Return-Path: Received: from mtain-dg09.r1000.mx.aol.com (mtain-dg09.r1000.mx.aol.com [172.29.65.17]) by air-mc04.mail.aol.com (v126.13) with ESMTP id MAILINMC042-a9304b6822f5130; Tue, 02 Feb 2010 08:04:53 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-dg09.r1000.mx.aol.com (Internet Inbound) with ESMTP id 1762938000232; Tue, 2 Feb 2010 08:04:50 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1NcIPo-0005ax-Ql for rs_out_1@blacksheep.org; Tue, 02 Feb 2010 13:03:36 +0000 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1NcIPo-0005ao-1G for rsgb_lf_group@blacksheep.org; Tue, 02 Feb 2010 13:03:36 +0000 Received: from web87001.mail.ird.yahoo.com ([87.248.114.53]) by relay1.thorcom.net with smtp (Exim 4.63) (envelope-from ) id 1NcIPl-0007HB-Bf for rsgb_lf_group@blacksheep.org; Tue, 02 Feb 2010 13:03:36 +0000 Received: (qmail 51050 invoked by uid 60001); 2 Feb 2010 12:25:44 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=btinternet.com; s=s1024; t=1265113544; bh=RCFA7B9U1vO7NJaVy5OuhKZwQDVBHiP90aec0SjIYoY=; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=aculaMHXW24dfBo6Y3KcGkoJThxNrwe78SimWW0qp2bVJQL0OJxqs0GwyQ2l33eFMpYgYLTW5solmebmgAMPURNnSy9VE8B6pVorTMJtopI6OYz1nFl7aBSpjrV+T4Nksna/vgJBj7DmpP+/dhA0M5ydpHNe6hDbCEGRzHwyjtw= DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=btinternet.com; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=eKfL4laF88cei3ZPtAWaeQBAfnVF2gpjqRgkiZrO0R53l392DFJ/lXqGM1aY4/5Qm4BtOFoAMZTVU+S6BLOTu/DllJGHrOWj9y5dyiPy6IVfr3dHAMF8UDU0oB6NOvWO2KQA/gBu+u67qeeTwT8aqOAA9ytlVpHf289744SvuRU=; Message-ID: <284438.50947.qm@web87001.mail.ird.yahoo.com> X-YMail-OSG: 5bSosmgVM1miNrvQkIto5cLs0NddSyiuoBW2hLeyUurf9KIpV3RI4qO36Pe938n.rBt46KRDbY09JnqLIf96YFepEwPe.6LdNK3UcLPb0kKnwHP4mg2EmvTiLJ8fz_eW_Eplwp9rAi.pqWevG07AU9pk.PYK5swr52ikZCfFCNmWuES0QYevDr6GzIbcfzfNGl4WtFyVcSngpzh_lhs9OolauND2iiuLskkRN3GMcaC0UwzV3WyNzBEdr.Mra.Vi8BbTZobnzDliifRaVNxYyN8wpQ637OptNbgsC.lwhgD1dU153w5ztartio14d9kSH4IQmg-- Received: from [86.153.188.195] by web87001.mail.ird.yahoo.com via HTTP; Tue, 02 Feb 2010 12:25:44 GMT X-Mailer: YahooMailRC/272.7 YahooMailWebService/0.8.100.260964 References: <12077821.1264946261487.JavaMail.root@wamui-cynical.atl.sa.earthlink.net> <38A51B74B884D74083D7950AD0DD85E82A1ACF@File-Server-HST.hst.e-technik.tu-darmstadt.de> <4C25D51A6FE646D5B8D9D37C87EA6BBC@lindavideo> <02E3EF3F48994AB88A1489042CE7EA02@JimPC> Date: Tue, 2 Feb 2010 12:25:44 +0000 (GMT) From: SAM JEWELL To: rsgb_lf_group@blacksheep.org In-Reply-To: <02E3EF3F48994AB88A1489042CE7EA02@JimPC> MIME-Version: 1.0 DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: LF: Loop preamp with the BF862 / optical link Content-Type: multipart/alternative; boundary="0-1171024689-1265113544=:50947" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=HTML_MESSAGE autolearn=no version=2.63 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-aol-global-disposition: G x-aol-sid: 3039ac1d41114b6822f215e3 X-AOL-IP: 193.82.116.20 --0-1171024689-1265113544=:50947 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Folks, I think it is worth pointing out that most cable TV systems use fibre link= s, at least as far as the cabinet. The light (laser) is amplitude modulate= d with the RF carrier(s) at the cable head end or regional Centre. These= carriers are usually locally generated but can also be from directly off-= air if the signal to noise ratio is adequate. The modulation index can be= held quite high for a single carrier, progressively reducing for multiple= carriers in order to minimize intermodulation between carriers. Ultimatel= y, with many carriers, the modulation spectrum will be noise-like. Those= of you who have worked with the old telecom carrier based systems will= recognise the same characteristics.