WSPR 17-Jan 18-Jan

Screen Shot 2018-01-18 at 15.13.29

WSPR 500 mW on 40m, overnight, nothing spotted in Antarctica yet.

Advertisements

WSPR receive mode Jan 13-14

Tried various bands (MF, 160m, 80m and 40m) overnight where I was in receive mode with the active antenna, cross-mode setting. Receiver was the airspy HF+ and apparently there are good band conditions:

jan1314bandmf
630 meter (usb at 474.2 kHz)
jan1314band40
40 meter (usb at 7038.6 kHz)
jan1314band80
80 meter (usb at 3592.6 kHz)
jan1314band160
160 meter (usb at 1836.6 kHz)

The mapping part of WSPR gave me errors, so I could only manage to make some quick resolution shots.

Last update: 14-Jan-2018

Airspy HF+

First impression

Pre-ordered it on Nov 11 and got it in the mail today, the 10 dB gain in the MDS (according to the specs on the airspy website) is impressive:

And this is what it looks:

IMG_1697

All specifications can be found on www.airspy.com.

What is the dynamic range and the noise floor?

Since the airspy HF+ comes with an 18 bit ADC rather than the 12 bit ADC for the airspy the dynamic range is extended. The dynamic range in dB is computed as 20 log10( 2^n ) where n is the number of bits of the ADC, this is 108 dB for 18 bits, and it is 72 dB for 12 bits. For the first SDR I once got it was 8 bits, so 48 dB. For the noise floor measurement it means that I have more possibilities to test the SNR than with all earlier software defined receivers.

For the airspy HF+ I measured the SNR of a known signal near 10 MHz which is directly into the receiver. The source is 120 mV rms over a 50 Ohm dummy load, this is attenuated with 42 dB (I need to find something larger actually) and I got an SNR of 69 dB over 500 Hz bandwidth. This corresponds to -146 dB per 500 Hz, add 30 to get dBm, thus -116 dBm over 500 Hz. The noise floor is therefore -143 dBm/Hz, we are 30 dB over the thermal noise floor at room temperature of -173 dbm/Hz, the excess noise is probably around 30dB. The vertical scale in SDRsharp looks like it is in dBm over a 500 Hz bandwidth.

The -116dBm over 500 Hz can be improved by decimating the IQ data, everything was measured at 768 kHz BW for the SDR, and the following steps are 384, 192, 96 and 48 kHz, with each decimation step you yield 3 dB in the noise floor, there are 4 steps so we win 12 dB. In this way I end up at -128 dBm over a 500 Hz window where the SDR decimation is step to 48 kHz.

Work to be done:

  • My results are different compared to what you find on the airspy website, they mention -140 dBm where the bandwidth is not mentioned.
  • The other possibility is that I need to repeat the test with a different signal source, because intermodulation and carrier phase noise of the test source may affect my results.

Last update: 16-Jan-2018