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Scanner / Receiver Antennas For discussion of any type of receiving antenna used by a scanner or receiver base, mobile or handheld.

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  #1 (permalink)  
Old 07-22-2009, 5:24 PM
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Arrow Home Brew 800-900MHz yagi

Decided to build and big yagi for local MARCS.

Should work between 800-900MHz
Antenna centered at 850MHz.
23 Elements
Overall length 6' 9"
Total weight 3.8lbs. (amazing)

Construction material
1" x 1" x 3/32" square aluminum tubing (main section)
3/16" x 1" aluminum flat bar (for joining the 2 sections together and adding strength)
3/8" O.D. round tubing (elements)
rubber end caps
buna (rubber) grommets (for isolation)
8-32 hardware (for mounting the flat bar)[plan to replace with stainless before mounting in the air]

Total material cost -> approx. $45.00

Project just about completed.
Here are the pics.










Last edited by digitalanalog; 07-22-2009 at 5:37 PM..
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Old 07-22-2009, 6:01 PM
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Wow! What is the estimated gain on that monster?
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Old 07-22-2009, 6:03 PM
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Not really sure at this point but i am looking in to it.

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Wow! What is the estimated gain on that monster?
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Old 07-22-2009, 6:07 PM
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Outstanding! excellent job

Where did you get the end caps? It always seems like the little details like that are the hardest parts to find.
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Old 07-22-2009, 6:10 PM
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McMaster-Carr
and they are very very cheap to buy.

EDIT:
I also got them smaller then they needed to be, so the would be really tight fitting
looking at the pics you can see they are not pushed all the way on, done that before and in the sun, it shrinks the
rubber and split's it, leaving it pushed on only half way or less, it won't split at the ends.

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Outstanding! excellent job

Where did you get the end caps? It always seems like the little details like that are the hardest parts to find.

Last edited by digitalanalog; 07-22-2009 at 6:14 PM..
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Old 07-22-2009, 6:28 PM
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If anyone is interested, here is a screen capture of the sotware used to build this antenna.

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Old 07-22-2009, 6:38 PM
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Curious, did you use an antenna calculator program to get spacing and element length?

EDIT:

I really do have to not answer the phone when posting.
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Old 07-22-2009, 7:01 PM
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That's a good looking piece. Any plans on how you are going to wire it up? Nice Job!!
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Old 07-22-2009, 7:24 PM
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All elements are isolated from the main section, so center conduction to one side of the driven element(which ever one is pointed to the sky)
and the shield to the other side of the driven element(element side facing the ground).

no gamma matching since all elements are isolated.


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That's a good looking piece. Any plans on how you are going to wire it up? Nice Job!!
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Old 07-22-2009, 7:24 PM
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Damn phones........................lol

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Curious, did you use an antenna calculator program to get spacing and element length?

EDIT:

I really do have to not answer the phone when posting.
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Old 07-22-2009, 7:30 PM
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Seems like bit of overkill for a trunked system.

Moon-bounce maybe?
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Old 07-22-2009, 9:53 PM
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Thats a nice looking piece. How do you plan to mount it? And how did you get the coax connected inside the boom to the driven element. Some pics of that would be super!
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Old 07-22-2009, 11:37 PM
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Wow, nice job!
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Old 07-23-2009, 4:52 PM
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More gain is more gain, Not overkill.
When you live in a low lying rural area as i do, you must
do whatever it takes to get any help you can.

my elevation is 102' below the surrounding areas, I live in a whole so................

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Seems like bit of overkill for a trunked system.

Moon-bounce maybe?
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Old 07-23-2009, 4:54 PM
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Mounting , i am not sure yet on that.

Coax is not connected to the antenna yet
still have that to figure as well.

As i stated in the OP, it's not done yet, but final install
pics and info will be given when it's in the air.......

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Thats a nice looking piece. How do you plan to mount it? And how did you get the coax connected inside the boom to the driven element. Some pics of that would be super!
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Old 07-26-2009, 1:49 PM
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Default Driven element

O.K., so i decided to get on with this project.

Isolating and getting the Driven element ready for coax.

1) Cut the driven element in half, drill and tap the end of the tube for
what will be the coax connections.


2) Drill 1/4" holes in main antenna section for plastic inserts
this is done on both sides of the antenna section. and spaced
accordingly. The length of the spacer is equal to the height of
the element hole and will act as a spacer as well for the element to
rest on.



3) Electrical tape put over the ends of the elements where they will
be close to each other inside the main section, then a piece of shrink
tubing placed over the two element ends to give them some stability
while sliding into the main section, a 1/32" spacing was left between
the 2 ends to make sure they don't touch each other, screws were then
threaded back into the elements and spacing was checked to make sure
everything would line up ounce slid back in the main section of the antenna.



4) Finished.
Re-inserted the section of driven elements,secured the screws
using rubber backed washers and nylon locking nuts to secure.
After all was finished, i checked the two coax feed screws with
an ohm meter and all was good, also checked each screw to
the main antenna section,and again all was good.




Mounting is next, should be pretty straight forward, mounting will be in the center
with 2 supports to the mast to keep it from bowing or leaning.
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Old 07-26-2009, 2:04 PM
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Quote:
Originally Posted by digitalanalog View Post
More gain is more gain, Not overkill.
When you live in a low lying rural area as i do, you must
do whatever it takes to get any help you can.

my elevation is 102' below the surrounding areas, I live in a whole so................
Not always the case with FM.

Did you investigate other designs that might fit your needs better?
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Old 07-26-2009, 2:19 PM
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Other then using a pre-amp what other type of antenna would you suggest for MARCS other then a Yagi with a bunch of elements for as much gain as i can get?
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Old 07-27-2009, 12:12 PM
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NICE! Wow the gain on that is going to be insane and directional. I would guess over 15dbi? Probably in the 20's


With that kind of gain, preamps would not be needed.

Last edited by prc117f; 07-27-2009 at 12:14 PM..
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Old 07-27-2009, 12:25 PM
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Quote:
Originally Posted by digitalanalog View Post
Other then using a pre-amp what other type of antenna would you suggest for MARCS other then a Yagi with a bunch of elements for as much gain as i can get?
If the goal is gain, probably a corner reflector, or even stacked corner reflectors, maybe stacked shorter yagis or stacked helical.

7 to 9 element commercially built yagis give about 10 dBd.

So built well, you should expect about 13 dB from 15 to 19 elements, and little more from going to 23 elements.

Then figure you lose a few due to being home built.

2 stacked corner reflectors give you 12 dBd (and 4 would be about 15 dB) and there is much less chance of loss in the design since they are simpler and rely on less critical physical measurements.

I was thinking a helical, since a non direct signal may not be perfectly vertically polarized (or may be not vertical at all) so your Yagi would show some loss from the expected gain.
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