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Sunday, May 13, 2012

Sibeband Inversion: 9 MHz, 5 MHz, and the ARRL Handbook

The 2006 ARRL Handbook had it right.  Jeremiah went back and took a look: 


I have a comment about the question of the LSB/USB convention mentioned in the most recent SolderSmoke podcast and the follow up blog post:

I checked the 2006 Handbook and there is a sidebar (page 9.27) explaining the 5/9 MHz connection with the Lower/Upper Sideband convention in use today. It explains that there was a popular rig that used a 5 MHz VFO and a 9 MHZ IF that were mixed to create the 75/20 meter RF signals. This is certainly a reasonable method, but would not result in the inversion. The article then goes on to explain, however, that other rigs used a 5 MHz tunable IF and a 9 MHz local oscillator which would indeed result in sideband inversion and thus the convention we use today. 

Jeremiah, KB0OFF

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  1. I sure would like to take a gander at that article.

    How could that configuration work as an SSB exciter?

    As Chuck Adams would say, "Inquiring minds, etc."

    73.......Steve Smith WB6TNL
    "Snort Rosin"

  2. Steve, a 5 MHz tunable IF could have been either a phasing exciter or mixed up from a 455 kHz crystal or mechanical filter (plus either 4.5 - 5 or 5.5 - 6 MHz as the VFO).

    The resultant 5 - 5.5 MHz output could be mixed with a bank of crystals for various HF amateur bands. Ditto on receive - crystal controlled converters feeding a tunable IF was a popular way of building a stable high performance amateur band only receiver).

    Because SSB was most useful for DX having 20m was a must. Mixing with a 9 MHz crystal also providing a bonus 3.5 - 4 MHz (with inverted sideband) which cut costs.

    By the way SSB for the Radio Amateur (1970) describes using 5.5 MHz xtals for the filter - cheap as these were surplus items. This would have inverted the sideband if subtracted from a 9 MHz VFO.

    K9STH gives another explanation at http://forums.qrz.com/archive/index.php/t-125756.html with regards to early commercial rigs. 73, Peter VK3YE

  3. I'll agree with the phasing theory using a 5.5 MHz SSB generator and a 9 MHz LO to generate either 3.5 LSB or 14.5 USB but since a phasing SSB generator will switch sidebands with the addition of a simple DPDT switch, it would be much easier to use a fixed 9 MHz SSB generator and a 5.0 - 5.5 MHz VFO. Also there's no worry about the RF phasing 'slipping' as the LO frequency changes.

    On the AC6V website "WHY LSB BELOW 9 MHz AND USB ABOVE" (about half way down the page), 3 entries clarify these issues:

    Karl-Arne Markstrom SM0AOM
    Jim N2EY
    Alan Larson WA6AZP

    Most of the other stuff under that heading is bogus or at least unclear.

    73.......Steve Smith WB6TNL


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