Dear LF Group,
I am currently (0120) running some tests on about 503.5k using DF6NM's
Chirped Hellschreiber mode - any reports welcome if anyone is still up.
I am testing a new HF - LF/MF transverter I have been working on. It takes
output from an HF SSB rig at 4.5MHz and mixes it down to 500kHz. It also
up-converts the receive signal. The HF rig (IC718) is set up to run "sound
card modes" from a PC (at the moment, the Chirped Hell signal is being
produced by DL4YHF's Spectrum Lab), so the system ought to work with just
about any mode that will run on the PC. The transverter has a linear 500kHz
output that could go to a linear PA, but I thought it would be more
interesting to modify my existing class D 500kHz TX to operate in an
envelope elimination and restoration (EER) mode. So the transverter also has
a limiting amplifier to produce a square wave carrier which drives the class
D PA, and an envelope detector that recovers the modulation envelope and
drives a series modulator that controls the PA output amplitude. The
modulator uses the existing DC current limiter/keying circuit in the TX.
Although the modulator dissipates some power, the overall efficiency is
quite good provided the modulaton has a reasonably low crest factor. I have
also tested the system with PSK31, and the unwanted high-order sidebands are
down 35dB or more on the main sidebands, so the output spectrum is fairly
clean and comparable with normal HF practice.
So I now seem to have a fairly universal 500kHz TX/RX system - does anyone
want to try any interesting modes?
Cheers, Jim Moritz
73 de M0BMU
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