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Thursday, 16 November 2017

Another PSU!


I've been fiddling today and have made myself another bench PSU.

I was looking for a 28V supply the other day, so I've knocked up something to give me a 28V, 12V and variable output.

The 28V line is a simple LM317 - there are plenty of calculators for that voltage regulator on line.

The 12V line is simply a 7812 regulator, I think I need to add a big heatsync through because the power dissipation at 500 mA will be 22 - 12 = 10V * 0.5 = 5W so its going to run quite hot.

The variable supply gives an adjustable output between about 2.5V and 15V; it's based on my favorite the old lm723:

The first pass transistor is a BD139 and then the main one is a TIP3055.

The current limiting is dictated by the voltage between pins 2 and 3 so we have a 0.1R resistor there on the main high current path, the voltage difference needs to be 0.6V to initiate the current limit so using ohms law we can easily calculate that the current limiting will happen at 0.6V/0.1R = 6A.

There's a really nice toroidal transformer which will deliver plenty of current.

It's all a bit of a bodge:

The case looks OK:

It's not bad for a few hours work. The bench looks like a bomb has hit it:

good, egh?

Friday, 10 November 2017

A bit more top band


Following the antenna I originally made here and then replaced here, I've been fiddling with the earthing arrangement for the system.

I've added some counterpoise wires which I have stapled to the fence and various other bits and bobs in the garden.

I've then made an artificial earth/counterpoise tuner thingamabob, much like this thing back here, and mounted it at the base of the antenna between the earth rods and the radials:

And then adjusted the capacitor for maximum smoke on top band when TXing.

There's quite a lot of current flowing, what improvement it makes I dont know.

Here's a map of FT8 and CW QSOs I've made on top band since the changes to the antenna:

Chopsey Cat (AKA Git Bastard Cat from Hell) is asleep in the conservatory:

whereas Maggie and Florrie Cat are tucked up in one of the dogs beds:

Local conditions.