The Red Pitaya - A Wsprer's View

It happened like this. I returned from a reasonable round of golf and plonked myself down on the sofa. I decided to have a look through Wsprnet on the iPad for no good reason other than I was tired. Then I saw it.

To rewind I have been nagging two people, I am fortunate enough to know, both of whom run their own radio businesses. What I need, I tell them, is a standalone Wspr receiver. One which does not require a computer and which can upload to Wsprnet via wifi. Yes that's what I want, what are you going to do about it? Etc. Sorry. Both of my friends are very busy, they too have kids and so I had given up hope. They did suggest I create my own, well... well I am very busy and I have kids too...

Anyhow what I'd read on Wsprnet was way beyond what I had imagined. In short, if what I had read was correct, a device had appeared from who knew where (alien tech anyone?) that could receive on 8 Wspr bands simultaneously and needed no computer. I think my fingers were shaking when I typed those two words into Amazon 'Red Pitaya'. There was one for sale. Just one. No review. No information. There it sat. Tempting as a Neal Asher Aug (you have to know your sci-fi here). Click I bought it.

Then I relaxed. What had I done? There was no information about how to use the thing. Worse than that it was £115 and I had not consulted the XYL. Should I cancel? NO WAY!

Two days later the small device was on our dining table. It resembled some kind of computer board/insect hybrid. My RP (Red Pitaya) came without a psu. Looking at the specs I discovered it required 2amps at 5v. So that was the iPad charger then. I connected it and watched the lovely lights.

My Red pitaya on the day it arrived

Next up I did my research and discovered I needed to make a couple of Micro SD cards up to run the thing. The first was the standard RP card, I made this just to see if it worked. Then I tried to make up the Wspr card from a guy called Pavel Demin. No joy. No matter what I tried it would not work. So I contacted Pavel and (what a great guy) he got right back to me and explained this was not a Windows system (which I knew) and that I could use a second program to unpack his files. Which I did. See video here. Things have since moved on and there is a new version which requires only one card and which can switch between various modes, including a superb SDR - see here.

I entered my callsign into the appropriate file along with my locator. Then attached an antenna and a Cat5 cable to the house router and waited. Nothing happened at first. I messed it up, I thought. I wondered if I had blown the cash and what I should tell the XYL. Then: BANG!

My callsign appeared on several bands all at once spotting stations all over Europe. Nowadays I take this for granted. At that moment as far as I was concerned the world shifted up a paradigm. EIGHT BANDS ALL AT ONCE NO COMPUTER! I was astounded. I told my friends. They purchased them also. But...

As with first love things can sometimes settle down quite quickly. I noticed the spots were on many bands true, but often the reports were weak and quite 'local'. Also I was concerned (see my LF experiments) that I could easily damage this delicate instrument. And, quite callously as it turns out, I threw it in a drawer - complete with the 3d printed case my good friend M0NKA had made for me. As a family we went on holiday. Just before we left I remember having a conversation with another radio friend Geoff, G0LUJ, about Wellbrook active antennas. Geoff was interested in them and said he might get one...

RP in the case Chris made for me - what a friend!

Upon our return I had a look around the bands - even before unpacking. I was astounded by the results Geoff was uploading to Wsprnet. Geoff told me he had changed the jumper on his RP and fitted a splitter to feed his IC7100 (Geoff really does make everything work to maximum efficiency) and suddenly the spots were much improved. I was intrigued. Reading around it seemed the impedance at the input of the RP can be as high as 1mega ohm. I reasoned that the input of the IC7100 being 50 ohm connected in parallel with the RP meant a net impedance just below 50 ohm - was this the source of the improvement? I tried the jumper change at Geoff's suggestion and added a 50 ohm load in parallel. Suddenly the RP was becoming a serious piece of receiving equipment - 8 times over!

Geoff wasn't done yet. One day his spots leaped another level. He announced the installation of his Wellbrook Large Aperture loop. Suddenly he was pulling in stations on LF-10m that my set up just could not see. Geoff had discovered something really impressive. Of course I had to follow suit. Results here shot up also. Unfortunately my neighbour moaned about the loop so I reduced it and added a further preamp - documented here.

This combination is a serious piece of equipment. Geoff and I regularly appear on WsprChallenge with little to no effort on my part at least. Much of this is thanks to the endeavours of both Pavel for the firmware and and Geoff for his persistence and ingenuity cheers Geoff!

A positive side effect of having such a powerful receiver is the ability to provide a service to your fellow LF/MF amateurs. When I was trying to put out a signal on these bands I was somewhat hampered by a lack of stations capable of receiving me. It took large antennas and expensive receivers and anyway most people only transmitted in the darkness. So if you wanted to make changes to your antenna, or amplifier - which you would - it was likely you'd be doing this in daylight. Having 8 bands available on RP it is simple to dedicate 2 bands to MF/LF - as I do - in that way any 'local' MF/LF station can have a constant point of reference. It was very useful to have Geoff's RP feedback, located about 30 miles away, as he monitors constantly. His station provided instant feedback as I messed about with the large amplifier on LF. Naturally I did not use my own RP so close to such a potentially huge EM field. Never underestimate your service to the amateur community. Somewhere there is someone like you tying to get RF out of his/her tiny garden. Of course I must remember to power down my active loop if I decide to run anything above QRP here - which is a rare event these days.

One aspect of the RP less spoken of is the ability to use it as a computer based SDR. In this format you use your computer and switch the RP into SDR mode. With a suitable client program (I like HDSDR) you get a fully featured Software Defined Receiver. If, like me, you have good computer speakers it is a very pleasant way to tune around the bands, as well as a serious piece of equipment for investigating the spectrum I really enjoy this aspect of the RP. The new single card version released recently is very convenient as I can switch modes from the shack, from SDR to WSPR at the click of a mouse. In Wspr mode there is (as before) no need of a computer.

RP in HDSDR Mode

I wonder what will come along next? All band, all mode, standalone data box? With TX/RX? I would still not be as surprised as I was the day the RP came online! Oh and that £115 I spent turns out to have been a bargain. Perhaps it is the price of success, these things appear to sell around £270 just now, or maybe it's Brexit?

PS the RP can transmit Wspr also - I just have not discovered how to use it. I am content with what it can do... so far.