The Nautel J-1000

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 requirements
Harmonics measurements
WINE folded unipole feed point

The antenna is a skirted tower that has many other services colocated on it. At the top is WRKI.

WINE 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.

Another Low Power TV installation

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 sweep
WZPK 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 filter
Post-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:

Rabbit Ears has a good signal search page if you are interested in OTA TV:

More information on Low Power TV (or Local Power TV) and be found here:

For a sometimes interesting discussion on cord cutting in general, try this:

A brief note

My apologies for the lack of posts; I have been extremely busy with the end-of-year business administration things; contracts to renew, taxes to file, new business to acquire, etc. A few projects are going on but nothing exciting or blog-worthy.

There are a few things in the works that when finished, would make some interesting material. In the meantime, feel free to rummage through the older posts.

Measuring FM Harmonics

Anytime a new transmitter is installed or major changes to an FM transmission system are implemented, the performance measurements described in FCC 73.317 should be completed to ensure no interference to other radio services. This is becoming a larger issue with the advent of LTE and 5G mobile data. These services along with E911 and other mobile services are often co-located at FM transmitter sites.

The FCC stipulates that emissions removed from the carrier by more than 600 KHz must be attenuated 80 dB below the carrier. These days, that is not enough. We have had issues with older tube-type transmitters interfering with cellular and mobile data service, even though they met or were far below the FCC specification. The first in, first out rule also didn’t seem to matter either. Those mobile phone providers paid a lot of money when they purchased chunks of RF spectrum at auction, and the FCC will side with them if there is any dispute.

Having a record of measurements that show compliance with the FCC regulations can go a long way in heading off any future problems. I make measurements out to the 10th harmonic.

To get the best results, I have been using a couple of high-pass filters from Mini-circuits.

Mini-Circuits NHP-200+

These attenuate the carrier power seen by the spectrum analyzer by approximately 90 dB depending on the frequency. That allows the instrument noise floor to be lowered to -130 dB which should be well below any receiver noise floor being used by other wireless services.

100.7 MHz no HPF
100.7 with two HPF-200+ High Pass Filters

The carrier is attenuated by 92.44 dB. The rest of the measurements are made with the attenuation set to zero and the preamp turned on. For the lowest FM frequency, 88.1 MHz, the filters are on the edge of their shoulder at the 2nd harmonic. I measured the return loss and found that they matched the manufacturer’s datasheet.

Mini-circuits HPF-200+ X 2, 176 – 216 MHz S21 Return loss

That loss is counted as attenuation for the second harmonic. For the rest of the harmonics, I used 0.5 dB attenuation, which represents connector loss. I could have also measured the cable loss at each harmonic, but that seems unnecessary, given several of the readings were below the noise floor.

To speed things along, I made this handy Excel spreadsheet, which does all of the calculations for me:

FM harmonics spreadsheet

A copy of that spreadsheet can be downloaded: FM Harmonic template

Once completed, I printed a copy and put it with the station maintenance log at the transmitter site.