Adapting a Computer PSU

[ppppenguin]

Good result. Thanks for letting us know.

[Mark Hennessy]

Looking good!

The HP PSU is still in pieces on my desk at work, and I am hoping to get there eventually, as it is an interesting design that has many interesting features compared to generic ATX power supplies. Just been too busy lately.

[Crackle]

Thanks Mark, I do believe this to be a useful project for others who want to re-utilise these scrapped supplies as a bench supply.

Mike

[Nick]

Some time ago I got one of these for a few quid off Banggood or similar.

   

[Crackle]

Hi Mark
I was just wondering if this project was still on your horizon .
Thanks
Mike

[Mark Hennessy]

Sadly not - they've just asked for it back. Only yesterday, funnily enough. Luckily I put all the screws in a plastic bag, so reassembling it was easy enough. Annoying, as I hoped to get there. Must have traced out about 75% of the circuit as well...

[Crackle]

Oh well thanks anyway, the PSU is working away nicely at 12.3v I tested it up to 32 amps with a bunch of 10 watt 1 ohm resistors strapped together and it seemed quite happy.
However it didn't like it when I connected up the 12 volt lamp circuit in my MFJ 949E ATU and keyed the transmitter. The PSU shut down, I think the RF leaked back into the cable to the PSU and it didn't like it.
Still its not a problem as I don't need the meter illuminated.

thanks
Mike

[pamphonica]

Previously when I tried my transceiver with an "Avair AV-2025D", I had purchased specifically for this use, the DC negative supply to the transceiver was connected to the mains supply earth. This had the unfortunate result in the RF signal leaking from the coax into the mains earth and going all around the house. This was tested by using a non earthed 13 amp plug and lead to supply the PSU, which cured the problem of RF leaking into the mains earth.

Going back to the original problem with RF on mains earth, I suspect that you are feeding your dipole directly with coax. That immediately unbalances the dipole and leads to lots of RF coming back down the coax outer, and hence to earth.
Jeffrey has already suggested a common-mode choke, which is a good idea for stopping rf on the sheath.
The other thing is to put a balun at the feedpoint of the dipole. That will ensure a balanced feed to the antenna, but a nicely screened and matched feed up to that point. Worth a try, surely. Especially as the power you are using goes up.
There are lots of plans for baluns, using either toroids (use the T-200 type for 100W+ rating), or a bundle of ferrite rods bound together (can be very effective). You need a 1:1 balun.

The new psu does look very smart though!

-Jeremy