Dave wrote:
"Douglas W Adair" wrote in message
...
I like them two at a time--co-phased. Is there any gain to be had that way
or am I just skin pipe dreaming at the petro?


the real gain in that arrangement is in the thickness of the sales man's
wallet.

They certainly look better just like dual stacks look better than a
single stack.

"Top" wrote in message
.. .
richard wrote in
:

On Mon, 1 Dec 2008 04:37:39 -0500, "Douglas W. \"Popeye\"
Frederick" wrote:

"Dave Platt" wrote in message
...
I like them two at a time--co-phased. Is there any gain
to be had that way
or am I just skin pipe dreaming at the petro?

If fed in phase and spaced correctly, there could be gain
to the front and to the back with a decreased propogation
to the sides. This is usually desirable if traveling on a
mostly straight stretch of highway. I think the spacing
is a little too far apart for use on most cars.

I believe you're correct. This is a "broadside array"
configuration.

Its gain over a single radiator rises roughly linearly
(measured in dB over a single radiator) up to separations
of around 5/8 wavelength. A separation of 1/2 wavelength
gives around 4 dB gain over a single radiator and a very
nice clean pattern (deep null to the sides) - this is the
spacing most frequently described in the literature (e.g.
Kraus, Terman) for broadside arrays. Gain maxes out at
just under 5 dB at a 5/8-wavelength spacing (at the cost
of a small side-lobe). [Figures are from the ARRL Antenna
Book of a few years ago]

Whether it's worth doing for a vehicle-mobile system is
another question. You need more than .4 wavelengths of
separation to get 3 dB of gain (half a nominal S-unit) -
at 11-meter frequencies that's around 14 feet of
separation, which I think not many vehicles will allow.
Perhaps if you're driving a "wide load" transporter
truck?

At 6 feet of separation between antennas you'd have only
around .2 wavelength, which yields less than 1 dB of gain
over a single radiator. Hardly seems cost-effective.

It might make more sense for 2-meter operation... but as
most 2-meter mobile seems to be repeater-based, you
really want omni rather than shaped-beam-down-the-road
most of the time.

There's also the matching issue. Each radiator in the
array will have a feedpoint impedance different than what
would have if used alone. You'll have to take this into
account when designing the phasing harness, and you may
need an impedance-matching network at the combining point
to establish the 50-ohm load that your transceiver
expects. If you don't match properly your transceiver
won't see the load it expects, and may not deliver full
rated power into the load - you could easily lose more
signal strength this way than the array will gain back.
If you do match properly, there will be some amount of
loss in the matching network.

There ain't no free lunch, alas.

Wow, Richard.

This guy seems 7 ****loads smarter than you.

Wonder if he ever "held an FCC license for radio work"?


If i had said it, you would have a field day accusing me of
all kinds of ****.

Since the late 60's i've been working with CB and have done
all kinds of experiments with antennas on a car. You name
it, I had it.

As he pointed out, the big problem with CB is, you need way
much more space than a vehicle offers to truly get any
usable gain from cophasing.

Do you know the wavelength of 11 meters?
if 27 feet, the normal height of base antenna, is equal to
5/8 or 1/4 wave, then what is 8/8 or 100%? Well over 100
feet.

So to get the true proportion for proper cophasing, the
road aint wide enough and neither is the vehicle.

The only reason truckers run two antennas is because it
looks cooler.

The effectiveness of cophasing in a truck is screwed by the
factory installed crap.


You still didn't give any useful information. No surpise since
you have none. For an average of the cb band running 1/4 wave
the antennas should be spaced 54 inches apart. Use a
commercially produced cophase harness if you can find it. Make
sure you match the SWR and you will out do any other mobile
off the front or rear.

Top




Thanks Top!




--
Popeye
"Best thing for him, really. His therapy
was going nowhere," -Hannibal Lector.

www.finalprotectivefire.com
http://picasaweb.google.com/Popeye8762

On Dec 1, 6:42*pm, "The Honorable Dr. Rocky Roads Presiding Judge"
wrote:
Dave wrote:
"Douglas W Adair" wrote in message
...
I like them two at a time--co-phased. Is there any gain to be had that way
or am I just skin pipe dreaming at the petro?

the real gain in that arrangement is in the thickness of the sales man's
wallet.

- They certainly look better just like dual stacks
- look better than a single stack.

breaker, Breaker. BREAKER !

Ken I Gita Ray Di Oh Checka !?!

Phuck off you scumbag loser. Nobody and I mean nobody is a better trucker
than I.

In article ,
Douglas W. \"Popeye\" Frederick wrote:

You still didn't give any useful information. No surpise since
you have none. For an average of the cb band running 1/4 wave
the antennas should be spaced 54 inches apart. Use a
commercially produced cophase harness if you can find it. Make
sure you match the SWR and you will out do any other mobile
off the front or rear.

