Last week, I posted a message asking for suggestions for 80/75
meter antennas for ARRL Sweepstakes use. My original message
and responses received are summarized below.
After reading the responses and doing a little supplemental
reading, I've settled on a 80 meter horizontal full-wave loop
(either delta or diamond, depending on how I situate it), mounted
at 40 feet. This is 0.15 wavelengths, and is the height cited in
the NVIS (Near Vertical Incident Skywave) literature as the best
compromise between ground losses and high-angle radiation.
I'm also going to install a similar loop for 40-meters at around
20 feet up, also to gain the benfit of NVIS - the close-in
QSOs.
Thanks to everyone who provided inputs!
73, Jeff K8ND
_______________________________________________________________________
From: Jeffrey Maass <jmaass@freenet.columbus.oh.us>
To: Contest Mailing List <CQ-contest@contesting.com>
Subject: [CQ-Contest] Sweepstakes Antennas: 80/75 Meters
After an absence of several years, I'm rebuilding my antenna system with
an eye towards ARRL Sweepstakes. Today I'm considering how to improve my
80/75 meter coverage domestically. Located in Central Ohio, I'm interested
in saturating a 500-mile circle to cover the population centers, and that
means I want to maximize my high-angle lobes.
I have available one 70-foot tower, and some fairly tall (up to 70-80
feet) trees, ranging from 50 to 150 feet away. I currently have up an
inverted-V broadside E-W with the peak at 70 feet and fed with half-inch
hardline.
I'm considering a delta loop, broadside E-W, bottom corner fed, supplemented
by an inverted-V broadside N-S.
Any better ideas? Delta- or diamond-loop oriented horizontally 50-60 feet
up?
Jeff Maass (jmaass@freenet.columbus.oh.us) Amateur Radio K8ND
USPSA/IPSC # L-1192 NROI/CRO NW of Columbus Ohio
25000 Members in 2000!
_________________________________________________________________________
From: Kresimir Kovarik <9a4kk@geocities.com>
I beleive that the best for this short contacts would be a horizontally
oriented delta loop or quad (doesn't make some differences).
I am using horizontally oriented delta loops for 80 and 40 meters bands
to work Europe, and it's doing a really nice job for me.
The difference between this delta loops and inv v antenna is big for
short contacts.
Chris, 9A4KK
_________________________________________________________________________
From: JOE and TAM BV/N0IAT <joentam@transend.com.tw>
When I lived in Indiana, I found that any antenna higher than about 50
feet would work east or west coast well, but did little to get my signal
into the surrounding states. For the surrounding states, a low dipole at
about 30 to 40 feet worked well with my barefoot rig -- it was fed with
ladder line and would load all bands 80 thru 10, but was resonant on 80M.
One field day, as I recall, we strung a ladder-line dipole between two
stadium lamp posts at about 100 foot level -- our ability to hold a
frequency was hindered by the high dipole, though we did work some good DX
on 80M, we had a tough time working the folks close in.
Why not try a couple X dipoles switchable from inside the shack. This
will give you some directionality while taking advantage of the high lobes
that low dipoles create.
_________________________________________________________________________
From: "Douglas L. Klein, K4LT" <k4lt@fuse.net>
Try the trusted cloud burner if you have enough room. It is a 2 element
wire beam with reflector UNDER the dipole.
73, Doug K4LT (ex-WD8AUB)
_________________________________________________________________________
From: Pete Soper <psoper@encore.com>
You're in a great location for the 500 mile strategy. In your shoes I'd
investigate the NVIS designs aimed at providing gain at high angles.
_________________________________________________________________________
From: Randy Thompson <k5zd@ultranet.com>
For SS, I don't think you can do much better than what you have!
If you had said DX contests, then it might be worth investigating the
delta loop or perhaps even a quarter wave sloper.
_________________________________________________________________________
From: HENRY <n4vhk@summitschool.com>
Nothing sounds better than saturating a 500 mile radius with
strong low band signals! Here's what I did last weekend.
