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G8MNY > TECH 05.08.23 10:31l 74 Lines 3350 Bytes #999 (0) @ WW
BID : 51709_GB7CIP
Read: GUEST
Subj: 23cm Skeleton Alford Slot
Path: IW8PGT<IZ3LSV<ED1ZAC<ED1ZAC<IQ0FO<GB7COW<GB7CIP
Sent: 230715/0910Z @:GB7CIP.#32.GBR.EURO #:51709 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
WALK-ABOUT ATV AERIAL
By G8MNY (published in BATC's CQTV 8/92, Updated for Packet Dec 03)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
This is a modified skeleton Alford slot a antenna with gain of 6dB or so, but
still small enough to be mounted on a hat. An unusual feature, is the "short
circuit ends" of the slot, that have been neatly folded inside the end loops to
keep the size down.
PARTS
1.4M of 1.5mm Copper Wire
1M of Solder.
2M of UR43 Coax.
1 UR43 coax plug.
1 Drinks Bottle/Toy Baseball bat (Ray dome)
.5"x2"dia Expanded Polystyrene
1 Hard Hat/Camera mount
12" of Tin Foil (if no tin hat)
1 idiot to ware it!
The aerial is simple to construct, even if fiddly with the small Balun &
matching stubs. Tuning up should just be a matter of bend adjustments to alter
the gap of the slot.
P L A N S I D E F E E D E R
V I E W V I E W
100ê balanced
__0_ / \ ÚÂÄÄÄÄÄÄÄÄÄ¿ o o
/~~ :: ~~\ ³ ³³ ³ 15mm\ /
/' : : `\ 160 ÃÅÄÄÄÄÄÄÄÄÄ´ Slot of wire`\ ___/' Balanced
³ : : ³ 5x mm ³³ ³ ÃÁ¿ ÃÄ¿ /|\
³ : : ³loops ÃÅÄÄÄÄÄÄÄÄÄ´<100ê Feed ³ ³ ³ ³Dead |
\ : : / 131mm ³ ³³ //³ Matching wire ³ ³ ³ ³Coax 6cm
`\_o o_/' each ÃÅÄÄÄÄÄÄÄÄÄ´ <coax ³ ³ ³ ³ |
Slot 45mm dia ³ ³³ // ³ balun ³ ÃÄÁÄÙ \|/
Gap 10mm \ / ÃÅÄÄÄÄÄÄÄÄÄÙ ³ ³ \joint to
³³ /coax ³ ³ braid
support 50ê
Unbalanced
: = shorting Vs on top &
bottom of slot 2x 43mm long
o = slot verticals
0 = supporting backbone
HARD HAT MOUNTING.
Put a piece of polystyrene foam onto bottom of the aerial & affix this to the
hat, secure the coax (tape or clips). Cut a drinks bottle with suitable tabs to
fix onto thy hat, to form raydome. This is required as doorways, tend to
completely wipe out the aerial when one doesn't duck! Line the inside of the
hard hat with tin foil, to reduce any chance of becoming a hot head.
BASEBALL BAT MOUNTING.
Cut open a toy plastic bat down one side, carefully insert the aerial. Use foam
polystyrene pieces to centrally locate & support the aerial. Run the coax out
of the handle. Tape up the vertical cut. Mount the aerial on the rear of a
shoulder camera mount etc.
IN USE
Although I had lots of comments as to what it looks like, (even from police
at shows) the performance of this aerial has been very good. From low lying
ground level with 1 watt of Colour ATV & sound pictures have been Rx at P2
over 5km. From RSGB VHF Convention at Sandown Race course years ago, in the
building on the 1st floor, GB3HV at High Wycombe gave a P3 Colour report over a
distance of 35km. Pictures from it were being Rx by the HCATV group on the BATC
stand at the rally.
Why don't U send out an interesting bul?
73 de John G8MNY @ GB7CIP
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