Monday, June 15, 2020

-Hermes-Lite 2 - HF SDR transceiver

Minor assembly required.
Hooked up to power, antenna, and ethernet for interface to PC.
The Hermes-Lite can listen on an unlimited number of virtual receivers which can concurrently monitor 4 bands at up to 384 kHz x 4 total bandwidth. 

HF digital modes allow many simultaneous transmissions to fit into a relatively narrow slice of bandwidth. 

The receiving capability of the Hermes-Lite coupled with specialized software and the processing power of the computer allows for monitoring a significant chunk of the HF digital mode frequency range using a single radio. 

SparkSDR - Transmitting on 20m with the built in 5W amplifier and N2ADR filter board. Just over 20 virtual receivers monitoring HF digi modes with one DigiU dedicated to JS8Call.

It is somewhat intensive for the PC and LAN.

I was initially using a 2014-vintage i5 laptop which handled it but was a bit strained and the cooling fans were noisy in that state.  Since then I have switched to a i5-3470 desktop machine which handles it better and with less noise.  I am seeing about 2.5 TB/week (45 Mbit/sec) of data transfer between the HL2 and SparkSDR in the above receiver configuration with 192 kHz sampling bandwidth. The gigabit LAN has plenty of capacity left.

24/7 automated decoding of these signals contributes to an online reporting database allowing visualization of world-wide HF propagation activity:

Pskreporter stats - HL2 with about 20 receivers over a 24 hour period.  Each marker represents a station heard and color denotes the frequency (40m, 30m, 20m, or 17m).  Transmissions between Alaska and Europe travel over the north pole.
On Raspberry Pi 4:

VNC into Raspberry Pi 4 with about 16 receivers (SparkSDR).  Sampling bandwidth 96 kHz. 26 Mbit/s going between HL2 and RPi4.
The Raspberry Pi 4 May be comfortably usable with up to about 4-6 receivers.  Of note is the fact that VNC server uses a significant amount of CPU.  I already disabled the "waterfall summary" for each virtual receiver with some CPU savings, but it seems driving the waterfall graphics adds a significant load especially over a remote connection. 

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