Return-Path: <majordom@post.thorcom.com> Received: (qmail 12074 invoked from network); 31 Jul 2002 23:23:53 -0000 Received: from murphys.services.quay.plus.net (212.159.14.225) by mailstore with SMTP; 31 Jul 2002 23:23:53 -0000 Received: (qmail 22807 invoked from network); 31 Jul 2002 23:23:55 -0000 Received: from post.thorcom.com (193.82.116.70) by murphys.services.quay.plus.net with SMTP; 31 Jul 2002 23:23:55 -0000 X-SQ: A Received: from majordom by post.thorcom.com with local (Exim 3.33 #2) id 17a4MK-0003Rl-00 for rsgb_lf_group-outgoing@blacksheep.org; Thu, 01 Aug 2002 02:02:32 +0100 Received: from ns2.etecsa.net ([206.49.67.1] helo=mxb.etecsa.net) by post.thorcom.com with esmtp (Exim 3.33 #2) id 17a4MG-0003Rd-00 for rsgb_lf_group@blacksheep.org; Thu, 01 Aug 2002 02:02:29 +0100 Received: (from daemon@localhost) by mxb.etecsa.net (8.10.2+Sun/8.10.2) id g6VNAv500883 for rsgb_lf_group@blacksheep.org; Wed, 31 Jul 2002 19:10:57 -0400 (EDT) Received: from ppp-inforhc.pppn.etecsa.cu(10.10.0.2), claiming to be "user" via SMTP by mail, id smtpdAAAc.aWTb; Wed Jul 31 19:10:50 2002 Message-ID: <000401c238df$3e996d20$02000a0a@user> From: "Prof. Arnaldo Coro Antich" <inforhc@ip.etecsa.cu> To: rsgb_lf_group@blacksheep.org References: <7D653C9C42F5D411A27C00508BF8803DCB9B57@mail.dstl.gov.uk> <002601c238ac$2dc7e2c0$09dc9384@jka> Subject: LF: Re: Re: Droitwich carrier Date: Wed, 31 Jul 2002 13:40:09 -0300 MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2600.0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: <majordom@post.thorcom.com> Let's see if this gets to the list ! 100 percent modulated AM transmitter will show 22 percent power output increase during a sustained 100 percent modulation condition ! Processing modulation to achieve up to 140 percent positive peaks ( strongly assymetric modulation ) is standard practice, as well as segmented band processing ( i.e., having the audio frequency range between 50 Hz and 5000 Hz ( in Region II ) or between 50 Hz and 4500 Hz ( in Regions I and III ) processed separately in three, four, six and even eight sub-bands.... This can lead to a nightmare when trying to adjust the system for a "more competitive on the air signal ".... BUT, nothing in my opinion justifies DOWNWARD MODULATION..... amplitude modulation applied to a carrier wave properly, MUST ALWAYS result in an increase in antenna current ( more properly current delivered by the feeder to the antenna tuning network ) .... PSM transmitters, using minimum economic steps ( 48 steps ) will follow the audio waveform, but never as well as 64 or 96 step PSM modulators.... and PSM using fiber optic coupling to the power supply IGBT modules sometimes produce rather "funny"audio when for some odd reasons an IGBT module falls "" out of step "" !!! This may cause downward modulation for obvious reasons. AM modulation of present day broadcast transmitters faces yet another problem.... and it is no other than the type of radio receivers involved at the receiving end... Mainly small portables with tinny speakers, home table top radios ( a few of them ) in plastic cases and with poor low quality speakers, and automobile radios ( that in most cases are normally tuned to the FM broadcast band anyway ) The poor quality receivers then require a very special form of audio processing.... that includes the shaping of the audio frequency response curve, the above mentioned segmented band audio processing, and a lot of tweaking to achieve the MAXIMUM PUNCH demanded by station managers... Commercial stations with mostly voice content like talk shows do totally different processing than stations running the ""oldies"" format , and international shortwave broadcast stations, many of which are running on shoestring budgets sometimes don't even reach 100 percent modulation when the modulator tubes or "valves" are used until the filaments ( directly heated cathodes )are almost exhausted. Again, there is nothing like a well designed Class B high power modulator with enough reserve power to handle modulation peaks, working with a well designed Class C RF power amplifier, and both powered from a well regulated and well filtered HT power supply. The problem with that old technology is simply COST... something that is hard to forget... A Pulse Step Modulation AM transmitter with 64 IGBT modules, will NEVER require changing extremely expensive modulator and driver tubes that have a rather limited service life... Changing 5 or 10 IGBT modules per year is nothing compared to the cost of a pair of modulator tubes for even a small by today standards 50 kW AM transmitter. This has led even to "" conversions kits "" that replace the whole AM Class B modulator and three phase HT power supply with an ""adapter"" that turns a standard AM high level plate modulated transmitter into a PSM rig ! By the way, as more and more 1kw and 5 kW standard AM transmitters are seeing retirement they should become available for LF conversions that can be done easily and at low cost... Only problem is you will need an extension to the house to install them !!! 73 and DX Arnie Coro CO2KK Soon, hopefully, to be on LF !!!