Top

Thanks Top!

I think that Top's calculations (and recommendations) are a bit off?

CB has an 11-meter wavelength. There are just over 39 inches in a
meter. Hence, the wavelength is around 430 inches.

A 54-inch separation is only .12 wavelength. From the chart in the
ARRL Antenna Book, it looks as if you'll get less than .5 dB of
directional gain, compared with a single radiator of the same type and
size. That's less than one tenth (!) of a nominal S-unit. You'd be
very hard put to be able to detect this small of a difference in
practice - it'll be less than the amount of signal variation you'll
encounter due to reflections from nearby objects.

In terms of getting yourself a directional-gain benefit, I think a
co-phased two-radiator broadside array with a 54-inch separation is
essentially useless on CB frequencies. There just isn't enough gain
to matter.

Now, as somebody else suggested, using such an array might get you a
more consistent near-omnidirectional pattern than a single radiator
would deliver, if your antennas are mounted less than optimally (e.g.
on your sideview mirror post). Using two co-phase antennas might be
worthwhile for this reason, even if you don't get a significant amount
of directional gain.

I suspect you'd get more bang for your buck by simply mounting a
single antenna in a better location (e.g. roof mount) and paying
attention to making the antenna's grounding to the chassis/groundplane
as direct and solid as possible.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

(Dave Platt) wrote in
:

In article
, Douglas
W. \"Popeye\" Frederick
wrote:

You still didn't give any useful information. No surpise
since you have none. For an average of the cb band
running 1/4 wave the antennas should be spaced 54 inches
apart. Use a commercially produced cophase harness if you
can find it. Make sure you match the SWR and you will out
do any other mobile off the front or rear.

Top

Thanks Top!

I think that Top's calculations (and recommendations) are a
bit off?

CB has an 11-meter wavelength. There are just over 39
inches in a meter. Hence, the wavelength is around 430
inches.

A 54-inch separation is only .12 wavelength. From the
chart in the ARRL Antenna Book, it looks as if you'll get
less than .5 dB of directional gain, compared with a single
radiator of the same type and size. That's less than one
tenth (!) of a nominal S-unit. You'd be very hard put to
be able to detect this small of a difference in practice -
it'll be less than the amount of signal variation you'll
encounter due to reflections from nearby objects.

In terms of getting yourself a directional-gain benefit, I
think a co-phased two-radiator broadside array with a
54-inch separation is essentially useless on CB
frequencies. There just isn't enough gain to matter.

Now, as somebody else suggested, using such an array might
get you a more consistent near-omnidirectional pattern than
a single radiator would deliver, if your antennas are
mounted less than optimally (e.g. on your sideview mirror
post). Using two co-phase antennas might be worthwhile for
this reason, even if you don't get a significant amount of
directional gain.

I suspect you'd get more bang for your buck by simply
mounting a single antenna in a better location (e.g. roof
mount) and paying attention to making the antenna's
grounding to the chassis/groundplane as direct and solid as
possible.


Cophase being omindirectional? You need to do some more
reading before you try to correct anything.

In article ,
Top wrote:

Cophase being omindirectional? You need to do some more
reading before you try to correct anything.

The directionality of a broadside array (with the two radiators fed
exactly in phase) depends very strongly on the separation between the
two antennas. For separations of 1/4 wavelength or less, there's very
little directionality - the pattern is very close to omnidirectional.

Every dual-antenna truck setup I've seen has been a side-by-side
mounting (e.g. one on the left mirror and one on the right), and the
harness feeds them both in-phase. I've been assuming that this was
what was being meant by "co-phase".

If so, I stand by my statement that two CB antennas, fed in phase
through a co-phase harness (i.e. no phase difference between the two),
and separated by only 54 inches, produces a nearly-omnidirectional
signal. The two antennas need to be further apart, before the pattern
becomes significantly directional.

Take a look at the NEC plots at http://www.cosjwt.com/index.php?a=20
to see... the 4.5-foot separation model produces a pattern which is
almost circular. There is little gain towards the front and back, and
very little loss off to the sides. These plots seem to jibe well with
other references I've read (Terman, Kraus, and the graphs in the ARRL
Antenna Book).

The other alternative is an end-fire array, with the antennas fed
signals of opposite phase - with these then there can be significant
directionality even with close spacing of the antennas. In a
truck-antenna system, this would require placing the antennas one in
front of the other, separating them by several feet, and inverting the
phase of the signal sent to one of the two antennas (perhaps by having
the feed coax to one antenna be 1/2-wavelength longer than the other).
You could get several dB of gain this way... but the close spacing
will cause the antenna feedpoint impedance to drop a lot, and some
form of matching network will certainly be required to keep the radio
happy and develop maximum power from the transmitter.

