ChannelSPURIOUS EMISSIONS
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Episode 5 · Shortwave · Series 01: The Listening Station

How does one box hear 0 to 30 MHz at once?

A frame from the draft of episode 5, ShortwaveComing soon
Release
Length
4:53
On the dial
0 to 30 MHz

What it covers

Most radios tune to one small slice of the spectrum. My shortwave receiver measures the whole antenna signal 64.8 million times a second, so every shortwave signal is in the numbers at the same moment. I explain how that works, why shortwave travels around the world, and how one old office computer cuts that stream into more than seventy channels for ten kinds of decoder.

The written guide: set this up yourself

Chapters

  1. 0:00Intro
  2. 0:26The straw
  3. 1:06Shortwave
  4. 2:01The receiver
  5. 2:49The software
  6. 3:18All at once
  7. 3:58Honest numbers

Frames from the draft

Shortwave: Intro
01 Intro
Shortwave: The straw
02 The straw
Shortwave: Shortwave
03 Shortwave
Shortwave: The receiver
04 The receiver
Shortwave: The software
05 The software
Shortwave: All at once
06 All at once
Shortwave: Honest numbers
07 Honest numbers

Gear in this episode

MLA-30+ loop antennathe small active loop antenna for shortwave
RX-888 Mk IIthe receiver that hears all of shortwave at once (mine is from OpenSourceSDRLab)
TAPR RF Limiterprotects the receiver input from strong signals
HP EliteDesk small form factor PCthe shortwave computer I call Raphael (mine was rescued from e-waste)
Turn Island Systems F3060 filterthe 30 MHz low-pass filter in front of my shortwave receiver
RG-6 quad-shield coaxthe long cable from the loop; on shortwave it loses very little
F to SMA adapterjoins the RG-6 cable to the SMA parts
Snap-on ferrite chokeskeep noise off the loop cable and the USB cables
Coax grounding blockgrounds an outdoor antenna cable where it enters the house
CyberPower CP1500PFCLCD UPS (1500 VA, sine wave)the battery backup that keeps almost all of my station running through a power cut

Software and references

ka9q-radiogithub.comthe program that cuts the stream into channels (open source, by Phil Karn)
dumphfdlgithub.comthe decoder for aircraft messages on shortwave (a later episode)
ft8_lib (ka9q fork)github.comthe FT8 and FT4 decoder (a later episode)
NOAA: the ionosphereswpc.noaa.gova short explanation of the layer that bends shortwave back to the ground

What is simplified, and what is invented

  • The spectrum trace is an illustration, not a measurement.
  • The ionosphere drawing is simplified and not to scale.
  • The waveform in the receiver scene is five invented test signals with no noise. The time axis and the sample spacing are to scale.
  • Channel widths on the spectrum strip are not to scale. The channel frequencies are the real ones.
  • The antenna sketch shows no real layout.
  • The decode count is one hour from my station, rounded.