The Combe Raleigh Offset Centre Fed Antenna, design and build

The antenna has been designed using a number of information sources, both from the internet and from books on the subject, collected over the years.

Located between two aluminium 6ft sectioned posts spaced at 133ft, 30ft (5 sections) above ground the antenna uses DX Engineering components and the antenna is designed for 160m - 6m use with an antenna tuner.

Design

Based on the Windom calculations, where a 14% offset from centre is used to locate a 200ohm feed point impedance and terminating with an 4:1 balun, this seems the ideal implementation. The antenna has the following requirements :

  • Power handling of 400w (UK Legal Limit)
  • Antenna being Omni-directional, or biased to E-W.
  • Able to handle high duty cycle modes (PSK31 / SSTV)
  • Complement Hustler 6BTV vertical coverage
  • Provide some level of NAVTEX reception on 514Khz

The initial cut length to be used is the 90ft / 45ft split, to then identify the 200 Ohm feed point, thus 4:1 insertion point. 

 

Components

  • DX Engineering COMTEK Jerry Sevick W2FMI Series Current Balun 4:1
  • DX Engineering Antenna Support Cord
  • SSE UK End Insulators
  • SSB Ecoflex 10 Co-axial Cable
  • Concrete Counterweight
  • Haydon Comms Aluminium Antenna Poles - 5 x 6ft (30ft) x 2
     
  • Palstar AT-2K Antenna Tuner

EZNEC Plots

Antenna model by EZNEC, using 10m elevation and 200 Ohm feedpoint values for 4:1 balun.

 

80m Plot


40m Plot


AIM Vector Analyser Plots

To be supplied when in service

 

Pictures

To be supplied when in service