WDIV TV Operating On Stand-By Antenna

[jimh]

I notice there are several threads concerning problems in reception of WDIV in the past few months. One possible cause is the switch at WDIV to their stand-by antenna for an extended length of time around August, September, and November 2025.

WDIV transmits on Channel 32 (578 to 584-MHz). Their normal or main antenna is at an elevation of 1,008-feet, and authorized power is 720-kW Elliptical, with 215.6 kW in the vertical plane and 504.4 kW in the Horizontal plane. The radiation pattern maxima are approximately at NW (687-kW), NE (720-kW), and SW (720-kW), with a significant power reduction to the general SE with a minimum power as low as 245-kW. This is because their service area ends at the Canadian border located about 12-miles to the southeast of the transmitter.

The auxiliary antenna is lower, at 831-feet, and is authorized for 1,000-kW ERP, all in the horizontal plane. The main lobes of the auxiliary antenna are still in the NW, NW, and SW, but the power in the SE direction (toward the city of Detroit and Canada) is very much reduced, with some nulls down to only 36 to 50-kW ERP.

When operating on the auxiliary antenna, reception in the area SE of the antenna was affected by both the loss of all vertical plane radiation and a reduction to as little as 36-kW ERP.

More details can be found at

https://www.rabbitears.info/market.php? ... y_id=53114

Operation on the auxiliary antenna for an extended period of time was due to a failure of the transmission line for the main antenna. This transmission line is about 1,200-feet long and dates from c.1999, when the main antenna on the top of the tower was changed to a UHF antenna for the new allocation on Channel 45 for the new digital ATS 1.0 signal.

Historical Antennas at WWJ-TV and WDIV-TV

The first television transmissions from WWJ-TV originated from the top of the Penobscot Building in downtown Detroit, using a two-bay antenna and a 5-kW Dumont transmitter.

In c.1954 WWJ-TV moved its transmitter site to Southfield where a new transmitter building and 1,000-foot tower were erected, and began transmitting on Channel 4 (67.25-MHz) with a 6-Bay RCA Super Turnstile array, providing a horizontally polarized radiated signal at 100-kW ERP. This antenna was in use for about 33-years. There were occasional problems with the antenna, mostly occurring at the "feed straps", where the coaxial hard-line phasing lines terminated and were physically strapped onto the radiating elements of the bat wings. These straps would burn off, resulting in one half of one of the six antenna bays not getting any power, and upsetting the antenna's radiation pattern. Curiously, when this occurred the problem was often detected when viewers who were rather close to the tower called to complain about poor reception. More distant viewers seldom were affected by this problem.

Around 1987, the RCA Super Turnstile was replaced with an RCA-designed Dielectric-brand circularly polarized antenna, still operating on Channel 4, but now with circular polarization, and still fed by the original transmission line. Using circular polarization helped in the more urban areas of downtown Detroit, but I doubt many viewers had circularly polarized antennas. In actual fact, at the studio location in downtown, the only way WWJ-TV/WDIV could receive a stable signal off-air downtown was to use a rather large commerical-grade circularly-polarized antenna on a tall tower on the roof of a five-story parking garage building.

The big change in antennas occurred in April 1999, when (now) WDIV prepared to switch to ATS 1.0 digital television, which would be transmitted on Channel 45 using elliptical polarization. In order to reduce transmission line loss over the approximately 1,200 feet of line, a new and larger rigid transmission line (8-3/16-inch diameter) was installed. I don't recall the exact authorized power, but accounting for antenna gain, transmission, line loss, and power output at the transmitter, a choice was going to be made whether a two-cabinet (dual final amplifiers with combiner) or a three-cabinet (three final amplifiers and combiner) would be ordered. To reduce costs, a decision was made to employ the two-cabinet approach, which, if each cabinet were able to produce 100-percent of their rated power output, would just make the necessary TX POWER OUT to produce the authorized ERP signal, accounting for transmission line loss and antenna gain.

The final amplifier stage in these transmitters used a klystron tube that cost about $40,000 (in c.2000 prices), and burning out a final tube was thus a rather expensive operating and maintenance cost. Another problem with the transmitter was running it at absolute maximum power tended to be slightly unstable, contributing to much-too-frequent shut down of a cabinet and attendant loss of ERP in the transmitted signal. To be nice about it, this transmitter was not exactly the Rock of Gibraltar in terms of stability or reliability.

