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I've been mulling over the idea of a voltage fed vertical for a while now, and finally got one up for 20 meters yesterday. At 0003, so the contest had just ended and the band was suddenly quiet.

Why a voltage fed antenna? Ah, dunno, just never had built one, thought I'd try it. Feedpoint is 16 ft off the ground, top of antenna is just over 49 feet. Wooden mast, 20 foot crappie pole. Black gold, Texas tea...

20 is in its usual crummy shape today so there's not much of a basis for comparison to a nearby dipole at 30', but my main reason for building this was to see how the expected lower angle of radiation would compare to the 2 element yagi at 35' it replaced.

Impressions so far:

1. No RF in the shack at 600W.
2. Having an .05 wavelength "counterpoise" makes no noticeable difference in RF in the shack or in tuning.
3. With what DX signals are available, the vertical is averaging 2-3 S units better on receive than the dipole (I am not comparing signals that are in the dipole's nulls, the difference there is pretty dramatic, as you would expect).
4. On some signals, there is no difference, and only one one of about 25 has the dipole beaten the vertical-- but it will probably win more when the band is in better shape.
5. Too early to tell how the angle will work out in exchange for the low yagi, but I was unable to break a pileup to a 9K this morning. I'd like to think the beam would have given me a better fighting chance, but since I don't have room for both of them at the same time, I'll never know.

Most of the voltage fed antennas I've known have been low band ground mounted verticals or Bobtails. It could be that few people build these for the higher bands becuase they're more trouble than they're worth. Guess we'll see.


Rick

What did you use to build the matching system? Got pics?

Yep-- now these aren't pretty, but:

I figured a tapped LC circuit would need somewhere around 6.5 uH and 20 pF, and since RG-8 has 30 pF/foot a 10" length or so would work for the capacitor. An online calculator showed an air-wound coil with 10 turns in 4" with a 2.5 in diameter would be about 10 uH, so I figured I should be able to find a tap on that someplace to match 50 ohms at 14.175.

So I bought 10 feet of #8 bare copper at Home Depot, and started looking around the garage for something close to 2.5 inches... All the pint paint cans and spray paint cans have that lip on them, so I ended up using a white vinegar bottle, the plan being to hold the turns in place with epoxy. That turned out to be not such an easy thing, so this is what I came up with for that:




The 1 minute epoxy ran more than I thought so it's not very neat-looking, but it worked:




The coax capacitor was just soldered across the coil:




Test setup with the noise bridge and VSWR meter, using a 4.7K resistor across the coil. 3rd turn on the coil and about 2 1/2" trimmed off the coax made for a near perfect match (whether it would really match the end of a 1/2 wave remained to be seen):




I picked up a 6x6 inch weatherproof junction box while at Home Depot to mount the matching network in:



Long story short, I didn't have to change a thing when I got it connected to the actual antenna. I cut the antenna 1" short to compensate for the lead between the coil and the antenna (and as a SWAG for the velocity factor of the insulated wire), and that helped a bit as the antenna favors the low end of the band but is still under 1.5:1 at 14.350.

This is the feedpoint with eveything mounted- that coil of coax is the CATV feed:



So there's the whole thing:




I figured if it didn't work I'd remove the matching network and use a 1/4 wave section of open wire, maybe even make it a J-pole since it was 16 feet to the ground. The mast is just spliced-together 16' sections of 2x2 that were made from ripping a 16' 2x4.

The key word here was cheap, and I nearly pulled the trigger on ordering a 4BTV, but decided to try this first since I'd only be out a few bucks if I didn't like it.

Hope that wasn't overkill.


Rick

Awesome!

__________________
Highlander, NA-821 on 11 Meters.
N9RZF, David on Ham Bands.

Yaesu FT-847, Galaxy DX-2517, President Lincoln, Cobra 150 GTL, Uniden Grant LT.

Nice pics and details. On that matching section, are the green wires where you attach to the feedline or is that going to the vertical section and radials?

Hey thanks-- I've seen some guys use that epoxy trick and make coils you'd swear were commercial stock. I couldn't quite pull that off, I'm afraid.

Yeah, those green wires are what attached the coil to the antenna and to the ground lug. I had some 8x32 hardware in the garage and used that and spade lugs for those connections as well as the antenna wire, which is just 14 ga stranded insulated house wire.

The coax was just soldered directly to the coil and the common ground connection. If I had it to do over again I'd use a piece of a buss bar where the coil, coax shield, coax capactor shield, and green wire for the "ground" connect. All I have is a 250W gun and even though those were added one at a time it took forever to heat that up once it was all connected. That coil, 33 feet of wire, and 70 feet of coax make a very good heat sink! There are no radials.

A ground plane would have been much easier to make, could have been multiband, and I could have used the push-up pole that was already there-- but I wanted to avoid the multiple tie-off points, and for some reason was just Jones'n to make one of these. If the band will cooperate I can decide whether I like it.

Rick

Makes you feel good when something works, doesn't it? May not be the absolute 'cutting edge' of the latest materials known to man, but who cares? It works.
- 'Doc


...now, if you could just get it above those pine trees...

Ha! Yeah, this one almost would earn me a degree in the Crude Arts. Man, some of those pine trees are 150 feet tall!

One of them supports one end of my multiband dipole, using a 3/8" rope and pulleys that terminates into a ground-anchored screen door spring hidden in the azaleas. Several mornings after storms I have expected to walk out and find that antenna gone, but it's survived four years of some pretty strong winds so far.

Rick