G5RV in a V pattern? Possible?
Tom
due to a home move and limited space I am curious to know the
following:
Is it possible to a G5RV in a V pattern, about 20' above the ground.
legs and the end.
The 2 legs being about 20' apart.
Ie.
\ 20' apart /
\ /
\ /
\ /
\ /
\ /
\ /
\ /
\/
Feeder Point
CJ
Of course it is "possible". If random length wire antennas are useful
than most any "configuration" will radiate and basically "get you on the
air" even if the swr is 3:1 you'll do fine.
There is IMHO way too much "antenna analysis" and "religious
philosophy" about Ham Radio antennas and which ones are better than
others. While there are measurable differences between antenna types
and overall designs I have done well with a W9INN 5-band
(80,40,20,15,10) resonant dipole at 54 ft above ground. Last DXCC check
shows me at 311 countries..all on a simple dipole.
Also IMHO (and not to toot my own horn) what - is - important (and
totally free to everyone that pursues it) is "operator skill" especially
in DX plie-ups. Many times those ops with 200 ft towers and "legal
limit power" (or more!) and stacked mono-banders have to wait till I get
done with my DX qso (on a dipole!) before they can call. Also being at
5412 ft above sea level helps too!!!
--
73 / DX de AB7SL - Charles
AB7SL - Ham Radio Pages
Prescott, Arizona - USA
www.ab7sl.com
"Tom" <auctio...@yahoo.co.uk> wrote in message
news:1Xb59.2315$wp2.1...@newsfep1-win.server.ntli.net...
Wes
Chuckie Boy is fantasizing again.
| There is IMHO way too much "antenna analysis" and "religious
|philosophy" about Ham Radio antennas and which ones are better than
|others.
Since this an amateur radio discussion group about antennas, what the
hell do you expect here? If it's too much for you, leave.
|While there are measurable differences between antenna types
|and overall designs
Why I didn't know that, thanks for pointing it out.
|I have done well with a W9INN 5-band
|(80,40,20,15,10) resonant dipole at 54 ft above ground.
Here we go again with the shilling for a so-so commercial product.
| Also IMHO (and not to toot my own horn)
Then whose horn are you tooting, Chuckie? Uh oh I forgot, W9INN's.
|what - is - important (and
|totally free to everyone that pursues it) is "operator skill" especially
|in DX plie-ups. Many times those ops with 200 ft towers and "legal
|limit power" (or more!) and stacked mono-banders have to wait till I get
|done with my DX qso (on a dipole!) before they can call.
Right, they're two hours away from the band opening at their location.
BTW, if you quit relying on that DXcluster crutch, you could find the
DX first and work them before the pileup starts.
| Also being at
|5412 ft above sea level helps too!!!
You make a lot of absurd statements, but this one is tops. I guess
you must do a lot better than those guys down on the beach who just
have all of that nasty old sea water for a horizon.
BTW, is that 5412 feet elevation at ground level or at the antenna
height? We need to be precise, as I'm sure it makes a difference.
Thanks for the nice usenet post.
'Doc
Tom,
It will work, just not very well. The 'legs'
of the antenna are too close together. The
input impedance is going to be some rediculous
value that a tuner may not even be able to handle.
Not knowing what the area you have to play with
looks like, I can't even guess at a good alternative.
Sorry 'bout that...
'Doc
Tom
Bob Miller
>I have no interest in the experimentation with antenna, however
>due to a home move and limited space I am curious to know the
>following:
>
>Is it possible to a G5RV in a V pattern, about 20' above the ground.
>legs and the end.
>
>The 2 legs being about 20' apart.
I tried a 75-meter dipole at about the same height you're planning, with the
legs highly V-ed, about 20 or so feet apart. Didn't work worth squat, even with
a heavy duty tuner. I doubt the g5rv would fare much better.
Bob
k5qwg
George, W5YR
Antenna driving-point impedance is of importance but is not the problem
with this proposal.
The problem is that the radiation from one leg will be largely cancelled by
the radiation from the other leg. Spread them out as far as possible and
see what happens . . .
73/72/oo, George W5YR - the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121 Kachina 505 DSP #91900556 Icom IC-765 #02437
Roy Lewallen
isn't necessarily that the overall radiated field is less. Take for
example an 8JK antenna. This consists of two parallel elements fed out
of phase, and spaced much closer than a half wavelength (typically 1/8
to 1/4 wavelength). The fields from these two elements don't fully
reinforce in any direction; they partially or fully cancel in all
directions. Yet the antenna produces more gain than a single element.
