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Technical Bulletin 2m Full wave Dipole

2m Full wave Dipole

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By G8MNY (Updated Mar 07) (8 Bit ASCII Graphics use Code page 437 or 850) I have a design for a full wave dipole. It is only suited for loft environments as it is made from 2.5mm bare copper wire hanging from the roof apex, & giving vertical polarisation. LOFT APEX string Half wave Dipole TROMBONE MATCHING LINE T S chock COAX FEED block =============\ T \ S / \ \________/ 4:1 balun Half wave Dipole The half waves are both 1M long, & the 2 matching lines are 2cm apart, & are just over a 1/4 wave long. There is a plastic insulator (Chock block) at the dipole feed point (6000Û). Point S is a sliding "Chock block" connector with a shorting wire link. Point T is another connector but with the 200Û balanced feed connections. The 50Û unbalanced coax feed is made into a balanced 200Û, with the addition of half wave of coax (x velocity factor 0.8 or 0.66). All the coax braids are joined to each other but nothing else. The feeder inner is connected to the start of the half wave 4:1 balun, & the load (chock block line taps) connected across either end of the half wave phase reversing balun coax. 200Û Balanced T )========================= ) ½ Wave T ) length All Braids Joined RIG Coax 50Û

When the line tapping point (impedance) & shorting point (tuning) are adjusted to give a balanced 200Û the coax will see a good 50Û load, e.g. 100Û one side in parallel with a 100Û seen down the half wave of balun coax. The advantage of this design is it can always give 1:1 SWR even if the lengths are not quite right, or the aerial is being de-tuned by the roof, & being a symmetrical centre feed system all the power should go out to the horizon.

G4APL

GB7CIP

1.10.2007

Technical Bulletin

2m Full wave Dipole

Page 2 of 2

The feeder must be taken away horizontally to the roof & then down so not interfere with the very tight horizon radiation pattern. ___ ___ _---_ /~ ~\ /~ ~\ /~ ~\ | \../ | | | .X. -> Horizon o | / \ | +6dBi | OMNI | \_ _/ \_ _/ \_ _/ ~~~ ~~~ ~---~ Gain to the horizon is substantially more than slim jims & 5/8 wave aerials. The design can easily be made into an outdoor version with solid tube for the elements & TV aerial booms for the matching lines with the shorted end clamped to a pole. Other band versions are also quite easy to construct. Why don't U sent an interesting Bul? 73 De John, G8MNY @ GB7CIP

G4APL

GB7CIP

1.10.2007

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Microsoft Word - 2m_Fullwave_Dipole.doc