Posted by
w7aqk on
Jan 04, 2008; 4:33pm
URL: http://elecraft.85.s1.nabble.com/dipole-antenna-efficiency-tp458071p458073.html
Shaun, Dohn, and All,
Your proposal to wrap wire around pipe will probably end up being a "bust".
In essence, you would just be loading a coil, and it would be very
inefficient as a radiator. Some have tried to use a "helical" approach in
order to shorten the overall length, but again that doesn't work all that
well either. An example would be using the old "Slinkey" wire toys that we
all probably had at one time or another. Those can work, after a fashion,
but are generally poor performers.
I disagree about the G5RV also. That is not a very good antenna,
notwithstanding the huge amount of use those antennas get. The problem is
that the G5RV was never intended to be an "all band" antenna, and it is a
performer on all but a couple of bands. Unless you use a tuner, you will be
very unhappy with the results you get with a G5RV design, particularly with
modern rigs that don't have the advantage older tube-type transmitters had
with pi-network coupling. The warts that a G5RV has is well documented,
and the latest thing I remember reading about it was in a recent issue of
Sprat--the Spring 2007 issue. Therein is a discussion by ex-ZS6BKW, who is
famous for originating much of the variations for the G5RV that are in use
today. Paraphrasing his own words, don't expect much from a G5RV unless you
at least use a tuner!
Unless you want to put up some sort of trap dipole, or a multi-band
vertical, your best option is to get a decent tuner and put up a dipole with
balanced line feeders. The 88 foot antenna described by L.B. Cebik on his
website (www.cebik.com), is an excellent choice for a simple antenna that
will work well on 80 meters through 10 meter. You can shorten that to 44
feet if you want to give up 80 meters. That will fit in just about anyone's
backyard, unless you live in a condo. The higher you get it, the better it
will work. Just don't use coax, or the losses will eat you alive! You can
coax feed an antenna that is resonant with good results. But when you try
to use it on a higher frequency (like using an 80 meter coax fed antenna on
40 meters), the results turn to mush. The same antenna fed with balanced
line through a tuner will work substantially better at higher frequencies.
The resonant antenna (130 feet on 80) works better than the 88 foot antenna
does on 80, but the 88 foot version (or the 44 foot version) is intended to
standardize your radiation pattern, and is still a decent performer on 80
meters.
Another option would be a remotely tuned vertical on your roof. Dr.
Megacycle (KK6MC), suggested this to me not long ago when he visited my
shack. His advice was to put up a 22 foot vertical, remotely tuned, and
using balanced feedline. This would give you pretty decent performance from
40 meters through 10 meters. You would need as many radials (random length)
as possible. This was a suggestion as an alternative to my R7 vertical,
which is a pretty good performer, but perhaps not as good as the suggested
alternative. I haven't tried that yet, but I'd like to. I'm sure the
suggestion is a good one.
This may be more than you wanted to hear, but it seemed as if you were
struggling to come up with a solution. Hopefully it helps some in that
process. If wire antennas, or verticals, are just not practical for you,
you might want to try a mini-loop. These aren't nearly as efficient as a
good wire antenna, but they are quite small, and the results can often
surprise you. Besides, they are fun to build!
Dave W7AQK
----- Original Message -----
From: "Dohn" <
[hidden email]>
To: "'Shaun Oliver'" <
[hidden email]>;
<
[hidden email]>
Sent: Friday, January 04, 2008 2:50 AM
Subject: RE: [Elecraft] dipole antenna efficiency
> Shaun,
>
> For materials needed vs. radio theory, you just can't beat a G5RV antenna.
> IMHO I've used mine with my K1, K2 and several home brew projs and it
> works
> great time and again. Yes, you want to get the center up there a ways.
> Say
> around 35-40 feet, but the payoff was good for me. There are a number of
> sites out there that have good versions of a very old, classic antenna.
> Very few parts (all of which can be made with junk around the house. Very
> little investment for a sound payoff.
>
> Dohn N8EWY
>
> -----Original Message-----
> From:
[hidden email]
> [mailto:
[hidden email]] On Behalf Of Shaun Oliver
> Sent: Thursday, January 03, 2008 9:20 PM
> To:
[hidden email]
> Subject: [Elecraft] dipole antenna efficiency
>
> Hi all,
> if I were to make a dipole, would coiling it round a piece of plastic
> piping decrease the efficiency of the thing? I intend on making one for
> 40 meters, one for 80 meters, and one for 10 meters. I've worked out
> that1 meter of piping will suffice for each leg of each antenna.
> thanks in advance.
> shaun
> _______________________________________________
> Elecraft mailing list
> Post to:
[hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>
http://mailman.qth.net/mailman/listinfo/elecraft>
> Help:
http://mailman.qth.net/subscribers.htm> Elecraft web page:
http://www.elecraft.com>
> _______________________________________________
> Elecraft mailing list
> Post to:
[hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>
http://mailman.qth.net/mailman/listinfo/elecraft>
> Help:
http://mailman.qth.net/subscribers.htm> Elecraft web page:
http://www.elecraft.com>
_______________________________________________
Elecraft mailing list
Post to:
[hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help:
http://mailman.qth.net/subscribers.htmElecraft web page:
http://www.elecraft.com