Saturday, March 16, 2019

Power Your SDR From a USB-C Port

It has become common to power SDRs that need separate 5V power from a PC USB port. However, there are limits to how much current a USB port can deliver. The RFSpace Cloud-IQ can - barely - cope with a USB 2.0 port. It is best served with a USB 3.0 port, because USB 3.0 can deliver almost 1A of current while the USB 2.0 is limited to around 0.5A. The Perseus definitely needs USB 3.0.

But other SDRs need more! The RFSpace NetSDR and the KiwiSDR need more than 1A. Enter USB 3.1 with type-C connector. New laptops are usually equipped with one USB-C port, hence it should be possible to power these devices from a laptop. Next on the list was finding a USB-C to 2.5mm pigtail. Finally I found some on eBay and ordered from two different sellers.

I was quite surprised when I got the first batch and tested them via a DVM from a USB-C port on my Latitude laptop. No voltage! Long story cut short: Check if the PC actually delivers current through the USB-C port! So what to do next? Last year I bought a 20A/75Wh Li-Ion battery, also known as "Power bank", with two USB-A and one USB-C outputs. Capacity is 2.4A. I'm mostly charging my mobile phone and headphones with it. But why not power an SDR from a battery?

So, moment of truth: Would the USB-C port on my power bank power up the NetSDR? Indeed it did! And noise-free at that. The powerbank allows pass-through charging, so a noise-free 5V power supply on the charging end should enable continous powering of three SDRs with this battery. Well, at least in theory, as long as the drain isn't larger than the charge.

The coming summer I will receive a much larger powerbank and a high-capacity charger. Potentially capable of powering six SDRs.

But the real novelty is if your laptop's USB-C output can deliver the necessary current.
But always, always, always remember to check polarity when you buy no-name cables or adapters from unknown eBay sellers. And others for that matter. A fried SDR is not a pretty sight.

NetSDR below, power bank on top.