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G8MNY > TECH 24.03.08 13:00l 60 Lines 1684 Bytes #999 (0) @ WW
BID : 51096_GB7CIP
Read: GUEST
Subj: A simple 3 ele yagi for 144Mhz
Path: IZ3LSV<IW2OHX<I0TVL<ED1ZAC<GB7CIP
Sent: 080324/0115Z @:GB7CIP.#32.GBR.EU #:51096 [Caterham] $:51096_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
From: G0FTD@GB7SXE.#38.GBR.EU (Updated Mar 06)
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 reflector & 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 & 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 & trim by
*5 mm* each time. It is essential to trim by 5mm because the exact point of
matching is quite narrow.
(I recently changed from a coaxial stub to a 5-15pf trimmer across the)
(feedpoint. This too works a treat. - Andy -)
Earlier on I scribbled some figure in my notepad about element size on this 3el
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 & it will not impair
performance, but you will have a slightly different length needed for the
tuning stub.
- Emperor Andy - G0FTD@GB7SXE.#38.GBR.EU
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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