16 el coaxial colinear (2.4ghz) question
 

I built this antenna expecting better performance from my WiFi
setup. Stock antennas are 1/2 wave verticals at the back of the
router. New antenna is a 16 element coaxial collinear @32' agl.
Total transmission system losses work out to 5.299db @2.412
ghz (includes feedline + N connectors).

So, why does this antenna only have about (rough measurement)
1-3 db gain over the stock antenna? I was meticulous in my work,
measuring the antenna parts with a digital caliper and checking
the connections with a DVM along the way.

Maybe my design is a fault? I built the antenna just like this:

http://wireless.gumph.org/content/4/...s-antenna.html

Except in my version, I've got 16 elements made from RG58. I also
made 2 four element antennas for the back of my thinkpad and they
seem to be working about twice as far as the antennas they replaced
(inverted V's).

Any ideas?

73's de Ken KG0WX - Kadiddlehopper #11808,
Flying Pigs #-1055, Grid EM17io,
Elecraft K2 #4913, XG2, 4SQRP Tenna Dipper,
Heath GD-1B, MP-1(X)antenna

16 el coaxial colinear (2.4ghz) question
 

On Sun, 9 Apr 2006 12:45:06 -0500, "Ken Bessler"
wrote:

New antenna is a 16 element coaxial collinear @32' agl.
Total transmission system losses work out to 5.299db @2.412
ghz (includes feedline + N connectors).

So, why does this antenna only have about (rough measurement)
1-3 db gain over the stock antenna? I was meticulous in my work,
measuring the antenna parts with a digital caliper and checking
the connections with a DVM along the way.

Maybe my design is a fault?

Hi Ken,

What did you compute as being the Velocity Factor for the shield being
covered with thick PVC?

The problem with this modified Franklin Array is that you are cutting
for half-wave dimensions once, for two Velocity Factors along the same
length. Only one is going to be correct, and it is going to impact
the theoretical application of the other.

You might want to try again using bare wire, twin lead fashion.

73's
Richard Clark, KB7QHC

16 el coaxial colinear (2.4ghz) question
 

"Richard Clark" wrote in message
...
On Sun, 9 Apr 2006 12:45:06 -0500, "Ken Bessler"
wrote:

New antenna is a 16 element coaxial collinear @32' agl.
Total transmission system losses work out to 5.299db @2.412
ghz (includes feedline + N connectors).

So, why does this antenna only have about (rough measurement)
1-3 db gain over the stock antenna? I was meticulous in my work,
measuring the antenna parts with a digital caliper and checking
the connections with a DVM along the way.

Maybe my design is a fault?

Hi Ken,

What did you compute as being the Velocity Factor for the shield being
covered with thick PVC?

The problem with this modified Franklin Array is that you are cutting
for half-wave dimensions once, for two Velocity Factors along the same
length. Only one is going to be correct, and it is going to impact
the theoretical application of the other.

You might want to try again using bare wire, twin lead fashion.

73's
Richard Clark, KB7QHC

To Ken

Hi Ken, I'd always take Richard's advice before mine. But, I wonder if
you realize how difficult your task is. It is a very difficult project to
develop the design of any array of radiators thats about 5 wavelengths long.
And, it *is* a project, not just a matter of precise measuring and cutting.
I'd think that 3 dB improvement over the antenna that was designed for
optimum performance shows that you are doing something right.
This project is a great learning opportunity for you.

I'd suggest that you get a directional coupler and get some idea of the
match of the array while it is being made longer. If you can manage to keep
the VSWR under 2:1 with 6 or 8 elements, at your operating frequencies, you
will be way ahead of me.

