Return-Path: X-Spam-DCC: paranoid 1169; 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=-2.6 required=5.0 tests=BAYES_00 autolearn=unavailable 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 s77KgTOi023401 for ; Thu, 7 Aug 2014 22:42:31 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1XFUPc-00021M-Oj for rs_out_1@blacksheep.org; Thu, 07 Aug 2014 21:35:48 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1XFUPc-00021D-3B for rsgb_lf_group@blacksheep.org; Thu, 07 Aug 2014 21:35:48 +0100 Received: from smtpout4.wanadoo.co.uk ([80.12.242.68] helo=smtpout.wanadoo.co.uk) by relay1.thorcom.net with esmtp (Exim 4.82) (envelope-from ) id 1XFUPa-00039F-8s for rsgb_lf_group@blacksheep.org; Thu, 07 Aug 2014 21:35:46 +0100 Received: from AGB ([95.145.230.195]) by mwinf5d52 with ME id bwbk1o00Q4Dc3Db03wbkfv; Thu, 07 Aug 2014 22:35:45 +0200 X-ME-Helo: AGB X-ME-Date: Thu, 07 Aug 2014 22:35:45 +0200 X-ME-IP: 95.145.230.195 Message-ID: From: "Graham" To: References: <53E3983D.9050606@gmx.net> In-Reply-To: <53E3983D.9050606@gmx.net> Date: Thu, 7 Aug 2014 21:35:44 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 14.0.8117.416 X-MimeOLE: Produced By Microsoft MimeOLE V14.0.8117.416 X-Scan-Signature: ebba021850e0a5d4120636e52401e975 Subject: Re: LF: Receivers for LF and MF 136 KHz @ 477KHz ??? Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=response 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: 175 Yes Tobias, All is not as it seems , but as you say , adding filtering , reduces the problems , and with direct conversion , the noise floor is the lowest possible , stability is at maximum , having only 1 oscillator , In have good decode results on 477 using the £5 dongle , behind the TX atu and inv L ae For the £150 sdr , the description lists 80 msps , which , I assume moves the image problems out side the HF spectrum ? at 12 bits , that starts to provide a reasonable , post processed dynamic range ? 12- bit 80 MSPS A/D conversion I would not link the barlow-wadley , too closely to lack dynamic range , may be a lack of engineering integrity , the RA17 with pentode rf stage , then later cascode , with beam deflection mixer , was reasonable , though there was a pre selector for use at close tx/rx sites , the ra1771/1772 was the first to better the ra17 , but again that also tends to question the models before .. the ra1772/1 is fitted with rf-pre selector , for those 'unexpected' situations , the ra6790gm , with no pre-amp is the closest I have seen to a bullet proof front end , that runs , where the ra1778 needs the pre-selector But in terms of noise etc , one of these 'reasonable sdr's' may be better .. I don't think I would recommend any one go down the racal path these days ! 73-G, -------------------------------------------------- From: "Tobias DG3LV" Sent: Thursday, August 07, 2014 4:16 PM To: Subject: Re: LF: Receivers for LF and MF 136 KHz @ 477KHz ??? > 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 the£5dongleriggedfordirectsample , 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 >> >