@richardpowers This probably goes to Rich Powers, but anyone is welcome to answer... As I know it the original AM band ended at 1500kHz. On what date was the band extended to 1600kHz? On what date was the X-Band added, up to 1700kHz?
Well.. I hesitate to answer off the top of my head, but I think they expanded to 550 in 1938 coinciding with the creation of part 15. I know Halstead was broadcasting 550 from the George Washington bridge in 1940 and some articles said to tune your radio "to the top of the dial" to receive it.
But somehow that doesnt sound right. Seems it expanded to 1500 later in the 1940s and 1600 in the 1950s, then to 1700 about 20 years ago...
I shouldn't even be trying to answer without looking.. I'm just not certain know off the top my head and dont feel like digging out the facts at the moment.
In fact, just ignore this answer altogether..
This should answer Carl's question:
http://earlyradiohistory.us/buildbcb.htm
https://en.wikipedia.org/wiki/AM_expanded_band
@mark Wow.. that's some in depth history that guy wrote.. but it's not going answer any of Carl's questions.
I knew something didnt sound right in my response, the correct answer appears to be found at https://www.oldradio.com/current/bc_am.htm
The Growth of the Standard Broadcast Band
- The Standard Broadcast Band began in 1921 with just one frequency (833 kHz).
- In December 1921, 619 kHz was added for Weather and Market reports.
- In September 1922, 750 kHz was added as a new "Entertainment" frequency.
- On May 15, 1923, the Standard Broadcast Band was expanded to 550-1360 kHz using 10 kHz steps.
- In April 1925, this was further expanded to 550-1500 kHz.
- November 11, 1928 saw the first big "realignment" as the FRC shifted many stations, and deleted others, in an attempt to reduce interference.
- On March 29, 1941, the band was extended to 550-1600 kHz. On this date, the NARBA frequency shift changed many stations spot on the dial.
- In the early 1950s, the band was extended to 540-1600 kHz. The first 540 was
WGTH, Richmond, VA. A CP was granted for 540 on 12/17/53, with a License to cover on 5/21/54. - In mid-1961, most Class IV stations were permitted to increase power from 250 Watts to 1/.25 kW.
- In 1983, most Class IV stations were permitted to increase power from 1/.25 kW to 1 kW.
- In 1995, the FCC again extended the Standard Broadcast Band to 540-1700 kHz.
But something there still doesn't sound right.... I dont know what's bothering me
@richpowers Maybe the 50kW stations are not mentioned?
1050 CHUM in Toronto was in it's heyday a 50,000 watt station along with all the big boomers at night like WABC, WLS, WOWO, and many more. This was in the 60s, 70s.
@mark No, that's not what's bugging me.. I dont know, I'm probably just got some facts mixed in my head. But I not ever researched the history of the AM band, but naturally it comes into play when researching part 15. I do know in 1938 the FCC was talking about expanding the AM band -- but obviously the top of the band was not 550 then like I said.
I don't know, the topic is really outside my territory.
In the Wikipedia article on the subject, even Part 15'ers get a mention, in a indirect sort of a way. In the section for United States, directly under the sub-heading "Later Activities" -
"A 2006 accounting by Radio World reported that, out of 4,758 licensed U.S. AM stations, 56 were now operating on the expanded band.[33] The expanded band frequencies have also become popular for use by hobbyist microbroadcasting transmissions (which don't require licenses) due to the relatively limited number of broadcasting stations compared to the more congested standard/legacy AM band."
They didn't mention that a big part of why we like the higher frequencies is due to the slightly higher efficiency of our very short antennas at the top part of the band.