Another question about broadcast bands

[s***@stever.net]

The recent topic about FM bands reminded me of a question that I haven't quite been able to answer for myself.

My question revolves around the dials for AM Broadcast band.

Early radio dials were indexed roughly from 1-100 and later dials started at "54" or "540". My understanding is that the current indexing scheme represents the station's broadcast frequency.

When did this transition occur, and why?

Thanks!

-Steve

[Peter Wieck]

Post by s***@stever.net
My question revolves around the dials for AM Broadcast band.
Early radio dials were indexed roughly from 1-100 and later dials started at "54" or "540". My understanding is that the current indexing scheme represents the station's broadcast frequency.
When did this transition occur, and why?

Back before voice broadcast was common, communications was in code. And back far in the day, spark transmitters were used that were essentially omni-frequency devices. In the early teens, it became possible to regulate wave-lengths, very broadly.

In 1919, regulations were promulgated around the early AM Band, then 600 - 1600, with higher ranges starting to get assigned to official bands (Police/Fire) and lower ranges to Air Band, taxi cabs and the like.

Starting even earlier, stations were starting to get assigned call-letters, and shortly thereafter, very broad frequency ranges and power limits. By the time that regulations started to become more efficient and more specific, manufacturers (mid-1920s, and on) started to put the frequency range on their dials, some even the station names and call-letters. Things evolved rapidly from there, with most everything (but not everything) from the late 1920s and on calibrated in frequency.

Note that the present AM band is a relatively recent development, many early AM radios did not reach past that original 1600, or so, and those that did added "Police Band" to their dial at that end, thereby getting to call themselves multi-band radios. Go figure.

Peter Wieck
Melrose Park, PA

[Jim Mueller]

Post by s***@stever.net
The recent topic about FM bands reminded me of a question that I haven't
quite been able to answer for myself.
My question revolves around the dials for AM Broadcast band.
Early radio dials were indexed roughly from 1-100 and later dials
started at "54" or "540". My understanding is that the current indexing
scheme represents the station's broadcast frequency.
When did this transition occur, and why?
Thanks!
-Steve

In the early days of broadcasting, there were only two frequencies that
were allowed for that purpose. That worked because there were so few
stations on the air and they only transmitted a few hours a day.
Stations were supposed to coordinate with the other stations on the same
frequency to prevent interference. So there was no need for frequency
markings on the dials.

Soon there came to be many more stations that wanted to broadcast more
hours so that system broke down. Stations were then assigned frequencies
(actually wavelengths) in a band, only about half of today's band. As a
result, some radios had their dials marked in wavelength while most
continued the 0 to 100 markings.

Broadcasting outgrew this system as well and more frequencies were
assigned in a new band that was only slightly smaller than the present
one. About this time, one dial radios were getting popular and dials
were frequently marked in frequency or wavelength, sometimes in both.

Later, the wavelength marks disappeared and only frequency was indicated.

[spsfman]

Post by Jim Mueller

Post by s***@stever.net
The recent topic about FM bands reminded me of a question that I haven't
quite been able to answer for myself.
My question revolves around the dials for AM Broadcast band.
Early radio dials were indexed roughly from 1-100 and later dials
started at "54" or "540". My understanding is that the current indexing
scheme represents the station's broadcast frequency.
When did this transition occur, and why?
Thanks!
-Steve

In the early days of broadcasting, there were only two frequencies that
were allowed for that purpose. That worked because there were so few
stations on the air and they only transmitted a few hours a day.
Stations were supposed to coordinate with the other stations on the same
frequency to prevent interference. So there was no need for frequency
markings on the dials.
Soon there came to be many more stations that wanted to broadcast more
hours so that system broke down. Stations were then assigned frequencies
(actually wavelengths) in a band, only about half of today's band. As a
result, some radios had their dials marked in wavelength while most
continued the 0 to 100 markings.
Broadcasting outgrew this system as well and more frequencies were
assigned in a new band that was only slightly smaller than the present
one. About this time, one dial radios were getting popular and dials
were frequently marked in frequency or wavelength, sometimes in both.
Later, the wavelength marks disappeared and only frequency was indicated.

It is therefore interesting to note that much later radios, including
real multi-band (short wave) radios included a "log" scale on the dial.
Typically it was calibrated 0-100 or some such. I guess it was useful if
you noted that say, KFI was at say 15 or so. Perhaps such notations were
more useful for intermittent overseas shortwave broadcasts. One could
note, channel 38 at 10:30 PM and/or, "BBC Ch. 45 at 11:00" to make it
easy to return to a broadcast. I guess the log number could be used,
regardless of frequency, as it would be the same dial position
regardless of band.

Sort of a useless feature in later years, but now I understand how it
evolved. And why it left.

Cheers,

D.