tech stuff – Page 24 – Engineering Radio

The curious case of the WKZE Notice Of Violation

On June 19th, WKZE received a notice of violation from the FCC’s New York Field office. The crux of the issue seems to be interference being generated on 784.8 MHz (WKZE 8th harmonic) to a new Verizon Wireless installation located nearby:

47 C.F.R. §73.317(a): “FM broadcast stations employing transmitters authorized after January 1, 1960, must maintain the bandwidth occupied by their emissions in accordance with the specification detailed below. FM broadcast stations employing transmitters installed or type accepted before January 1, 1960, must achieve the highest degree of compliance with these specifications practicable with their existing equipment. In either case, should harmful interference to other authorized stations occur, the licensee shall correct the problem promptly or cease operation.” The eighth harmonic of Station WKZE-FM (784.8 MHz) was causing interference to the Verizon Wireless transmitter located approximately 500 feet away.

First off, we note that the WKZE transmitter is not allegedly causing interference to a Verizon Wireless transmitter, but rather to a Verizon Wireless receiver. That may be splitting hairs, however, since the FCC is quoting a technical rules violation, they can at least get the technical language right.

A brief examination of the rest of FCC part 73.317 is in order to find the specification cited in section (a). Section (d) 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.

Since 784.8 MHz – 98.1 MHz is greater than 600 KHz, this is the section that applies to the WKZE situation. Thus, the interfering signal must be greater than -80 dBc to trigger the Notice Of Violation (NOV) from the FCC. The station ERP is 1,800 watts or +62 dBm. Measurements were made with an Agilent N992A spectrum analyzer using an LPA-1000 log periodic antenna. At a 12-foot distance away from the WKZE transmitter cabinet, the signal on 784.8 MHz was found to be -94 dBc or 0.000063 watts. At the base of the Verizon Wireless tower, the measurement was -124 dBc, or 0.000000025 watt, which is barely perceptible above the -130 dBm noise floor. There does not appear to be any violation of 47 CFR 73.317. Rather, the issue seems to be Verizon Wireless’s deployment of the 700 MHz LTE band and the use of high-gain antennas coupled with high-gain preamplifiers on frequencies that are harmonically related to broadcast stations nearby. In this particular installation, the antenna has 16 dB of gain, minus a 4.5 dB of transmission line loss into a 21 dB preamplifier before the receiver. At the output of the Verizon preamplifier, the signal on 784.8 MHz was measured at -89 dBc, which is still in compliance.

By these measurements, clearly, WKZE is not in violation of any FCC regulation. It makes one wonder, does the FCC understand its own rules? Or, is this a matter of favoritism towards a huge corporation over a small independent radio broadcaster? Is it a matter of “broadband at the expense of all others?” There are several of these broadcast to 700 MHZ LTE interference cases pending throughout the country. This could set a dangerous precedent for broadcasters and other RF spectrum users as wireless giants like Verizon throw their weight around and eye even more spectrum to press into broadband service.

Commlaw blog has a good post on this subject: Harmonic Convergence?

Update: The response from the WKZE attorney can be found here, including the above-mentioned actual measurements.

HAARP Facility OTA

Operation of the High-Frequency Active Auroral Research Program (HAARP) array in Gakona Alaska has ceased due to a lack of funds. I can imagine that would put a damper on things. According to this article from the ARRL website:

The proximate cause of HAARP’s early May shutdown was less fiscal than environmental, (James) Keeney said. As he explained it, the diesel generators on site no longer pass Clean Air Act muster. Repairing them to meet EPA standards will run $800,000. Beyond that, he said, it costs $300,000 a month just to keep the facility open and $500,000 to run it at full capacity for 10 days.

Which, ouch! It looks like they generate all their own power on-site with diesel generators, which is not inexpensive. Still, it is an interesting-looking facility and it would be fun to poke around a bit. As the above-quoted article says, the site will likely be bulldozed unless some other funding to operate the array is found.

As a result of this, I fully expect that there will be no more hurricanes, earthquakes, tsunamis, tornadoes, and so on.

Servicing the UPS

A client of ours, WDST in Woodstock, NY, has this Best FE7KVA UPS. This unit is several years old and has already been through a couple of battery replacements. These are good units, however, Best Power has been bought up by Eaton/Powerware and they are ~~no longer made~~ apparently are still made.

Regardless of that, the UPS is still functional, but like all UPS’s, it needs battery replacement every so often. This unit has three battery cases, each holding four 75 Ah (20 hour rate) 12 volt sealed lead acid batteries. Each battery is slightly larger than an average car battery. There is one important detail here, the batteries must be gas recombinant because the UPS has a four stage battery charging system. Gel or AGM batteries will not make it past the first or second equalizing charge.

