Air Band Yagi

[UlteriorModem]

I put together an 'air band' yagi mostly from stuff I had laying around.
Only 'purchased' items was the 1 1/2" wood 'stick' and some U bolts.
Elements are some #8 bare Cu I had laying around for years.
I put a 40" 'yard stick' out for some sense of scale.
Figured I would get these shots before I painted it. Will paint it with camo green to sort of blend in with the trees. The wood is pre-treated with Woodlife classic clear wood preservative.

20210402_141026 by Tom Whit, on Flickr

20210402_141041 by Tom Whit, on Flickr

20210402_141045 by Tom Whit, on Flickr
Detail of the 'driven' element, note the glob of silicone for water proofing.

Any questions or comments please feel free to ask.

 

[KB4MSZ]

This is so cool. I have built a number of these for the air traffic control frequencies but I can't use them myself, too much broadcast interference around here. I give them to others who are away from the bigger cities.

 

[UlteriorModem]

Yea I hope that is not an issue. There is a nearby AM/FM 'religious' broadcast station. But hopefully it will be in the null as the local airport is almost due south of me and the station is ExSE.

Will probably be putting it up tomorrow will check back with results.

 

[n6hgg]

Should totally work like gangbusters! I've used those little three element homemade ones for years and they are awesome. If you have an offending interference source and you know the direction of it, you can null that out with one of those things also.

 

[iMONITOR]

Yea I hope that is not an issue. There is a nearby AM/FM 'religious' broadcast station. But hopefully it will be in the null as the local airport is almost due south of me and the station is ExSE.

Will probably be putting it up tomorrow will check back with results.

AM broadcasts shouldn't cause you problems but strong or nearby FM broadcast can. In that case you will want to insert a FM-NOTCH filter in the coax.

 

[UlteriorModem]

Or have a good reciever with a tight front end

The broadcast station does not bother me all that much other than I cant use my antenna analyzer because there is too much signal on the antenna.

But it does not interfere with any of my Amateur Radio equipment from 440 all the way down to 160 meters

 

[mass-man]

If you didn’t already, make sure those zip ties are UV resistant! And/or wrap them with some new Scotch 88 electrical tape! But the end don’t stretch it!!!

 

[mass-man]

If you didn’t already, make sure those zip ties are UV resistant! And/or wrap them with some new Scotch 88 electrical tape! But the end don’t stretch it!!!

That’s CUT the end!!!

 

[iMONITOR]

Or have a good reciever with a tight front end

The broadcast station does not bother me all that much other than I cant use my antenna analyzer because there is too much signal on the antenna.

But it does not interfere with any of my Amateur Radio equipment from 440 all the way down to 160 meters

I was refering to the VHF aircraft band which is what the antenna is being built for, correct?

 

[prcguy]

I suspect this Yagi is only going to cover maybe 5Mhz or so in band width. To cover the entire VHF air band I would use a folded dipole or other broader band driven element. Its also a good idea to snap on at least three ferrite beads right at the feedpoint to isolate the coax from the dipole.

 

[KB4MSZ]

Here is a design I use to experiment in the VHF and UHF range. It allows working with different ranges of frequencies quickly by simply changing the element tips for a given range. It's 3 driven element arrangement gives really good coverage for wider bands such as ATC.

 

[majoco]

Personally I would have put a 1:1 balun at the cable/antenna junction - possibly in a small waterproof plastic box so you could seal the wires in and cable out joints. Just my 10cents.

 

[UlteriorModem]

Thanks all for the suggestions.

Well I got it up and frankly and somewhat disappointed. Main problem is it is only up about 12'-0" so not exactly line of sight.

Frankly I get better results with a random longwire dipole (a G5RV) which is up about 30 feet. Yea I know crazy right?

A balun may help but it is already a bit heavy and the losses would probably overcome any real benefit. I'm probably going to take this one down.

Was a fun little project none the less.

 

[KB4MSZ]

Frankly I get better results with a random longwire dipole (a G5RV) which is up about 30 feet. Yea I know crazy right?

I'm wondering how you arrived at that conclusion by comparing to a long wire. In order to really test a Yagi it would need to be pointed at signals from a known direction and then rotated away to see the pattern the antenna provides. It would need, in most cases, to be in vertical orientation. It should out perform, by a long shot, any simple quarter wave vertical when pointed in the direction of the signal. It is not going to be effective in a general omni directional pattern.

 

[Ubbe]

Well I got it up and frankly and somewhat disappointed.

I hope you realise that the front of the antenna, that points at the source, are where you have your coax exiting the boom. If you have the antenna pointing the other way it will work with much less effeciency. The suggestions about balun are good. Either choke balun with ferrites that covers VHF on the coax right at the point where you solder the coax to the elements, or that 1:1 transformer balun which should be even better. And check that you have not any contact between your solder work and the other element.

Yagi Uda Antenna (Rothammel)

Free Online Engineering Calculator to find the Dimensions of a yagi Uda Antenna for a given Frequency Range and Length.

www.changpuak.ch

/Ubbe

 

[prcguy]

At this point I would question first, what is the design frequency and where did the dimensions come from? Second, was the antenna tested for at least VSWR at the design frequency? The antenna could be working fine, just at some frequency far away from where you think. Or the dimensions are random and meaningless.

Thanks all for the suggestions.

Well I got it up and frankly and somewhat disappointed. Main problem is it is only up about 12'-0" so not exactly line of sight.

Frankly I get better results with a random longwire dipole (a G5RV) which is up about 30 feet. Yea I know crazy right?

A balun may help but it is already a bit heavy and the losses would probably overcome any real benefit. I'm probably going to take this one down.

Was a fun little project none the less.

 

[UlteriorModem]

It was based on this article.

A9R9015.tmp (wa5vjb.com)

Yes the shortest element is pointing towards the source. Might have been a perspective thing in the pictures. The airport is almost due south of me and it it pointed south, I used a compass. 🤷‍♂️

No I did not test the swr. Might dig out the antenna analyzer and give it a run.

The 'comparison' was based on purely objective observation. Greater signal strength and 'more' heard. As in with the Yagi I could barely hear tower. with the long wire tower was fully quieting.

 

[Ubbe]

Yes the shortest element is pointing towards the source.

The elements lenght are important but the distance between them are even more important. The distance between reflector, the one closest to the mount, and dipole, where you attach the coax, should be much longer than the distance between dipole and director, the end element that points at the source. It looks like you have the antenna backwards but the elements lenghts are correct in the picture.

Use my suggested calculator to check the distance of each element measured from the reflector element.

/Ubbe

 

[UlteriorModem]

The elements lenght are important but the distance between them are even more important. The distance between reflector, the one closest to the mount, and dipole, where you attach the coax, should be much longer than the distance between dipole and director, the end element that points at the source. It looks like you have the antenna backwards but the elements lenghts are correct in the picture.

Use my suggested calculator to check the distance of each element measured from the reflector element.

/Ubbe

Did you have a look at the article I posted above? Author claims the spacing of the director is to mitigate impedance matching. Dont know if that is true to be honest.

 

[UlteriorModem]

Well I got out the antenna analyzer and evidntly it is resonant at around 156mhz. With a crap swr of 3.2

So yea back to the drawing board