4-bay VHF dipole array project

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prcguy

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This project was inspired by someone wanting a better antenna for VHF RR and this is about the best you can get. It will cover 2m through RR and can be custom tweaked if you have an antenna analyzer.
The pdf instructions are a first draft, but it took longer to document the project than it did making the antenna, which was less than 4 hours. Have fun and if you make one please let me know how it works.
prcguy
 
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prcguy

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Hmm, need to shrink the pdf a little. Will post again soon.
prcguy
This project was inspired by someone wanting a better antenna for VHF RR and this is about the best you can get. It will cover 2m through RR and can be custom tweaked if you have an antenna analyzer.
The pdf instructions are a first draft, but it took longer to document the project than it did making the antenna, which was less than 4 hours. Have fun and if you make one please let me know how it works.
prcguy
 

mtindor

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This project was inspired by someone wanting a better antenna for VHF RR and this is about the best you can get. It will cover 2m through RR and can be custom tweaked if you have an antenna analyzer.
The pdf instructions are a first draft, but it took longer to document the project than it did making the antenna, which was less than 4 hours. Have fun and if you make one please let me know how it works.
prcguy
Umm, so you just remove it rather than tease people by saying here it is and then removing it while you decrease the bloat? bah.

I'm anxious. Please post the link again :)

Mike
 

walterb

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Ok, hopefully this will work since I hacked a bunch of stuff out of the article. If not I'll have to find another place to host it.
prcguy
WOW!!!

Very cool. Thank you so much.
 

gcgrotz

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Commercial versions of that antenna work very well, they are the standard for high performance and reliability at VHF. The biggest pitfall to avoid with this design is to make sure of your weatherproofing and cut the phasing harness very carefully.

I think it may get on my project list soon as it is probably decent on air band too.
 

prcguy

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Air band you say? What a coincidence, I'm going to scale one specifically for the VHF air band next. The BW should just make it and I have a bunch of F type T adapters on order so the phasing harness will be easy and cheap. Compression type F connectors are waterproof with internal O rings and I use a dialectic grease on all outdoor F connectors anyway.

I didn't show the weather proofing details in the pdf, but the cables that connect to the dipoles were stripped to leave a small ring of braid that a short ground wire solders to. Then the junction where the center conductor and ground wire split is coated with silicone sealant and then covered with a length of heat shrink tubing with hot melt glue inside. When the heat shrink cooled I forced in more silicone sealant. I think its easier to weather proof with an individual ground wire than dealing with an exposed length of braid for the dipole attachment.
prcguy
Commercial versions of that antenna work very well, they are the standard for high performance and reliability at VHF. The biggest pitfall to avoid with this design is to make sure of your weatherproofing and cut the phasing harness very carefully.

I think it may get on my project list soon as it is probably decent on air band too.
 

walterb

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Ok, hopefully this will work since I hacked a bunch of stuff out of the article. If not I'll have to find another place to host it.
prcguy
Just wondering would F connectors and RG-6 Quad Shielded work as well?

thanks
 

prcguy

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F connectors and RG-6 is fine and I just got a big bag of F type T adapters in the mail today to use on the next phasing harness. I don't see a need for quad shield, the loss specs do not improve, its harder to install connectors and the bend radius is worse. F connectors probably have an RF power rating less than other connectors due to the 2 point contact on the female side but they should be able to handle the 100w or less that most of us use on VHF/UHF.
prcguy
Just wondering would F connectors and RG-6 Quad Shielded work as well?

thanks
 

walterb

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F connectors and RG-6 is fine and I just got a big bag of F type T adapters in the mail today to use on the next phasing harness. I don't see a need for quad shield, the loss specs do not improve, its harder to install connectors and the bend radius is worse. F connectors probably have an RF power rating less than other connectors due to the 2 point contact on the female side but they should be able to handle the 100w or less that most of us use on VHF/UHF.
prcguy
thanks. This is going to be fun project.
 

wx5uif

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Pretty neat. Quick question. Do you know off top of head what would be required for a uhf, centered around 450, antenna what the pipe sizes and the spacing would need to be?
 

prcguy

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I think 1/2" to 3/4" dia elements would give you more than enough BW and the dipoles are spaced 3/4 wavelengths center to center. The phasing harness would use the same formula in the pdf file and checking each cable length with an antenna analyzer is a good idea. I'm not sure on the distance out from the mast, I just copied what several other companies did for a 155MHz centered array. I believe the dipole to mast spacing is very close (less than 1/8 wavelength) to squish the pattern wide so 4 dipoles will fill in a 360deg pattern. It also has an effect on the dipole impedance at resonance and I believe its less than 50ohms. If I had more time it could be run in EZNEC. Just picked up some parts today for a VHF air band version but its going to be larger, at least 23ft long.
prcguy
20MHz
Pretty neat. Quick question. Do you know off top of head what would be required for a uhf, centered around 450, antenna what the pipe sizes and the spacing would need to be?
 

commscanaus

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Love your work there prcguy,

Thankyou for going to the trouble of publishing your design and sharing it with us.

I would very much like to try the same sort of array for 420Mhz- to suit a local P25 trunking system.

Please keep up the great work!

Regards, Commscanaus.
 

Mikey54

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Well done, and extremely well written. This style of antenna is written up in the old ARRL Antenna handbook, but I really like your choice of materials, and the wording on your spec sheet is much more understandable. Great Job! :p
 
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