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G8MNY > TECH 09.03.05 19:35l 57 Lines 1569 Bytes #999 (0) @ WW
BID : 35859_GB7CIP
Read: DK7JAN GUEST
Subj: A simple 3 ele yagi for 144Mhz
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0ACC<DB0GOS<DB0EEO<DB0RES<ON0AR<GB7CIP
Sent: 050309/1001Z @:GB7CIP.#32.GBR.EU #:35859 [Caterham] $:35859_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
From: G0FTD@GB7SXE.#38.GBR.EU (Updated Nov 04)
Here is a simple 3 ele yagi for 2m /P work which I made up from
an old Band 2 FM antenna with elements about 5mm diameter.
_______________________ 976 mm
Distance = 300 mm
___________o___________ 1000 mm
Distance = 590 mm
________________________ 1004 mm
Construction notes:
The reftr and director are touching the metallic boom in the centre.
A coaxial matching stub is used to match the driven element to 50ê due
to the coupling effect of the other elements. Attach a length of approx
20cm RG58 coax at the feedpoint of the dipole (in parallel with the
feeder cable and leave it open ended).
Some trimming will no doubt be needed of the matching stub for best match.
I find it best to star off with a slightly longer length than required
and trim by *5 mm* each time. It is essential to trim by 5mm because the
exact point of matching is quite narrow.
Earlier on I scribbled some figure in my notepad about element size on this
3ele design.
With elements @ 2.5mm diam = 7.34dbd gain
With elements @ 5mm diam = 7.01dbd
With elements @ 10m diam = 7.42db
R changes about 2 ohms but j varies a bit more.
Not a problem with a coaxial stub ;-)
You may vary the length of the driven element slightly and it will not
impair performance, but you will have a slightly different length needed
for the tuning stub.
- Emperor Andy -
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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