If you put 100 watts into an antenna, 100 watts is radiated, less the
power dissipated as heat. Pattern or field cancellation isn't a lossy
process -- it's simply the superposition of waves in space. The 100
watts of power radiated is the power *after* fields are all added up and
cancellation and reinforcement have taken place. You don't put 100 watts
into an antenna and make it disappear by field cancellation. So an
antenna whose fields cancel doesn't necessarily radiate any less power
than one whose fields reinforce.
Here's what does happen. In a W8JK, the mutual coupling between the
elements causes the element feedpoint resistance to be lower than for a
single element. This results in higher current for a given power input,
which in turn causes the fields to be greater. The result is that the
overall radiated power is the same as it would be for a single element
-- the extra field strength resulting from the heavier current just
makes up for the loss of field strength due to field cancellation.
There is a practical limit to this technique, however. Heavier currents
result in higher I^2*R loss in the elements. This can be reduced by
increasing the conductor size, and can be made negligible for reasonable
element spacings. But if spacing gets too close, the currents become
high enough that significant loss occurs for any practical conductor size.
An inverted vee works the same way. One with a narrow angle radiates
just as much power as one with wider spacing, less loss which occurs due
to higher currents. For moderately narrow angles, the loss is usually
insignificant. But with narrow angles, the feedpoint impedance is low,
and it's difficult to match and feed without too much loss in the
matching network or feedline. The tuning will also be narrow band. And
if the wires are cut to be the proper length for a wider-angle inverted
vee, a substantial amount of reactance will be present, making matching
more difficult. So if a narrow-angle inverted vee works poorly, it's
because not enough attention was taken to feeding and matching a low
impedance antenna with low loss, not because of field cancellation. The
problem truly is one of getting power to the antenna. Once there, nearly
all of it will be radiated.
Roy Lewallen, W7EL
George, W5YR
question is a G5RV mounted in a horizontal V configuration, not the usual
vertical-plane inverted V, with the ends of the antenna some 20 ft apart.
I was attempting to point out that having the ends of the legs too close
together would result in poorer performance relative to that of a dipole
than with them further apart, as in 180 degrees.
No argument that all the power reaching the antenna is radiated. But what
if the two ends were placed only, say, 4 " apart and the antenna were a
1/2-wave dipole? Would the antenna not then constiute a 1/4-wave open-ended
transmission line with equal and opposite currents in each leg? And would
not all radiation be essentially cancelled?
What happens to the power applied in this case? The line termination is a
direct short which would produce total reflection and no power would be
accepted by the antenna to be radiated. Hence, no conflict with
Conservation of Energy.
As the ends of the legs are moved apart, a real component in the driving
point impedance is developed and power begins to be accepted and radiated -
all of it, as you point out - in some field form or other.
As the spacing increases until it reaches 180 deg, the driving-point
impedance becomes whatever it is for that piece of wire at that location.
And the real part will accept power and it will be radiated in the manner
of the dipole it has become.
Anywhere close? <:}
73/72/oo, George W5YR - the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121 Kachina 505 DSP #91900556 Icom IC-765 #02437
Roy Lewallen
George, W5YR wrote:
> Roy, unless I totally misunderstood the original posting, the antenna in
> question is a G5RV mounted in a horizontal V configuration, not the usual
> vertical-plane inverted V, with the ends of the antenna some 20 ft apart.
Sorry, I came in late an missed that. The principle is still the same,
though.
> I was attempting to point out that having the ends of the legs too close
> together would result in poorer performance relative to that of a dipole
> than with them further apart, as in 180 degrees.
>
> No argument that all the power reaching the antenna is radiated. But what
> if the two ends were placed only, say, 4 " apart and the antenna were a
> 1/2-wave dipole? Would the antenna not then constiute a 1/4-wave open-ended
> transmission line with equal and opposite currents in each leg?
Yes, but not an ideal one. See below.
And would
> not all radiation be essentially cancelled?
The fields from the two wires would very nearly cancel. But for a given
power input, the fields would be huge (due to heavy currents due to
mutual coupling). So the radiation would be pretty normal if the losses
could be kept reasonably low. With the wires that close, though, it
would actually be impossible to keep losses really low.
