On Fri, 08 Apr 2005 19:31:47 GMT, Lancer wrote:
Dave;
I know this was directed to Frank, hope you don't mind if I
comment?
This is a public forum, comments from participants is what it's all
about.
A dipole is a dipole. It has 0 db of gain, and that assumes a resonant
dipole . If the dipole is non-resonant and requires a tuner to force
an impedance match, it will have further losses. It won't stand a
chance against a commercially produced (or home made if you are
so-inclined) 5/8th wave vertical (with proper radials, not an Imax).
Because a dipole/antenna is non-resonant it doesn't automatically mean
it will be a more "lossy" antenna. A non-resonant dipole fed with
ladder line can/will end up being a more efficient antenna than a
resonant dipole fed with coax and a balun.
In what way? If the length of the dipole is at a no resonant length,
you have to "force" it to a proper impedance match through the use of
a tuner. Standing waves will still be present after the tuner, and
efficiency will suffer as a result.
Why have a resonant antenna at all if a non-resonant antenna works
better? It doesn't make sense.
I've tried loading up different antennas that I've had to run on bands
they were not designed for, and while I could certainly get better
than a 1.5:1 SWR, they might as well be a load of bed springs for as
well as it worked.
I have built non-resonant antennas that beat a 5/8ths. A 5/8ths is
hard pressed achieve the claims for gain that it has.The only
commercial 5/8th that I seen that was properly decoupled was an
Isotron.
An Isopole maybe? IIRC, that's a 2 meter antenna. I never particularly
liked them. I've had better performance from a Hustler G7. Especially
on VHF, you don't see people running non-resonant dipoles. Gain is
particularly important there.
Proper decoupling can be achieved through the proper use of a radial
counterpoise, which is what is lacking in the "stick" style antennas
we're discussing on CB
I've done this type of
antenna myself and never had any problems with local contacts -- in
fact, it worked a lot better than the 9' whip on the truck.
I find that very hard to believe, assuming identical height and
conditions, as my own experiences prove otherwise.
I ran a home brewed wire dipole on CB years ago, and used it in
addition to my main 5/8th wave antenna. While the dipole worked well
when the skip was running, locally, the signal from the dipole was a
few "S" units less than the ground plane. With 4 watts of power, you
don't get much range on a horizontal wire dipole strung in a tree.
Well there's your problem, Dave -- I didn't say anything about
horizontal. On the contrary, it's better if it isn't.
Yea, if you're talking local. For DX, horizontal is usually better for
a number of reasons, most notably a lower noise floor and better take
off angle.
Horizontal antennas are dependant on height above ground and the
conductivity of the ground they are above. The closer to the ground
and more lossy the ground, the higher the take off angle.
That is correct. For best performance, a dipole needs to be at least
1/2 wave above the ground.
Since most
man made noise tends to be vertically polarized, a horizontal antenna
tends to quieter.
Also correct.
Like I said
before, just throw some wire up into the trees (or whatever tall
object happens to be available). Didn't you read the link I posted?
Of course. But a dipole is a basic antenna. It has no gain. A properly
made purpose built CB antenna will out perform it.
Let's look at this from a practical standpoint. If a non-resonant,
tuner fed dipole worked so well, then why aren't all CB'ers using one?
Why would people want huge 5/8th wave antennas then? Better tell Jay
to forget about selling his Interceptor, since a simple non-resonant
dipole will work just as well and for far less money.
A non-resonant dipole has ONE big advantage. It's a compromise antenna
that will work on all the HF bands. That's great if you don't have the
room to put up single band antennas for each band. But like any
compromise, it will not work as well as a dedicated antenna for each
band. Such a compromise is usually acceptable for a ham who has 1500
watts on tap. But for a 4 watt CB'er, who needs to squeeze every watt
of ERP he can for best local range, he needs a high gain efficient
antenna.
Again, non-resonant deosn't mean that its not efficient. Your looking
at a non-resonant antenna as a chunk of wire thats just tossed in a
tree. A resonant antenna doesn't have any magical gain over a
non-resonant antenna just because its resonant.
An antenna radiates most efficiently at its resonant frequency.
Practical experience with local communications pretty much supports my
observations (or more accurately is the basis for them). I've made
many dipoles over the years, and none of them have ever matched or
even came close to the 5/8th wave ground plane for local work on CB.
DX is another matter. Dipoles work very well there. Perhaps that's why
many H.F. hams have several different antennas to switch to, to take
advantage of varying DX conditions or groundwave, as their
communications dictate. When working 40 meter groundwave, a ground
mounted vertical is often a superior choice.
Dave
"Sandbagger"
http://home.ptd.net/~n3cvj