Envelope-to: dave@picks.force9.co.uk
Delivery-date: Mon, 23 Jan 2006 18:07:29 +0000
From: Warren K2ORS/WD2XGJ <k2ors@comcast.net>
To: rsgb_lf_group@blacksheep.org,  rsgb_lf_group@blacksheep.org
Cc: "james moritz" <j.r.moritz@herts.ac.uk>
Date: Mon, 23 Jan 2006 18:05:54 +0000
Message-Id: <012320061805.1968.43D51B01000D5014000007B022007358340B97010D0A020E06979D0E03@comcast.net>
Subject: Re: LF: RE: ZL1BPU QRV
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Jim,

    Do you have your linear regulator for the Decca written up? I'm particularly interested in how it is interfaced to the serial data comming from the computer.  

Thanks & 73 Warren 
K2ORS/WD2XGJ
FN42hi
http://www.w4dex.com/wd2xgj.htm

 -------------- Original message ----------------------
From: "james moritz" <j.r.moritz@herts.ac.uk>
> 
> ...The transmitter is VERY interesting. Only a few years old, it is a
> broadband design, and uses a Class D H-bridge FET transmitter, each 500W
> module with its own Class S modulator / power supply adjustable 0 - 130V at
> 7A. The modulator has 0 - 4kHz bandwidth, so is AM capable. Anyone for Kahn
> EER? ...
> 
> Dear Murray, LF Group,
> 
> Yes, I have been using an envelope elimination and restoration system to
> transmit various BPSK modes for some years now. The PA is one of the "Decca"
> 1.2kW class D units re-tuned for 136kHz. The HT supply to this is 0-60V,
> 0-22A supplied via a modulator that is basically a big series regulator.
> Using a linear modulator sounds like a bad idea, but with BPSK the crest
> factor of the signal is not very great, and most of the time the PA is
> running near full output, so consequently only a modest amount of power is
> dissipated in the modulator. The overall efficiency is still around 80%.
> Andy, G4JNT, has published a switch-mode modulator design for a class D
> amplifier. 
> 
> Originally, I used it with VE2IQ's "Coherent" mode, which generates straight
> binary data via the serial port. This was used to key a hardware phase
> modulator, and, via a waveform-shaping circuit, to generate the envelope for
> the amplitude modulator. I have also used it with KK7KA's "Wolf" mode, which
> was the first successful transatlantic 136kHz data mode signal. Also I have
> used it to generate PSK31 and a slowed-down "PSK08" version, using DL4YHF's
> Spectrum Lab software to generate an on-off keyed tone to provide the binary
> data. At the moment, I am considering modifying it to obtain envelope and
> phase signals from a sound-card generated signal, which should make it more
> easily compatible with most data-mode software now around.
> 
> The main problem with the more exotic modes on LF is very few stations are
> able to transmit them, and also receiving them is more complicated. The
> "visual" modes like QRSS and DFCW are simple to generate, and several
> signals can be received at once, without precise frequency calibration, etc.
> PSK31 has been tried by several LF stations; it works OK when there is
> little QRN, but because there is no error correction, each impulse of static
> has a 50% chance of corrupting 1 bit, so it rapidly becomes unreadable when
> the QRN builds up, even though the signal may remain quite audible. Since
> the European band is only 2.1kHz wide, and some of that is occupied by
> utility signals, SSB and the wider data modes are not very practical here!
> 
> Cheers, Jim Moritz
> 73 de M0BMU
> 
> 
> 
> 
> 
> 
> 
>