> What happens to the power applied in this case? The line termination is a
> direct short which would produce total reflection and no power would be
> accepted by the antenna to be radiated. Hence, no conflict with
> Conservation of Energy.
Even if you had lossless wires, you wouldn't see a short circuit looking
into the input. There would be a small but finite value of resistance.
This is the radiation resistance, and it would be present because of the
fact that the parallel wires will radiate. (Only in a perfect and
lossless coaxial cable, or other fully shielded transmission line, would
the input resistance be zero. As long as fields can escape, the
resistance will be finite.) If you were able to match your transmitter
to that resistance value, all the power you applied would be radiated.
The currents in the wires would be very large, resulting in a very large
field from each wire. The sum of the fields, while only a fraction of
the field from each wire, would be comparable to that from a normal dipole.
I sent George an example EZNEC file, of two parallel wires 4 inches
apart at 14 MHz. The feedpoint resistance in this case is 0.02683 ohms
-- very small, but finite. A power of 100 watts would result in a
feedpoint current of 61 amps. Interestingly, the pattern is isotropic.
Introducing a realistic loss of #12 copper wire reduces the field
strength by 15 dB, underlining the practical limitations of loss and the
impracticability of this as an antenna.
> As the ends of the legs are moved apart, a real component in the driving
> point impedance is developed and power begins to be accepted and radiated -
> all of it, as you point out - in some field form or other.
There's no magic point where this occurs. The real component is present
down to the smallest spacing you'd like. Of course, it gets arbitrarily
small as the spacing gets arbitrarily small.
But if you did have a perfectly shielded pair of wires, where the fields
were confined by the shield and not allowed to radiate, you'd have zero
input resistance regardless of the spacing or the wire length. With zero
input resistance, no power could be applied to it.
> As the spacing increases until it reaches 180 deg, the driving-point
> impedance becomes whatever it is for that piece of wire at that location.
> And the real part will accept power and it will be radiated in the manner
> of the dipole it has become.
I keep stumbling over this "accept power" phrase. Any antenna with any
finite radiation resistance will "accept power". If you restrict
yourself to connecting a 50 ohm fixed impedance source to the antenna,
then yes, the amount of power you get to the antenna -- the amount it
"accepts" -- is strongly influenced by the feedpoint impedance. But if
you have the ability to match the antenna (as I assume is generally the
case), then all antennas will "accept power". As the spacing increases,
the real part of the resistance increases, and you have to adjust your
matching network. That's all.
I don't want to minimize the practical limitations of getting power to
an antenna with a very small radiation resistance, or the very real
losses that will occur in such an antenna. In fact, I don't think
antennas with these characteristics are generally a good idea because of
the practical problems involved in feeding them and keeping losses
manageable. My only point is that if an antenna with close spaced and
out of phase wires doesn't work well, it's not because the fields are
cancelling and the power therefore mysteriously disappearing. Field
cancellation commonly occurs, and ones with pretty severe field
cancellation, such as the 8JK, can actually have useful gain.
> Anywhere close? <:}
Sure, very close. And I've really liked the other postings you've made.
They're right on the mark.
W4WNT
Considering that a G5RV has a very complex pattern even when hung straight
and high, you may not affect it much by doing an "upside down Vee" if the
feed point is 20 feet off the ground. You could even do an inverted W which
might take less space. You will be using a tuner anyway you set it up.
Good Luck,
Bill, W4WNT
"Tom" <auctio...@yahoo.co.uk> wrote in message
news:1Xb59.2315$wp2.1...@newsfep1-win.server.ntli.net...
Fulano de Tal
>
> Hi Tom,
>
> Considering that a G5RV has a very complex pattern even when hung straight
> and high, you may not affect it much by doing an "upside down Vee" if the
> feed point is 20 feet off the ground. You could even do an inverted W which
> might take less space. You will be using a tuner anyway you set it up.
>
> Good Luck,
>
> Bill, W4WNT
Anybody know of a good weblink that shows the V and H patterns on the
various bands?
-BM
hillbilly3302
better than others
drc
k5drc
"Tom" <auctio...@yahoo.co.uk> wrote in message
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CJ
--
73 / DX de AB7SL - Charles
AB7SL - Ham Radio Pages
Prescott, Arizona - USA
www.ab7sl.com
" hillbilly3302" <daves...@alltel.net> wrote in message
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