WHAT TYPE OF FEED FOR A 2M YAGI?

[W6PJJ]

I am planning to build a 2 Meter Yagi out of Aluminum but I cannot decide on how to feed this Antenna. There are a number of designs but I cannot settle on one. I do not have access to a Machine Shop so some of the designs would be out for me. I am using 3/16" aluminum rod for the elements, the boom is 1 1/2" aluminum tubing 10.5' long. The elements will be insulated from the boom with delrin insert insulators pretty much like the commercial guys use. I would like to build a feed system that is not too complex and can be constructed in a garage with an average tool complement. I have consulted a number of Antenna Books but the actual descriptions of building are quite vague. Any suggestions would be welcome.

 

[Moleculo]

If you can easily split & insulate the driven element, the beta match is probably one of the easiest to build. Here's an example of a simple design that superantennas uses on their HF antenna:

 

[74IN]

]If you can easily split & insulate the driven element,[/U] the beta match is probably one of the easiest to build. Here's an example of a simple design that superantennas uses on their HF antenna:

Then it's a dipole and can be directly driven.

Braid to one and center to the other.

 

[Moleculo]

Then it's a dipole and can be directly driven.

Braid to one and center to the other.

It is going to be resonant at the dimension of a dipole, but the feed point impedance isn't going to be 50 ohms. Yagi feed feed point impedance is typically much lower.

 

[W6PJJ]

Well, I have seen this match before but always on HF Tri-Band Yagis. It may be difficult to size it down for 144MHz. I have also considered the folded Dipole match. But, it requires and Balun and I'm trying to keep all the extra stuff out of the way of the pattern. ?? We will have to see what surfaces here. TNX 4 your reply and the Images.

 

[WA8ZYT]

All you need to know: http://www.g0ksc.co.uk/

The LFA's are really easy. Looks harder than it actually is. I bought a tubing bender from Harbor Freight for $6.

 

[Moleculo]

A gamma match isn't that difficult to build either.

 

[W5LZ]

There are a number of methods to feed that antenna, the one to pick is the one that's easiest for you. There are some very slight efficiency differences between those 'feeding' methods, but the key word in that is 'slight', if it's done correctly, those differences really don't make any practical/noticeable difference in performance.
That goes for hanging a balun on the feed point too, just ain't no 'thang'. There are always some changing/shifting of the radiation pattern no matter how you feed the thing, that's normal. In most cases it will never be noticed at all.
Which impedance matching method is best? Whichever one you happen to have working for you. There are no absolutes.
- 'Doc