Return-Path: Received: (qmail 8323 invoked from network); 28 Aug 2001 17:45:39 -0000 Received: from unknown (HELO murphys-inbound.services.quay.plus.net) (212.159.14.225) by excalibur.plus.net with SMTP; 28 Aug 2001 17:45:39 -0000 Received: (qmail 27479 invoked from network); 28 Aug 2001 17:44:32 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by murphys with SMTP; 28 Aug 2001 17:44:32 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from majordom by post.thorcom.com with local (Exim 3.16 #2) id 15bmki-0005H1-00 for rsgb_lf_group-outgoing@blacksheep.org; Tue, 28 Aug 2001 18:34:16 +0100 Received: from imo-d04.mx.aol.com ([205.188.157.36]) by post.thorcom.com with esmtp (Exim 3.16 #2) id 15bmkd-0005Gv-00 for rsgb_lf_group@blacksheep.org; Tue, 28 Aug 2001 18:34:12 +0100 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from DL4YHF@aol.com by imo-d04.mx.aol.com (mail_out_v31_r1.4.) id l.a2.18ff43e5 (3700) for ; Tue, 28 Aug 2001 13:32:53 -0400 (EDT) From: DL4YHF@aol.com Message-ID: Date: Tue, 28 Aug 2001 13:32:53 EDT Subject: LF: Re: Dynamic range for FM link (was: Carriers) To: rsgb_lf_group@blacksheep.org MIME-Version: 1.0 Content-Type: text/html; charset=windows-1252 X-Mailer: AOL 6.0 for Windows DE sub 10506 Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: Content-transfer-encoding: 8bit Hi Larry, Rik,   and the group,

As Rik's wrote, the dynamic range of some cheap FM transmitters is possibly
just in the range of 40dB or so. But IMO, a homemade "simple but true FM"
transmitter could do better.
The designers of these transmitters certainly do everything they can to keep
the costs down (good engineering work :-) . But the dynamic range can vary
greatly between different rigs, depending on the principle how and at what
frequency the FM is generated, and how much attention is paid to the AF path
before the signal is applied to the varicap (or whatever). There is a lot of
noisy but cheap AF amplifiers and preamps out there...

Using a simple "straight" design where the FM'ed oscillator is multiplied to
the final frequency should do better, at least for the distortions of the
modulation. For example,  ( 27.11MHz+- 300 Hz) * 2 * 2 * 2 * 2 = 433.76 MHz
+- 5kHz.

The question is, how many dB's are required (see Larry's mail), and how much
effort must be put into the FM link vs the LF frontend...

Thanks Rik also for the idea of using a digital link instead of an analog one
(by direct mail). It doesn't necessarily have to be a high-speed packed link,
a simple serial 16-bit frame plus a startbit from a serial ADC (possibly the
LTC129x ) could possibly do the job, even without a microcontroller at the
remote RX site.


Now I'm off to think about all this for a little longer. Thanks to everyone
for their suggestions, and apologies to others for drifting into the HI-tech
corner again..


73  Wolf,   DL4YHF.