Today's Message Index:
----------------------
1. 09:43 AM - Re: Dipole antenna fabrication (Eric M. Jones)
2. 10:38 AM - Re: Re: Dipole antenna fabrication (Richard Dudley)
3. 11:34 AM - Re: Dipole antenna fabrication (Eric M. Jones)
4. 12:13 PM - Re: Re: Dipole antenna fabrication (Dj Merrill)
5. 08:38 PM - Re: Re: Dipole antenna fabrication (Robert L. Nuckolls, III)
6. 11:10 PM - Re: Re: Dipole antenna fabrication (Mike Wynn)
Message 1
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| Subject: | Re: Dipole antenna fabrication |
The Wiki site shows a simple dipole and the caption says:
"A schematic of a half-wave dipole antenna connected to an unbalanced coaxial cable.
Better practice is to connect the balanced dipole to the unbalanced line
with a balun."
I've been thinking of putting aluminum foil on the TV rabbit ears....
Proper termination is the key to antenna efficiency. If Cessna didn't do it, that
doesn't mean the homebuilder shouldn't do it right.
Bob et al. having flown extensively in the Western states and Mexico, I have plently
of experience with being a zillion miles from a station. At those times
I start to think that having a good radio and good antennas is a wise and cost
effective thing to do. But do what you want.
--------
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones@charter.net
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=367293#367293
Message 2
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| Subject: | Re: Dipole antenna fabrication |
A wise (and practical) person once said:
"Perfection is the enemy of good enough."
Anymouse
RHDudley
On 2/26/2012 12:41 PM, Eric M. Jones wrote:
> --> AeroElectric-List message posted by: "Eric M. Jones"<emjones@charter.net>
>
> The Wiki site shows a simple dipole and the caption says:
>
> "A schematic of a half-wave dipole antenna connected to an unbalanced coaxial
cable. Better practice is to connect the balanced dipole to the unbalanced line
with a balun."
>
> I've been thinking of putting aluminum foil on the TV rabbit ears....
>
> Proper termination is the key to antenna efficiency. If Cessna didn't do it,
that doesn't mean the homebuilder shouldn't do it right.
>
> Bob et al. having flown extensively in the Western states and Mexico, I have
plently of experience with being a zillion miles from a station. At those times
I start to think that having a good radio and good antennas is a wise and cost
effective thing to do. But do what you want.
>
> --------
> Eric M. Jones
> www.PerihelionDesign.com
> 113 Brentwood Drive
> Southbridge, MA 01550
> (508) 764-2072
> emjones@charter.net
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=367293#367293
>
>
Message 3
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| Subject: | Re: Dipole antenna fabrication |
A good job is sufficient. We disagree on what constitutes a good job.
--------
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones@charter.net
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=367298#367298
Message 4
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| Subject: | Re: Dipole antenna fabrication |
On 2/26/2012 2:28 PM, Eric M. Jones wrote:
> --> AeroElectric-List message posted by: "Eric M. Jones"<emjones@charter.net>
>
> A good job is sufficient. We disagree on what constitutes a good job.
>
Having made and used at least a few dozen of these types of
antennas, I can say they generally do perform a "good job". They
perform far better than a handheld antenna, and perhaps not as good as
some other types of antennas, but overall they are okay, and of course,
cheap to make! :-) Comparing $$ spent to value received they rank very
high.
-Dj
--
Dj Merrill - N1JOV
Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/
Glastar Flyer N866RH - http://deej.net/glastar/
Message 5
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| Subject: | Re: Dipole antenna fabrication |
At 11:41 AM 2/26/2012, you wrote:
The Wiki site shows a simple dipole and the caption says:
"A schematic of a half-wave dipole antenna connected to an unbalanced
coaxial cable. Better practice is to connect the balanced dipole to
the unbalanced line with a balun."
. . . and I published instructions for adding this
feature to a coax fed dipole at
http://aeroelectric.com/articles/BALUN/Balun_Fabrication.html
. . . the same technique could be applied to a comm
dipole.
