Low cost SDR update (2): Encapsulation

The next task was to put the receiver in a box. As I wanted to make the receiver powered by 12V I needed room for a DC to DC converter and possibly some external filtering (to get rid of 198kHz droitwich for instance). For the same reason I wanted a screened metal box

Searching the mouser diecast box lists I could not find on  just big enough but i did find one that would do, so i ordered it. I did have to 3D print some 3mm threaded spacers of appropriate lengths as the 2 boards were at different heights above the bottom of the box.

Initially I used an LT1084 Low volt drop regulator to regulate the incoming 12V down to 5V directly to supply the FPGA board and hence the Receiver board, but it got hot, not good for reliability. So I considered using just a chinese DC/DC converter to drop the 12V supply directly down to 5V. However having had these boards fail in the past and put the full input voltage at the output I devised an alternative. I used the Chinese LM2596  DC/DC converter set to produce 8V output then used an LT1084 Low volt drop regulator to produce the 5V. This way if the DC/DC failed and produced full output the LDO regulator would protect the board. This was the method eventually used.

Low cost SDR (1)

Occasionally interesting projects do get shown on the BATC QO100 net which runs on Thursday evenings.

One such occasion in November 2024 was when GI4DOH mentioned he was using a cheap A to D board in front of a commercial FPGA board to do cw skimming and rtty skimming instead of the expensive Red Pittaya board

I had been using my ANAN 10 to do my skimming which is overkill . It is limited to 4 receivers. His system could do 16 so time to Investigate!

Full information was available at https://pavel-demin.github.io/qmtech-xc7z020-notes/ who was the designer of the  A to D board. All the necessary files were available to get the boards assembled in China. Luckily I found someone who was getting a batch made so I ordered one from him. The cost (shipped) was £58

The FPGA board QMTECH ZYNQ7000 XC7Z020 Development Board was available from Aliexpress  for around £80. It came with a 5 Volt Power supply

The only other items needed were a 2x25 pin header and socket to mate the boards,  a heatsink to keep the FPGA from overheating and an edge mount SMA socket. I found the 2x25 pin connectors recomended in the links to be too tight a fit, needing a screwdriver to seperate them (risking damaging the board) so I ended up using some single row  headers and sockets, cut to length and superglued together

The A/D PCB has a reminder to remove R14 and R15 on the FPGA board before mating the two boards and to connect 3.3V wires between the 2 boards (the positive lead on the RX board goes furthest away from the edge of the board), It didnt take long to assemble.

 Software was easy. Format an SDHC card then copy the contents of qmtech-adc-20240614.zip to it. I also copy the start.sh from sdr_receiver_hpsdr_77_76 directory to the root directory so that on power up the receiver can be accessed by HPSDR

After power up I found the IP address assigned by the router and pointed HPSDR running on my PC . It connected and I could see signals

Overnight I compared the 600m WSPR decodes on the new receiver with the 600m WSPR decodes on the ANAN-10. They were within 1dB of each other, the new receiver has good sensitivity!

Now to make the receiver protected from accidents from falling items!

 

IARU TV Contest 2024 Day 2

 An early start was made from Membury services after coffee and pastries. I then drove to Combe Gibbet, IO91GI61 from where I could see Gareth G4XAT/P on top of Walbury. 

He was worked on 5GHz, 10GHz and 24 GHz easily, it didnt really matter which way the antenna was pointed

Noel, having driven from Devon appeared from Stockbridge and was worked from IO91GC on 5GHz, 10GHz 24 GHz 47 GHz and 76GHz 

Dave G8GKQ/p appeared from Lane end, IO91JA and was worked on 5GHz, 10GHz and 24 GHz

Noel then moved to Morestead Road, IO91IB and was worked on 5GHz, 10GHz 24 GHz 47 GHz and 76GHz

While Noel moved to Butser Hill IO90 MX. I moved to Combe Masts which had a good takeoff in that direction.  On the way past I visited Gareth

G8GTZ/P was worked on 5GHz, 10GHz 24 GHz 47 GHz and 76GHz. 76GHz was fairly easy and set a new UK distance record of 53km. 

76 GHz

47GHz was harder, taking 30 minutes, mainly due to Noels synthesised LO not locking up

47 GHz

Having worked all I could on the TV contest I had a quick tune around 144MHz and found a 2m QRP contest was happening and was surprised to work GW1YBB/P using the IC705 and vertical whip on the car roof. I think he was equally surprised by the locator of G4FRE/P!!

IARU TV Contest 2024 Day 1

 Noel G8GTZ decided he would be starting the contest at Dunkery beacon IO81FD so the obvious place to start the contest was Cleeve Common IO81XW, at the roadside position which always completes the path. The normal road to the car park was closed for 6 weeks for repairs so a convoluted route was taken, which was full of sponsored walkers. However Noel was worked on 5GHz, 10GHz and 24 GHz easily as usual

10GHz towards Dunkery

Gareth G4XAT had meanwhile installed himself at Walbury hill IO91GI. I packed the gear into the man portable fishing trolley and moved to the trig point and worked him on 5 GHz 10 GHz and 24 GHz

5GHz man portable towards Walbury

Next I drove to Notgrove IO91BV and again worked Gareth G4XAT/P on 5GHz, 10GHz and 24 GHz easily

IO91BV 5 GHz

I then drove to Membury services on the M4 and stayed the night there at the Premier Inn hotel, which would be convenient for the day 2 activities. 

A visit to Dunkery Beacon IO81FD

 Having booked a 7 night walking holiday at the HF Holidays location at Selworthy, Devon I realised it was just down the road from the famous Dunkery beacon IO81FD which I had worked many times from Cleeve Common IO81XW. It was decided to take some narrowband microwave equipment to see how the site really was.

I parked at the layby previously used by Noel G8GTZ on the North side of the Beacon. First QSO was on 24 GHz SSB with G4UVZ IO80KX near Taunton.

G8CUB/P had been persuaded to go to Cleeve Common IO81XW and was a huge signal on 24 GHz NBFM, He was loud enough to work on 47GHz SSB for my best ever DX on the band at 136km. No signals were hear either way on 76 GHz.

The takeoff over the  Bristol Channel

24GHz towards IO81XW from the layby

47GHz (a dish was needed for the QSO)

Meanwhile G4LDR, G8GKQ and G8GTZ had gone to Bullbarrow Hill, IO80UU (96km)  I worked G8GKQ and G8GTZ on 24 GHz NB and DATV and G4LDR/P on 24 Ghz SSB and 47GHz CW

The setup to G4LDR/P on 47GHz CW

I also tried working G8IKP/P IO80RQ near Hardy monument and M0GHZ/P at Cold Ashton IO81KP (obstructed path the plots later showed) but no success was to be had

After packing away the gear I did walk to the Top of Dunkery Beacon to see if it was worth the extra effort of going man portable. I was not convinced!

The summit of Dunkery Beacon

The takeoff towards IO81XW from the summit