Davis RF makes a low-loss LMR-like coax made for direct burial, and can be
bought at a very good price. I've been very pleased with its performance &
reliability for HF.
I used the 18HT as a teenager in the late 60s in AK. I remember it being a
good performing DX antenna, and had about 30 straight radials, bare #14
stranded copper of varying lengths 40m - 5m long. But, then I built a
Sterba Curtain (over 10 acres on my parents' homestead) and didn't look back
to the 18HT. I'm still hooked on wires, and if you have the trees or other
supports to get 'em up at least 80ft, there are several designs that'll
out-perform that 18HT.
--Stephen W9SK
-----Original Message-----
From: antennaware-bounces@contesting.com
[mailto:antennaware-bounces@contesting.com] On Behalf Of Larry Banks
Sent: Friday, March 05, 2010 8:47 AM
To: Shon Edwards; antennaware@contesting.com
Subject: Re: [Antennaware] Installing a Hy-Gain AV-18HT vertical
-severalquestions, especially about radials
Hi Shon,
I can give you some info about radials. LB's web site
http://www.cebik.com/gp/gr.html -- cited by Jim, KG0KP -- has similar
information as the ARRL Antenna book and a lot more. W6RMK's comment...
---------------
Most people ultimately decide to just lay down as much wire as they
have, running it as far as seems practical (e.g. to a lot line or some
natural barrier). There's probably not much value in extending a whole
lot more than the antenna height.
---------------
...is probably the best practical advice.
I'll quote from the ARRL Antenna book:
------------------------------------------------
Practical Suggestions For Vertical Ground Systems
At least 16 radials should be used if at all possible.
Experimental measurements and calculations show that with this number, the
loss resistance decreases the antenna efficiency by 30% to 50% for a 0.25
wavelength vertical, depending on soil characteristics. In general, a large
number of radials (even though some or all of them must be short) is
preferable to a few long radials for a vertical antenna mounted on the
ground.
The conductor size is relatively unimportant as mentioned
before: #12 to #22 copper wire is suitable.
a.. If you install only 16 radials they
need not be very long - 0.1 lambda is sufficient.
b.. If you have the wire, the space and the patience to lay
down 120 radials (optimal configuration), they should
be 0.4 lambda long. This radial system will gain about 3 dB
over the 16-radial case.
c.. If you install 36 radials that are 0.15 lambda long, you will
lose 1.5 dB compared to optimal configuration.
---------------------
As for coax, I mostly use LMR-240 for HF. LMR-400 is better, especially at
12 and 10M. The antenna book also has attenuation/100' for many coax types
for various frequencies.
Grounding -- the radials give you the "RF Ground." For lightening
protection you do need ground rods. Most hams suggest three around the base
of the vertical -- and they must be connected to the ground system at your
shack, which must be connected to the electrical ground system at the
electrical entrance. Use #4 or #6 copper for these grounds runs.
The best way to learn all of this stuff is to buy and study the ARRL Antenna
Book.
Hope this helps!
73,
Larry
W1DYJ
----- Original Message -----
From: "Shon Edwards" <sre.1966@gmail.com>
To: <antennaware@contesting.com>
Sent: Thursday, March 04, 2010 2:19 PM
Subject: [Antennaware] Installing a Hy-Gain AV-18HT vertical -
severalquestions, especially about radials
> Hello all, I'm getting a Hy-Gain AV-18HT and have several questions about
> it, especially about a radial system. I am very new to HF and so am quite
> clueless, but would be grateful for any help possible.
>
> How deep do the radials need to be underground? Is 2 or 3" OK?
>
> I wonder if it's necessary (as some say) to put down radials only at a
> percentage of the wavelength of the lowest frequency you plan on working
on,
> or (as others say), do you need to put down radials at a percentage of the
> wavelength of all frequencies you plan working on? How many radials
should
> be put down for each band, if it is necessary to go this route?
>
> Also, how long should these be? I have lately read Rudy Severn's article
in
> QST this last month, which was excellent, but it doesn't always answer all
> my questions. Also, his 7 articles on the Internet he refers to don't
> readily answer all these questions, although very good articles, all of
> them. Is it .4 wavelength if I plan on doing 60 radials or .25? .2?
>
> I'm also wondering if I have a space problem, if I must absolutely, put
out
> my radials in a straight line, or if I can bend them, and go around things
> in my yard at angles of around 70 degrees, if need be. Will that have a
> negative effect on my radiation pattern? I have about a 90 degree section
> of my antenna radial field, where I will need to be bending lots of
radials
> up to 70 degrees. Unfortunately, this is the exact direction that I want
to
> focus on most for most of my communications, toward the east and
northeast,
> southeast.
>
> What is the best type of coax to use if I want to minimize losses the most
> at 1-30 MHz? It doesn't matter if it is expensive. I'd just like to get
as
> many dB of gain as possible.
>
> Also wondering how best to ground the antenna. This might be for a person
> who is familiar with this particular antenna. Apparently, an SO-239 is
> provided and connected to the antenna already. I understand that the
braid
> of the coax needs to be soldered to the ground rods and that they should
all
> be connected together, but if I am connecting a PL-259 to an SO-239 on the
> antenna, how would I do this? Solder some part of the SO-239 to the
ground?
>
>
> Also, if I want to add 30 M and 60 M capability to this antenna, which is
> 53' high (so it should be possible, I would think), how do I do it? I
> probably wil not be too good here with the technical terminology, but I'll
> do my best.
>
> Does the size/type of the wire of the radials matter? I've heard that it
> does not, but I imagine that stranded wire, though more pliable and easy
to
> deal with, would deteriorate faster than solid wire. Also, am thinking of
> using #14 wire. It seems to be the best I can get for the price at Home
> Depot. I've heard of people using chicken wire, but I want something more
> permanent than this. Also, I'm thinking if I use plastic-clad wire it
will
> last longer than bare wire. That is, it would not rust or fall apart over
> the years as fast as wire that is bare.
>
> Also, any other things that I might need? Like a balun or anything else
> that I'm not thinking of.
>
> Thank you and sorry I have so many questions. As I say, I'm just getting
> into this. Thanks, Shon Edwards, sre.1966@gmail.com.
>
> --
> Shon R. Edwards,
> Radio:
> Amateur Call: KO3U
> Commercial radio licenses:
> GROL: PG00016801
> GMDSS/O/M: DB00000391
> GMRS: WQKW341
> 2nd class radiotelephone: T2GB064388
> Accredited VE: W5YI, ARRL
> ARRL Instructor
> 1039 N 2575 W
> Layton, UT, 84041-7709
> USA
> e-mail: sre.1966@gmail.com
> phone: (801) 444-3445
> cell: (801) 336-7635
> _______________________________________________
> Antennaware mailing list
> Antennaware@contesting.com
> http://lists.contesting.com/mailman/listinfo/antennaware
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