The other day I got my copy of Grant Bingeman's (KM5KG) ARRL published
book "Short Antennas for 160 Meter Radio".
Short version:
As the title states, it's about short antennas, focuses on wires in
the air, and how to do it in a 30 foot cube space above ground. It's
about designing a 30 foot antenna to play well over radials, but the
radials are not limited by the cube.
A small lot ham might assume from the title that the book targets
them. But if you are looking for a builder's step-by-step instructions
to put up a simple efficient antenna, including counterpoise, to get
on 160 from a tiny lot, you will need to look elsewhere. It's a
technical textbook rather than a how-to book. Most of its content is
an electrical engineer grade compendium of NEC4 models with a rather
good technical discourse on the why's of the design. The book is a
keeper in that regard.
There is nothing new to be found on radials or counterpoises. He
depends on 30 mS/m conductivity "super-dirt" for efficiency in the
radials, and unfortunately dismisses lesser quality ground, rather
than designing to deal with it. But he does not hide that, and in one
place tables up the increased losses over poorer ground.
Most of Grant's designs are fairly complex and likely can't be strung
up around trees, need to be done out in the clear. Erection and
support could be tricky. Survival could be a real issue in areas
where ice is common in winter.
Some parameters he uses are hard to relate to common usage.
Long version:
There are some number of things that leap out at me in the reading.
1) Grant does not break any new ground in counterpoise. He has 20
foot radials in some designs, discusses advantages of 36 times 80 foot
radials elsewhere. His performance figures assume 30 mS/m ground
conductivity in designs that have a feed Z in the 2-3-4-5 ohm range,
that by ohms law could carry up to 27 amps RF at 1500 watts. He
presumes we can treat poorer ground to bring it up to 30 milli-Siemens
(what some of us refer to as upper midwest USA super-dirt). In
chapter 5 he states:
"The low value of 2 mS/m is something you might find in a sandy
desert. The value of 5 mS/m is a common choice, but I know you can do
better. I live in a warm climate where the land used to be farmed for
cotton, and the ground conductivity is typically 30 mS/m."
His "do better" apparently refers to a wet-it-and-salt-it treatment
for low conductivity soil from the prior page:
"However, if we keep the earth wet so the effective ground
conductivity is about 30 mS/m [then the antenna input impedance
lowers, indicating lower ground loss]. If we add salt to the soil,
the input resistance may drop even farther, improving efficiency
again. Salt will hasten corrosion, however. It may also disperse,
meaning it may have to be replenished periodically."
2) Then in his table 5.11, he delivers the death blow for those of us
who actually are in, and must remain in, moderate to poor dirt. I
have converted his percent of E field efficiency to dB to get results
in more commonly used units. The first two columns are from his table.
The third column is dB down from "100% E field efficiency". The last
two columns are watts radiated for a given power at the feedpoint.
Gnd Cond % E field Loss dB Radiated From
mS/m efficiency from 100% from 1500w 100w
2 18% -15.9 dB 49 watts 3 watts
5 37% -8.6 200 14
10 54% -5.4 437 29
20 59% -4.6 522 35
30 75% -2.5 dB 844 watts 56 watts
So there is a definite reason to NOT use these designs in so-called
"average" or "poor" dirt (5 mS/m and 2 mS/m respectively as termed in
EZNEC). His 5.11 table numbers for poor dirt are in line with those I
have gotten for sparse, short, or miscellaneous buried radials, using
various techniques, including NEC4. They are completely in line with
my large and growing story collection on poor performance for small or
irregular radials. Rain or no rain.
There is no magic bullet in the book for buried radials that fail
"full size dense and uniform all around", other than 30 mS/m
super-dirt. There is no help for short radials in ordinary to poor
dirt. So it's a very good thing to find this explicitly described,
explained and tabled up in the book. No BS numbers anywhere in there
that I saw.
We are free to personally assess his optimism and methods for
improving ground conductivity and choose accordingly.
Aside: If someone DOES come up with some kind of fertilizer goop or
such, that doesn't kill plants or ruin ground water in our wells or
cause algae blooms in our rivers, and doesn't leach out with every
rain, that can make our North Carolina 2 mS/m dirt into midwest US 30
mS/m miracle dirt, we all will improve some signals around here. Word
will get around fast and it will be a best-seller among Top Banders.
Someone please invent it. Or tell us what it is and who sells it.
3) Grant works a lot of the time with buried wires in his models. This
means many of the models you get from the ARRL web site to go with the
book only work in NEC4 calculating engines, requiring that expensive
license. That is stipulated in the book, it's not a surprise.
4) The work is apparently all based on his NEC4 modeling and broadcast
experience. I haven't seen a reference to a base of experienced ham
users of these designs and conductivity improvement methods, nor a
user's step-by-step guide.
