Ask anyone with a helix. It really is the best and simplest antenna for the job. Selected by the University of Surrey (SSTL) for the UoSat ground control station, and for their many international customers; used by hundreds of satisfied radio amateurs worldwide.
These stations demand assured circular polarisation and honest gain, and use this 70 cm helix with outstanding results on all satellites - UoSAT, PACSAT, AO-10, FO-20, AO-40 and especially terrestrial. Size for size it outperforms everything! Fully described in the June 1985 issue of Wireless World (GB), pages 43-46 and cover. A4 reprint available.
The 16 turn antenna, which is available in either left hand or right-hand circular polarisations (LHCP or RHCP), is designed for a maximum gain of 15.5 dbi at 450 MHz. Gain falls pro-rata at lower frequencies, 350 MHz being an approximate limit.
Matching is adjusted by means of a broad radial feed strap. An SWR of less than 1.1 is easy to achieve at the operational frequency by careful adjustment of the spacing. A small inductor is placed at the feed to prevent electrostatic charge build-up. (It has no effect on tuning).
The coaxial feed is via an N-type socket, forward facing. The antenna will handle 1 kW transmit power comfortably, more if the feed wire is enlarged.
The antenna uses HD40 aluminium for the boom, ultra-violet resistant black nylon for the spacers, and the helix structure is 10mm copper tube.
16 turn kits are available and made-up/tested antennas for collection only. A kit comprises reflector support and Expamet mesh; Ntype connector, feed strap, protective sleeve and anti-static coil; drilled boom and end plugs; pre-wound copper tube helix; spacers; boom clamp; all nuts, screws and washers. RHCP assumed, LHCP optional. Parts available separately.
Frequency 430-450 MHz Turns 16 Impedance 50 Ohm SWR typ. 1.1:1 3dB beamwidth ±18° Front-to-back ~15 dB Rating 1 kW Reflector 600x600 mm Helix diameter 240 mm Gain 15.5 dBic Length 2.8 m Weight 4.0 kgPrices
Full kit £130 It's in 3 parcels, and with packaging etc weighs a total of 6.5 kg. Shipping and handling at cost as follows: UK £ 35 (PF48) Europe £ 90 (air-mail) US £110 (air-mail) OZ/NZ/JA etc £150 (air-mail) Assembled & tested £150 * Collect only *
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Last updated: 2011 Jul 12