Heat spreader for 4 x MRF151 VHF PA

These surplus high power PAs using 4 x MRF151 were originally used in watercooled industrial VHF drivers. The devices and some of the other components protrude about 2mm below the PCB lower surface.

To minimise the amount of copper required, I decided to make a heatspreader to go under the devices and make aluminium spacers for the rest. I also decided to make a fixture to hold the spreaders so I could cut neat pockets for the devices. Not sure that was a sensible approach. It certainly meant I had to do some tricky machining.

I have some more to make, I won’t be doing the fancy pockets this time, just transverse slots.

One of the completed PAs
Underside of the PA board
My over-complex pocketed heatrspreader
Underside of the spreader
Spreader bolted and slathered with Arctic Silver
Spreader and spacers showing the PCB-facing side
Output side aluminium spacer
input side spacer with driver device pocket
Assembled and ready to attach to the heatsink
I milled the giant heatsink flat and drilled and tapped some mounting holes
Two more of the finished items

Dish arm extension

Tony’s 1.2m mast has a figure-8 style extrusion for the feed arm, so clamps need to have two holes and a centre relief. For the new dual-band horn mount, we needed a bit more length, so I made up some extension plugs from aluminium

The plugs, turned from ally rod
The plugs pressed into place and fixed cap bolts on the underside
Clamp and mounting place with 10GHz WR90-fed WA6KBL and Super-VE4MA 5.7GHz feedhorns that I made for him

Coax clamp for 5.7GHz masthead unit

I wanted to avoid an extra plug/socket on the LDF1-50 coax feed from the 5.7GHz horn to the masthead transverter/PA, so I used a plastic cable gland, but there was still too much movement. This clamp bolts to the inside of the steel masthead box and holds the coax rigidly so I can plug directly into the coax relay without any danger of movement and fracture.

Porthole heatspreader for 5.7GHz masthead enclosure

The new 5.7GHz system is ready to mount on the dish, on top of the SCAM12 pump-up mast with the tilting 95cm offset dish and 10GHz system. I’m using a Schneider IP66 rated case made from mild steel with a powder-coated finish. I’ll be adding cable glands and a Gore-Tex breather plug, and flushing the case with dry Argon, and adding a silica gel pack before it is locked and fitted on the mast. The existing 10GHz kit is in an identical case, but I’ll be moving it to the new dish, which has a -7 to +57 degree elevation drive and well as 450 degree azimuth rotation. Initially, I won’t fit the 12W PA, as I haven’t finished it yet, but everything else is sorted and will go in the box tomorrow.

Steel enclosure with milled “porthole”

The inside plate with 1.45mm raised section to fit through the porthole
The outside plate. External heatsinks will fix here
Milling the raised section on the inside plate
The two plates – too shiny to photograph so the M4 hex key is there to add context
Inside plate fitted
View inside with the inside plate fixed, ready for marking out
The view from the back with the outer plate bolted in place

Portable mast support with SCAM12 legs

As I have two sets of SCAM12 pump-up mast legs, one original, and one set I made, I thought to might be useful to make a cage so I could use them with a 2 inch aluminium mast for when the 90kg of SCAM12 is too much to haul about.

SCAM legs being put to good use

Simple cage with 1 inch steel box sections to fit the SCAM legs

Turned pins and snap-rings to lock the legs in place

I didn’t have any 3/8 inch roll pins so used a bit of M8 threaded bar instead.  The cap bolt is to lock the cage in place during deployment.

The cage is just made from scrap I had kicking about in the machine shop.

At the top of the pole, I use a nice simple collar and slip-ring/guy plate arrangement.  This is for a base-mounted rotator of course