Discussion in 'Ham Radio Discussions' started by N2EY, Jan 1, 2015.
Lighten up, Jim! Bill
Nice post Jim....Some folks will argue water being wet.......
No they won't!
No arguments here! My post is a good natured poke-in-the-ribs and joshing.
My statements are correct and true, if you take one step back from Jim's excellent explanation and history lesson and view the broad perspective of the beginning and end.
Many thanks for the refresher! b.
It isn't (wet).
Last night it was so cold here I'm pretty sure it was solid and looked dry.
Well, maybe not quite that cold...but really close!
I don't have time to do the homework, but a European ham pointed out here some years ago that the 10 MHz dividing line between USB and LSB was actually the result of some agreement made at the dawn of SSB in the late 1920's.
I remember my dad's pre-1950 SSB rig. It used a 'Silver Sentinel' filter that I'm pretty sure was at the 9 MHz IF, and used a 5 MHz Command Set oscillator as the VFO. Since that memory comes from not long after my avatar picture was taken, I could be mistaken. If someone could find the technical details of the 'Silver Sentry' filter, it might shed light on the IF frequency used. The filter could have been at 5 MHz, because it was easier to build them for the lower frequency. I don't really know. In any case, my father explained the LSB vs. USB thing to me in terms of the mixing of 5 and 9 MHz and inversion of the sideband. Everything I see says it was at 9 MHz...
I use 9.0000 MHz as the injection for my 160-meter transverter. However, I use 40-meters for the i.f. That inverts the sidebands and 7.000 MHz comes out at 2.000 MHz and 7.200 MHz comes out at 1.800 MHz.
Thank you for posting that!
I know - so was mine!
I recall something posted by SM0AOM to that effect. It was about commercial practice, IIRC. In the USA, at least, it was never a legal requirement for amateurs, but it's understandable that hams may have copied commercial practice.
Here's a rough timeline of SSB history:
The basic theory of SSB voice transmission was worked out in the 19-teens and first used in carrier telephone systems.
The first use of SSB on radio was fir the transatlantic telephone service, which went into commercial operation in early 1927. It operated on LF - down around 5000 meters IIRC. Development had started in 1923, Later commercial telephone links used HF, and were in operation by the early 1930s.
The first use of SSB in amateur radio was in the early 1930s, when W6DEI and some others built SSB transmitters using the filter method, with LC filters just above the audio range. But because of the expense and complexity, plus limited how-to information, only a handful of amateurs got on SSB before WW2.
After WW2, SSB was more widely used by amateurs, although it wasn't until the early 1960s that SSB really displaced AM as the primary voice mode on the amateur HF bands.
The "Silver Sentinel" filters commonly sold to amateurs were made by McCoy, and were 9 MHz filters. If that's what your dad's rig used, combined with a 5-5.5 MHz VFO, the sideband did not invert on 20 or 75 because of the heterodyning scheme. The math proves it.
However, it is likely that McCoy made filters for other frequencies. And there were common ARC-5 transmitters that went to 9.1 MHz. So it's possible that a custom filter was in the 5.2 MHz region and a 9 MHz VFO used.
The McCoy filters first appeared in the late 1950s. They came complete with two carrier crystals, one for LSB and the other for USB, so that no matter what heterodyne scheme or band was used, you could be on the "right" sideband.
It is also possible that your dad's rig started out as a phasing unit, and was later modified into a filter rig when the filters became available.
If you have access to old ARRL Handbooks, look in the 1964 or 1965 edition, in the SSB chapter. There's an SSB transmitter which uses a 9 MHz McCoy filter, and a VXO in the 5 MHz region for both 75 and 20 meters. Note the use of both carrier crystals in the SSB generator.
The National NCX-3, Eico 753, and Swan 240 triband transceivers used SSB generators at approximately 5.2 MHz, with the VFO in the 9 MHz range for 75 and 20, and in the 12 MHz range for 40. That arrangement gave the "correct" sideband for all three bands without changing the carrier crystal.