Ham Radio - 70cm Homebrew Antenna

[Patrick Mullaney - N1JEQ]

I'm currently working on a project to build a portable yagi for 70cm.   I'm basing my design off of this 2m version designed in the UK:  http://www.m0ukd.com/144MHz_Homemade_Portable_Yagi_Beam/

Has anyone had any success, with anything similar, or has any other portable designs to recommend? 

I'll be stopping by HSL after 8:00 tonight, for the first time, to check it out.

73

Patrick.

[Jasper Nance]

I did this way back int he day... had great success.

 

https://web.archive.org/web/20120727094639/http://uirise.wikidot.com/70cm-quagi

[Larry Campbell]

I made a couple yagi antennas like this before and kept one in my backpack when doing search and rescue back in california, they certainly work much better than a nub on top of an icom-w32... 

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[Larry Campbell]

medium gauge solid copper wire makes for simple directors and a reflector elements that can be stored inside the body when you use a piece of sch40 pvc with 2 endcaps...and you have most of it right there, the coupler and a driven element can be wire tied in place as needed...

[Jeff Covert]

Is there an antenna analyzer at HSL?  these make building much easier and fun. 

I made a nice 70cm yagi for DF to find my rockets. it was made out of brass welding rod and a small brass tube. I even made slide of section that had most of the directors for when I got close.

I now have a 2m yagi made of PVC pipe and measuring tape. I use it for fox hunts and search and rescue training.

On Wednesday, July 23, 2014 4:05:06 PM UTC-7, Patrick Mullaney - N1JEQ wrote:

[Jasper Nance]

I have a dummy load and an HF/VHF/UHF SWR meter if you would like to borrow it. You still need a radio to generate the signal. I have an analyzer for HF but not VHF/UHF.

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Jasper Nance - KE7PHI
Creative and Scientific Imagery
http://www.nebarnix.com/

[Larry Campbell]

I have a MFJ analyzer.... thought it was a model 269 but it might only be a 259, I havent used it in probably 4-5 years...should be buried in the hall closet

On Thursday, July 24, 2014 6:10:17 AM UTC-7, Nebarnix wrote:

I have a dummy load and an HF/VHF/UHF SWR meter if you would like to borrow it. You still need a radio to generate the signal. I have an analyzer for HF but not VHF/UHF.

On Wed, Jul 23, 2014 at 9:54 PM, Jeff Covert

wrote:

Is there an antenna analyzer at HSL?  these make building much easier and fun. 

I made a nice 70cm yagi for DF to find my rockets. it was made out of brass welding rod and a small brass tube. I even made slide of section that had most of the directors for when I got close.

I now have a 2m yagi made of PVC pipe and measuring tape. I use it for fox hunts and search and rescue training.

On Wednesday, July 23, 2014 4:05:06 PM UTC-7, Patrick Mullaney - N1JEQ wrote:

I'm currently working on a project to build a portable yagi for 70cm.   I'm basing my design off of this 2m version designed in the UK:  http://www.m0ukd.com/144MHz_Homemade_Portable_Yagi_Beam/

Has anyone had any success, with anything similar, or has any other portable designs to recommend? 

I'll be stopping by HSL after 8:00 tonight, for the first time, to check it out.

73

Patrick.

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Jasper Nance - KE7PHI
Creative and Scientific Imagery
http://www.nebarnix.com/

[Jasper Nance]

Those are SOOOO NICE!

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[Larry Campbell]

Does Jasper wanna play with my analyzer???????? come onnn you know you wanna...

On Thursday, July 24, 2014 8:31:34 AM UTC-7, Nebarnix wrote:

Those are SOOOO NICE!

[Jasper Nance]

I am not even remotely sure what I am supposed to say to that. 

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[Patrick Mullaney - N1JEQ]

I'm planning on using 1/4" aluminum rod for the elements.  They are slightly more bend resistant than their copper counterparts.

[Jasper Nance]

I always use brass tubing or steel piano wire. I have had too many bad experiences with malleable wires. The problem with tubing is that you can only bend it once. Even if that's on accident. Then it snaps.

[Larry Campbell]

Thats part of why I liked using THHW, even when its mangled all you have to do is lay it on a flat surface with a board on top, roll it a few times and it straightens right back out...

On Thursday, July 24, 2014 1:53:40 PM UTC-7, Nebarnix wrote:

I always use brass tubing or steel piano wire. I have had too many bad experiences with malleable wires. The problem with tubing is that you can only bend it once. Even if that's on accident. Then it snaps.

[Jasper Nance]

Be careful using insulated wire for two reasons. One is that the dielectric constant is higher so the velocity propagation is slower making it appear electrically longer than it is, and the other is that you are limited to small diameters which limits the effective bandwidth of the antenna (larger bandwidth also makes it easier to "fudge")

[Larry Campbell]

I had spools of solid 8 gauge ground wire....I usually stripped it so it would fit inside the PVC for storage... good to know about the velocity propagation issue though....  

On Thursday, July 24, 2014 4:13:12 PM UTC-7, Nebarnix wrote:

Be careful using insulated wire for two reasons. One is that the dielectric constant is higher so the velocity propagation is slower making it appear electrically longer than it is, and the other is that you are limited to small diameters which limits the effective bandwidth of the antenna (larger bandwidth also makes it easier to "fudge")

[Mike Bushroe]

And here I was thinking how smart I was being about a design to use tent pole fiberglass segments to hold the wire so that they wouldn't get bent at all!. If there was enough room, you could even still keep the shock cord inside as well and fold the elements along the outside, then pull them out and shock cord pull them into machined aluminum sockets so they would be both rigid and held at just the right angle!

  Once again, I am over engineering the problem. I was imagining a 4-segment folding boom with elements that folded to the sides. Each hinge in the boom would have a short overshoot on one side, pull that up even with the other and slide a locking ring over it. In the process, it would pull a cord the pops the elements out from the sides up against 90 degree stops so that the whole thing unfolds itself. Maybe even add some nylon (fishing line) rigging lines to hook over notches in the boom to hold the elements into position. That way you could have nearly twice as many elements in the yagi and still fold up to under 6 feet.

  Of course, that would also mean lots of time in a machine shop making all the precision pivots and stops, measuring out the fishing line to just snugly hold the elements open, running a very inelastic cable without using steel aircraft cable down the inside and then out a hole to each half element, and make those nice over shoot and locking ring connections and their pivot joints. Or, just one piece of PVC with well drilled holes and pre-cut lengths of 6 gauge bare copper with mechanical limit stops and maybe a rubber band to keep them from sliding back out again. If you just want to go for the simple design! :)

Mike

[Jasper Nance]

Mike, tent pole antennas are very common in HF land where your dipoles are huge. you can even spiral wrap them with foil tape to make a loaded travel antenna that is shorter than it would otherwise be.

In the 70cm band though, things are pretty small.

[Patrick Mullaney - N1JEQ]

Yea, I'm going with the simple design!  :)

[Jerry Davis]

Sorry I am late to this. My gmail filtering has been screwed up, and didn't know it.

I just recently built a portable yagi (PVC type) for 2m. I figured that a 70cm could be built the same way, only dimensions would be different.

Here is one page I have found. http://www.ph7at.net/experiments/portable70cmyagi.php

jerry

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