Antenna system

The Antenna and Feeder system as used on MB7VV

MB7VV uses a retail purchased Diamond X50NA dual band antenna.

This provides two functions:-


• Primary VHF antenna for MB7VV

• Emergency spare antenna for GB3BS/GB7BS if the main antenna fails.



Technical specifications (from Diamond X50NA site)


• 4.5dB gain (Measured as 5.5dB)

• 200w Maximum power rating.

• 135mph wind loading (no ice)

• Height 1.67m

• Element construction 3 x ¼λ (3 x ⅝ λ)



The antenna system is mounted 7m A.G.L. on a set of T/K brackets.



The coaxial feeder is 20m of CLF400 low loss cable.


Technical specifications and construction of CLF400 (from data sheet for 100m)


• 50Ω Nominal Impedance

• 85% Velocity factor

• 78.4ρF/m

• 5.0dB/100m @ 150MHz

• 16KW Peak Power.


Scaled values for 20m run (the actual specification used)


• 50Ω Nominal Impedance

• 85% Velocity factor

• 1.56nF

• 0.81dB @ 144MHz

• 16KW Peak Power.

• Terminated with pre-crimped N-Type connectors.


Physical construction of CLF400 cable.


• Inner conductor: Copper covered Aluminium wire. 2.77mm O.D.

• Dielectric: Gas injected Foamed Polyethylene 7.24mm O.D.

• Outer Conductor: Double side Aluminium Foil, covered by a tinned copper braid covering 90% of the foil. Total 8.13mm O.D. (Braid made up of 24x7 0.66mm wire)

• Outer jacket: Black PVC

• Over all Cable size: 10.3mm (20m weight 2.3Kg)




E-Plane plot for VHF. Remember it is an Omni Directional antenna!

Diamond X50NA Antenna

Construction of CLF400

Pre-fitted "N-TYPE" connectors

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