=20 The earliest cable (HFC) systems carried AM VSB signals in the VHF and UHF= frequency range in their native transmission format with minimal distorio= n and added noise. Digital modulation (using QAM modulation, but still amp= litude modulation of the light) came later. >From the laser (or LED) input to photodiode/PIN/APD output there will be= a certain link loss and system noise figure. If the system parameters are= known, this can be modelled using e.g. AppCAD, Noisecalc. In some system= s signal to noise ratio is critical. For LF systems, where there is a fair= ly high noise level, it may be far less critical (famous last words). Not all fibre systems use digital modulation of the light, although in mos= t cases it is still amplitude modulation. I should also point out that fibre is often used to carry the RF and IF si= gnals from the SHF rooms (at the back of the big dishes) at satellite eart= h stations across the site to the demodulation and signal processing build= ings, in preference to using waveguide, as was done many years ago. Whilst= working at BT Research Labs my team produced one of the first radio over= fibre test systems for BT's Goonhilly and Madley Earth stations. These ea= rly fibre links used multimode 50/125u fibre and multimode lasers. As I mentioned in an earlier posting, microwave and LF are just the adjace= nt ends of the spectrum. Not opposite ends! 73 de Sam, G4DDK ________________________________ From: James Moritz To: rsgb_lf_group@blacksheep.org Sent: Tuesday, 2 February, 2010 11:57:13 Subject: LF: Loop preamp with the BF862 / optical link Dear Ken, Stefan, LF Group, If I remember correctly, the components Stefan is discussing use a polymer= fibre and are intended for short-distance optical links of a few metres,= rather than telecomms-type applications with miles of fibre, so fibre los= s is not really an issue. The ones I encountered some years ago used visib= le red LEDs, although I think there were infra-red ones too. The plastic= fibre could be simply cut with a sharp knife, and clamped into the emitte= r/detector components with reasonable results, rather than requiring preci= sion optical connectors. There is an overview at http://www.avagotech.com/= docs/AV00-0143EN Of course, since the optical link is effectively a signal-frequency gain= component in the receiver front end, its noise figure will contribute tow= ards the receiver noise figure. Since the overall efficiency of the electr= ical/optical/electrical conversion is rather low, with the loss of the fib= re in addition, there will be much less signal power coming out of the det= ector than going in to the emitter. Also the detector and emitter will con= tribute their own noise. So the noise figure of the optical link by itself= is probably rather high. But the FET voltage-to-current input stage drivi= ng the emitter will have a high power gain due to the very high input impe= dance, which would greatly reduce the impact of noise in the optical link= - clearly the overall noise level in Stefan's system is reasonably low. Most optical links are used with digital signals, so this analogue optical= link is quite unusual - as well as noise, distortion products will also= be produced by the optical link. But DK7FC's antenna obviously works, so= the principle is viable. Cheers, Jim Moritz 73 de M0BMU ----- Original Message ----- From: "Ken" To: Sent: Monday, February 01, 2010 5:56 PM Subject: Re: LF: 2nd try of sending the pic of my loop preamp with the BF8= 62 > Hi Stefan. > 150dB/km, is a very high loss for modern fibre, even thhe early 850nm mu= ltimode fibre was only 1 or 2dB /km...=20 --0-1171024689-1265113544=:50947 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
Folks,
I think it is worth pointing out that most cable TV sy= stems use fibre links, at least as far as the cabinet. The light (laser)= is amplitude modulated with the RF carrier(s) at the cable head end or re= gional Centre. These carriers are usually locally generated but can also= be from directly off-air if the signal to noise ratio is adequate. The mo= dulation index can be held quite high for a single carrier, progressively= reducing for multiple carriers in order to minimize intermodulation betwe= en carriers. Ultimately, with many carriers, the modulation spectrum will= be noise-like. Those of you who have  worked with the old telecom ca= rrier based systems will recognise the same characteristics.

