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G8MNY > TECHNI 13.03.23 09:04l 45 Lines 2070 Bytes #999 (0) @ WW
BID : 42694_GB7CIP
Read: GAST
Subj: Making a Phasing Harness
Path: DB0FFL<OE5XBL<DB0RBS<DB0ERF<DK0WUE<PE1RRR<PI8LAP<OK2PEN<GB7CIP
Sent: 230313/0757Z @:GB7CIP.#32.GBR.EURO #:42694 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (updated Jan 05)
Calculate 1/4 wave lengths of 75R coax using the coax's velocity factor & the
wave length for your frequency of interest. None of this is too critical unless
above 1GHz, where cable Z changes if you bend them, & cutting to length is more
of an art, so the use of a solid power splitter is more common.
Decide which harness design you want:-
Join Tee == to aerial tee ========#== to aerial
50R =======<ðððððððð[ 2x 50R OR 50R =======[ 2x75R 2x 50R
37R == to aerial ========#== to aerial
(2x75R)
e.g. both matching lines in a single feed plug (or socket) & an aerial plug (or
socket) with a aerial T connector. Or use the matching lines as the T with 3
plugs (or sockets). The latter is mechanically less strong, & waterproofing may
be more difficult. Alternatively you could splice in the matching sections, but
again waterproofing can be a problem.
Use good quality 75R cable with heavy braid. You should find that 2 coaxes can
be made to fit N connectors with some difficulty. Use silicon rubber or grease
to seal/fill connectors once tested.
Testing can be done with a sensitive SWR meter a 1W rig & 2x small 47R
resistors (not wire wound with minimum leads) mounted one the ends of the lines
to simulate the 2 aerials. This should prove the cut lengths are OK before you
terminate the aerial ends.
The Aerials must be identical types (no early/later multibeam type mix). And
mounted so that the connections feed the same side of the driven aerial element
to be in phase. If the aerials are mirror images (one up side down) & the
element cannot be rotated, then add 1/2 wave length (x Velocity factor) to one
of the 50R aerial feeders. The two aerial feed coaxes between the splitter &
aerials must be identical lengths & type.
See my bulletin on Stacking, Baying or Boxing Ant.
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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