Return-Path: Received: (qmail 20752 invoked from network); 26 Mar 2001 13:50:52 -0000 Received: from unknown (HELO warrior-inbound.servers.plus.net) (212.159.14.227) by excalibur.plus.net with SMTP; 26 Mar 2001 13:50:52 -0000 Received: (qmail 12410 invoked from network); 26 Mar 2001 13:50:50 -0000 Content-Transfer-Encoding: 8bit Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by warrior with SMTP; 26 Mar 2001 13:50:50 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.16 #2) id 14hXJi-000361-00 for rsgb_lf_group-outgoing@blacksheep.org; Mon, 26 Mar 2001 14:45:54 +0100 X-Priority: 3 X-MSMail-Priority: Normal Received: from mail.cc.kuleuven.ac.be ([134.58.10.6]) by post.thorcom.com with esmtp (Exim 3.16 #2) id 14hXJf-00035w-00 for rsgb_lf_group@blacksheep.org; Mon, 26 Mar 2001 14:45:51 +0100 Received: from LCBD15.fys.kuleuven.ac.be (LCBD15.fys.kuleuven.ac.be [134.58.80.15]) by mail.cc.kuleuven.ac.be (8.9.3/8.9.0) with SMTP id PAA42588 for ; Mon, 26 Mar 2001 15:45:21 +0200 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Message-ID: <3.0.1.16.20010326144713.21b765b2@mail.cc.kuleuven.ac.be> X-Sender: pb623250@mail.cc.kuleuven.ac.be X-Mailer: Windows Eudora Pro Version 3.0.1 (16) Date: Mon, 26 Mar 2001 14:47:13 To: rsgb_lf_group@blacksheep.org From: "Rik Strobbe" Subject: Re: LF: RE: WOLF (BPSK) modulation continuous phase modulation. In-reply-to: <65AECDF1F89AD411900400508BFC869F9C03FA@pdw-mail-1.dera.gov .uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: Over the weekend I had a closer look at the possibilities of reducing the bandwidth of a BPSk signal by continuous phase modulation. Simple simulations show that the bandwidth of the signal is reduced when continuous phase modulation is applied. When 5% of the bit-time (= 5ms) is allowed the continuous phase shift the bandwidth of the BPSK signal should be less than that of a normal keyed CW transmission at 12WPM. Next question was how to implement the continuous phase shift? One way would be to implement this digital, but this would require a rather high reference oscillator (in the 30-100MHz range, depending on how 'soft' the signal should be). But there might be an alternative and much simpler way : If you send an RF signal through a (resonant) LC-circuit this circuit will act as a kind of 'freewheel' where any change of amplitude ... and phase will be 'softened'. So if one would send a 'rude BPSK' signal (as is created with an XOR gate) through a resonant LC-circuit you will get continuous phase shift at the output. The phase shift time will depend on the Q of the LC-circuit, for our purposes (+/- 5ms phase shift time) we would need a Q of about 700. At 136kHz it should not be impossible to achieve such a Q, especially if we not use a simple passive LC circuit but a LC-circuit with feedback amplifier. A side effect will be that there is also some AM created, but this can be 'corrected' by an AGC amplifier (or just hard clipping, but this might increase bandwidth too much). A main advantage would be that the whole BPSK modulation circuitery can be inserted between VFO and PA. 73, Rik ON7YD