Our contest club, W4WS in Winston-Salem, NC decided to run
the NAQP from my house. I live on a 90 x 1590 lot in the
downtown area- a rather high area, close to the highest peak
in the city- with trees in the front and back yard. I have
a Gap Challenger, and felt it waas time to experiment with a
second antenna. NAQP was perfect timing. Anyway, I put up a
full wave horizontal loop for 80 meters- 68' on a side- Its
in a ROUGH square pattern( more like a stretched diamond)
due to my tie off points. the tie points are 2- @40' and
2- @50'. I fed it with 450 ohm ladder line on one of the 40'
corners and used a roller inductor tuner. The results were
amazing. A small station like ours- no yagis- no monster
beverages- RAN 80 meters during NAQP for about 2 hours when
it seems everyone else had terrible noise problems. It
seemed to asttenuate atmo noise, tuned up on all bands,
including 160- I was impressed and as a GAP user, found it
too be a quiet antenna with big rx/tx capability. For a
smaller area, i'm convinced. In fact, I told my wife after
the contest that it is "staying up for more extensive testing."
.
I took the borrowed roller tuner back to our local club station,
and for kicks, tied the ladderline to a 1:1 balun , fed it with
coax from just outside the shack to my ts930SAT. The radio tuned
it, and again, it put out fine, but I really enjoyed the rx-
standard ragchews through the noise came jumping out of the radio.
I have to buy a tuner- will probably buy one at Shelby, the
granddaddy of em all- over Labor Day weekend. Good luck with
the antenna-
PS- Use copper line that is easy to handle- I had fits from tangles!
73, Henry Heidtmann, N4VHK
_________________________________________________________________________
From: Larry Lindblom-wa0etc <wa0etc@ix.netcom.com>
The loop is usually a gud low angle ant. How about the old cloud warmer
special-a dipole at 30-50 ft on 80/75 has losts of high anle rad.
_________________________________________________________________________
From: Patrick Croft <mai@iquest.net>
Look at a two element beam pointing UP. You can install a inverted vee
reflector element under your present vee and get excellent high angles with
gain into the 500-600 mile region you seek.
_________________________________________________________________________
From: John Nitzke <nitzke@sprynet.com>
For high-angle radiation, multi-band operation and QRN-reduction, a
horizontal loop sounds like a good idea. If your tower and trees allow the
geometry, you would do well with a loop in the horizontal plane. Cost is
very low.
Consult:
QST, November 1985, p 20
QST, May 1990, p 28
73, April 1996, p 18.
_________________________________________________________________________
From: "Milt Jensen, N5IA" <miltj@aepnet.com>
JEFF, THE GUY WHO DID REAL WELL LAST YEAR USED A TURNSTILE. GIVES YOU A
REALLY LARGE OMNI-DIRECTIONAL HIGH ANGLE LOBE. YOU GUYS HAVE IT MADE FOR
THAT SORT OF OPERATION. OUT HERE IN SW NEW MEXICO I MIGHT MAKE A DOZEN
CONTACTS WITHIN A 500 MILE RADIUS. GOOD LUCK ON ALL. 73 DE MILT, N5IA.
_________________________________________________________________________
From: "Roderick M. Fitz-Randolph" <w5hvv@aeneas.net>
Jeff, I would suggest the quad loop, horizontally placed, at about 30 feet
for local (500 miles) coverage.
Rod, W5HVV
_________________________________________________________________________
From: Steve Lufcy <km0l@tfs.net>
Jeff-
My vote goes to the Delta loop. I used one for a number of years and always
felt like I owned 80 meters. I came in 2nd in US in 1986 WPX single band
80 with that antenna. I fed mine at the bottom corner for vert polarization
but for SS moved it to feed it in the middle of bottom leg for higher angle
horizontal polarization. Good luck and I'll be looking for a BIG 80m signal
from you this year in SS.
73 de KM0L Steve in KC
_________________________________________________________________________
From: "T. A. Russell" <n4kg@juno.com>
You want to MAXIMIZE your HIGH angle radiation
and you are considering a VERTICALLY polarized antenna?
