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Old May 15, 2012, 02:58 AM
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That's a great link, thanks Markus. I've searched the thread and I can't find an answer. I'd appreciate it if someone could advise what the "separation of the adapter section" should be.

Sub
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Old May 15, 2012, 03:04 AM
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Originally Posted by subsonic View Post
That's a great link, thanks Markus. I've searched the thread and I can't find an answer. I'd appreciate it if someone could advise what the "separation of the adapter section" should be.

Sub
Hmm, I don't know either what that should be. Just build your helical acroding to the calculator and you will suceed. Place the coax feed below the spot wher the helix starts. Make sure the helix starts "a" above the reflector, and as such the center conductor of the coax obviousely must extend up to that point. Usually that's not that much unless you want to build a helical for the lower frequency bands. Add the wave trap as mentioned in Alex first posts as this is truly the easiest way to make one, and in general follow the instructions giving in this tutorial.

HTH

Markus
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Old May 15, 2012, 10:21 PM
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what is my loss on 1240 with antennas tunes to 1280?
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Old May 16, 2012, 03:33 AM
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what is my loss on 1240 with antennas tunes to 1280?
There is no way to tell as it depends on how "sharp" the antennas resonance is. It will be in the area of 10 to 20dB though.

Markus
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Old May 16, 2012, 09:55 AM
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Originally Posted by slowjett View Post
what is my loss on 1240 with antennas tunes to 1280?
My testing has shown 85% efficency for your scenario. Not bad. That's less than 1 db

-Alex
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Old May 16, 2012, 07:36 PM
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I am building a 5.8ghz helical and I am trying to figure the right length pigtail out the back of the reflector that will work with my tiny pan and tilt unit and not bind or tangle.

I know I will loose dB with more coax, but how much loss per inch?

-Todd
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Old May 16, 2012, 07:55 PM
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Originally Posted by wannabe View Post
I am building a 5.8ghz helical and I am trying to figure the right length pigtail out the back of the reflector that will work with my tiny pan and tilt unit and not bind or tangle.

I know I will loose dB with more coax, but how much loss per inch?

-Todd
Rg316 is about .7-1db loss per foot.
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Old May 16, 2012, 08:11 PM
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Originally Posted by gundamnitpete View Post
Rg316 is about .7-1db loss per foot.
Thanks. I should have mentioned I am using RG58.

I just found this about RG58 in case anyone else wants to know: Loss = 0.14dB at 100MHz, 0.27dB at 900Mhz, 0.50dB at 2.4GHz (400mm length).

My crappy math skills tell me this means that for 5.8ghz, it is 1.5dB loss over 400mm. I think....
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Old May 16, 2012, 08:19 PM
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made a helical today. I didnt have ANY multi pathing at all. I did have two dropouts though. Just for a second when the tricopter duct behind the house.

I had all sorts of trouble soldering the sma connector. It kep shorting on me. I did TWO of them and they both shorted. Managed to get one to work without shorting. Any tips for attaching those? I do not have a crimp tool.
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Old May 16, 2012, 10:47 PM
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Originally Posted by wannabe View Post
Thanks. I should have mentioned I am using RG58.

I just found this about RG58 in case anyone else wants to know: Loss = 0.14dB at 100MHz, 0.27dB at 900Mhz, 0.50dB at 2.4GHz (400mm length).

My crappy math skills tell me this means that for 5.8ghz, it is 1.5dB loss over 400mm. I think....
1 foot on rg58 is .4 DB loss at 5.8ghz.
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Old May 16, 2012, 11:52 PM
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A fairly sloppy first attempt. Next time solder will be cleaner. Also I stoopidly wound a left hand coil at first. I did not have enough extra wire to make a proper right hand coil so I had to try and smooth out the wire to re-make it into a right hand coil. It's got a few slight bumps in it.....

I basically tried to follow Mictronics design for a 5.8GHz with slight variation.

Antenna dimensions:

Design frequency 5800MHz
7 turns
Wavelength ??
Internal diameter 17.5mm ish
Wire diameter 1.5mm 14THHN
Coil spacing 11.8mm
Reflector 40mmx40mm
Wave Trap size 6.5mmx3.2mm
Wave Trap spacing from feed point 2mm
Feed point height 2.5mm (wire center), maintained over 1/4 turn (sort of).

Initial testing in front of my house at about 60 feet indicates it is definitely uni-directional . How far do you think I can go with this using antenna tracking?
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Old May 17, 2012, 03:14 AM
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Is ot a big difference if you use a square reflector as opposed to a round one?
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Old May 17, 2012, 01:06 PM
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Is ot a big difference if you use a square reflector as opposed to a round one?
Not really.

-Alex
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Old May 17, 2012, 01:07 PM
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Originally Posted by wannabe View Post
A fairly sloppy first attempt. Next time solder will be cleaner. Also I stoopidly wound a left hand coil at first. I did not have enough extra wire to make a proper right hand coil so I had to try and smooth out the wire to re-make it into a right hand coil. It's got a few slight bumps in it.....

I basically tried to follow Mictronics design for a 5.8GHz with slight variation.

Antenna dimensions:

Design frequency 5800MHz
7 turns
Wavelength ??
Internal diameter 17.5mm ish
Wire diameter 1.5mm 14THHN
Coil spacing 11.8mm
Reflector 40mmx40mm
Wave Trap size 6.5mmx3.2mm
Wave Trap spacing from feed point 2mm
Feed point height 2.5mm (wire center), maintained over 1/4 turn (sort of).

Initial testing in front of my house at about 60 feet indicates it is definitely uni-directional . How far do you think I can go with this using antenna tracking?
Too bad you don't live near me or I'd tune it in for you. I'd like to see that with my own eyes. It really is a nice piece of work.

_Alex
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Old May 17, 2012, 01:10 PM
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Originally Posted by wannabe View Post
I am building a 5.8ghz helical and I am trying to figure the right length pigtail out the back of the reflector that will work with my tiny pan and tilt unit and not bind or tangle.

I know I will loose dB with more coax, but how much loss per inch?

-Todd
This depends on the quality of coaxial cable you use. It is preferable to use a coaxial cable with a full braid and/or foil inside. These are lower loss and better quality cable.

Typically loss begins to increas significantly after 3GHz and thus for 5.8GHz I recommend keeping your runs less than 4 wavelengths. You are right on the edge of the measurement, but if I had to guess (and assume you are using a good cable) your loss is around .8db or so.

-Alex
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