Return-Path: X-Spam-DCC: paranoid 1290; Body=2 Fuz1=2 Fuz2=2 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-0.9 required=5.0 tests=BAYES_00,RATWARE_GECKO_BUILD autolearn=no version=3.1.3 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by paranoid.lipkowski.org (8.13.7/8.13.7) with ESMTP id s77FK4vT022618 for ; Thu, 7 Aug 2014 17:20:06 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1XFPQW-0000pp-8l for rs_out_1@blacksheep.org; Thu, 07 Aug 2014 16:16:24 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1XFPQV-0000pg-WE for rsgb_lf_group@blacksheep.org; Thu, 07 Aug 2014 16:16:23 +0100 Received: from mout.gmx.net ([212.227.15.19]) by relay1.thorcom.net with esmtp (Exim 4.82) (envelope-from ) id 1XFPQU-0002J3-BH for rsgb_lf_group@blacksheep.org; Thu, 07 Aug 2014 16:16:22 +0100 Received: from [127.0.0.1] ([91.38.33.242]) by mail.gmx.com (mrgmx003) with ESMTPSA (Nemesis) id 0LaFmY-1Wa3be3FdO-00m1Wz for ; Thu, 07 Aug 2014 17:16:21 +0200 Message-ID: <53E3983D.9050606@gmx.net> Date: Thu, 07 Aug 2014 17:16:13 +0200 From: Tobias DG3LV User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: In-Reply-To: X-Provags-ID: V03:K0:E7oHOSda422F7GXk2e5fNODpAYkQz3/3rw5bd1IrEfhT9XXRz+v LIjs1GQS3dU5Mhl4uy9CPH2K8R8omaCfL5nJm6VGOfgambS5mpNPCC+v6IlXz5RDK8zZptp QzdPGEpklMIsArc6BDG+HwnBJD/Z56nHPXkpzTWWg6P2rO7EwTu8wIFkfvJOpI7/jMy1REd GmrdYfR6ifC7SYGWYTXNg== X-UI-Out-Filterresults: notjunk:1; X-Scan-Signature: 3f8d74a8c70dd416d0a3a1dbcb9bb89f Subject: Re: LF: Receivers for LF and MF 136 KHz @ 477KHz ??? Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-Scanned-By: MIMEDefang 2.56 on 10.1.3.10 Status: O X-Status: X-Keywords: X-UID: 174 Hi Graham ! This type of device has a dynamic range of 48dB at maximum (8 Bit), so they need help from a narrow-band frontend plus input-attenuators to reduce the load to the A/D-converter. The conversion speed is variable from 1 to 3 Megasamples/second, leading to a Nyqist-frequency of 0.5 to 1.5 MHz. This filter should have a deep attenuation above the Nyqist-frequency to avoid unwanted reception at harmonics/aliases of the sampling frequency (= "undersampling"). The advertized usage of 100kHz to 30MHz (in direct-sampling method) is based on this normally unwanted harmonics/aliases, i.e. the receiver uses a method that has become "famous" with the ancient "Barlow-Wadley" all-band receivers. (at least equivalent to). Their (large-signal-)problems of the past are reborn at the direct-sampling method of these DVB-T sticks. Without narrow-band selective frontends this is just a "proof of concept" and not a usable receiver. For the use at 136 kHz and 475 kHz a steep lowpass-filter (7 to 9 pole Tscheby with toroids) at (e.g.) 500kHz would be mandatory. An actual bandpass may not be necessary. Equipped with such filters the lack of resolution (8 Bit) will become more acceptable. Using a pre-amplifier without using filters will do no good. When home-brewed, such filters will not cost much, but it takes time, measurement-tools and effort to build and tune them. 73 de dg3lv Tobias Am 07.08.2014 14:13, schrieb Graham: > Receivers for LF and MF136 KHz@ 477 KHz > > A question, > > Startingat theŁ5dongleriggedfordirectsample , as > acheapeffectivestartingpoint > > A pre amp and pre - selector [ band pass filter ] would help for lf/mf > > Whatwouldbein a scaleofincreasingperformance[ notcost !] > > be seen asreasonable in terms ofconfigurationand hardware ? > > Any particular equipments stand out as good cost/performance choices ? > > Tnx > > Graham > > G0NBD >