[Heath] Heath Digest, Vol 68, Issue 3

[Al & Dottie Skierkiewicz]

Rob,The offset has to do with the carrier generation, modulator and the filter arrangement.  Working from my HW101 schematics, the balanced modulator produces both sidebands and nulls out the carrier (3395.000kHz).  For the upper sideband, there is no offset and the double sideband audio passes through the crystal filter with the "carrier" on the high side of the audio.  The filter is 2.1kHz wide so only audio gets through and any remaining carrier is nulled out.  The sideband is reversed later in the radio.  
In lower sideband, the carrier is offset about 2.8kHz which then sends the audio through the filter with the carrier below the audio.  Again whatever carrier remains is also attenuated by the filter.  The lower sideband is reversed in the later stages of the radio.  
In this way, only one audio filter is needed for all modes of the transmitter, CW included.  All stages following the modulator are then linear, including the finals which are running AB1. 

    On Thursday, August 4, 2016 11:00 AM, "heath-request at puck.nether.net" <heath-request at puck.nether.net> wrote:
 

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Today's Topics:

  1. Re: SB-401 / SB-303 LMO question (Robert Myers)


----------------------------------------------------------------------

Message: 1
Date: Thu, 4 Aug 2016 03:34:17 -0400
From: "Robert Myers" <rsmyers at rogers.com>
To: <heathkit at yahoogroups.com>, <heath at puck.nether.net>,
    <heathkit at mailman.qth.net>
Subject: Re: [Heath] SB-401 / SB-303 LMO question
Message-ID: <001401d1ee22$9e0d8540$da288fc0$@rogers.com>
Content-Type: text/plain;    charset="iso-8859-1"

Thanks for all your answers everyone.

---Rob
------------------------
Hi

I have an SB-303 and SB-401 working together as a transceiver in ?locked?
mode with the (same) operating frequency for both the Rx and Tx controlled
by the Rx.? Can someone explain to me why the LMO frequency on the SB-303 is
suppose to change slightly when moving between USB and LSB, please?? I
thought I sort of understood this one time.

Thanks,
--- Rob VE3JQL



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End of Heath Digest, Vol 68, Issue 3
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