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G8MNY > TECH 23.07.06 01:00l 60 Lines 1692 Bytes #999 (0) @ WW
BID : 39408_GB7CIP
Read: DL1LCA GUEST OE7FMI
Subj: A simple 3 ele yagi for 144Mhz
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DB0RGB<DB0MRW<OK0PKL<OK0PCC<SR6BBA<SR7DWI<SR1BSZ<CE8FGC<ON0BEL<GB7CIP
Sent: 060722/1835Z @:GB7CIP.#32.GBR.EU #:39408 [Caterham] $:39408_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 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.
(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 and 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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