I receive several emails a week from interested readers. One noted that the blog seems to be focused on RF. Yes, that is what I do most, but the company does studio installs as well.
This was from a few years ago.
WDST moved out of their Bearsville studio location into the former Methodist Church in West Hurley.
WDST Studios, West Hurley, New York
We installed a new SAS audio router and console system.
Eaton UPS powers rack room and studiosSmall Rack Room for NextGen servers and STL equipmentAir Studio, Under ConstructionRack RoomEthernet Patch PanelOffice areaLive Performance StageRack RoomBack of the racksWDST Air StudioWDST Production Studio
Pictures of their old Bearsville studio can be found here:
I Finished up this installation of a J-1000 in Brookfield, Connecticut for Nossa Radio. That is a Portuguese broadcaster that owns three other stations in the US.
WINE 940 KHz Brookfield, CT
These Nautels are fairly simple affairs; a controller and two RF amps with incumbent power supplies.
Nautel AM-RF and AC mains surge suppressor
Be sure to install the surge suppressor that comes with the transmitter.
The J-1000 is replacing the 43-year-old Harris MW-1A which will function as a backup. Like all new transmitter installations; some things must be done to complete the job.
Harris MW1A
Harmonic measurements out to about the 5th or 6th harmonic need to be documented and compliant with NRSC-2 (AM mask requirements). Although NRSC-2 measurements are required, I don’t see how they can enforce that specification after AM HD radio came into being. Nevertheless, it was measured and passed. With the station carrier power of 680 watts, I used the RF monitor port on the back of the transmitter to make the measurement. Otherwise, I would need to find an empty field somewhere 1 KM away and stand in the middle of it to reduce all of the electrical noise.
Spectrum Mask from a Spectrum Analyzer
The NRSC-2 mask is mainly a function of High-Frequency limitation in the audio processor—certain transmitters, like the aforementioned MW1A did make some contributions to out-of-tolerance measurements.
NRSC-2C AM mask requirementsHarmonics measurementsWINE folded unipole feed point
The antenna is a skirted tower that has many other services colocated on it. At the top is WRKI.
WINE ATUWINE daytime coverage map
Driving away from this site, I would have to agree with the predicted contour map above, at least on the highway. I think it may be a bit different driving around in town.
One of the many projects we are currently finishing up. Over-The-Air TV is making a comeback.
A few things about LPTV; These stations usually have an ERP of 15 KW or less, and they are a secondary service, like FM translators, which a full-power TV station can displace.
Alive Telecom ATC-BCE48BB-V3-31 UHF slot antenna
This is an ATT microwave site built in 1977 according to county records. This may have been one of those VHF Mobile Telephone sites which existed before cellular telephone systems. ATT owned it until 2022 when it was sold to a private business.
This station is on channel 31 or 575 MHz center frequency. UHF TV stations often use slot antennas, which have gobs of gain. Slot antennas are simple designs that have a broad bandwidth and until recently were mostly horizontally polarized. This particular antenna is elliptically polarized which is becoming more common as TV providers are looking at mobile video applications.
WZPK 20 MHz VSWR sweepWZPK 20 MHz return loss
Example of UHF slot antenna with Radome cover removed
Slot antennas are the inverse of a dipole antenna. A dipole is two conductive poles approximately 1/2 wavelength surrounded by free space whereas a slot antenna is 1/2 wavelength of free space surrounded by a conductive plane. The width of the slot determines the bandwidth of the antenna. Radiation from a dipole is in the plane of the two poles versus the radiation from a slot that is perpendicular to the slot. At UHF frequencies, many slots are placed on the radiating plane, giving large gain figures.
Transmitter rack with 6-pole Comtech mask filter
All TV transmitters require a bandpass or mask filter. This is to keep out-of-band emissions out of the tightly packed TV spectrum.
S11 return loss, looking at the antenna through the mask filterPost-mask filter channel bandwidth
These filters need to attenuate the upper and lower shoulders of the digital carrier by 46dB +/- 3.25 MHz from the center frequency.
