I can't get any more scientific than that, other than to say I'm happy with it.

 

[gcgrotz]

Thanks everybody. My problem is the sloping lot I live on. The back, where the vert would be, is about 8' below the front, which is about 6' below the street, which is about 12' below the elevation of the house across the street about 125' away. It also slopes down another 12 or 15 ft or so to a creek and then back up maybe 30' to the train tracks. So, the vertical would be in somewhat of a hole for very low angle radiation. The other house where I had it was fairly level (for around here that is) but on a small 30x120 city lot. The radial space was about 30x40 and some radials were only 12' and some were as much as 50' from the vertical. I went vertical because there was no way to put up a dipole without going over the top of the house which I couldn't do. BTW, the MFJ analyzer showed the feed impedance to be around 37 ohms at resonance so I figured the radials were working.

Any wire antenna would be over the sloping part with house end being 20-25ft and the creek end 40-50ft if I can borrow a spud gun. I've built a replica Carolina Windom short with the 16' hanging down ends so the whole thing is 100' long. If I can't get that to fit, I will lengthen the downhill end to 32' for an overall lenghth of 84ft. I used one of these in the house before the vertical and it worked well on 80 and was pretty killer on 20.

If I can get across the creek after the leaves fall and the weeds die this winter, I want to try a 270ft 80 meter horizontal loop. Not sure if there is enough room, if I can get close, I will just go with that. I have a BalunDesigns remote balun ready to put outside since I can't get open wire feed into the shack. I also have a 102' doublet and open wire line balled up in the truck from where it landed after i bought it at a swap meet.

Well, that's half the fun of ham radio, playing with antennas...right?

 

[zz0468]

You have some options. The nice thing about the doublet fed with open wire line is that, with a tuner, it'll load up and radiate. The limitation on how well it loads up is more dependent on the tuner you use. How efficiently it radios and the pattern is, of course, dependent on the antenna itself. But they're surprisingly effective because they don't depend on a good ground.