The Alford Antenna

I have been doing a bit of work in this building recently.

5th Avenue Lobby, Empire State Building, New York, NY

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.

Alford Antenna, courtesy of NECRAT

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.

Circa 1936, RCA television transmitter on 85th floor, from the Early Television Museum

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.

Alford antenna name plate
Alford Antenna on my dinning room table
Alford antenna, covers removed

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.

Heating element return wire, broken off

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.

Ebay; good or bad source for test equipment?

Update: This was delivered on May 2, 2025 in good condition. It took 24 days to get here, 21 of which were sitting in Memphis. Also, it works great!

A cautionary tale.

I have purchased and sold several things through Ebay over the years. Most of the time the transactions go smoothly. The item is more or less as described and it arrives in a reasonable time period.

All good.

Recently, I saw this very nice looking Agilent E5061B Vector Network Analyzer. The price was right and it even came with this nice hard case. This is great, I need something like this for an upcoming project.

The only very small, almost too small to notice possible issue was; its in Canada. With all the trade rhetoric going around, I thought, perhaps I should look to buy something from the US. Nah, its fine, after all, it is not coming from China.

Nope.

The order went in, the seller shipped the package, it arrived in Memphis, TN and the trail goes cold after that:

I have emailed and called FedEx several times. They say, “all good, we have all the documentation we need, it will be shipped out shortly.” Last time I called, I spoke to a woman in the Philippines who’s phone cut out with every other word.

It seems probable that all international shipments are stuck in some giant FedEx terminal waiting for someone to say okay or calculate some tariff. The pessimistic view is that it has been stolen. I have lost things in transit.

I should have listened to my little voice. While the problem is not with Ebay itself, importing equipment from another country is problematic. I would advise anyone bidding on Ebay to pay close attention to the location of the item you are purchasing.

In the mean time, I still need to finish my project…

Measuring Guy Wire tension

I was watching the tower crew measure the guy tensions on this tower the other day:

AM tower

The preferred method is to use a pulling force to move the guy wire slightly off of the turnbuckle or hairpin bolt then measure that force. Hydraulic rams with a pressure gauge are used more often then not.

hydraulic ram, showing 7,000 lbs pulling force

These guy wires are called “Bridge Strand,” the bottom wire is is 7/8 and the top is 1 1/8 inches. Normally, these are tensioned to around 5 – 10% of their breaking strength at 60 degrees F. In this case, it was slightly colder so the tensions are a little bit higher. If it would have been warmer, then they would be a few percentage points lower.

A couple of videos for your viewing enjoyment:

Lower guy tension 7,400 lbs, Upper guy wire tension 10,500 lbs. Both are well within their ranges.

I love work. I can watch people do it all day.

The Pace Accelerates

Update 2: The picture above is the former side of WUPE-AM 1110 KHz, Pittsfield, MA. On March 27, 2025 the license was cancelled upon request of the owner.

Update: I decided to to a major edit to this post due to an error in the FCC’s LMS showing more stations as Licensed and Silent than there actually are. Here is a screen shot from the LMS showing most of Audacy’s AM licenses as “Licensed and Silent.”

Regarding the Audacy AM licenses, A little more research shows that they filled for MDCL on April 10th.

WFAN Licensed and Silent, MDCL applied for

Someone at the FCC must have confused “Licensed but coverage area reduced,” with “Licensed and Silent.” It is an easy mistake to make or it is some sort of late April Fools joke. They are now properly listed as “Licensed.”

There are 116 AM stations listed as licensed and silent.

As of this writing, there are 103 full power FM stations and 46 Low Power FM stations in the LMS listed as licensed and silent.

Reading various sources about AM and FM licenses being taken silent around the country. Often, after 12 months, these licenses are quietly surrendered to the FCC. I thought it would be interesting to see exactly how many stations are now deleted.

In the last 12 months the FCC has deleted:

  • 60 full power AM licenses
  • 20 full power FM licenses
  • 53 Low Power FM license
  • 28 FM translators

60 Full power AM licenses deleted in one year is a record.

Sometimes, I get the feeling that licenses that could be sold are instead surrendered because the current owner does not want new competition. Given the shrinking pool of potential advertizers, this makes a little bit of sence. This is a thing we see in American business culture, sort of the “Walmartization” of various business sectors. In other cases, the facility is in such bad shape that it would be cost prohibative to bring it back.

A few people have suggested that once a license is deleted, the allotment can be resurrected and applied for. That is not a bad idea with some caveats for AM class C, D, and FM low power stations. If there is any loosening of broadcast regulation, particularly in AM antenna design, community coverage contours, city of license requirements, and so on, then this could be a way to get more interest in the AM band.