lørdag den 18. august 2018

DSLWP-B satellite signals received today

😊 I've finally received JT4G signals from the Moon-orbiting satellite Longjiang-2 alias DSLWP-B alias LO-94. I am so happy for this event! 😊

When is the signal available?
BG2BHC announces date and time for the DSLWP-B transmissions. He does it via his Twitter account as you can see in the screen-dump below.

Tweet from BG2BHC.
Frequencies. There are two different frequencies used by DSLWP-B: 435.400 MHz and 436.400 MHz. To receive on 435.400 MHz, I set my Yaesu FT-847 dial to 435.401.500 MHz. The lowest JT4G tone was 600 Hz when I used this dial setting.

Antenna and preamp
I decided to deploy my 18 element 70 cm LFA yagi antenna. The boom length is 4.30 meter, and the claimed gain is 18.0 dBi. My preamp is Extra-70 from HA8ET. The premap went into oscillation earlier. However, the preamp performed normally when I fitted a different type of balun!

18 element LFA yagi for 70  cm.
The antenna follows the Moon as it traverses the sky. Antenna elevation is performed by a Kenpro KR-550 rotator. There is automatic antenna control by PstRotator.

Azimuth and elevation
The timeslot for reception of DSLWP-B this Saturday was 2 hours. The slot is from 18:30 to 20:30 local time. There were other timeslots mentioned by BG2BHC in his tweet, but the Moon was below the horizon in Denmark during these times. The antenna direction is shown in the table below. AOS = Acquisition of Signal. LOS = Loss of Signal. AZ = azimuth (horizontal direction). EL = elevation (vertical direction).
AOS and LOS for DSLWP-B as seen from Denmark (Aug 18, 2018)
JT4G decoding

The WSJT 10 waterfall.
The DSLWR-B downlink contains telemetry sent with GMSK. Every 10 minutes there is an JT4G transmission to identify the spacecraft by its callsign BJ1SN. The JT4G protocol has 4 tones spaced 315 Hz. All tones are clearly visible in the WSJT 10.0 waterfall (see screen above).

The call BJ1SN decoded by WSJT 10.
I decoded the callsign BJ1SN 7 times. The signal strength was -12 dB maximum, and -16 dB minimum.

73 from OZ1BXM Lars