I've been thinking of putting aluminum foil on the TV rabbit ears....
Which will lower the resonant frequency of the antenna
and perhaps lower the Q . . . wider bandwidth. But
no benefit for relative efficiency compared to an "ideal"
dipole at the same frequency.
Proper termination is the key to antenna efficiency. If Cessna didn't
do it, that doesn't mean the homebuilder shouldn't do it right.
I can assure you that Dr. Wood read the same books
we've all read about antennas with professional
attendance to "better practice." The point I endeavored to
make was that after he came to understand all the
deleterious effects over which we had no control on
a C-172, adding baluns on the VOR antennas yielded very
small gains compared the sum of other losses.
Next time I can get into the test lab, I'll do some
measurements on the difference between a balun-fed
dipole and a bare foot, coax-fed dipole.
Bob et al. having flown extensively in the Western states and Mexico,
I have plently of experience with being a zillion miles from a
station. At those times I start to think that having a good radio and
good antennas is a wise and cost effective thing to do. But do what you want.
But you paint a picture suggesting that a balun would
make the difference between communicating with some distant
station . . . and not. Given the light of sight character
of VHF+ frequencies, you're more likely not to have a useable
path because you can't see the other station than because
your effective radiated signal is down by a few db due
to violations of feed point protocols. Further, it's
insufficient to be able to see the other station
peeking over the horizon (or mountaintop). The effects
of intervening "roughness" in the "Fresnel zone" can
have some profound effects on what might otherwise be
considered a free-space, line of sight situation.
http://web.arundale.co.uk/docs/ais/PathlossCalculationsforAmateurs.pdf
Mountain peaks and valleys intruding into the Fresnel
zone can kick your free space performance predictions
in the teeth.
Currents flowing on the coax shield are but part of
the 'violations' . . . the center impedance of a perfect
dipole is on the order of 73 ohms. This means that the
BEST SWR to be achieved without application of some
impedance matching is on the order of 73/50 = 1.46:1
So we've tossed off some efficiencies right out of the
box. When we plot radiation patterns on VHF antennas
on airplanes, one generally expects 10 db or greater
'lumpiness' in the pattern due to geometry of the
conductive elements around the antenna. So again,
if one is at 'extreme range' for useful communications,
it's more likely that you'll improve the path by turning
the airplane a few degrees as opposed to optimizing
feed point design.
Yes, a BALUN can be "better" but experience on small
aircraft has shown that the difference is so small
compared to all other effects combined that the balun
was not 'cost effective'. Further, it won't fix the
fundamental mis-match so 1.46:1 is still the best
we can expect. The textbooks are full of examples of
data taken from the idealized antenna and feed line
examined in the anechoic chamber with test equipment
that can split a DB into small pieces.
As soon as you put that same antenna is a real world
environment, lots of things with potential for
altering performance happen. This is why
the guy flying 'around with a radio capable of
talking to another one just like it 1000 miles
away finds that the practical limits are much
shorter for reasons mostly beyond control of
the antenna designer.
But just for grins, I've got some DIY antenna's I've
used in my weekend seminars and articles. I'll
fit one with a balun and leave the other barefoot.
Then see if my buddy Don P can tell the
difference without looking to see which one is
hooked up. Hmmmm . . . I think I know how to
do the experiment with equipment I have. Need
warmer weather though . . .
Bob . . .
Message 6
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| Subject: | Re: Dipole antenna fabrication |
Extremely educational dissection [of antenna logic] from bystander
viewpoint. Many thanks Bob.
Mike W.
Moab, UT
****************8's
----- Original Message -----
From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
Sent: Sunday, February 26, 2012 9:35 PM
Subject: Re: AeroElectric-List: Re: Dipole antenna fabrication
> <nuckolls.bob@aeroelectric.com>
>
> At 11:41 AM 2/26/2012, you wrote:
> <emjones@charter.net>
>
> The Wiki site shows a simple dipole and the caption says:
>
> "A schematic of a half-wave dipole antenna connected to an unbalanced
> coaxial cable. Better practice is to connect the balanced dipole to the
> unbalanced line with a balun."
