[Elecraft] OT: USB and LSB - How we got there

[donovanf at starpower.net]

Thanks Ian, very interesting reading! 


http://p1k.arrl.org/pubs_archive/28966 


73 
Frank 
W3LPL 

----- Original Message -----

From: "Ian White" <gm3sek at ifwtech.co.uk> 
To: elecraft at mailman.qth.net 
Sent: Thursday, February 15, 2018 11:27:15 AM 
Subject: Re: [Elecraft] OT: USB and LSB - How we got there 

Clarification: 

W2KUJ first published the design concept for a 20/80m SSB exciter 
using 5MHz SSB generation and a 9MHz VFO, in QST for June 1948. 

W1DX then expanded W2KUJ's block-diagram concept into a practical 
design for others to copy, and this was published in January 1949. 

73 from Ian GM3SEK 

>-----Original Message----- 
>From: elecraft-bounces at mailman.qth.net [mailto:elecraft- 
>bounces at mailman.qth.net] On Behalf Of Ian White 
>Sent: 15 February 2018 10:11 
>To: 'Alan'; elecraft at mailman.qth.net 
>Subject: Re: [Elecraft] OT: USB and LSB - How we got there 
> 
> 
>In 2003 I researched the subject for my RSGB Q&A column, 'In 
>Practice', and was fortunate to be in contact with some amateurs 
who 
>were personally involved in the decision to switch sidebands at 
>10MHz. This decision was made in April 1952 and eventually became 
>an 
>IARU standard - but its origins are surprisingly technical. The 
>standard came out of two totally unrelated design decisions, made 
by 
>different people on different continents, and at different times in 
>the late 1940s. 
> 
>Those post-war years saw a rapid development in intercontinental HF 
>telephone links. These links used independent-sideband (ISB) 
>modulation to carry two separate voice channels on opposite 
>sidebands, and a major manufacturer of ISB equipment at this time 
>was the Marconi company. The ISB signal was created by up- 
>converting 
>two separately generated USB and LSB voice channels to the same 
>suppressed carrier frequency, and the Marconi engineers made the 
>smart decision to generate the ISB signal on 10.000MHz (a frequency 
>on which they would never need to transmit, because it was already 
>occupied by beacons such as WWV). 
> 
>For transmitted frequencies above 10MHz, Marconi used a 
>crystal-controlled LO that was 10MHz below the output frequency; so 
>the IF frequency was added to the LO and the two independent 
>sidebands remained "the right way up". But for transmitted 
>frequencies *below* 10MHz, the LO frequency was 10MHz *above* 
>the 
>output frequency; so the IF frequency was *subtracted* from the LO 
>and the opposite sidebands were *inverted*. In an ISB system, that 
>meant that the two telephone channels might very easily become 
>swapped, so station engineers all around the world needed to be 
sure 
>when to flip the appropriate switches. 
> 
>Out of these working arrangements between engineers, a worldwide 
>CCIR standard emerged that 10MHz would be the frequency where the 
>sidebands in ISB systems changed over. 
> 
>So what has this to do with amateur SSB? Amateur development in the 
>late 1940s quickly followed the developments in commercial world - 
>and sometimes involved the same individuals. A major influence was 
>the W1DX SSB exciter, published in 1949, which automatically 
>produced a sideband inversion between 80m and 20m. The W1DX 
>design 
>used the phasing method which allowed easy sideband selection by 
>flipping a switch at AF, but by the early 1950s there were also 
many 
>filter-method exciters that were not so agile. 
> 
>By 1951-52, experimenters in Europe and the USA were beginning to 
>talk to each other on 20m, and quickly realised that they were 
>heading for a mess. Most people were using USB on 20m, but there 
>was 
>no international agreement on 80m... and what about the other 
>bands? 
>>From eyewitness accounts, April 1952 was the moment when the 
>agreement crystallized as we know it today. 
> 
>The two key points in this history are: amateurs were *already 
>aware* of the commercial dividing line at 10MHz; and the popular 
>W1DX exciter was *already compatible* with the new proposed 
>standard 
>[1]. 
> 
>And so it was that two entirely separate and obscure design 
>decisions - by Marconi engineers and by W1DX - came together to 
>create the standard that we have today. 
> 
> 
>[1] SSB exciters using 9MHz SSB generation and a 5MHz VFO are not 
>relevant to this history. They all came *after* the 10MHz standard 
>was already in place. 
> 
>73 from Ian GM3SEK 
> 

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