[SECC] ARRL SS 40m antenna that works!
n4uk@mindspring.com
n4uk@mindspring.com
Tue, 27 Nov 2001 18:01:42 -0500
Bill, SECC,
I have pasted and copied a text file of an e-mail I sent to the contest reflector around 1997/88 describing my secret SS weapon for 40 meters. You might want to consider it. Those that have tried this antenna have been quite pleased with its performance for domestic contests! If I ever find the time I might try the same version for 80 meters form domestics.
Ken, N4UK
Hello to all!
Are you interested in a kick ass Sweepstakes
antenna that doesn't eat into your budget? Then read on OM!
This project began with the thoughts of entering the ARRL
Phone Sweepstakes for my first ever serious effort. I set some
goals that I thought to be within reach. One of my goals was to
win the division and try to break the Roanoke division SS Phone
record held by W4MYA. Another goal was to be able to run
stations who were using average,run of the mill high angle
antennas on 40 meters. Sort of like high angle meets high angle!
40 meters was to be my bread and butter band since I don't have
any rotating antennas on any of the higher bands.
After some careful thought I came up with a list of
what I thought I needed to do for antennas in order to achieve
my goals. Here is what I came up with:
1- I needed a 40 meter antenna that performed well into the
populated areas that were within daytime 40 meter range from my
QTH here in NorthWest South Carolina. I.E. W2,W3,W5,and W8/9
2- The 40m antenna needed a fairly high angle of radiation to
"reach" into the 400-700 mile range with a loud signal.
3- I needed to be loud in all those areas at ALL times and not
only when the proper antenna was switched in line. Read this as
Omnidirectional!(helps to hold the frequency too)
4- I needed a 20m antenna that performed well to the NorthWest
where I might have trouble on the low bands picking up those
"remote" ARRL sections.
I Put up a 2 el wire quad beaming NW for 20 meters and
found it to be an admirable performer to the intended direction
though I learned during the contest that the West RULES on 20
during the Sweeps. Which returns us to the 40 meter antenna.
The antenna I put up on 40 meters is so simple as to
be laughable yet I cannot find any reference to it in any of my
old or new antenna books nor have I found anyone who has ever
tried one. It performed beyond my expectations and netted me
nearly 1,100 qsos on that band during the phone SS. I would have
had even more Qs if I had known earlier how well it was working
which would have kept me from wasting time on 20 meters. The
signals from w9/w8/w3/w2/w1/and w5 just kept rolling in and
rolling in at all times of the day. I had no problem holding on
to a run frequency for as long as I wanted it. At night I had an
abundant supply of W0 and w6/w7 to work and still had w8,9 and
w3 calling with loud signals . I dubbed this antenna "Project X"
due to its configuration but now call it "The NUKer" because of
its nice round, Mushroom Cloud pattern and the way it blanketed
the intended target areas with RF. (not fallout)
The Antenna-"This is NOT your Father's turnstile"
The NUKer is 2 inverted Vees at 90 degree angles to each
other both fed at the same point on the tower with apexes at 40
feet with a T connector and a 1/4wl of 75 ohm line on one side
of the T feeding one of the antennas. They form an X at the
apexes albeit sloping downward. I used 50 ohm coax(80ft) to feed
the center of the T connector and an ELECTRICAL 1/4 wavelength
of Radio Shack bought RG59 for the phase line. RG6,RG11 or any
other 75 ohm coax can be used. The Velocity factor of R.S. RG6
and RG59 is stated as 78 percent. The 1/4 wl section was
calculated as 234/7.1mhz x .078. The 75 ohm coax phase line was
coiled up and taped to the tower at the feedpoint of the T
connector. The 50 ohm "stub" of coax from one port of the T
connector to the other inverted vee should be kept as short as
possible. The stub I used is about a foot long. Both inverted
vees are exactly the same length physically. The angles of the
inverted vee legs are as close to 90 degrees as possible and the
ends are about 10 feet off the ground. I installed one vee at a
time and tuned it for resonance at 7.1 MHZ. I used Budwig HQ-1
dipole center insulators which have an SO239 connector built in
to them. This made it a snap to swap the feedline during the
tuning process. After the lowest SWR was attained I put up the
second Inverted vee at a 90 degree angle to the first one. The
apex of the top vee is about 6 inches above the apex of the
second vee. It too was then tuned for lowest swr using the same
feedline as the first Vee. The T and the phasing line were
installed, the 50 ohm feedline connected to the T and voila,a
low swr across the band.
This antenna has a flat swr from 6900-7400
with a slight "bump" (increase) in swr at around 7080. The
usable bandwidth practically doubled compared to a single
inverted vee. An added bonus was a very low swr all across 15
meters!(I can't vouch for its performance on 15 since I haven't
had the time to test it much on that band) A little touching up
may have to be done if the center isn't where you want it to be.
