All content is Copyright of The Bristol 70cms Repeater Group
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
• 5.0dB/100m @ 150MHz
• 16KW Peak Power.
Scaled values for 20m run (the actual specification used)
• 0.81dB @ 144MHz
• 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