Howdy, The fellow who made the comment about the noise being all over the eastern part of the US is correct. We have been unindated for years on the 3810 AM net that meets on Sundays in the NC/SC area. What is really strange about our RFI is that it seems to drift up and down the band, but when it finds an AM signal, it will stop there and hang around, many times while a station is transmitting, only to resume its drift after the station stops radiating. It will zero in on the stronger AM signals too, marginal signals during the net it will pass by. Various members of the group have done the usual, call Riley, and they have received replies from him. They all run along the lines of, "yes we (the FCC) looked into it and it is is military and don't ask again." I have RDF'd it from my location in Western NC using an old Bendix RDF and get a consistant south (180 deg) angle on it, which points to a myriad of military installations in SC and GA. Don't know if it is still in use, but years ago, there was a military emergency comm set that rode the carrier of WWV to enhance coverage. You all have probably noticed that a signal placed just in the right spot on a strong AM carrier will actually ride along and sound much stronger than if transmitted in the clear. Perhaps the signal down here in the south is something along this line. At least it is more of a nuisance than a source of serious QRM. Charlie, W4MEC in NC
__________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com From [EMAIL PROTECTED] Wed Jul 13 12:50:56 2005 Return-Path: <[EMAIL PROTECTED]> X-Original-To: amradio@mailman.qth.net Delivered-To: amradio@mailman.qth.net Received: from hotmail.com (bay104-f18.bay104.hotmail.com [65.54.175.28]) by mailman.qth.net (Postfix) with ESMTP id F0F28859C06 for <amradio@mailman.qth.net>; Wed, 13 Jul 2005 12:50:50 -0400 (EDT) Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Wed, 13 Jul 2005 09:39:09 -0700 Message-ID: <[EMAIL PROTECTED]> Received: from 65.54.175.208 by by104fd.bay104.hotmail.msn.com with HTTP; Wed, 13 Jul 2005 16:39:09 GMT X-Originating-IP: [65.54.175.208] X-Originating-Email: [EMAIL PROTECTED] X-Sender: [EMAIL PROTECTED] In-Reply-To: <[EMAIL PROTECTED]> From: "Donald Chester" <[EMAIL PROTECTED]> To: amradio@mailman.qth.net Subject: Re: [AMRadio] power ratings Date: Wed, 13 Jul 2005 16:39:09 +0000 Mime-Version: 1.0 Content-Type: text/plain; format=flowed X-OriginalArrivalTime: 13 Jul 2005 16:39:09.0870 (UTC) FILETIME=[64C474E0:01C587C9] X-BeenThere: amradio@mailman.qth.net X-Mailman-Version: 2.1.4 Precedence: list Reply-To: Discussion of AM Radio <amradio@mailman.qth.net> List-Id: Discussion of AM Radio <amradio.mailman.qth.net> List-Unsubscribe: <http://mailman.qth.net/mailman/listinfo/amradio>, <mailto:[EMAIL PROTECTED]> List-Archive: <http://mailman.qth.net/mailman/private/amradio> List-Post: <mailto:amradio@mailman.qth.net> List-Help: <mailto:[EMAIL PROTECTED]> List-Subscribe: <http://mailman.qth.net/mailman/listinfo/amradio>, <mailto:[EMAIL PROTECTED]> X-List-Received-Date: Wed, 13 Jul 2005 16:50:56 -0000 Gary K4FMX said: >The best quality audio of all can be gotten from low level modulation and a >linear amplifier. A linear amplifier has the same kind of distortion as a class-B modulator. With tubes, the best quality audio can be had from low distortion plate modulators such as class-A series or Heising modulation, or pushpull plate modulators running class A or AB1. Pulse-width series modulators produce perhaps the best audio. I suspect the best quality of all comes from the new class-E rigs. According to the tube manuals, class-B audio service has inherent distortion levels on the order of 3-5%. It can be reduced with negative feedback. My Gates BC1-T manual claims less than 2% distortion at 100% modulation. The signal driving a linear amplifier has its own distortion, since the original signal has to be produced somehow. Pushpull class-A audio or series modulation, with feedback, might be a good candidate for the driver stage of a linear. If the linear is run properly in class AB1, that would be near the best possible audio out of a tube transmitter, even though the efficiency is not all that good. Speaking of efficiency, an AM linear or grid modulated amplifier has close to the same overall efficiency as plate modulation, when calculated from the ratio of power drawn from the a.c. mains, to rf carrier output. A linear amplifier running AM has exactly the same efficiency as when it runs SSB. It's just that the duty cycle is different. Actually, since with the human voice, the average power is 7-8 dB lower than peak power (equivalent to around 30% modulation), the average efficiency of a SSB linear is similar to that of an AM linear because the efficiency of a linear is a function of the amplitude of the signal (0% at idling current, and a maximum of about 67% at maximum peak output just below the point of saturation or flat-topping). AM linears got their reputation as "low efficiency" on AM because of the 100% duty cycle carrier runs about 30% efficiency to allow enough headroom for the positive peaks. With an AM linear, you can see the glow on the plates DECREASE when you whistle into the mic to produce 100% tone modulation. The DC input is the same regardless of modulation, but the rf output is higher, since sideband energy is now included. That power has to come from somewhere, so the efficiency of the amplifier goes up to generate the sidebands. The advantage of plate modulation with AM is the ease of tuning up and QSY'ing. You simply dip the final and load to the desired carrier output, while maintaining enough grid drive to assure class-C service. With low-level modulation (linear or grid modulated), the rf drive level and degree of antenna coupling are critical to the modulation linearity of the final.