Make sure both vees are increased or decreased equally in length
when doing so.
Computer modeling done after the Phone
Sweepstakes (Thanks K3MM!) confirmed what I had hoped and what I
discovered about this antenna during the Sweepstakes. It is
perfectly Omnidirectional and exhibits a 3db gain over a
dipole at an equal height! This is 3 db over the dipole towards
the directions that a dipole favors. I am not sure how many DB a
dipole is down at its ends but assuming it is down 10-15
db vs. its optimum directions, the NUKer is then 13-18 DB better
in the direction a dipole DOES NOT favor and you don't have the
hassle of switching between antennas. What about nulling out qrm
you say? I prefer to null out QRM using the brain filters.
Besides, when you null out qrm you are also nulling out possible
contacts in that direction too. QRM for me is the broadcast junk
from Europe. This also is the highly populated Northeast
corridor. I couldn't afford to null them out too.
The A/O model also predicts maximum gain from
60-90 degrees above the horizon. Those figures are perfect for
my QTH for DOMESTIC contests. A single support, easy to
construct and cheap too! A cloudwarmer with gain! You may want
to increase or decrease the angle of radiation by raising or
lowering the antenna. It all depends upon the distance from your
QTH to a highly populated area. At a decent height this thing
may even perform well as a DX antenna. Though it doesn't exhibit
huge gain compared to other antennas that could be used, the
important consideration is that you are equally loud in all
directions and not just louder in one direction. It's OKay to be
3 or 4 db weaker in one direction vs a yagi when you're 15 db
louder in the other direction!
I plan on putting up an 80 meter version to see how
it plays vs my so-so single inverted vee at 50 feet. If I had
the tower height I would install another 40m NUKer at a half wl
above the present one and feed them in phase. This could
possibly increase the gain from 3 to 6db over a dipole.
Hopefully the Omnidirectional pattern would remain. ( how about
a model for that Ty,K3MM??) Anyone interested in trying a set of
these antennas spaced either 1/4wl or 1/2 wl above and below
each other??
The success you might have with this
antenna will vary with your location. Someone who duplicates the
exact antenna I have up and who lives in Eastern,PA or Chicago
will be Loud at all times into South Carolina which probably
won't help you much in Sweepstakes or NAQP. Play with the
heights,combinations,etc. The results may surprise you!
Before the antenna went up numerous hams told me it wouldn't
work. Something about the proximity of the vees and
cancellation,etc. Well, I am happy to report that it really does
work!
73 Ken N4UK
P.S. I fell short of the Roanoke division record by about 20k
points but not because of the antennas. Hey, I made a couple of
booboos that I shouldn't have made. Looking forward to next
year! Ken
P.S. The ARRL Roanoke division record was broken the next year with 40m again
having the most Qs.
I take no responsibility for typos,miscalculations,errors,poor
assumptions etc. If you spot such an animal please E-mail me
personally and let me know and don't embarrass me publically in
front of the whole reflector. Tnx :)
RE: The Great Sweepstakes Antenna
Tyler, K3MM (KF3P) sent me some more info based on a model
using A/O modeling software. There was some confusion as to
where the 3db "gain" was and this sets the record straight.
Compared to a dipole at 40 feet, it's about 1 db more gain
straight up.Note that all these are measurements over
ground...ie with ground "bounce"DB's added in.
The broadside direction gain of the dipole is at least 2 db
higher from 5 degrees up to 45 degrees.Off the ends of the
dipole, the N4UK beats it at all angles, with about .7
db advantage overhead, 3db at 45 degrees up , and 8 db at 10
degrees.So, it's a good high angle omni antenna, but it's not as
good as a dipole at most takeoff angles in the perfect broadside
direction. I set them both the same at 7.1, which is what I did.
73, Tyler K3MM
I think Tyler might have meant 8db at 70 or 90 degrees and not
10 degrees. The 3-8 db better at the 45-90 degree range is what
works at MY QTH due to the distances from here to the Major
Metro areas NE,NW,and NW of me. A dipole and a vertical that was
previously used here had takeoff angles that were just too low
for use in domestic contests. My signal was going above and
beyond the intended Metro target areas using those antennas.
Remember that this antenna was not intended as a DX contest
antenna.
Thanks to Tyler for the modeling work! 73 Ken N4UK
Bill Coleman <aa4lr@arrl.net> wrote:
I know many of you have moved on to CQWW CW, but I'm still digesting what
happened during SS Phone. Here's some of my thoughts.
* 40m sloper just does not cut it when the band is full of region 1 QRM.
Thinking seriously of the 40m option for the A3S. It would buy me another
10 feet, and allow me to rotate the dipole.
Anyone have any suggestions?
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