Quote:
Originally Posted by emeritus
According to the 1956 edition of the "ITT Reference Data for Radio Engineers", standardisation of frequency band designation seems to have been first agreed at the Atlantic City Radio Convention of 1947, although the CCIR later recommended that the use of such arbitrary names be discontinued.
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Yes, the decadic classification system came out of the 1947 Atlantic City ITU Meeting. It was mentioned in Wireless World (WW) 1948 April, page 150 (with some deprecatory remarks about the series of superlatives used), and here is the pertinent page from the Annex to that ITU meeting.
Hitherto, it appears that the terms USW, UHF and EHF were both used for anything above 30 MHz (below 10 metres).
Terman used UHF in his 1943 book:
Sturley used both UHF and USW when discussing FM receivers (VHF) in Part II of his book. The 2nd Impression was published in 1948, and I suspect that the manuscript predated the availability of the outcomes of the 1947 ITU meeting.
In 1949 WW was still using EHF for Band II transmissions. In fact, I think that this (mis)use of EHF by WW was found even later than that.
Although the ITU decadic system was essentially administrative, one may make a small number of approximate connections with radio wave behaviour. The international HF broadcasting bands, where long-distance skywave propagation is used, all fall into the 3 to 30 MHz range. The 75- and 11-metre bands represent about the lowest and highest frequencies that have utility for this purpose. Ground wave utility falls off below around 2 MHz, except over sea paths hence the 2 MHz marine band. So, from a little under 2 to a bit over 3 MHz is a transitional area, with more narrowly-based ground wave and skywave applications. The latter refers to NVIS propagation in the 120- and 90-metre tropical bands. Upper HF and lower VHF (into Band I) is also a transitional area.
The VHF-to-UHF transition is marked more by the change in circuit requirements, at least in the valve and early solid-state days. VHF techniques, such is in VHF TV tuners, worked up to about 220 MHz (valves) and maybe 250 MHz (solid-state), after which UHF techniques such as striplines took over. The technique frequency boundary was a bit below the classification boundary. One may see this for example in the Eddystone 990R (VHF) and 990S (UHF) receivers of the later 1960s. The 990R used VHF techniques and tuned up to 230 MHz. The 990S covered 230 to 870 MHz and had two front ends, one covering 230 to 510 MHz and the other 470 to 870 MHz. The latter was more-or-less a UHF TV front end; the former a UHF TV front end modified to cover a lower frequency range. Thus, one could infer that the frequency division point for the two receivers was chosen to suit the circuit techniques best matched to the frequencies respectively below and above that point.
Re the 11-metre HF broadcasting band, as best I can determine, it stayed unchanged after the ITU 1947 meeting, although some other HF bands were expanded slightly. So, it probably had some, but perhaps not much use before then. But I don’t think that it was ever used all that much. It depended upon sunspot cycles, and maybe was usable for about 3 or 4 years out of 11. When it was open, the major user seemed to be the BBC WS on 25.75 MHz – perhaps about the only used in the early 1990s.
Cheers,