Saturday, September 03, 2016

Powering Your Perseus (or any 5VDC SDR): Does The Source Matter?

SDRs like the Perseus and Cloud-IQ are sold with switching 5VDC power supplies. While the Perseus PSU is in fact rather quiet, I am no fan of switching power supplies. So I try to avoid, and find linear devices instead. This consideration is for one purpose alone: To minimise noise. In a noise-free environment, even a 5 dB higher noise floor will affect DX.

A couple of years ago I bought this Friwo 1A transformer-based linear wall mount from Germany. It's quite heavy and runs a bit warm since the Perseus takes up around 750 mA of its capacity. But it has worked well. I don't remember what I paid, and it doesn't really matter because they are no longer made. I understand that a 5V linear wall mount is still manufactured in the US (Jameco, 1A), but it will fry if you connect it to 240VAC.
With the advent of USB 3.0 ports on PCs came an alternative way of powering my Perseus. A USB 3.0 port is limited to 900 mA, which is enough to power a Perseus and Cloud-IQ (but not enough for a NetSDR). I have a few cables designed for the input connector of the Perseus, and they are abundant on eBay for around USD 6.50 including shipping. The one pictured below was a lot more expensive though, but hey! It's blue!  USB 3.0 ports have very accurate voltage, mine measured 5.01V (a Dell Latitude desktop PC).

This summer I thought I'd try a different approach, to find one psu to power them all (LOTR DX style), and ended up with this linear, pro-grade Bel Power Solutions 5VDC, 3A, after a recommendation from the KiwiSDR project site. It set me back less than USD 60 from Mouser - including UPS shipping! It takes a bit of preparation to get it going as it's open frame and sort of barebone -

you need to place the correct jumpers and solder the AC and DC cords to the correct solder lugs. My DVM shows the voltage output to be 5.03V, so it's very accurate. It should easily power my three Perseus.

So which is less noisy? Most important for many perhaps: Is the power supplied from my PC's USB 3.0 port acceptable?

I set up a test with the Perseus connected to a 270 meter beverage antenna at daytime, when no signals were present on the MW spectrum (but a few local NDBs and other UTEs on LW). As you can see from the spectrum displays below, there is practically no difference, except a couple of more pronounced spikes from the PC power.

Taking into account that not all PCs are necessarily alike, it does appear that a USD 6.50 cable from your available USB 3.0 port will provide an efficient and noise-free power for the Perseus, Cloud-IQ, and probably many others. The noise level will not be noticeably higher than using a more expensive linear supply.

If you wonder about the increased noise floor below 800 kHz, it's likely due to a wind power facility 9 km away. It probably causes the variations further up as well.
Bel Power Solutions

USB 3.0 port

Friwo linear wall mount

1 comment:

Chuck said...

Just so it is clear to everyone, the Bel Power unit is a linear supply. I don't see that mentioned.

And it is called "assumedly pro". Bel Power is the new name for Power One, who has been making industrial power supplies for at least 30 years. Their equipment is widely used in the telecommunications industry.