Jerry KD6JDJ

16 el coaxial colinear (2.4ghz) question
 

Hi Ken

My first thought would be that a collinear with such a high gain would
have a very narrow vertical beamwidth. ie a small angle off the vertical
where mounted would have the remote site some dB down off the main lobe.
The test for this will be to tilt the antenna back and forth whilst
checking the RSL. Also keep in mind that reflections on 2.4GHz will
cause a similar picket fence effect you might have heard on 2m/70cm.
Your antenna could be mounted in a semi null. (I might try and model
this some day and post you the results)

Next idea is that with such a long colinear you are getting losses along
the coax elements to the point where the upper element is radiating less
than the lower ones. This will cause some skew in the radiation pattern.
(upward tilt) TG213 would have been a better choice for this many
elemets for this reason.

Thirdly... Although RG58 is suppose to have a VF of 0.66 it does vary
some from manufacturer to manufacturer. I havent bothered to work out
how much difference it would make but would suspect that the longer the
antenna (in elements) the worse it would become.

Am thinking of making a Sterba curtain for WiFi. Looks easier than
playing with bits of coax!


Cheers Bob W5/VK2YQA East Texas

Ken Bessler wrote:
I built this antenna expecting better performance from my WiFi
setup.

16 el coaxial colinear (2.4ghz) question
 

"Jerry Martes" wrote in message
news:qCc_f.2174$wH1.1885@trnddc03...

"Richard Clark" wrote in message
...
Hi Ken,

What did you compute as being the Velocity Factor for the shield being
covered with thick PVC?

The problem with this modified Franklin Array is that you are cutting
for half-wave dimensions once, for two Velocity Factors along the same
length. Only one is going to be correct, and it is going to impact
the theoretical application of the other.

You might want to try again using bare wire, twin lead fashion.

73's
Richard Clark, KB7QHC

To Ken

Hi Ken, I'd always take Richard's advice before mine. But, I wonder if
you realize how difficult your task is. It is a very difficult project
to
develop the design of any array of radiators thats about 5 wavelengths
long.
And, it *is* a project, not just a matter of precise measuring and
cutting.
I'd think that 3 dB improvement over the antenna that was designed for
optimum performance shows that you are doing something right.
This project is a great learning opportunity for you.

I'd suggest that you get a directional coupler and get some idea of the
match of the array while it is being made longer. If you can manage to
keep
the VSWR under 2:1 with 6 or 8 elements, at your operating frequencies,
you
will be way ahead of me.

Jerry KD6JDJ


Thanks to both of you for your help. I took the antenna down and by-
passed the 40' of LMR 400. Still, my Rssi with the OEM antennas was
only 3db better on the big antenna. Thinking maybe the radome was an
issue, I took it off and saw about another 2db improvement.

I had fun building the antenna and I learned a lot. I just bought a pair
of OEM high performance (9dbi gain) antennas off of eBay. Someone
suggested running the router up my tower in an enclosure. Neat idea...

Ken KG0WX

16 el coaxial colinear (2.4ghz) question
 

"Ken Bessler" wrote in message
news:h5d_f.557$B42.127@dukeread05...

"Jerry Martes" wrote in message
news:qCc_f.2174$wH1.1885@trnddc03...

"Richard Clark" wrote in message
...
Hi Ken,

What did you compute as being the Velocity Factor for the shield being
covered with thick PVC?

The problem with this modified Franklin Array is that you are cutting
for half-wave dimensions once, for two Velocity Factors along the same
length. Only one is going to be correct, and it is going to impact
the theoretical application of the other.

You might want to try again using bare wire, twin lead fashion.

73's
Richard Clark, KB7QHC

To Ken

Hi Ken, I'd always take Richard's advice before mine. But, I wonder if
you realize how difficult your task is. It is a very difficult project
to
develop the design of any array of radiators thats about 5 wavelengths
long.
And, it *is* a project, not just a matter of precise measuring and
cutting.
I'd think that 3 dB improvement over the antenna that was designed for
optimum performance shows that you are doing something right.
This project is a great learning opportunity for you.

I'd suggest that you get a directional coupler and get some idea of the
match of the array while it is being made longer. If you can manage to
keep
the VSWR under 2:1 with 6 or 8 elements, at your operating frequencies,
you
will be way ahead of me.