Eventually wiser technical minds were able to get authorization for the purchase of a third cabinet. This allowed the three final amplifiers to run at a more gentle power setting, down to about 66-percent of rated maximum, and the transmitter reliability improved. This transmitter was quite a beast to observe in operation, as it ran with about 37,000 Volts on the final tubes and used an enormous volume of forced air cooling to handle the heat it was generating.

The final antenna and transmitter evolution (still in use today) was in c.2020 when the UHF TV band was "re-packed", resulting in WDIV-TV moving down to Channel 35. This change required getting an entirely new transmitter and new antenna. The GATESAIR ULXTE transmitter is embodied in four cabinets of multiple small-height rack-unit plug-in modules, each a separate solid-state water-cooled transmitter, with all modules and cabinets combining into the final output of about 50-kW. The transmitter operates more or less silently due to the water cooling, and individual modules could be hot-swapped in case of a fault in one module.

With the new transmitter and its drastically different approach to producing RF power at UHF frequencies than that old three-cabinet beast, the transmitter became a much less maintenance-intensive operation, which eventually likely led to some other aspects of the plant getting less oversight than they probably needed, such as the monitoring of the nitrogen-gas pressure and humidity in that giant 8-3/16-inch rigid 1,200-foot transmission line.

By 2025 the transmission line was about 26-years-old, and perhaps not unexpectedly was no longer quite as well sealed as it was when new. At some point, lack of de-humidified nitrogen gas and perhaps a leaking seal to two (or three or four) lead to failure of the transmission line. This was the proximate cause of the long-duration operation at WDIV on their auxiliary antenna.

The process of replacing a long, high-power, rigid transmission line composed of very big, very heavy, solid copper flanged tubes of length of not more than 25-feet, which typically need to be carefully suspended from above, sometimes on spring-tensioned supports, is not something done easily or quickly. And getting the proper and qualified installers to do the work on a 1,000-foot tower is also something that needs careful scheduling. I suspect that these factors contributed to the delays.

The new transmission line is only 6-1/8-inch rigid line, resulting in more transmission line loss than the previous (larger diameter and lower loss) line. In order to met the licensed ERP, the transmitter power output was increased.

More details about the present antenna and transmitter operation using the new transmission line can be found in an FCC technical filing, available for download from the FCC at:

https://enterpriseefiling.fcc.gov/datae ... 8fea21194d

The above document is dated November 18, 2025, which probably indicates the approximate time when the replacement transmission line was installed, ready for service, and the main antenna was back in use.

Also interesting to note: the initial 8-3/16 diameter rigid transmission line used when changing to a UHF channel and the subsequent replacement 6-1/8-inch rigid transmission line were both 75-Ohm impedance, not the usual 50-Ohm (or 52-Ohm) coaxial transmission lines. The reason for using 75-Ohm impedance transmission lines was to reduce loss, as the 75-Ohm impedance is optimized for lowest loss, whereas 50-Ohm lines are generally chosen as a compromise between lower-loss and higher-power-handling capacity. With the 75-Ohm transmission line choice, I suspect that the transmitter output tuning and the antenna input impedance were also changed to 75-Ohms, in order to prevent generation of standing waves on the transmission line due to impedance mismatch at the antenna. Standing waves on the transmission line cause an increase in loss and also produce reflected signals that arrive delayed, similar to multi-path reception problems.

[km1125]

Very interesting!! Thanks for posting!

[hb2]

Very interesting indeed

https://youtu.be/ODUtaDhn7lo?si=GEMyXw2HcDO4Eo-3
https://youtu.be/3Gs8YI31J2M?si=DCdE4P1ONEVai2b1

These 2 videos document a similar situation that happened to an FM station in Nashville. Videos are done on helmet cam and work involved replacing only one segment of rigid feedline, not the whole line.

I know it isn't TV but you can kinda get an idea of the work they did on the WDIV tower except from the sounds of it this was a full transmitter to antenna rebuild of the whole feedline.

(I am not related to nor am I endorsing this Youtube creator, I am linking the videos just for entertainment/education in regards to this field and it's relevance to this topic)

Edit: fix typo

[Plate Cap]

Very interesting post, jimh. Such a breath of fresh air and a return to the past from the usual silliness posted on this site.

[hb2]

I just happened to pull up google street view of the WDIV tower from Greenfield rd NB and you can actually see the crew on the tower working. They appear to have a service elevator inside the tower raised to position and a worker box hanging on the outside of the tower nearly adjacent to the elevator. When the sstreet view image was taken they are inside of the second white paint section counting up from the ground. Google dated it as 'September 2025' which would align with both what was mentioned by the original post regarding backup antenna usage and roughly when other users complained about weak signal issues on 97.1 whose main antenna is also located on this tower.

https://maps.app.goo.gl/Xy8K6cqvRtpk369D6
Edit: found another view of them from along Lincoln dr. Note the piece of presumably old conduit hanging off side of tower.
https://maps.app.goo.gl/eQtbwoV3HTSQsJRx6?g_st=ac

[billmich88888]

this is a wonderful thread!!!!!!!

