Return-Path: Received: (qmail 11362 invoked from network); 31 Jul 2001 13:25:43 -0000 Received: from unknown (HELO murphys-inbound.services.quay.plus.net) (212.159.14.225) by excalibur.plus.net with SMTP; 31 Jul 2001 13:25:43 -0000 Received: (qmail 23969 invoked from network); 31 Jul 2001 13:25:22 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by murphys with SMTP; 31 Jul 2001 13:25:22 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.16 #2) id 15RZRI-0003oH-00 for rsgb_lf_group-outgoing@blacksheep.org; Tue, 31 Jul 2001 14:20:00 +0100 Received: from relay.dera.gov.uk ([192.5.29.49]) by post.thorcom.com with smtp (Exim 3.16 #2) id 15RZRE-0003oC-00 for rsgb_lf_group@blacksheep.org; Tue, 31 Jul 2001 14:19:56 +0100 Received: (qmail 3497 invoked from network); 31 Jul 2001 14:17:10 +0100 Received: from trtnmail.dera.gov.uk (146.80.9.56) by relay.dera.gov.uk with SMTP; 31 Jul 2001 14:17:10 +0100 X-Priority: 3 X-MSMail-Priority: Normal Received: (qmail 20469 invoked from network); 31 Jul 2001 14:21:18 +0100 Received: (ofmipd 192.5.29.90); 31 Jul 2001 13:20:56 -0000 Received: by bob.dera.gov.uk; (8.8.8/1.3/10May95) id OAA10874; Tue, 31 Jul 2001 14:25:07 +0100 (BST) X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: (qmail 18494 invoked from network); 31 Jul 2001 14:10:37 -0000 Received: from gauntlet.mail.dera.gov.uk (172.16.9.10) by baton.dera.gov.uk with SMTP; 31 Jul 2001 14:10:37 -0000 Received: by gauntlet.mail.dera.gov.uk; id NAA26606; Tue, 31 Jul 2001 13:58:16 GMT Received: from unknown(10.71.64.31) by gauntlet.mail.dera.gov.uk via smap (3.2) id xma026586; Tue, 31 Jul 01 13:58:10 GMT Received: from mailex.dera.gov.uk (unverified) by mailguard.dera.gov.uk (Content Technologies SMTPRS 4.1.5) with SMTP id for ; Tue, 31 Jul 2001 14:18:59 +0100 Received: (qmail 25284 invoked from network); 31 Jul 2001 13:07:36 +0100 Date: 31 Jul 2001 14:17:36 +0100 Message-ID: <7D653C9C42F5D411A27C00508BF8803D55C56F@pdw-mail-r1.dstl.gov.uk> From: "Andrew Talbot" To: rsgb_lf_group@blacksheep.org Cc: "GUO \(E-mail\)" X-5Received: from softdnserror (HELO cchecker.dstl.gov.uk) (192.168.248.52) by mailex.dstl.gov.uk with SMTP; 31 Jul 2001 12:07:36 -0000 X-4Received: from FRN-MAIL-R3.dstl.gov.uk (unverified) by cchecker.dstl.gov.uk (Content Technologies SMTPRS 4.1.2) with ESMTP id ; Tue, 31 Jul 2001 13:07:25 +0100 X-3Received: by FRN-MAIL-R3 with Internet Mail Service (5.5.2650.21)id ; Tue, 31 Jul 2001 14:17:39 +0100 Subject: LF: LF Receivers MIME-Version: 1.0 X-Mailer: Internet Mail Service (5.5.2650.21) Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: I am now putting the finishing stages to a custom LF receiver, designed to be a useful accurate measurement tool as well as for operating. The design is optimised for narrow band and ultra narrow-band working, but with an audio bandwidth suitable still for CW. An A/D converter is included as an integral part, with formatted data sent to a PC via the serial port making soundcards, with their poor frequency stability and difficulties in driver software, unnecessary. ALL frequencies and A/D timing are derived from one master oscillator which may be an onboard TCXO (< 1ppm) or a highly stable external 5 / 10MHz reference. The basic receiver line up is as follows : A 7th order LP filter cutting off at 150kHz to give greater then 100dB rejection of the image frequency in the MF broadcast band. LPF cutoff frequency could be higher, but we have very high power LF broadcasting in Europe and I didn't want to tempt the possibility of overloading if close to a transmitter. MAR-3 modamp RF amplifier driven at constant current supply for temperature stability and interference rejection at low frequencies SRA-8 Double balanced mixer, upconverting to 455kHz IF Low phase noise LO derived from a DDS module over-clocked at 10MHz, with extra filtering to eliminate spurii Automatic External / Internal reference switching, with frequency doubling of a 5MHz signal if needed 300Hz bandwidth mechanical filter at 455kHz IF gain provided by an Analog Devices AD603 prescision voltage controlled gain stage, from a manual gain control pot. This chip is laser trimmed to provide 10 - 50dB gain with 0-1V and enables relative gain to be determined very accurately, to a fraction of a dB by just measuring the applied voltage with a DVM. AGC is not an option in a measurement Rx ! A BFO at 456kHz derived from the 10MHz reference mixes the IF to 1kHz centre frequency. Audio Bandpass filter at 1kHz reduces the bandwidth to 100Hz 12 Bit A/D converter sampling the 1kHz audio at 4kHz, generating 14 bit Complex I / Q pairs at 1kHz sampling rate, centred on 1kHz. ie a 1kHz tone appears in the data as if it were at zero frequency with up to +/- 50Hz sidebands Sensitivity of the receiver is sufficient to be used directly with a 0.8m loop (at least for urban noise levels) without having too much gain that the IF has to be wound back too far when connected to a full size antenna. The receiver hardware is working perfectly, but at the moment tuning is only under computer control of the DDS and I still need to add a manual tuning mode. This will be 10 turn potentiometer which, via an 8 bit A/D, can set 0 - 255 frequency increments from a base value. Channel (increment) readout can use the same DVM module already in use for gain setting, by measuring the voltage directly. Both Base frequency and Increment will be programmable from a PC and stored in non-volatile memory in the PIC controlling the DDS, ready for instant turn on. Doing it this way means the simple addition of the A/D chip to my existing DDS module with new PIC software. By setting an increment of, say, 10Hz, the whole 137kHz allocation can be covered without reprogramming, as well as most of 73kHz for aural CW listening. Alternatively the DDS LO could be replaced with the other designs around that make use of rotary encoders and LCD displays. When finished a write up will follow which will hopefully be published in one of the magazines, QEX or RadCom - haven't decided who to send it to yet ! This is not a cheap low cost receiver just for routine operating, but has been designed to be almost a laboratory grade piece of equipment useful for precise frequency and amplitude measurements. Andy G4JNT > -----Original Message----- > From: Andre Kesteloot [mailto:akestelo@bellatlantic.net] > Sent: 2001-07-31 12:58 > To: rsgb_lf_group > Subject: LF: LF Receivers > > > We have posted on our website at > > . > > some details of the new AMRAD receiving antenna that will > appear in QST > for September. > > In addition you can now also find there the complete > instruction manual > for the Cubic 3030 receiver, in PDF format. (The Cubic 3030 > is a US Mil > Spec receiver that covers from 5 kHz through 30 MHz. Both Sandy WB5MMB > and I own one). > > 73 > André N4ICK. > -- The Information contained in this E-Mail and any subsequent correspondence is private and is intended solely for the intended recipient(s). For those other than the recipient any disclosure, copying, distribution,o r any action taken or omitted to be taken in reliance on such information is prohibited and may be unlawful.