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jrgagne99 25-Nov-2019 1:47 PM

Transmitter Fire in VT
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I'm not sure if this is the right place to post this, but I thought it would be interesting to discuss among us all...

In the Burlington, Vermont market, the WCAX (CBS) and WPTZ (NBC) transmitter tower caught fire last week and as a result, I am currently without these two networks. Bad timing for me, since it is right in the middle of NFL football season. Here is a link to an article describing the situation:

And here is a picture of the fire:

Within three days, both stations restored service to subscription-based cable and satellite providers, I believe by putting up a temporary truck-based transmitter with enough power to be received by those companies for redistribution. But their full-power OTA broadcast is a different story. I called the stations and they currently have "no idea" how long it will be before OTA is restored and would not even take a guess at a timeline.

So my questions for forum discussion are:

1) Assuming the transmitters are completely destroyed, how long do you think it will take to replace them?

2) How long if both the transmitters and the tower itself are destroyed?

Note that the tower is on top of Mount Mansfield and the only way up there this time of year is by Snowcat (ski-slope groomer). Conditions up there are very difficult to work in, with high winds (often 70+ mph) and fog/icing conditions dominating at this time of year.

3) Also, have any of our more experienced forum members ever seen anything like this? I wonder if the fire had anything to do with WCAX's recent re-pack-related move from RF-22 to RF-20, for which I don't think they installed new transmitter hardware. I could be wrong, but I think since the new frequency was so close, they just decided to drive their existing hardware at the new lower frequency. If so, could that have caused unexpected heating that led to the fire?

jrgagne99 25-Nov-2019 3:55 PM

I just saw an update on this, it looks like it will only be a matter of days (not months) for WCAX to restore signal:

No update yet on the WPTZ antenna.

Tower Guy 25-Nov-2019 8:04 PM

Unfortunately you live in a weak signal area for WCAX. I think that they need to be at full power for you to receive them.

The antenna fire covers a good portion of the antenna itself. The repair is likely to be more extensive than the article infers. The antenna is built using 40 panels wrapped around a square spire and covered with a fiberglass radome. Obviously, the radome is heavily damaged. You can assume that a problem on one or more of the 40 panels caused the fire. It is likely that the coax going to some of the panels have melted and will need to be replaced.

In order to get back on the air a temporary antenna may be used, but it won’t have as much gain as the main antenna, and may not be able to handle all the power the transmitter can make. Another approach to getting back on the air is to use the lower half of the existing antenna using panels salvaged from the side that didn’t burn.

Hopefully the transmitters sensed a problem on the antenna and shut down before they self destructed.

I also wonder if the repack was a part of the failure, but it’s also possible that the fire was due to significant ice buildup on the antenna and the new transmitters didn’t turn the power down to compensate for the excess ice.

jrgagne99 26-Nov-2019 1:20 PM

Thanks Towerguy! A couple of follow-up questions, and I'll try to be specific in my use of the words "tower", "antenna", and "transmitter"...

1) Where did you determine the configuration of the WCAX antenna (i.e. number of panels, etc.)

2) Another article (link) states: "The remote tower, owned by WCAX, hosts antennae used by Vermont Public Radio and Vox AM/FM, but only a television antenna shared by WCAX and WPTZ appears to have been damaged."

Does this mean that the WCAX (RF-20) and WPTZ (RF-14) signals are emanating from the same collection of panels, and that the signals are simply superimposed on one another?

3) I reread the first article and it says that they elected to ignore the damaged antenna and build a separate temporary antenna. So it doesn't seem like they are salvaging panels to construct a stand-in. Regardless, am I correct to assume the temporary one will likely have much less power than the old one?

4) I also found a WCAX news segment (video) that shows them putting in a new transmitter (I think this refers to the equipment that resides inside the building), so I think the antenna up on the tower was not changed during the repack. This would seem to make sense, as there was no interruption to the WCAX or WPTZ signal during the change-over 1 month ago.

