Need help building a directional Yagi to track my dog with my Icom R20

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d18ge

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Jun 14, 2009
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Hope someone wiser than me can help me on this.

I am wanting to build a 3 element Yagi to track my hounds tracking collar with my Icom R20 . The collar is 218 mhz. I am wanting to build something similar to this tape measure yagi . http://home.att.net/~jleggio/projects/rdf/tape_bm.htm
I found a yagi calculator and it generated the dimensions and spacing for 218 mhz. Will the plans for the "tape measure" yagi work if I modify the element length and spacing to match 218 ?

I wasn't sure if the hairpin match would work at a different frequency? The website said the spacing between the driven elements is what adjusts the SWR . Will it hurt the scanner if my SWR is high since I have no way of checking it ? I assume no since I am only recieving

Thanks for any help
 

hertzian

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May 28, 2009
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You are in luck! The R20 has an S-meter that has enough resolution to make yagi building fun.

Will you be using 50 ohm or 75 ohm cable to feed it?

That makes a difference as there are 3 major variables to choose from when building a beam:

1) overall gain
2) SWR
3) Front-to-back ratio

Typically you choose only one and optimize for that.

Here is the simplest beam that can get you started tracking, and you can optimize it later. At least you'll be on the field quickly with some gain and directivity - even if it isn't the perfect beam. :)

Take your typical dipole (468/f mhz) and use that as your driven element.
Add 4 or 5 percent to the driven element measurement to make your reflector.
Subtract 4 or 5 percent from the driven measurement for the director.

For 75 ohm cable, space the elements evenly at 1/4 wave apart. (234/f mhz)

For 50 ohm cable, move the reflector inwards a few inches.

With your dog's collar active, and using the s-meter on the R20, along with the attenuator turned on perhaps, you'll be able to dial into the element spacing pretty quickly - as long as the collar isn't sitting on the bench next to you. :)

These are directly connected to the coax, and try to bring the coax out from the back of the reflector. If you have some type-43 snap-on ferrite chokes, place them on the coax near the feedpoint - at least two - four is preferable. yes, these don't have the best match in the world - but a couple of rods and a yardstick can be a lot of fun.

That's it! Are these the greatest? - no way. BUT it can provide a start to keep the interest up as you finalize and improve on your design.
 
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