[LCC] 80 meter antenna recommendations?

[Marshall Stewart]

EZNEC+ 5.0 calculates that a flat top 80M dipole up 55 feet will have max
gain at 90 deg elevation – straight up.  At 75 feet up, the max gain will be
at 55 deg elevation.  An inverted vee with the apex at 75 feet up (max gain
at 75 deg) will be better than the 55-foot high flat top, but not as good as
a 75-foot high flat top.  The gain of an inverted vee is down slightly from
a flat top with the apex of the vee at the same height as the flat top.
Given my choice of #1 or #2 below, I’d opt for #2.

 

For max gain at a low take-off angle and a deep overhead null on 80M, a
vertical starts to look like a good way to go.  A full-length (approx 65
feet) vertical radiator is preferable over any loading method used to
resonate a shortened vertical radiator.  On 80M #12 wire is so thin relative
to a wavelength, the Q of the antenna will be high, and the 2:1 SWR
bandwidth narrow.  To cover the entire 80M band, the vertical radiator would
need to be about 3 feet in diameter – not very practical.  A wire “cage”
with multiple parallel wires separated by an insulator with all parallel
wires connected at each end could be used to make a “fat” conductor.  Bigger
would be better.

 

Radials – most Amateur Radio ops just don’t have the real estate to install
the ideal 120 radials each ¼ wavelength long.  To reduce the number
required, an alternative of above-ground radials might be a solution.  The
elevated radials can be shortened with inductive or linear loading.  I’d
stay away from a ground rod and 1 long radial – the feed point impedance
might be good and the SWR low, but the ground losses will be high and the
antenna efficiency low.

 

Two possibilities that may or may not be practical in your situation:

A.	A dipole hung from a tall tower like a guy wire.  At the center
feedpoint, a rope continues on to the ground, and the “second half” of the
antenna goes back to the tower - like an inverted vee hung vertically from a
tower with the apex pointing away from the tower.  
B.	A lazy H (vertical dipole with end loading) hung between 2 supports
(towers, trees, masts, etc.) fed at the bottom.  The vertical part of the
antenna 40-feet in length with 38.3-foot end loading wires could be starting
dimensions. (The vertical part attaches to the center point of each end
loading conductor.)

 

Sources:  ARRL’s Vertical Antenna Classics, The Antenna Handbook, Antenna
Compendium Vol 1

 

In your case what would I go with?  #2 with the apex as high as possible for
NA, and # 3 with as many radials as possible each as long as possible (or
elevated radials) for DX.

 

I’d be interested to know what you decide to put up for 80M.

 

73,

Marsh, KA5M

 

 

  _____  

From: lcc-bounces at louisianacontestclub.org
[mailto:lcc-bounces at louisianacontestclub.org] On Behalf Of Mark, K5ER
Sent: Wednesday, September 26, 2012 4:54 PM
To: lcc at louisianacontestclub.org
Subject: [LCC] 80 meter antenna recommendations?

 

Okay, now its my turn to ask the group. HFTA doesn't model these
combinations, and I'm not good enough with EZNEC to trust I get them built
right within that software. I plan to review info from the antenna book, as
well as Low Band DXing, but there is collectively A LOT of knowledge within
this club, so I'd like to tap into that, too. 

I need to replace my 80 meter antenna, and am considering three options:
#1. go back up with a flat top dipole (actually, center always seems
slightly below ends) height abt 55 feet
#2. replace with inverted vee - feedpoint can be about 75-80 feet
#3. ground mounted vertical - feed point at 6" above ground, one #12 thhn
conductor running up in an oak tree, one ground rod and (maybe) only one
radial.*

 *The #3 antenna started out from the NCJ article last year "an easy
inverted-L for 160. They showed with only ONE radial, it should give close
to a 50 ohm match, not needing a tuner or inductor/capacitor tuning at base.
Since there are FAR more contacts on 80, as compared to 160, I could convert
this inv-L to a vertical by simply cutting off the excess (leave it about
67' long). My issue here is I buried hardline from shack to feedpoint (about
260 feet), but did not realize I had used 75 ohm hardline for the last 120
feet of the run. I may have a mis-match to deal with at the feedpoint, so I
would need to address that. On the radial issue, I only have abt 30 feet of
yard in one direction, and the septic field lines are in the other, so a
complete set of radials is out of the question. I might be able to get 4-8,
MAX, but only if my wife goes somewhere for a weekend this winter and I get
them stapled in without getting caught.

Everything I have seen on other reflectors compares flat tops and inv-vee's
at the same height. I have read that a inv-vee is better for DX, but also
read that at the same height an inv-vee is 1/2 to 1 db down from a flat-top.
Because of tree location, in my case, the inv-vee feedpoint would be higher,
(20-25') than I could get a flat-top.

My standard reply when someone ask me about antenna is "who do you want to
talk to?" Although I enjoy SWEEPS, I haven't worked it from home is several
years. I do not regularly participate in 80 meter traffic nets, (though it
would be nice to be able to check in during emergency situation). I DO like
the NAQP contests in January and July. I have recently become more
interested in DX, and should have 4 band DXCC within a month or two, but I
am only 1/2 way there on 80, so I guess my primary focus will be DX, but
without giving up "some" domestic. There is a chance I could get away with
EITHER #1 or #2, and still do #3 as well.

What would YOU put up, and why?

Thanks and 73,
Mark, K5ER

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