FLDIGI Users Manual  3.21
Feld Hell Configuration


config-feldhell.png
Feld Hell Config Panel

The Hellschreiber modes all use a video display that is basically a character-by-character facsimile. The shape of the characters is determined at the transmitting station. You can select from 15 different fonts, all of which have been designed for Feld Hell use. In normal use each dot of the character font is transmitted twice. You can increase the effective video s/n by transmitting the dots 2 or 3 times the normal. That is controlled by the Transmit width.

FeldHell is a pulse amplitude modulated signal. The shape of the pulse is a raised cosine. This helps to control the bandwidth of the transmitted signal. It is customary to use a 4 millisecond risetime for the raised cosine, especially on HF. You can change that to 2 milliseconds. The video edges will be sharper, but the bandwidth twice as large. You might find 2 msec a better choice for VHF and above.

Fldigi provides three controls for the receive function. The video is normally black on white. You can change that to white on black. You can also compress the horizontal scan rate of the video. You might find this effective in displaying received fonts that are broad (or if the other end is using a multiple dot transmit width).

As you change Hellschreiber modes the optimum filter bandwidth will be set. You can change that and might find a narrower filter effective if you are experiencing CWI interference. FeldHell is susceptible to CWI. If you narrow the filter the received video will become blurred.


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