Mast Head preamps and control cables page and photo's
control cable mast head termination box
A pair of 4 core + shield cables go from the shack to the top of the southern cross tower.
Each item requiring power or control is fed from here.  the sheilds on each cable are combined as the negative feeds to allow 8 items to be controlled
 
control cable mast head termination box
left side
centre
lower
whole
top support
VHF / UHF Preamps
144 high power mast head
the almost finished high power 144MHz mast head preamp (for the eagle eyed, you will see the LED near left hand N socket is not yet connected)
The pre-amp used is one from Advanced Receiver Research, based on a MGF 1402 gasFET. It has internal relays that are used to provide an extra level of isolation from the transmitted RF.
start here
Here is how it started, an empty box and some bulkhead N connectors
inside N connectors and power gromet
I used a blue inked marking pen to wet the top of the mounts, this transfered the locations of the supports onto the back of the central template so I did not have to guess where to drill the securing holes. (took two goes)
mounting
mounting plate for attachment to the tower leg
support plate
the central mounting plate, both relays bolt to the sidea and the preamp is screwed to the bottom
support in place
central plate in place
bypass cable
bypass cable is RG142 and UT-141 hardline feeds to and from the premap.
12v regulator
24 volt to 12 volt regulators (7812 on otherside of the panel)
relays require 24V and pre-amp needs 12V, 100R provides some much needed pre regulator voltage drop.

This web page was last edited on Saturday, 17th March 2012 by vk5pj