At this time Charles Herrold was operating station 6XF in San Jose, California, under an experimental licence.
San Jose Mercury Herald, May 3, 1921, page 4:


Herrold  Station  Announces  Radio  Telephony  Programs  to  Be  Given.

    Tripping the light fantastic to strains of the latest jazz records transmitted by radio telephony may become quite a common thing in Santa Clara county. Approximately 750 owners of radio telephone sets in Santa Clara county last night listened in to a program given via wireless telephone in the Herrold college of engineering and radio located at 467 North First street. This institution, the oldest radio school in the United States, announces that the programs, to included classical as well as dance music, will be given semi-weekly.
    The Herrold school, which conducts a radio laboratory and experimental station, manufactures sets and improved radio appliances and handles any and all standard radio equipment on the market, recently sold to St. Joseph's high school a wireless outfit capable of tuning into any wave meter known, the set marking a great improvement in the radio world as formerly it was necessary to use two and three sets to cover the entire field.

Experiments  Conducted.

    The school is now conducting experiments with a coil aerial or direction finder, which in the concrete is a radio compass, to aid in plotting on a map the point from whence a signal is sent. This coil is now being used around the bay territory for the purpose of leading ships in and out of the harbor without the aid of lighthouses, and the experiments are for the purpose of improving the coil, the same being in the hands of a patent attorney.
    Just recently a squirrel cage aerial, which consists of the wire placed vertically around the pole instead of horizontally between two poles, has been installed on top of the building, and has been found more powerful than the old style ones.

Turns  Out  Many  Operators.

    The Herrold school, organized in 1909 by Charles D. Herrold, has turned out about 1200 operators and put 130 into the military service during the war. At one time practically all of the chief men in the twelfth naval district, which takes in Great Hill and Pearl Harbor, were Herrold graduates.
    Associated with Mr. Herrold is Robert J. Stull, the first graduate of the school, who wrote a thesis on radio telephony in 1916 which because of its thorough treatment of the subject resulted in much praise for the author.
    The Herrold school announces that the radio telephony programs will be given Monday and Thursday nights of each week. The numbers may be heard within a radius of from 100 to 200 miles. Records for the program will be furnished by J. A. Kerwin of 84 East Santa Clara street, dealer in phonographs.