Comtech 6 pole UHF TV mask filter
These are fairly straightforward filters, this one has six cavities with plungers that slide in and out to adjust the tuning. I watched one of these get retuned in the field, it takes quite a bit of time and patience to complete and requires a two-port network analyzer.
400-watt UHF amplifier, exciter, and IT gear; WZPK-LD
With the TPO of 400 watts, the ERP is 4.7 KW horizontal and 2.35 KW vertical.
Longley Rice coverage map; green is easy indoor, yellow is outdoor, red is difficult outdoor antenna
So, why bother with all of this? Indeed that is a good question. As cable companies continue to raise their rates (the average cable TV bill is $250 or so) people are looking for alternatives. Cord cutting is a thing and OTA (over-the-air) TV as well as OTT (over-the-top or direct streaming) are popular alternatives.
UHF “Bow Tie” consumer TV antenna
This station will run France 24 English service and NASA TV to start. Other things you can find on Low Power TV stations; Heartland (mostly country music with some cooking shows mixed in), Retro (old movies), Rewind TV (Old TV shows), Buzzr (old game shows), Court TV, Weather Nation, News Net, etc. More information on OTA TV networks can be found here: https://en.wikipedia.org/wiki/List_of_United_States_over-the-air_television_networks
This thing is on the air! There are still some tidying-up things to finish, but it is up and running and sounds great! Here are some pictures of various stages of the installation work:
Making harmonic measurements
The filing cabinets hold manuals and spare parts. There is not a lot of room left in this building, so workspace is at a premium. The filing cabinet on the left needs some Windex and elbow grease.
Main disconnect and conduit to 400-volt transformerOutdoor coolant run3/0 cables, 240-volt input to Hammond HPS Sentinal K transformer
The transformer does not have a neutral reference to the power company. The neutral for the transmitter is derived from the Y output connection. The transformer is also designed to suppress harmonics from non-linear loads like switching power supplies.
Wiring in Square D I line panelSquare D I-line panel rated for 600 volts#2 SOOW cable feeding upper and lower sections of transmitterWiring to disconnect switch on transmitterPump station during system fillHeat exchanger
The wiring on the pump station and heat exchanger needs a little more work. The client wanted to get this on the air as soon as possible because they are in a book and were running at 50% power. Once things calm down a bit, I will put the backup transmitter on for an afternoon and properly dress the wires.
FM modulation analysis
I found this FM modulation analysis function on my spectrum analyzer very useful. The station deviates slightly more than the allocated 75 KHz because of a subcarrier. Overall, it looks good. I measured the harmonics out to the 10th harmonic, most of them were in the noise floor. A few made a slight appearance, but well within FCC tolerances. It is important to document this, as this site has colocated cellular carriers and several E911 services.
FCC part 73.317 states:
(d) Any emission appearing on a frequency removed from the carrier by more than 600 kHz must be attenuated at least 43 + 10 Log10 (Power, in watts) dB below the level of the unmodulated carrier, or 80 dB, whichever is the lesser attenuation.
47CFR 73.317
WHUD fundamentalWHUD fundamental with two Mini-Circuits NHP-200 high pass filters installed
The rest of the harmonics were measured down to -130 dB with the two NHP-200 high-pass filters in the circuit. The 3rd, 4th, 5th, 6th, and 8th harmonics were unmeasurable. The 8th, 9th, and 10th made slight appearances.
WHUD 6th Harmonic, noise floorWHUD 8th harmonic makes a little appearanceMain antenna VSWRAntenna VSWR according to the transmitter directional coupler
Pretty close, the VNA was inserted at a patch panel, which is the last thing before the transmission line leaves the building. The transmitter goes through an ERI switchless combiner, which probably gives it a slightly better load.
Backup antenna SWR
Aside from the finishing details, I need to keep an eye on this for a week or so and top off the Heat Transfer Fluid as needed. It takes a bit of time to get all of the air out of the coolant loop. Another thing; the operating pressure on this is 4 Bar, which is almost 60 PSI. That is higher than other liquid-cooled transmitter systems I have installed before.
