Monday, June 29, 2020

Field Day 2020

KL3RR/P QTH BP53gd. East Fork Chulitna river. G5RV jr strung up back in the trees.

Icom IC-7300.  Laptop for WSJT-X and JS8Call digital modes on 10, 20 & 40m.

Wednesday, June 17, 2020

NanoVNA

The NanoVNA is a tiny, self contained, portable, but low cost Vector Network Analyzer.  It features a touch screen and built in lithium rechargeable battery.


NanoVNA with included accessories (minus SMA to UHF adapter).

Of interest to the radio operator is being able to measure reflected power and calculate the Standing Wave Ratio (SWR) over a frequency range.  The NanoVNA automates this resulting in an easy-to-interpret graphical summary of antenna radiation efficiency vs. frequency. 

Hooked up to the Firestik 2MCKB 2m antenna. 

Triangle "1" at 143.400 MHz showing 1.05 SWR.  Should work well on the 2m band 144-148 MHz.

This information is crucial for effective antenna building or diagnosing and many antennas can be adjusted to improve SWR around a desired frequency.

Monday, June 15, 2020

-Hermes-Lite 2 - HF SDR

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.