Posted by
N2EY on
Jun 18, 2004; 6:01pm
URL: http://elecraft.85.s1.nabble.com/K1-on-USB-CW-tp367868p367875.html
In a message dated 6/18/2004 12:20:57 PM Eastern Daylight Time,
[hidden email] writes:
> I am definitely not an expert on this, however, all of the early military
> manuals on the applications of SSB explained how "the only practical way of
> removing the unwanted sideband is with a 100 kc [old terminology for kHz]
> crystal filter, as the other filtering techniques are inadequate."
>
> You can even find some of these old Collins "mechanical" filters, in this
> range but usually up in the range of 455 kHz.
That was one philosophy, anyway. Collins held many mechanical filter patents, and RCA held some others.
The earliest SSB systems (such as Ray Moore's (W6DEI) 1934 rig) was to generate the SSB at frequencies just above the voice range - typically 11 to 20 kHz. Then it took at least two heterodynes to get to 75 meters, and maybe three to get to 20!
The very first SSB radio system was AT&T's transatlantic telephone system that went into service in 1927 and remained in service for at least 20 years. Besides the advantages of putting all the transmitter power into one sideband, the system reduced the need for a "wideband" antenna system because the frequency was in the LF region (55 kHz, IIRC).
The phasing system was known in principle back then but was not really practical until R.B. Dome described a practical RC audio phase shift network in the late 1940s.
Both systems were popular in the 1950s but the filter system won out for several reasons:
1) Filters could be made that had unwanted-sideband rejection far better than the 40 dB typically obtained in phasing systems.
2) In the mid-1950s, techniques for building high frequency lattice filters were perfected, reducing the number of heterodynes needed for the HF ham bands. (The ladder filters used in the K2 and K1 were a later development).
3) The filter system lent itself easily to transceiver implementations. This greatly reduced size, power consumption, cost and complexity, because the same oscillators could be used for both transmit and receive. Also, the task of zeroing the transmitter was mostly eliminated. (Trivia: what was the *first* manufactured HF SSB amateur transceiver?)
73 de Jim, N2EY
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