Return-Path: Received: (qmail 27938 invoked from network); 22 Mar 2001 16:34:09 -0000 Received: from unknown (HELO murphys-inbound.servers.plus.net) (212.159.14.225) by excalibur.plus.net with SMTP; 22 Mar 2001 16:34:09 -0000 Received: (qmail 14462 invoked from network); 22 Mar 2001 16:33:35 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by murphys with SMTP; 22 Mar 2001 16:33:35 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.16 #2) id 14g7pF-0005n3-00 for rsgb_lf_group-outgoing@blacksheep.org; Thu, 22 Mar 2001 16:20:37 +0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from hestia.herts.ac.uk ([147.197.200.9]) by post.thorcom.com with esmtp (Exim 3.16 #2) id 14g7pD-0005mw-00 for rsgb_lf_group@blacksheep.org; Thu, 22 Mar 2001 16:20:36 +0000 Received: from gemini ([147.197.200.44]) by hestia.herts.ac.uk with esmtp (Exim 3.16 #4) id 14g7oV-0005Gh-00 for rsgb_lf_group@blacksheep.org; Thu, 22 Mar 2001 16:19:51 +0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Message-ID: <28702.200103221619@gemini> From: "James Moritz" Organization: University of Hertfordshire To: rsgb_lf_group@blacksheep.org Date: Thu, 22 Mar 2001 16:24:40 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 8bit Subject: LF: WOLF Transmit X-Mailer: Pegasus Mail for Win32 (v3.11) Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: Dear Mike, LF Group, Mine is certainly not the only way of generating a BPSK signal, and it is certainly true from experience that little trouble results from key clicks on 136k, in spite of the fact that a lot of TXs on the band have less than ideal keying. But in my own position, being in an area relatively densely populated with LF stations, having a high ERP compared to most, and transmitting beacon signals over extended periods means I feel obliged to try and produce as clean a signal as possible. Actually, key clicks are never likely to be a huge issue on LF; when compared to HF standards, even a full 1W ERP is a sub-QRP signal, and the higher noise level will tend to swamp clicks from all but the most local stations anyway. Both "WOLF" and (usually) "Coherent" BPSK use a 10 bits/second rate; so the number of phase transitions per second will be similar to the number of on-off transitions of a 12wpm CW signal. Cutting the drive before a phase transition would eliminate the click due to the phase change, but would add 2 more, when the drive was switched off and then back on again, so little would be gained. Having "redundant" envelope modulation when no phase transition occurs would actually increase the sideband levels - the explanation I gave was something of an over-simplification. It would still be neccessary to synchronise the amplitude modulation with the phase modulation somehow, so little saving in complexity would be acheived. A perfectly good way of generating BPSK would be to first low- pass filter the logic level signal, and then mix it with the carrier in a linear balanced mixer (rather than an ex-or gate). A linear PA would be required. This would be a good option if you do have a linear, but do not have an SSB exciter that will give output on 136k. To put the complexity into perspective, my prototype modulator is built on 2 100 x 160mm prototyping boards, plus a heatsink assembly carrying the MOSFETs. Implementing the waveform generator part on a PIC - type microcontroller would roughly halve the number of components and interconnections. If a PCB were designed, the small-signal parts of the circuit would be no more difficult to build than, say, a fairly elaborate audio filter kit. The MOSFET pass element obviously needs to be quite big to handle the power. The Heatsink assembly could be simplified by using a really big MOSFET power module instead of 8 small ones, but I doubt if this would be cost-effective. cheers, Jim Moritz 73 de M0BMU