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February 1960 Electronics World
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
from
Electronics World, published May 1959
- December 1971. All copyrights hereby acknowledged.
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If you think the
ISM (Industrial,
Scientific, and Medical) unlicensed bands were a relatively new spectrum allocation,
you might find this 1960 Electronics World news piece interesting. Individual
countries generally acknowledge the ISM emissions specifications set forth by the
International
Telecommunication Union (ITU), which created the bands in 1947. The 900 MHz,
2.4 GHz, and 5.8 GHz WiFi bands are well known to most people. 24 GHz
is gaining traction as current spectrum gets more and more crowded and high bandwidth
data channels are needed. Interestingly, the first few ISM bands are integer harmonics
of the lowest (6.78 MHz, center of band 1). To wit:
6.78 MHz (band 1)
2 * 6.78 = 13.56 MHz (band 2),
4 * 6.78 = 2 * 13.56 = 27.12 MHz (band 3),
6 * 6.78 = 2 * 13.56 = 40.68 MHz (band 4),
64 * 6.78 = 32 * 13.56 = 16 * 27.12 = 433.92 MHz (band 5).
According to some sources, the harmonic band allocations are to accommodate use
of higher powers on the lower bands that generate harmonics which will fall within
other ISM bands. RF heating ovens are an example of such applications.
Canada Puts Limit on R.F. Interference
 By J. E. Kitchin
Inspector, Telecommunications Department of Transport
Audio noises have been well tabulated in the past but how does one set a tolerable
limit for radio-frequency noise? A recent Canadian Department of Transport regulation
(known officially as SOR 59-116 by the Queen's Printer, Ottawa, Canada) has defined
radio-frequency noise as any electrical disturbance "produced by any mechanical,
electrical, or other device" and capable of being received on a radio receiver.
The regulation refers specifically to r.f. generators in the ISM industrial bands,
in which the amount of r.f. energy produced is without limitation. However, any
r.f. generator in those bands must not have any emission outside of the band in
excess of 25 microvolts-per-meter at a distance greater than one-thousand feet from
the r.f. generator. A provision is also made that if r.f. generators are operated
on any frequency outside the ISM bands the limit shall be 15 microvolts-per-meter
at 1000 feet.
Allowance is also made for higher power industrial equipment (over 5 kw.) and
high-frequency arc welding equipment where it is not practicable to apply the limits
mentioned above. In these cases the field intensity is restricted to ten microvolts-per-meter
at a distance of one mile from the industrial equipment.
It is also Interesting to note that these measurements must be made on field
strength meters of a make and type approved by the Department of Transport, or by
meters having an equivalent standard of measurements. Field-strength meters must
be adjusted to read the "quasi peak" values of field strength and the prescribed
antenna system is a horizontally polarized dipole seven and a half feet high for
measuring the frequencies above 25 mc.
Any records of measurements made to ensure compliance with the regulation must
be kept for three years and be available to Inspectors of the Department of Transport.
It must also be remembered that, as usual in such regulations, the provision is
made that in certain cases or circumstances suppression may be required by the Department
at values lower than those specified in the regulation.
Posted October 12, 2023
(updated from original
post on 6/19/2018)
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