All posts by smithn

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




Measuring wire thickness with a ruler

One low-tech way to measure the thickness of very thin wire if you don’t have a micrometer is to use a ruler on a flat surface (sheet of glass maybe?),  and something of a known thickness several times as thick as the wire. (a drill or coin perhaps?).

Put the drill or coin on the flat surface and hold the ruler with one end on the it at the 300mm point and the other on the glass, so there is a very narrow triangular gap between the ruler and the surface. Slide the wire into the wide end of the gap and move it along towards the thin end until it sticks. Read off the distance on the ruler. Say it is 56mm and the coin is a newish 2p piece, which is 2.08mm thick.

The wire size is then 2.08 x 56 / 300 = 0.39mm.

Checking the wire with a micrometer shows an actual diameter of 0.375mm, about 4% error.

GB3FNY rainscatter storm recording

This is a waterfall recording of off-axis rainscatter from GB3FNY.  The this vertical lines are from a wind turbine 3km SW from here.  FNY is about 20km south, the storms were to the SW as well.  600Hz doppler shift is about 10m/sec or about 20mph. Carrier frequency is at around 940Hz.  Interesting to see the frequency-domain patter change with drop size, wind speed and rain intensity.  Graph covers about two hours this afternoon, 24th August 2018. I am in IO93NR, beacon is in IO93NN on 10368.952MHz