Go back to your antenna books and look at the radiation patterns!
(There may be some merit in placing a reflector .15 wavelengths
BELOW a dipole such that the pattern is aimed straight up. Such
configurations are affectionately called "CLOUD WARMERS". The
claim is that it improves the reflection efficiency at high angles.)
de Tom N4KG
_________________________________________________________________________
From: Tom Osborne <w7why@mail.coos.or.us>
I think if you fed the delta in the bottom center, it would be
horizontaly polorized and better for close in contacts. Bottom corner
feed will give it vertical polorization and a lower angle of radiation.
> Any better ideas? Delta- or diamond-loop oriented horizontally 50-60
>feet up?
Those are real cloud warmers and good for close in contacts.
_________________________________________________________________________
From: Don Nutt <don@kcnet.com>
What you need to do is NVIS (Near Vertical Incident Skywave). The only
trick (if you will) is to place the antenna between 1/8 and 1/4 wave from
the ground. Inverted vee's work well, Horiz. work well to. I have done
quite a bit of study for EOC's and mobile deployments in the early to mid
80's. If you model the antenna, you will find that the lobes will be
nearly (or purely) spherical with an optimum angle(s) from 45 to 135
degrees off the horizontal plane. This will allow you to cover a 600+ KM
range from your QTH. In real world practices in CA, I was able to
provide excellent coverage over the whole state and several adjacent
states from Sacramento. This allowed reliable communications over a 500
mile radius. Oh, yes the frequencies that were tested were in the 75/80
and 40 meter ranges.
The key was to not exceed 1/4 wavelengnth above the ground at the desired
frequency of operation.
This technique was proven in the field during Operation Desert Storm.
(9K2WR after the ground war was over).
Don Nutt
N6TDM/0 (newly transplanted in MO)
______________________________________________________________________
From: Nd3f@aol.com
Take a look at the ARRL handbook and build a "loop skywire"
horizontal loop for 160 and 80 meters. I have one, and so do several
other folks around here. Mine is about 65 feet average height
and 540 feet in length. Fed with 450 ohm ladder line, but coax
works OK and just about anything feeder works (feedpoint impedance is
high, and varies from band to band from about 300 ohms to
about 1600 ohms for mine). For 80 as the primary band, 270 feet long
is about right. (1000/freq in MHz is close enough). Can be used
on all ham bands with a tuner, no problem.
It hears great--has noise immunity because the horizontal
loop has natural cancellation properties. It works great short because
it has a lot of high angle lobes, but also FB for DX.
I have a bunch of wallpaper on various contests running QRP
or low power and using this antenna. I have even worked more
than 20 countries on 6M with it! In this area, WK3I (perennial
160M QRP champ) and K2YWE both have one and are happy.
I tried a 1000 foot arrangement, but the 540 foot one works best
on 80M and especially 40M at my installation, and is OK on 160.
BTW, the loop hears as well as my EWEs (I took 'em down) but
not as well as the beverage I put up for SS.
In general, no one distant believes I could be running QRP...
Brian ND3F
_____________________________________________________________________
From: "Raymond G. Crepeau" <crepeau@tech.iupui.edu>
I don't recall the specific objectives you cited in your original post.
But when living in Asheville, NC a year ago I used a 1/2 wave 80 meter
dipole up about 20 feet. The main lobe is up! My objective was to
enable emergency communications within the state of North Carolina on
the Tarheel Emergency Net on 3.923. The theory here is called "near
vertical incidence radiator (NVIR). Located in the far west end of the
state I routinely worked the east coast (475 miles) very well. You
might consider this alternative. 73
Ray Crepeau, K1HG (ex WB1HGO)
_________________________________________________________________________
Jeff Maass (jmaass@freenet.columbus.oh.us) Amateur Radio K8ND
USPSA/IPSC # L-1192 NROI/CRO NW of Columbus Ohio
25000 Members in 2000!
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