Tower Guy 26-Nov-2019 1:58 PM

I looked up the antenna type here;

The antenna listed is a Dielectric Model TUP-O4/C4SP-10/40H-2-R

This model number contains clues to the configuration of the antenna.
T Television
P Panel
04 4 sided
C4 omnidirectional
SP special configuration
10 10 panels high
40 40 total panels
H horizontally polarized
-2 dual feed line configuration
-R radome

You are right, the antenna was not changed during the repack.

Tower Guy 26-Nov-2019 2:04 PM

Yes, the transmitters for WPTZ and WCAX are combined and then sent out by the same antenna.

Tower Guy 26-Nov-2019 2:09 PM

It makes sense to use an interim antenna as the main antenna can be repaired. Dielectric has spare antennas in stock, and/or owners have antennas in storage as a part of the repack.

The repair of the antenna will mean removing at least 10 panels, determining if there is damage on the feeders to the panels, replacing all damaged feeders and panels, and then replacing the fiberglass radome.

jrgagne99 26-Nov-2019 3:06 PM

Before the fire, even though I'm 70+ miles away I had very good reception of WCAX and WPTZ, typically with close to 15 dB of margin on SNR. It will be interesting to see if I can get reception from whatever temporary antenna they are able to rig up, since its power is almost certainly going to be less than the original. I'm still holding out hope for watching the Patriots on WCAX (CBS) this weekend and also Sunday Night Football on WPTZ (NBC).

Towerguy, what is your WAG time-estimate for them restoring full-power? Is it true that the FCC will require them to restore the original broadcast radius as part of their license agreement? Or is there a chance that this temporary solution will eventually become the permanent solution, which would probably not be a very good outcome in terms of my reception?

jrgagne99 26-Nov-2019 5:30 PM

WCAX just posted a very interesting update on their progress, which answers some of my previously posted questions (link).

The temporary antenna is being mounted on an adjacent tower on Mount Mansfield that is currently used by the FOX and ABC affiliates. It is expected to provide coverage to "most of the same geography" as the old antenna. Shooting from the hip, I give myself 50% odds of of receiving the temporary signal. Depending on the weather, it looks like the temporary antenna will be up in a week or less. It will be used over the winter months while work on the main antenna system is impossible due to weather conditions.

As an outsider looking in, this has been a very interesting story to watch develop and very educational in terms of the various engineering details associated with bringing these pictures to our screens via OTA.

Tower Guy 26-Nov-2019 7:57 PM

The most likely antenna that can be obtained and installed is a TFU-8WB.

That antenna covers channels 14-51. It can handle 20 KW of power.
If each station runs 10 KW the effective power would be 184 KW, or about 30% of full power.

Insurance should cover the repair costs.

jrgagne99 1-Dec-2019 12:41 PM

WCAX is back on the air using the temporary antenna. No WPTZ as of yet. It is not clear to me that WPTZ will be broadcasting from the same antenna, as this hasn't been explicitly mentioned in their status updates, though the two teams are cooperating to get the work done, so it would seem logical. Singal strength (SNR) for WCAX at my location is currently 21 dB, whereas it is usually 29. So their temporary range is apparently less, but it seems we will have football for the rest of the year. Fingers crossed for WPTZ.

jrgagne99 1-Dec-2019 9:09 PM

And now WPTZ is up and running too. Presumably, both WCAX (RF-20) and WPTZ (RF-14) are broadcasting from the same (temporary) antenna. At my location, the signal strength for both is every bit as strong as it was on the old antenna.

Just in time for Sunday Night Football. Go Pats! :)

Tower Guy 2-Dec-2019 12:48 PM

WCAX/WPTZ are sharing a TFU-16WB antenna. The gain is similar to the burnt out antenna. The power handling is slightly lower. It is directional with less power toward the northeast.

jrgagne99 2-Dec-2019 2:36 PM

Thanks for sharing that document Towerguy. Some interesting information in there for sure. I will update this thread if/when I see any new information such as determination of the cause of the fire, and when the new antenna is brought back online next spring/summer.

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