Australian Ham Radio Discussion Forum ( AHRDF )

I've got a couple of Digitech branded UPS units (Jaycar link below), one in the shack for a PC and the other for backup power for our NBN modem.

Both generate S2-3 and higher noise across the HF spectrum. I've tried clip-on ferrites and toroids and much messing around but no change.

Anyone recommend a UPS for this type of use that doesn't generate crud??

Reading around it seems the pure sinewave type might be the type to go for.

650VA/390W Line Interactive UPS with LCD and USB

I was about to put a post up asking for solutions re RFI from a UPS, and discovered I'd posted this above last year.

Has anyone had experience with using these or similar to suppress RFI on mains leads, which seems to be where the noise is being radiated from:

U16 Ferrite Voltage Spike Protectors/Noise Suppressors
U15 Ferrite Voltage Spike Protectors/Noise Suppressors

I used something like that to quieten the RFI from a fridge a few years ago, they can work.

Another option might be to ask a friendly sparky to make an IEC lead from an offcut of screened cable - something like 

https://lappaustralia.com.au/en/grey-scr...flex-3g075
https://www.jaycar.com.au/iec320-240v-fe...t/p/PS4006
https://directwholesale.com.au/products/...ansparent/

If the screen is joined to earth at the supply end you should get suppression. There's a whole discussion over whether it should be connected to earth at both ends, which I'll leave to others.

I didn't know screened mains cable existed - well there you go

I can understand the discussion re earthing the screen. One would think that there is probably an AS specifying that.

I shall do some more noise sniffing to determine which cables are radiating.

I once used a CRO and AC cable clamp to investigate noise source cables in an outside inverter air conditioner

I found that unless the cable is looped a few times around the ferrite core the suppression it is minimal. 

Using one with suitable ferrite material is also somewhat important.

Yeah, I think type 31 is usually the go for HF.

I used one of these on the output of a noisy inverter generator. The noise was being radiated by the extension lead plugged into the generator.I put it in a diecast box with a mains outlet socket and a short (30cm) lead to the generator. Very effective.
Jaycar EMI Filter

I hadn't noticed those on the Jaycar site - thanks for this.

I guess that might filter out the crud close to the source, whereas a screened mains cable likely still has it and delivers it to the device.

Actually looking at the graphic on the unit, how did you wire it up - the generator to the two pin end and the extension cord with earth to the other end?

I use a Power Shield Defender 1600 UPS.
No noise.

(26-05-2022, 01:44 PM)VK3RX Wrote: [ -> ]Actually looking at the graphic on the unit, how did you wire it up - the generator to the two pin end and the extension cord with earth to the other end?

Yes, commonly the "two pin end" is connected to the incoming supply, the UPS in your case and the other end to the load.

That middle pin on the load side is connected to the common earth line running from the supply side to load side.

[attachment=584]

For the circuit with the fuse built in, the power source (mains or genset) should be on the side of the filter feeding the fuse otherwise the fuse does not provide any protection in event of the filter failing.