>
> . . . and I published instructions for adding this
> feature to a coax fed dipole at
>
> http://aeroelectric.com/articles/BALUN/Balun_Fabrication.html
>
> . . . the same technique could be applied to a comm
> dipole.
>
> I've been thinking of putting aluminum foil on the TV rabbit ears....
>
> Which will lower the resonant frequency of the antenna
> and perhaps lower the Q . . . wider bandwidth. But
> no benefit for relative efficiency compared to an "ideal"
> dipole at the same frequency.
>
>
> Proper termination is the key to antenna efficiency. If Cessna didn't do
> it, that doesn't mean the homebuilder shouldn't do it right.
>
> I can assure you that Dr. Wood read the same books
> we've all read about antennas with professional
> attendance to "better practice." The point I endeavored to
> make was that after he came to understand all the
> deleterious effects over which we had no control on
> a C-172, adding baluns on the VOR antennas yielded very
> small gains compared the sum of other losses.
>
> Next time I can get into the test lab, I'll do some
> measurements on the difference between a balun-fed
> dipole and a bare foot, coax-fed dipole.
>
> Bob et al. having flown extensively in the Western states and Mexico, I
> have plently of experience with being a zillion miles from a station. At
> those times I start to think that having a good radio and good antennas is
> a wise and cost effective thing to do. But do what you want.
>
> But you paint a picture suggesting that a balun would
> make the difference between communicating with some distant
> station . . . and not. Given the light of sight character
> of VHF+ frequencies, you're more likely not to have a useable
> path because you can't see the other station than because
> your effective radiated signal is down by a few db due
> to violations of feed point protocols. Further, it's
> insufficient to be able to see the other station
> peeking over the horizon (or mountaintop). The effects
> of intervening "roughness" in the "Fresnel zone" can
> have some profound effects on what might otherwise be
> considered a free-space, line of sight situation.
>
> http://web.arundale.co.uk/docs/ais/PathlossCalculationsforAmateurs.pdf
>
> Mountain peaks and valleys intruding into the Fresnel
> zone can kick your free space performance predictions
> in the teeth.
>
> Currents flowing on the coax shield are but part of
> the 'violations' . . . the center impedance of a perfect
> dipole is on the order of 73 ohms. This means that the
> BEST SWR to be achieved without application of some
> impedance matching is on the order of 73/50 = 1.46:1
> So we've tossed off some efficiencies right out of the
> box. When we plot radiation patterns on VHF antennas
> on airplanes, one generally expects 10 db or greater
> 'lumpiness' in the pattern due to geometry of the
> conductive elements around the antenna. So again,
> if one is at 'extreme range' for useful communications,
> it's more likely that you'll improve the path by turning
> the airplane a few degrees as opposed to optimizing
> feed point design.
>
> Yes, a BALUN can be "better" but experience on small
> aircraft has shown that the difference is so small
> compared to all other effects combined that the balun
> was not 'cost effective'. Further, it won't fix the
> fundamental mis-match so 1.46:1 is still the best
> we can expect. The textbooks are full of examples of
> data taken from the idealized antenna and feed line
> examined in the anechoic chamber with test equipment
> that can split a DB into small pieces.
>
> As soon as you put that same antenna is a real world
> environment, lots of things with potential for
> altering performance happen. This is why
> the guy flying 'around with a radio capable of
> talking to another one just like it 1000 miles
> away finds that the practical limits are much
> shorter for reasons mostly beyond control of
> the antenna designer.
>
> But just for grins, I've got some DIY antenna's I've
> used in my weekend seminars and articles. I'll
> fit one with a balun and leave the other barefoot.
> Then see if my buddy Don P can tell the
> difference without looking to see which one is
> hooked up. Hmmmm . . . I think I know how to
> do the experiment with equipment I have. Need
> warmer weather though . . .
>
> Bob . . .
>
>
>
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