[jimh]

Regarding the tower structure at WWJ-TV/WDIV:

The 1,000-foot tower is a monster. It is a Blaw-Knox triangular section tower that is 14-feet on each face. There is an internal elevator that rises from about 80-feet to the 900-foot level. The vertical structural members of the tower are not tubular, but are solid rounds. The bottom section verticals are about 8 to 10 inch diameter; the upper tower sections use smaller diameter. At the base, the three vertical members slant inward, and the entire load of the tower weight and significant downward compression force of the guy strands is transmitted to the foundation via a single ball mount point.

When first erected (c.1954) there were guy wires at only three levels: 300, 600, and 900-feet. In addition to the main TV antenna, there were many others, such as the NOAA Weather Broadcast Service station KEC-63, auxiliary broadcast antennas for TV, the WWJ-FM antennas, and microwave Studio-to-Transmiter link antennas. When “electronic news gathering” began in the 1980’s, a large steerable microwave tracking antenna was added for helicopter-transmission. At some point the added wind loading on the tower required that more guy levels be added, so currently there are new guys levels in the intermediate levels between the original levels.

Having an elevator to 900-feet has made working on the antenna much easier, as it avoids having to make a 900-foot vertical climb and later descent—a task that only very fit individuals could accomplish. I have been up to the work platform at 900-feet via the elevator, and the perspective is quite impressive. Looking downward the tower narrows into a vanishing point. But the sensation is more like being atop a very tall building rather than hanging onto a guyed tower. As for the next 100-feet of unassisted climb to reach the beacon lamp at the very top—that was something I would never try.

Legend has it the tower was specified to be so massively constructed was because in c.1952 television broadcasting was in its infancy, and there was some speculation that perhaps as the population grew and cities expanded outward, antenna heights for TV stations might be increased to extend the coverage area. Accordingly, The Evening News Association (who published The Detroit News newspaper and were the licensee of WWJ-AM/FM/TV at that time) wanted to be able to add additional tower height, should there be a future authorization to expand coverage.

Also interesting to note: the initial aural power for a 100-kW ERP low-VHF TV signal could be as high as 50-percent of the visual power, so the aural carrier could be as much as 50-kW ERP. In actual practice many stations found that the minimum power of 10-percent was sufficient, as otherwise the reception range of the aural carrier would exceed that of the visual carrier. At WWJ-TV the aural power was reduced to 10-kW ERP. With about 6 dB antenna gain, the actual aural power needed at the antenna input was only 2.5 kW. Allowing for transmission line loss, combiner loss, and filter loss, at the transmitter perhaps about 3-kW would be necessary. The WWJ TV General Electric TV transmitter aural final stage (that could produce almost 10-kW output) was deactivated, and the intermediate plate amplifier stage was routed to the antenna instead. The IPA final was a pair of Eimac 4-1000 power beam tetrodes. To produce the necessary output power of about 3-kW at 71.75-MHz of Class-C FM modulated carrier the tubes had to be run quite hard. They required frequent replacement. The used 4-1000 tubes taken out of VHF TV service often found their way into home-brew final amplifiers of local amateur radio stations. The original G.E TV transmitter was still being used into the 1980’s, but eventually it was removed along with the “operator’s console” (as the operator was also eliminated), so the stream of good used 4-1000 tubes available to radio amateurs dried up with that change.

[jimh]

I just happened to pull up google street view of the WDIV tower from Greenfield rd NB and you can actually see the crew on the tower working...

That is very good investigating. I was out of town all during the transmission line replacement project, else I would have gone to the transmitter site and gotten some better views.

[MWmetalhead]

Given its status as a VHF-lo station, the lack of "noise" on WDIV's analog signal was impressive to me.

WDIV always came in much more cleanly using rabbit ears than WJBK.

Even in Ann Arbor, WDIV reception was fairly good. WJBK meanwhile always had silver colored lines dancing across the screen and some minor "snow."

[jimh]

WDIV always came in much more cleanly using rabbit ears than WJBK.

The change at WDIV to circular polarization in c.1987 would likely have improved reception on rabbit-ear antenna.

They are still using ellipical polarization with their present ATS 1.0 digital signal.