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3 element, home brew 2M yagi

Posted: Sun Oct 15, 2017 12:47 pm
by VE3PCP
Hi folks:
I put together a home brew, 3 element 2M yagi for our portable set up on October 21, 2017 for Jamboree on the air.
I modelled the design using 4nec2 software and optimised it for low swr using 52 ohm coax feed line.
In doing so, I sacrificed a small amount of gain but at 2M, gain can quickly be lost if swr is very high so I went for the low swr.
I am also working on some other designs for 4 and 5 element and optimising for both gain and low swr for one to put up at the home qth.
Will report back on that one.
Material used as follow.
Boom and non metallic mast are both from 1X2 Poplar from the local lumber yard.
Galvanised 14 ga steel wire
A length of RG58 coax that I had hanging on the rack.
#8 X 3/4" metal screws, not countersunk heads.
The elements are made by taking 2 equal lengths of wire, I used 48" for reflectors and directors.
Clamp them in a vise in the middle, grip the loose ends in a drill on low speed. Start the drill and twist the wires while keeping pull tension on them. They wind up quite nicely this way. I repeated the process for all elements.
The Driven Element was in 1 piece starting with 48" long wire and folded in the middle to form the loop.
Of note, before twisting the pairs, you can straighten each length by twisting with the drill as well. Grip one end in the vice, other end in the drill, start the drill on low speed and watch all of the kinks and curves disappear. Only twist is as much as you need to get it straight. No need to overdo it. remember to keep tension on the wire.
I marked the elements where they needed to be cut and soldered them at that point before using a zip cut in the grinder to trim them.
I laid out the boom and drilled pilot holes for the #8 screws. Attached the elements and the mast to the boom,
Soldered the coax to the feed point, centre conductor to the top element.
Note: I cut all elements to the design length and made no adjustments.
Below is the video and the output from the 4nec2 software for the design.
Design frequency in the model is 147 Mhz. Actual swr at 147.95 was 1:1. It was around 1.15:1 at 147. So I could adjust the length of the DE slightly longer to lower the 1:1 point. I can do that by moving the both outwards under the mounting screws hopefully. It won't take much, may 1/8" each.
Hope you enjoy it and maybe make use of the design if you need a cheap and easy yagi!
73s
Rob, VE3PCP

https://youtu.be/mQQZqYlhbeA

Re: 3 element, home brew 2M yagi

Posted: Sun Oct 15, 2017 6:54 pm
by VE3PCP
Hi folks:
I did a follow up video today.
Took my hand held and went back to the same spot as yesterday and corrected the aim for Paisley and Berkely repeaters.
Was able to hit both with 1 watt, paisley with .5W and neither with 50 mw.
Still pretty good results for the antenna!
73s
Rob, VE3PCP
https://youtu.be/sYWq1B0OiVc

Re: 3 element, home brew 2M yagi

Posted: Sun Oct 15, 2017 8:30 pm
by ve3efq
Looks good.

I made a yagi a while ago following the plans given for the tape measure yagi:

http://nt1k.com/blog/2012/vhf-3el-tape-measure-yagi/

It worked well - adding a good batch of range for my HT, and this was without hauling it high up in a tree. I even used it to try some satellites too.

I really need to make a portable, collapsible version for when out in my camp. I had my homemade, 2m vertical about 35 feet up this afternoon but I could not get a signal to Paisley (though it did go to OSR, around 20km from my camp). Maybe a yagi up that high would get me to Paisly (60km away from that camp)?

I tried using a modelling program before; never had much luck; I should get you to give me a lesson!

'EFQ

Re: 3 element, home brew 2M yagi

Posted: Mon Oct 16, 2017 9:39 am
by VE3PCP
I'll have to plug the numbers for the tape measure design into 4nec2 and see what it says. the flat element may not behave exactly like a wire but should be close.

It's to bad that you can't get telescopic walkie talkie antennas like you once could. They would work great for a portable antenna.