16 turn Helix Antenna for 70 cm Band


Introduction
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.

Description
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.

Summary

  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     kg
Prices
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 *

Methods of payment


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Last updated: 2011 Jul 12