A bit about batteries and battery charging. Most battery chargers are three stage units; bulk, absorption, and float. The rate of charge depends on the voltage of the battery. Bulk charging sends the most current to the battery and for 12 volt cells, this anything below 12.5 volts or so. Absorption stage reduces the charging current and supplies a steady current until the battery reaches full charge of 13.8 volts or so. Float or trickle charging draws very little current, just enough to maintain the battery at full charge.

The forth stage of charging is equalizing which is important for multiple battery series/parallel installations. This is when the batteries are deliberately overcharged for a period of time. The reason for equalizing charges is to intentionally boil off some hydrogen gas and knock any sulfur crystals off of the lead plates. With multiple battery banks in a parallel configuration, it is important to maintain the battery resistances as close as possible so that each bank of batteries is drawn on and charged equally.

In flooded lead acid batteries, this works well and the battery either vents off the hydrogen gas or recombines it will oxygen to make water again. In non-gas recombinant cells, the hydrogen will be released into the room which may pose an explosion hazard. Additionally, the electrolyte level will need to be checked after every equalization charge. With a sealed non-recombinant battery, the case my bulge and split, spilling electrolyte and ruining the battery and battery enclosure. Thus the importance of ordering the correct replacement batteries.

Best Power FE7KVA UPS and battery enclosures

After all, the reason for the UPS is to protect the expensive computer equipment connected to it. It simply will not do to install the wrong stuff and do more damage than if the UPS did not exist at all.

Mounting a new satellite dish

Something that almost every radio station has but no one really thinks about; is the satellite downlink. I think radio stations began installing satellite downlink equipment around 1982. Before that, all network programming was carried hither and yon via Ma Bell’s extensive terrestrial microwave network.

Those early dishes were almost always Scientific Atlanta 9000 series 2.8-meter antenna system, which went with the SA 7300 DATS satellite receiver. Fast forward 31 years and things have changed. The satellite constellation is now spaced at one degree and those old SA 9000 dishes are not one-degree compliant.

Scientific Atlanta 9000 series satellite dish

Therefore, when it came time to re-aim a dish at AMC8, something new was required. A Prodelin 1374 3.7 meter center-fed C band dish was ordered up.

The first thing to do is look at the dish specifications and decide if the suggested mounting procedure is a good one. The soil in this area is sandy loam. The mounting design calls for a six-inch schedule 80 steel pipe at least six feet into the ground. This calls for renting an excavator, digging a six-foot deep hole, buying a 36-inch sono-tube and a 16-foot piece of 6-inch schedule 80 steel pipe, and a couple of yards of concrete from a truck. This work is all being done on the ground system for the WDCD antenna array. All the while, abandoning the old pad and dish in place. Seems like a lot of money and wasted materials. Reusing the old pad and part of the old mount made more sense. I did some rough calculations on paper regarding wind forces, this was the results:

The maximum static force is 1,555 N on the back bolts of the mounting ring into the concrete pad. Maximum wind force is 5,603 N, and a maximum wind from bearing 76° T will exert a force of 7,158 N or 730 Kg force on the back bolts of the mount. The concrete that the mounting bolts is embedded in will withstand 4,267 Kg of force at six inches deep. The the existing pad and 3/4 inch J bolts are well within their rating to handle this load, so it seems like a good design. Putting that to practical use:

Scientific Atlanta 9000 series dish mount

First, we unbolted the azimuth mounting ring and removed the old dish, leaving the bottom of the mount. I drilled down 6 inches into the old concrete pad and inserted 1/2 inch re-bar. These re-bar are somewhat diagonal toward the center of the tube towards the new mounting pole.

Scientific Atlanta 9000 series dish mount reuse

Then, we placed the 6 inch by 8 foot schedule 80 pipe in the center of the tube and attached it to the tube with 1/2 inch all-thread. We used the all thread to adjust the 6-inch pipe to be vertical.

Next, we filled the old mount up with 4,000 PSI (280 Kg/square cm) ready-mix concrete and let it cure for one week.

While that was curing, I bolted the new Prodelin 1374 dish together on the ground. Follow the directions closely on this one, there are many pieces of hardware that look the same and are almost the same but will not work if exchanged.

We used a loader with a lifting bar on it to sling the new dish into place. I was going to video tape this evolution, but we were short handed and I ended up helping bolt the dish on the mount once it was placed there.

Once the dish was mounted, I installed the feed horn and LNB.

WDCD Albany, NY, Prodelin 1374 dish installded — WDCD Albany, NY, Prodelin 1374 dish installed

Then there was the aiming; this dish is pointed at AMC-8, for which I found this information from dishpointer.com most helpful:

WDCD AMC-8 information, courtesy of dishpointer.com

This is a crowded neighborhood and finding the right satellite took a bit of trial and error.