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G8MNY > TECH 08.09.17 11:11l 77 Lines 2571 Bytes #999 (0) @ WW
BID : 56549_GB7CIP
Read: GUEST
Subj: Using a G5RV on 160M
Path: IW8PGT<IZ3LSV<I0OJJ<GB7CIP
Sent: 170908/0655Z @:GB7CIP.#32.GBR.EURO #:56549 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Aug 13)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
To use a G5RV or any HF dipole conveniently to a Marconi T aerial on topband
you will need..
1/ A good earth
2/ A matching coil
3/ Double Pole Relay/switch
4/ Outdoor Box
AERIAL
Tree 2nd
Supports Support
- -oÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÒÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄo- -
Insulator º
Balancedº
Feederº
º
º
º
º
Switched===================Coax to shack
Matching ³Earth
Box ³stakes
³
SWITCHED MATCHING BOX
This has to house the relay or manual double pole high voltage switch with the
loading coil.
Balanced
Feeder
³ ³
³ oÄÁÄÂÄÄÄÄÄÄÄ(((()
RL1³_/o o RL2 L /³\
³ o\_________³
³ ³_ ³
³ ³/| ³
³ === C ³ ___
³ /³ ÀÄÄÄÄÄÄÄÄ)___ Shack
ÀÄÄÄÁÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÂÙ Coax
Earth ÚÄÄÁÄÄ¿ _³_
Stakes ³Relay³ \_/
ÀÄÄÂÄÄÙ ³ Select
ÀÄÄÄÄÄÁÄÄÄ<160M
This circuit is with no HF balun for use on a G5RV or half sized G5RV. If a
dipole is used with then a switched balun & more complex switching is needed.
With the relay released L is shorted out & the feeder is connected to the coax
in the normal way.
With the relay operated the feeder is shorted together & connected to the coax
via the L & a SWR triming cap C. The voltages can be very high (1kV) so a relay
or switch with good contact separation & contacts to spacing is need.
TUNING
Generally a series L (tapped 60 turns on a 3cm dia former) is all that is
needed to get the resonated Z down to near 50/75ê with most aerials. But if the
SWR is still to high at resonance the C across the coax (via RL2 contact) of
100-2000pF should bring the Z to an exact match.
BOX
A black plastic box is best. Hermetically sealed boxes really don't seal that
well outdoors. A better approach is to leave a breathing hole in the bottom
(lowest point) so that any water can drain way, but put a fine mesh over it to
stop insects. Paint up & spay all parts with a light oil to resist rusting.
Grease up well, all screws & connectors use outside so any water has no where
to go.
Why Don't U send an interesting bul?
73 de G8MNY @ GB7CIP
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