G8MNY TECHNI 29.08.19 03:15l 46 Lines 2071 Bytes #180 (0) @ WW
BID : 19331_GB7CIP
Subj: Making a Phasing Harness
Path: OK0NBR OK2PEN N3HYM WH6FQE W0LVJ GB7CIP
Sent: 190829/0608Z @:GB7CIP.#32.GBR.EURO #:19331 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW

By G8MNY (updated Jan 05) Calculate 1/4 wave lengths of 75Ω 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
50Ω ======= ≡≡≡≡≡≡≡≡[ 2x 50Ω OR 50Ω =======[ 2x75Ω 2x 50Ω
37Ω == to aerial ========#== to aerial
(2x75Ω)

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 75Ω 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 47Ω 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 50Ω 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?


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