VK2MEV's blog

There's a VHF/UHF field day contest coming up in VK land so in preparation for it I swapped a vertical 2m yagi to horizontal. It's currently running WSPR, 7 elements (10dBd) beaming SW over Sydney from Newcastle. This is my first experience with VHF DX so any reception reports would be most welcome!

I've recently been working on getting WSPR working on my Raspberry Pi with a cheap USB audio adapter and though that a others may be interested in the problems/solutions I've worked through.

This is just a quick post to document an improvement on the AVR based audio source I posted a few weeks ago. My main concern was the quantization noise introduced by the very cheap and cheerful 4-bit R-2R ladder. My solution was to throw in a 2nd AVR (ATMEGA168P, at $6.50 it's not a big deal) and program it to be a delta-sigma DAC.

The screenshot attached shows me getting a lot more spots than others around me (~16 Vs 1 to ~5). I'm using an honest 5W into a 1/2 wave vertical about 8m above ground and am somewhat amazed by its performance.

Without knowing the setups of the other operators it's hard to compare but my fairly modest (ok, probably not modest for a city block) setup can't possibly be the best that's running right now.

Just put up a new 10m antenna: a converted "Station Master" 27MHz CB antenna. It's just an end fed half wave aluminium pole with a homebrew matching unit.

The matching unit is just a 13 turn autotransformer wound on some 15mm PCV pipe and tapped at turn 4 (ish). The parallel tuning capacitor is ~15cm of RG58.

The first WSPR Tx gave a lot of spots:

2011-11-09 00:30 VK2MEV 28.126030 -25 0 QF57ua 10 N6GN CM88ok 11861 55
2011-11-09 00:30 VK2MEV 28.126048 -25 0 QF57ua 10 WA7HL DM51ck 12558 66
2011-11-09 00:30 VK2MEV 28.126024 -21 0 QF57ua 10 KF7O DN06tb 12568 49
2011-11-09 00:30 VK2MEV 28.126052 -22 0 QF57ua 10 ZL1JA RE66ir 2155 128
2011-11-09 00:30 VK2MEV 28.126041 -19 0 QF57ua 10 VK2XN/2 QF59ar 340 332
2011-11-09 00:30 VK2MEV 28.126052 -4 0 QF57ua 10 N7GLS CN85qo 12249 48
2011-11-09 00:30 VK2MEV 28.126030 -18 0 QF57ua 10 K6PZB CM88nk 11855 55
2011-11-09 00:30 VK2MEV 28.126044 -18 0 QF57ua 10 W5CGC EM13ka 13722 70
2011-11-09 00:30 VK2MEV 28.126030 -24 0 QF57ua 10 VE6OG DO33 13220 43
2011-11-09 00:30 VK2MEV 28.126009 -18 0 QF57ua 10 KO6SY DM14ka 12074 61
2011-11-09 00:30 VK2MEV 28.126014 -22 0 QF57ua 10 W1MNK EL87uv 14863 81
2011-11-09 00:30 VK2MEV 28.126044 -9 0 QF57ua 10 N7KJW DM43au 12492 63
2011-11-09 00:30 VK2MEV 28.126020 -18 0 QF57ua 10 VK4ZBV QG62ml 620 12
2011-11-09 00:30 VK2MEV 28.126041 -4 0 QF57ua 10 AC0NM DM12jt 12004 62

No complaints there! Those -4dB spots to the US are very encouraging :).

Attached is the current version of my AVR WSPR audio source code. It's written and tested on an ATMEGA8L running at 4MHz but thanks to AVR's fairly general architecture it should compile and work on a large number of AVRs.

Yesterday I started working on a WSPR audio generator built around an ATMEGA8.