OnAirDecode Hellschreiber with an SDR
Hell: text drawn as a picture.
- Group
- Amateur: digital
- Start frequency
- 14.063 MHz
- In the mode list
- Keyboard, 14.063 MHz
What Hellschreiber is
Hellschreiber (Hell) sends text as a picture of its letters: a mode from the fldigi family.
Frequencies and settings
| Start frequency | 14.063 MHz |
|---|---|
| Tuning range of the mode table | 1 to 30 MHz |
| Sample rate asked | 2 Msps |
| Lowest working rate | 250 ksps |
| Channel width | 3 kHz |
OnAir takes any frequency you type; the numbers above are the mode's starting point and the range its table describes. In the app the shortcut label is Keyboard, 14.063 MHz.
What OnAir shows
Hellschreiber (Feld Hell, Slow Hell, Hell 80, HellX5): text as a picture of dots, 14.063 MHz.
Limits and what it was checked with
Checked with generated signals and impairments; recordings of real signals welcome.
Which radio you need
This is a shortwave mode, so the radio has to tune HF. An SDRplay, Airspy HF+ or an RTL-SDR in direct-sampling mode do that directly; with a HackRF an HF upconverter or a direct-sampling receiver is the usual route. A long wire or loop antenna matters more than the radio.
Receiving and the law
Questions about Hellschreiber
Can I decode Hellschreiber with an RTL-SDR?
An RTL-SDR can receive HF only in direct-sampling mode, which OnAir offers in its radio settings; results depend on the antenna. SDRplay and Airspy HF+ radios are better suited.
Is it legal to receive Hellschreiber?
Amateur radio signals are meant to be received. Receiving needs no licence in most countries; OnAir does not transmit.
Can I try Hellschreiber in OnAir without a radio?
Yes. Most modes include a built-in synthetic test signal, so you can open the screen and try the controls before you own a radio.