The= earliest cable (HFC) systems carried AM VSB signals in the VHF and UHF fr= equency range in their native transmission format with minimal distorion and added noise.= Digital modulation (using QAM modulation, but still amplitude modulation= of the light) came later.

From the laser (or LED) input to photodi= ode/PIN/APD output there will be a certain link loss and system noise figu= re. If the system parameters are  known, this can be modelled using= e.g. AppCAD, Noisecalc. In some systems signal to noise ratio is critical= . For LF systems, where there is a fairly high noise level, it may be far= less critical (famous last words).
Not all fibre systems use digital= modulation of the light, although in most cases it is still amplitude mod= ulation.

I should also point out that fibre is often used to carry= the RF and IF signals from the SHF rooms (at the back of the big dishes)= at satellite earth stations across the site to the demodulation and signa= l processing buildings, in preference to using waveguide, as was done many= years ago. Whilst working at BT Research Labs my team produced one of the first radi= o over fibre test systems for BT's Goonhilly and Madley Earth stations. Th= ese early fibre links used multimode 50/125u fibre and multimode lasers.
As I mentioned in an earlier posting, microwave and LF are just the= adjacent ends of the spectrum. Not opposite ends!


73 de Sam,= G4DDK





From: James Morit= z <james.moritz@btopenworld.com>
To: rsgb_lf_group@blacksheep.org
Sent: Tuesday, 2 February, 2010 11:57:13
= Subject: LF: Loop preamp= with the BF862 / optical link

Dear Ken, Stefan, LF Group,

If I remember corre= ctly, the components Stefan is discussing use a polymer fibre and are inte= nded for short-distance optical links of a few metres, rather than telecom= ms-type applications with miles of fibre, so fibre loss is not really an= issue. The ones I encountered some years ago used visible red LEDs, altho= ugh I think there were infra-red ones too. The plastic fibre could be simp= ly cut with a sharp knife, and clamped into the emitter/detector component= s with reasonable results, rather than requiring precision optical connect= ors. There is an overview at http://www.avagotech.com/docs/AV00-0143EN
Of course, since the optical link is effectively a signal-frequency= gain component in the receiver front end, its noise figure will contribut= e towards the receiver noise figure. Since the overall efficiency of the electrical/optical/electrical conversion is rather low, with the loss of= the fibre in addition, there will be much less signal power coming out of= the detector than going in to the emitter. Also the detector and emitter= will contribute their own noise. So the noise figure of the optical link= by itself is probably rather high. But the FET voltage-to-current input= stage driving the emitter will have a high power gain due to the very hig= h input impedance, which would greatly reduce the impact of noise in the= optical link - clearly the overall noise level in Stefan's system is reas= onably low.

Most optical links are used with digital signals, so th= is analogue optical link is quite unusual - as well as noise, distortion= products will also be produced by the optical link. But DK7FC's antenna= obviously works, so the principle is viable.

Cheers, Jim Moritz73 de M0BMU


----- Original Message ----- From: "Ken" <ken.h.wright@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Monday, Februa= ry 01, 2010 5:56 PM
Subject: Re: LF: 2nd try of sending the pic of my= loop preamp with the BF862


> Hi Stefan.
> 150dB/km,= is a very high loss for modern fibre, even thhe early 850nm multimode fib= re was only 1 or 2dB /km...


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