Broadband 80m

[KU0DM]

We're putting up an 80m dipole at the K0KU club station, but need to cover most of (if not all) of 75/80 meters.

My current thoughts on achieving this is a parallel dipole, with the upper wire cut for 3.550 and the lower for 3.900 (which are our target areas). If the (-) is the wire, it'd look something like this:

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What are your thoughts?
Any other recommendations?

Only requirement is that it's coax fed.

[N8YX]

We're putting up an 80m dipole at the K0KU club station, but need to cover most of (if not all) of 75/80 meters.

My current thoughts on achieving this is a parallel dipole, with the upper wire cut for 3.550 and the lower for 3.900 (which are our target areas). If the (-) is the wire, it'd look something like this:

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|---------

What are your thoughts?
Any other recommendations?

Only requirement is that it's coax fed.

Cage antenna - with ~12" diameter elements - or a folded dipole with a 4:1 balun at the feedpoint.

[N1LAF]

How about a fan dipole? Cut one dipole for 3.600 and the other at 3.900, feed both as you would feed a single dipole.

[N2NH]

If you have the $$, How about a 5BTV?

Or a reduced footprint dipole? You could add the extra elements as needed to get full coverage.

[N8YX]

If you have the $$, How about a 5BTV?

I would go with the 6BTV. The 5 has capacitance hats on top of the 20 and 40M elements; these add a considerable amount of wind load. The 6, on the other hand, makes up the required length by virtue of its 30M trap and intermediate sections.

[W3WN]

We're putting up an 80m dipole at the K0KU club station, but need to cover most of (if not all) of 75/80 meters.

My current thoughts on achieving this is a parallel dipole, with the upper wire cut for 3.550 and the lower for 3.900 (which are our target areas). If the (-) is the wire, it'd look something like this:

|----------
|---------

What are your thoughts?
Any other recommendations?

Only requirement is that it's coax fed.

If you have the room (presumably on the building roof?) I'd build two dipoles -- one cut for 3550, one for 3900 -- that share a common feed point. Mount one in one direction (say, NS), the other 90 degrees to the first (say, EW).

Energy flows along the path of least resistance, or in the case of antennas reactance, so while there will be some interaction between the two, it won't be much. The effect will be that one antenna will be doing the work when the other (due to high reactance on that particular frequency) will be pretty much inert.

I've done this before, and it works well (both in the 80 CW/75 Phone configuration, and 80 CW/40 CW configuration). You may have to do some minor tweaking of the antennas to get them to play on the frequencies you want, so cut them a touch long and trim accordingly.

I don't know what would happen if you hung the two antennas in parallel with each other, such as this:
80 CW ------------------||------------------------ ____________(similar to a catenary wire used on electric trolleys and rail lines)
75 PH __ --------------- ||--------------------
(ignore the __ inserted to get the spacing right)

The interactions would be different, but I think in general it could work as well.

Either way, you would need to plan on a transmatch to work the DX phone part of the band.

Also, either way, try to raise the center feed as high as practical, to make the antennas more of an "inverted V" than a true "in plane" dipole. Brings the feedpoint impedance closer to 50 ohms than 75, and the better the feedpoint impedance, the easier it is to match the antenna with 50 ohm coax.

[W3WN]

If you have the $$, How about a 5BTV?

I would go with the 6BTV. The 5 has capacitance hats on top of the 20 and 40M elements; these add a considerable amount of wind load. The 6, on the other hand, makes up the required length by virtue of its 30M trap and intermediate sections.

Neither vertical is broadbanded enough on 80 meters to give them the range they want. Even with a transmatch, there are still practical limits.

I love my Butternuts, but even though they (and allegedly the Gaps) are have a wider 2:1 - 2:1 bandwith, that's just too big a stretch.

An end fed 43' vertical would give them the range, but again, a transmatch would probably be required. Frankly, if the club has a tower for the higher bands at it's disposal, I'd consider loading that with a gamma match to work 80/75. And any end-fed vertical would need a decent to good radial field underneath it, but that should go without saying (and more often than not does)

[KJ3N]

Only requirement is that it's coax fed.

Why?

And what's the purpose of this dipole? Local (under 500 miles)? DX (greater than 1,000 miles)?

A vertical of any flavor that isn't full-sized isn't going to have the bandwidth required either, and it's not very good at under 400-500 miles. Verticals shine as DX antennas.

[N8YX]

Frankly, if the club has a tower for the higher bands at it's disposal, I'd consider loading that with a gamma match to work 80/75. And any end-fed vertical would need a decent to good radial field underneath it, but that should go without saying (and more often than not does)

That, or a sloper arrangement with the lower part folded back into the tower and a set of relays to switch in a piece of wire at the ends of each for CW-band coverage.

With a decent radial setup (elevated mounting) I see a 2:1 SWR B/W of about 75KHz with my 6BTV, and I've parked the "dip" right in the middle of the CW subband. This, by the way, is using the "Super" resonator.

[KU0DM]

Ended up going with a single dipole for CW.

Purpose: Domestic contesting, and H&P during DX contests.

Why coax fed?: Simplicity. That and lack of ladder line.

Vertical vs. Dipole: Has to be on the roof, that's our only approved play area (Fortunately it's on a 50' tower atop a ~80' building), and I doubt we could get away with another tall structure.