History question, re:DAs

[w9wi]

OK, so it's reasonably well-known in the industry that the first DA was installed at WSUN in Florida in 1927, to protect WTMJ-620 Milwaukee.

A number of history sites have mentioned WLW had to install a second tower in the mid-1930s to null its 500,000-watt signal towards Toronto, where CFRB - then on 690 - was complaining about adjacent-channel interference. The context suggests that DAs were still quite rare at the time.

I've never seen an early station listing - nothing earlier than 1966 - that indicates which stations used DAs. I see earlier listings that seem unlikely without the use of DAs - for example, St. Paul and Washington were both already 50,000 watts on 1500 in 1942. Even on regional channels, the listed 5kw night power of WISN-1150, Milwaukee, seems unlikely to have coexisted with KSAL Salina, Kansas and WAPO Chattanooga (both 1kw night power) without DAs.

So the question is...

When did directional antennas become commonplace among AM stations?

[Deep Thought]

Check out the 1940 Report to Congress, page 52...

http://www.fcc.gov/ftp/Bureaus/Mass_Med ... s/1940.pdf

Here's a table indicating the number of DAs for the previous eight years, taken from that report...

The FCC started encouraging them about this time.

[R. Fry]

OK, so it's reasonably well-known in the industry that the first DA was installed at WSUN in Florida in 1927, to protect WTMJ-620 Milwaukee.

Dr. George H. Brown (RCA - Princeton) states in his autobiography and part of which I was that WFLA in Clearwater, FL started using a directional antenna system on 620 kHz in 1931, to protect WTMJ at night. He wrote that it was designed by Raymond Wilmotte, and was the first DA used by a commercial AM broadcast station in the US.

When did directional antennas become commonplace among AM stations?

Brown's book has an entire chapter on DAs he designed in the 1930s, including one for WLW in 1934 to reduce interference to a Canadian station on an adjacent channel when WLW was operating at 500 kW non-D.

Probably DAs could not be considered as commonplace in the 1930s, but they did exist then.
//

[K9EZ]

OK, so it's reasonably well-known in the industry that the first DA was installed at WSUN in Florida in 1927, to protect WTMJ-620 Milwaukee.

A number of history sites have mentioned WLW had to install a second tower in the mid-1930s to null its 500,000-watt signal towards Toronto, where CFRB - then on 690 - was complaining about adjacent-channel interference. The context suggests that DAs were still quite rare at the time.

I've never seen an early station listing - nothing earlier than 1966 - that indicates which stations used DAs. I see earlier listings that seem unlikely without the use of DAs - for example, St. Paul and Washington were both already 50,000 watts on 1500 in 1942. Even on regional channels, the listed 5kw night power of WISN-1150, Milwaukee, seems unlikely to have coexisted with KSAL Salina, Kansas and WAPO Chattanooga (both 1kw night power) without DAs.

So the question is...

When did directional antennas become commonplace among AM stations?

I thought that WLW installed a wire to give some directionality to their night signal.

[w9wi]

Check out the 1940 Report to Congress, page 52...

http://www.fcc.gov/ftp/Bureaus/Mass_Med ... s/1940.pdf

Here's a table indicating the number of DAs for the previous eight years, taken from that report...

48966116.jpg

The FCC started encouraging them about this time.

Most interesting. (wondered why I'd never read that, until I realized how big the PDF is. We're broadband-challenged up here... it was well worth the download time...)

Given the fair number of DAs operating by then, it's interesting that few if any station lists note *which* stations were using DAs. The lists I've seen after 1930 or so all seem to be printed by private interests for the benefit of DXers, who you'd think would care whether a given target was beaming at them or not.

[Shane]

One of the major reference's for DXers up to the 50's - and even into the 70's - was White's Radio Log which never listed anything but calls, COL, daytime power, and whether daytime only or not.

Is there yet any place that lists all the permutations of AM radio station assignments including PSRA/PSSA authorizations? The only place I have found those PSRA/PSSA auth's is by digging through individual station records on fcc.gov.

[Dale H. Cook]

Check out the 1940 Report to Congress, page 52...
The FCC started encouraging them about this time.

That was because the theory of directional antenna systems was then on a firm theoretical basis. Dr. George H. Brown's article "Directional Antennas" was published in January, 1937 (Proceedings of the IRE, 25:78-145).

[ai4i]

A similar and related question might be, When did AM stations transition from horizontal to vertical polarity? Early stations liked to suspend wires between towers and I think the few cars of the day that had radios, placed horizontal antenna wires under the running boards. I would assume that transitioning to telescopic (or at least solid) whips happened concurrently?

[rockmanac]

I think the few cars of the day that had radios, placed horizontal antenna wires under the running boards.

I swear that I remember them using the metal roof for the antenna. Been awhile, though, since I was at the Motorola museum on their campus in Schaumburg, IL. (6th grade field trip. Is the museum even still there anymore?)

-Adam