Jerry KD6JDJ


Thanks to both of you for your help. I took the antenna down and by-
passed the 40' of LMR 400. Still, my Rssi with the OEM antennas was
only 3db better on the big antenna. Thinking maybe the radome was an
issue, I took it off and saw about another 2db improvement.

I had fun building the antenna and I learned a lot. I just bought a pair
of OEM high performance (9dbi gain) antennas off of eBay. Someone
suggested running the router up my tower in an enclosure. Neat idea...

Ken KG0WX

Hi Ken

You might want to look at an "Acess point" to locate up at the antenna so
you can still use the other ports in your router.

Jerry

16 el coaxial colinear (2.4ghz) question
 

Hi Ken

Further to my last about a narrow vertical beamwidth.

http://members.cox.net/vk2yqa/pattern2.png

Is a quick and rough modeling of a 16 el collinear. Note the half power
beamwidth of only 4 degrees...

Cheers Bob

16 el coaxial colinear (2.4ghz) question - How 'bout this?
 

"Bob Bob" wrote in message
...
Hi Ken

Further to my last about a narrow vertical beamwidth.

http://members.cox.net/vk2yqa/pattern2.png

Is a quick and rough modeling of a 16 el collinear. Note the half power
beamwidth of only 4 degrees...

Cheers Bob

Wow - that's sharp! It explains why I lost the signal in my front yard.

How about this version?

http://martybugs.net/wireless/collinear.cgi

I just built it out of a coat hanger, soldered to the old coax
feedpoint from the last "experiment". It performs pretty good
but I calculate 2.14db of losses in the line. Something my
back of the set antennas don't have to deal with.

What about expanding the above antenna?

Ken KG0WX

16 el coaxial colinear (2.4ghz) question
 

"Bob Bob" wrote
My first thought would be that a collinear with such a high gain would
have a very narrow vertical beamwidth. ie a small angle off the vertical
where mounted would have the remote site some dB down off the main lobe.
_____________

As a point of reference, commercial UHF broadcast TV transmit antennas can
have elevation gains of 36X or more (~17.7 dBi); still they produce their
predicted signal strengths for their ERP and height above ground over their
line-of-sight coverage areas.

RF

16 el coaxial colinear (2.4ghz) question - How 'bout this?
 

Hi Ken

Note when I modeled the 16 element I did so as a series of dipoles fed
in phase rather than use the coax/crossover design.

I felt like checking your statement about being unable to receive in the
front yard. At around 45 degrees down from the antenna the NEC2 output
says that you'll get a lobe between 20 and 30dB down from an isotropic
(or 35-45dB down from the max gain) I'll admit my near close in signal
theory doesnt really exist but a path of 800m has about 106dB of loss.
If you knock that back to 12 metres (6dB every time you halve) you have
about 70dB path loss. If you then take a WAP kind of power level of
around 10dBm the RX signal at 12m with a halve wave is going to be
around (10-70-25) -85dBm. This kind of corelates with the lowest usable
signal for WiFi! There ya go!

I like the URL you sent as being more predictable/easier to construct
that using bits of coax. Keep in mind that progressively longer and
longer colinears are more and more critical to build and the
construction method that is being used is not really optimal in the area
of spacing between elements. You could probably pick a much better
design. I think however that you need to sit back and consider what you
are trying to achieve. Are you setting up a personal WiFi LAN for others
to use or just for specific contacts? If you are wanting to work in one
direction (or use a rotator) it might be more effective to use a corner
reflector and maybe 4 elements in phase. This will be much less critical
in construction. Remoting the WAP will make a lot of sense too as
you'll lose the line loss! Comments?

Cheers Bob


Ken Bessler wrote:



Wow - that's sharp! It explains why I lost the signal in my front yard.

How about this version?

http://martybugs.net/wireless/collinear.cgi

I just built it out of a coat hanger, soldered to the old coax
feedpoint from the last "experiment". It performs pretty good
but I calculate 2.14db of losses in the line. Something my
back of the set antennas don't have to deal with.

What about expanding the above antenna?

Ken KG0WX