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Discussion Starter #1
I'm interested in building a medium gain antenna with a wide beamwidth. I see that hkaye has experienced success using a double biquad with 15 cm sides for interior diamond and 10cm sides for outer diamonds. Is that the recommended dimensions? Someone else found through optimization that the smaller diamond whould be on the inside and bigger diamonds further away from the feedpoint. Which is right? Is there a recommended feed spacing? I'd like to use either 1-1/4 or 1-3/4 inch feed spacing. 300ohm showed excellent gain on a double biquad using 2x4 inch mesh. I'd probably use 300 ohm's reflector size but I didn't see the spacing from the antenna to the reflector? For me, 4-1/2 inches works well with my method of constructing antennas from pvc components, hopefully that is close optimum for the double biquad.

Also, I don't know how to run the nec models. What is the beamwidth for the double biquad at say 470, 600 and 680?

Thanks!
 

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IDRick: I played around with bigger in the interior and small on the end but there is no advantage. The one I did had a 2" feed gap, from there a leg of 5.15" up(3.25') and out(5") then a leg of 6.9" at the cross over (8" off the feed) then a 5.32" leg(11.5" off the feed) and 5.32" to 15" off the feed. This giver about 60*beamwidth at all. The reflector I had at 5", but 4.5" should work ok.
 

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Discussion Starter #4
Xauto, thanks for the personal "boots on the ground" review and the dimensions! :)

All the best,

Rick
 

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Discussion Starter #6
That's a good question OTA. Hkaye insulated the crossovers on his double biquad with electrical tape and I suspect Xauto also insulates or somehow separates them.
 

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If you look in area 51 post #183(that in page 13 for me). You will see a pic. Yes the crossover is separated. Also in #184 I give a jump to a pic. of one I built( X032).
 

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IDRick: The one that you reference in post #8 (here) is the same one that 300 ohm is talking about(X032). The one that I gave info. in post #3 (here) is small at the top and bottom and larger at the feed gap. The X 034 is x032 with a reflector. You can make either. The gain is about the same 11+ with reflector.
 

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Discussion Starter #10
Xauto,

Thanks for sharing your build, build instructions, gain data, and personal experiences with this antenna! It'll be a piece of cake to build one of these with 1/2" pvc, carlon straps, 12 guage wire, and plastic rods for spreaders! Will post pictures and test results after completion.

Best,

Rick
 

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If you use stiffer wire (number 6 or 8), it will hold its shape and there is no need for spreaders. I just wrap it around 1/2 inch PVC and it is very sturdy. The standard plastic clamps for conduit provide a nice spacing for the feed point. There are a few pics in this post (on another topic):
A Portable OTA Signal Finder Setup
 

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Discussion Starter #12
Thanks for sharing the link jpasadena! Very nice build! I do agree that carlon straps work very well with a pvc spine, my preferred method for building a M4. I was thinking that heavier wire could eliminate the need for spacers, great to have confirmation! It does come down to cost versus benefit discussion though. 6guage copper wire is very expensive here. It would be cheaper to use 12 or 14 guage wire, 1/2" pvc spine, and 1/4" plastic rod as spacers. But when one considers the difference in time and ease to construct, well, heavier guage wire wins hands down. :)

Where did you buy the 3 way pvc couplings? I've been looking for those but can't find a local source. Very handy for many pvc projects. Thanks!

Best,

Rick
 
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