I have been doing a bit of work in this building recently.
Therefore, when I saw the opportunity to acquire a piece of NYC radio history, I took it. The SBE Ennes Workshops are designed to bring affordable education to the Broadcast Engineering community. One major problem in the Broadcast Engineering field is the aging workforce. Any resource that can spur interest by younger people is important. Named after Harold E. Ennes, the Ennes Educational Foundation Trust funds scholarships, workshops, seminars, and helps underwrite the costs of producing text books. Making a donation by bidding on an element of the Alford antenna was an easy decision.
The Alford antenna was manufactured and installed in 1965 on the 102 story observation deck of the Empire State Building. It was designed by Andrew Alford, an electrical engineer, who designed antennas for ILS and VOR aviation navigation systems. It is the first purpose build combined FM master antenna system in the world. Both the antenna and combiner system were novel ideas at the time.
The master antenna was becoming a necessity because the spire and tower on top of the Empire State building had become over crowded with FM and TV antennas. In the 1931, RCA/NBC leased the 85th floor of the ESB for their development laboratory.
Once both services became commercial, the FCC forced RCA/NBC to allow other FM and TV stations to locate on the building.
According to the IEEE paper written about it, the idea of a master antenna came about in 1959. It was not until the mid 1960’s that the first three stations agreed to the idea.
The requirements for the new antenna included:
1) System should accept the output of seventeen different FM station transmitters at a power level of 10 kW each.
2) The antenna should radiate an essentially omnidirectional signal in both horizontal and vertical polarizations in approximately equal amounts.
3) The antenna gain and multiplexer losses should be such that each station can achieve an ERP of approximately 5.5 kW in both polarizations (the maximum power presently authorized by the FCC for that height above ground and that location).
4) The antenna system should be well matched over the entire frequency band from at least 92 to 108 MHz and preferably from 88to 108 MHz.
5) The external portions of the antenna should be deiced.
6) System VSWR should be 1.1 or less at each station’s input over a 200 kHz band centered at each station’s carrier frequency.
7) Isolation between antenna and other antennas on building should be at least 40 dB.
8) Isolation between FM transmitters connected to the system should be at least 40 dB for adjacent FM carrier frequencies and at least 36 dB for non-adjacent FM carrier frequencies.
9) The frequency-phase characteristic of the system as measured at each station’s input should be linear within ±50 throughout a 200 kHz band centered at each station’s carrier frequency.
10) System should allow for any number of stations to participate at the beginning and should allow for additional stations to be added from time to time as required up to a maximum of seventeen in any arbitrary order of carrier frequencies.
IEEE TRANSACTIONS ON BROADCASTING, VOL. BC-13, NO. 3, JULY 1967, The Empire State Building Master FM Antenna.
That article is an interesting read.
This is one of 32 elements of that antenna. It was in position 10L, according to the name plate. Date of manufacture was 7-65. It is 81.28 x 139.7 x 13.9 cm (32 x 55 x 5.5 inches) and weighs about 45 KG (100 lbs). The RF input is 1 5/8 inch EIA flange, located in the middle of the mounting plate.
Of course, the covers had to come off so I could see what was inside. The antenna is cast from non-magnetic (AKA stainless) steel. The elements were installed with the covers down, as they are not water proof and have weep holes to allow condensation to drain out of the element.
Inside contains the resistance heating element. Interestingly, the return wire for the element is tied to ground and does not have an insulated path to neutral. Each return wire was burned open, meaning that at least this antenna element had no heaters. In the northeast, that will certainly lead to problems.
I wonder if that was one of the reasons to replace it with a new master antenna. Other reasons would be that newer antennas have better circular polarization, more even signal pattern giving better reception, better gain characteristics, better combining systems with more isolation and the ability to pass HD Radio side bands, etc.
No doubt, this antenna section will end up in my radio room, but I am still working on how I will display this interesting piece.