The two bottom plots on the site I mentioned above, show the effect of
feeding the antennas with signals of different phase. In these
examples, the pattern is being skewed off to one side - the difference
in feedline length is converting the antenna from a broadside array to
an end-fire array. With the right amount of phase shift, you end up
with a cardioid pattern, with a broad lobe in one direction and a very
deep null in the other.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

"Dave Platt" wrote in message
...
In article ,
Douglas W. \"Popeye\" Frederick wrote:

You still didn't give any useful information. No surpise since
you have none. For an average of the cb band running 1/4 wave
the antennas should be spaced 54 inches apart. Use a
commercially produced cophase harness if you can find it. Make
sure you match the SWR and you will out do any other mobile
off the front or rear.

Top

Thanks Top!

I think that Top's calculations (and recommendations) are a bit off?

I'm a "single antenna" guy myself.

I think, in a truck, at least, that "big radio" is synonymous with "big
wris****ch". :-)

We can't mount the antennae high or center, because the 13', 6" height of
the truck is where the low bridges start.

Also, most tractors have this horrific system that intergrates AM/FM with
the CB coax.

A CB stick on the left mirror and an AM/FM on the right, and a splitter in
the coax, so I always run my own coax seperately.

And I have a cellular antenna on one side, any way, for dual plane signal
boost, and it has to be 8" (I think) away from other sticks.

But hhhhhere's a question for the braintrust:

I'm after a (mobile) VHF radio that's common to northern (i.e., the Yukon,
and Northwest Territories) Canadian truckers- who don't monitor CB bands.

(info http://forums.qrz.com/showthread.php?t=171741

I'm sure, as a sine wave challenged layman, that I can't use the same
antenna and coax as my CB?


CB has an 11-meter wavelength. There are just over 39 inches in a
meter. Hence, the wavelength is around 430 inches.

A 54-inch separation is only .12 wavelength. From the chart in the
ARRL Antenna Book, it looks as if you'll get less than .5 dB of
directional gain, compared with a single radiator of the same type and
size. That's less than one tenth (!) of a nominal S-unit. You'd be
very hard put to be able to detect this small of a difference in
practice - it'll be less than the amount of signal variation you'll
encounter due to reflections from nearby objects.

In terms of getting yourself a directional-gain benefit, I think a
co-phased two-radiator broadside array with a 54-inch separation is
essentially useless on CB frequencies. There just isn't enough gain
to matter.

Now, as somebody else suggested, using such an array might get you a
more consistent near-omnidirectional pattern than a single radiator
would deliver, if your antennas are mounted less than optimally (e.g.
on your sideview mirror post). Using two co-phase antennas might be
worthwhile for this reason, even if you don't get a significant amount
of directional gain.

I suspect you'd get more bang for your buck by simply mounting a
single antenna in a better location (e.g. roof mount) and paying
attention to making the antenna's grounding to the chassis/groundplane
as direct and solid as possible.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!



--
Popeye
"Best thing for him, really. His therapy
was going nowhere," -Hannibal Lector.

www.finalprotectivefire.com
http://picasaweb.google.com/Popeye8762

On Mon, 1 Dec 2008 21:58:02 -0800, (Dave Platt)
wrote:

In article ,
Douglas W. \"Popeye\" Frederick wrote:

You still didn't give any useful information. No surpise since
you have none. For an average of the cb band running 1/4 wave
the antennas should be spaced 54 inches apart. Use a
commercially produced cophase harness if you can find it. Make
sure you match the SWR and you will out do any other mobile
off the front or rear.

Top

Thanks Top!

I think that Top's calculations (and recommendations) are a bit off?

CB has an 11-meter wavelength. There are just over 39 inches in a
meter. Hence, the wavelength is around 430 inches.

Almost got it right but a little off.


The higher the "meter" the frequency gets lower.
11 meters is roughly 27mhz.
10 meters is roughly 28mhz.
2 meters is 144 mhz.

A "wave" is based on the physical length between nodes of the
frequency.

In reality, one wavelength at 27mhz is about 36 feet long.
A standard 102inch whip is a 1/4 wave antenna.

Just for you mister know it all top,
you might want to gander at this site.

http://www.cosjwt.com/index.php?a=20

It blows your 54" theory right straight to hell and then some.

As you'll see by the charts, there is virtually no difference between
1 and 2 antennas mounted on a truck.

On 2 Dec 2008 06:15:20 GMT, Top wrote:

(Dave Platt) wrote in
:

In article
, Douglas
W. \"Popeye\" Frederick
wrote:
I suspect you'd get more bang for your buck by simply
mounting a single antenna in a better location (e.g. roof
mount) and paying attention to making the antenna's
grounding to the chassis/groundplane as direct and solid as
possible.


Cophase being omindirectional? You need to do some more
reading before you try to correct anything.



IF the cophased antennas are less than 1/4 wave apart, there is
virtually no change.