5) Bandwidths are stated in SWR (VERY large) at 1800 and 2000 with a
center of 1900, making it hard to visualize how narrow that would be
for 2:1 or less around 1.825 in the shack. He has a computational
reason for doing it that way, but I still don't know from these how
many kHz up and down from 1.825 before the amp faults. I'd have to
pull the models from ARRL, run them on NEC4 and see. Adding the 2:1
bandwidth after tuning out reactance would have been helpful.
6) Some of the designs and schemes would be very difficult in a small
yard with trees, especially the salting, and quite complicated in
actual construction out in the clear. Most of them involve complex
construction and erection in any circumstances.
7) But it's what ISN'T there that talks the loudest.
For most small lot hams, until it is solved efficiently, counterpoise
is the big gorilla in the room that buries all other issues. For
counterpoise Grant offers short radials in 30 mS/m dirt for 30 foot
short antennas. But is the antennas' complexity and dependence on 30
mS/m dirt what is needed out in 160m small lot hamdom? Is his
dismissal of the problem of poorer dirt realistic?
In my ongoing slog of email on the 5/16 wave single wire folded
counterpoise (FCP) **, essentially all of the correspondents can get
up some kind of a 1/4 wave wire, starting with at least a 30 foot
vertical run. Some can do better with a small self-supporting tower.
Some can do a lot better with a convenient big tree, but none can do
radials to spec. They have already suffered very disappointing results
with radials, which were of necessity well short of "full size, dense
and uniform all around" in one aspect or several.
I am currently corresponding about FCP construction with a ham in
Scotland, whom I will call Steve, whose rear lot is 24 by 6 meters.
Yes, that's 78' x 20'. Steve's back yard is a TRUE small lot. But
Steve's problem is NOT his vertical radiator.
Steve will have a 1/4 wave inverted L of modest height, pulled up at
an angle to his small self-supporting tower for the bend, with the far
end of the horizontal wire run above part of the house to a pole on a
gable, and a prune and tune drooper wire down to the fence to finish
the far end. The L+FCP will have a feed Z up at least into the upper
20 ohms, and involve the counterpoise with less than a fourth of the
current in Grant's designs, and none of the urban poor-dirt penalties
in Grant's table 5.11. The linear footprint FCP goes at the long
property edge, out of the way, visually blended with the boundary
fencing.
In chapter 3, Grant refers to asymmetry in the radials and ground
connections as "sabotage" (I'm in complete agreement with that), and
his "symmetry" means the same as the "uniform all around" that I keep
bringing up. AND he was calling it sabotage in 30 mS/m super-dirt.
Steve had attempted 90 degrees worth of radials (one quadrant only of
360) in his 78' by 20' space with whatever length could be managed per
individual radial (way far into radial sabotage in Grant's
terminology). If square foot coverage by radials in whatever manner
actually got us on with a good signal, many users should have been
happy with schemes they have now abandoned. But Steve was far more
asymmetrical than Grant's bemoaned example. Where did Steve get the
idea for his radials?
How many times have you heard, "Just put down whatever radials you can
manage and get on." No one mentioned the penalty for not doing
"uniform all around," for being short, and how the penalty multiplies
over poor soil.
Steve's controlling problem, just like nearly everyone else, was
counterpoise, not the antenna above ground.
Frank, VO1HP, has a vertical radiator with similar shape and
dimensions to Steve's, over an FCP and does well. Neither Steve nor
Frank could put down efficient radials using any method, nor come
close, though they both gave it the good old college try with the
space they had. Frank's available yard is about 25m x 15m. Neither
has 30 mS/m dirt, nor will wetting it down make it any better. They
both get plenty of rain. We're talking about Scotland and
Newfoundland, not the arid USA desert states.
The other practical problem is that complicated designs and
constructions rarely get used unless they are manufactured for us.
Workable simplicity in construction is a must for a design to be
widely used. Understanding HOW that workable simplicity does it's job
is highly desirable, but not required to put it up or chase DX. As
they say, KISS. What works well, and is simple, is what is needed.
Bottom Line: Grant's book skirts around the one 160m issue that always
buries the others until it is solved, which is counterpoise and dirt.
Some readers looking for a small lot solution might say he went to a
lot of effort to skin the wrong cat. But it's an idea book about
skyhooks, not counterpoise. It's a good technical exercise down in the
muck of basic issues if you go through it carefully. I stuck it up
there on the shelf next to W2FMI's balun book, a lot of ways similar
in approach, layout, difficulty of read, and potential usage. I use
W2FMI as a reference to various concepts for winding my own devices.
I'm curious to know what Grant would have done over an FCP.
73, Guy.
** http://www.w0uce.net/K2AVantennas.html
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