A tale of five signals

I am currently finishing an interesting project involving putting up two translators on a diplexed AM tower which also holds a mobile phone/data tenant as well.  All-in-all, this seems to be a very efficient use of vertical real estate.

WMML WENU tower, Glens Falls, NY
WMML WENU tower, Glens Falls, NY

The AM stations are WMML and WENU in Glens Falls, NY.  The AM stations are diplexed using a Phasetek diplexor/ATU.

Diagram showing WENU/WMML tower with W250CC/W245DA antenna installed
Diagram showing WENU/WMML tower with W250CC/W245DA antenna installed
Diplexor diagram, WENU/WMML Glens Falls, NY
Diplexor diagram, WENU/WMML Glens Falls, NY

The translators are W250CC and W245DA which are using a NICOM BKG-77/2 two bay 3/4 wave spaced antenna mounted at 53 meters AGL.  The translators use a Shively 2640-04/2 filter/diplexor which as a broad band input port in addition to the translator input ports.  Since these translator signals are only 1 MHz apart, the higher power Shively filter was installed because it has better rejection characteristics.  The broadband input port allows the NICOM antenna to be used as a back up for any of the three FM stations; WKBE 107.1, WNYQ 101.7, or WFFG 100.3.  Two transmitter sites for those stations are mountain top locations which are very difficult to get to in the winter time.  Having a backup site available takes some of the pressure off during storms or other emergencies.

Shively 2640 -04/2 filter for W250CC and W245DA

The NICOM FM antenna was mounted on the tower when W250CC went on the air in October of 2016.  When it was installed, the base impedances for both AM stations were measured.  For some reason, WENU 1410 KHz seems to be more sensitive to any changes on the tower, thus the WENU ATU needed a slight touch up.  When working on diplexed AM systems, it is also important to make sure that both trap filters, which are parallel resonant LC circuits, are tuned for maximum rejection of the other signal.  During this particular installation, nothing was added to the tower and no change in the base impedance for either station was noted.

Shively Filter, connected to transmitters and antenna
Shively Filter, connected to transmitters and antenna

As a condition of the construction permit, measurement of spurious emissions of all stations sharing the common antenna needed to be completed to ensure compliance with FCC 73.317(b) and 73.317(d).  I made careful measurements of the potential intermod products between the two translator frequencies.  This measurement was completed with my TTI PSA6005 spectrum analyzer.

The primary concern here is mixing products between the two transmitters. Both transmitter are BW TXT-600 with low pass filters before the output connector. There are three frequencies of interest;

  1. (F1 – F2) + F1 or (97.9 MHz – 96.9 MHz ) + 97.9 MHz = 98.9 MHz
  2. F2 – (F1 – F2) or 96.9 MHz – (97.9 MHz – 96.9 MHz) = 95.9 MHz
  3. F2 + F1 or 97.9 MHz + 96.9 MHz = 194.8 MHz

That, plus harmonic measurements out to seven or eight harmonics of the fundamental frequency should be enough to demonstrate compliance with FCC out of band emissions standards. Being that this site has LTE carriers, it is very important to measure the harmonics in those bands. Mobil data systems often use receiver pre-amps, which can amplify harmonics from the FM band and make them look out of compliance. Having a base set of reading to fall back on is always the best course in case the “out of tolerance” condition gets report to the FCC.

Measurements on these frequencies must meet the emissions standards outlined in FCC 73.317 (d), which states:

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.

Harmonic frequencies to be measured:

Harmonics for 96.9 MHz fundamental Harmonics for 97.9 MHz fundamental Comments
193.8 195.8
290.7 293.7
387.6 391.6
484.5 489.5
581.4 587.4
678.3* 685.3* US LTE Band 71
775.2* 783.2* US LTE Band 5
872.1* 881.1* US LTE Band 5
969.0 979.0

*Frequencies that fall within the mobile data LTE bands. Traces where recorded and saved for these frequencies.

All of that information, once compiled is attached to the FCC form 350-FM, which, once filed grants Program Test Authority.

BW TXT-600 V2 translator transmitters
BW TXT-600 V2 translator transmitters under test and measurement

North Adams tower update III

And final.

It has been a year and a half since the tower collapse in North Adams, Massachusetts.  Since that time, WUPE-FM (Gamma Broadcasting), WNNI and W266AW (New England Public Radio) have been operating with STAs at lower than licensed power.   We have completed the installation of the combined antenna, filters and combiners and now all stations are back to full power.  Here are a few pictures of the transmitter room:

WUPE-FM and WNNI transmitter racks, North Adams, MA
WUPE-FM and WNNI transmitter racks, North Adams, MA

WUPE-FM (left hand rack) is using a Crown FM-2000 transmitter, loafing along at 1,060 watts. WNNI (right hand rack) is using a Gates Air Flexiva 2 running at 1,650 watts. Those stations are combined with a Shively Combiner:

Shively combiner
Shively 2 way star junction combiner

We are still doing some grounding and neatening work behind the racks:

Behind racks
Behind racks

The Shively versa tune antennas that were mounted to the wooden utility pole as emergency antennas will be retained as backup antennas for both stations.

Transmitters for WUPE, WNNI and W266AW
Transmitters for WUPE, WNNI and W266AW

We share the room with Access Plus, which is a wireless internet service provider in western Massachusetts. There stuff is in the open frame racks to the right of WNNI.

Another view:

Transmitter racks for WUPE-FM, WNNI and W266AW
Transmitter racks for WUPE-FM, WNNI and W266AW

TL;DR: Tower collaspes, facility is rebuilt better than before.

North Adams Tower update II

Work continues on rebuilding the North Adams tower after the collapse of March 2014.  Over last winter, a new tower was erected.  This is a fairly substantial tower.

New North Adams tower on ground
New North Adams tower on ground
North Adams new tower erected
North Adams new tower erected

In the interim, a new Shively 6810 four bay half wave spaced antenna was ordered. This antenna will be combined for two stations, WUPE-FM and WNNI using a Shively 2630-2-06 branched combiner. The 70 foot utility pole next to the building will be retained as backup facility for both stations. The Shively Antenna went up in stages.

New WUPE-FM and WNNI Shively 6810 antenna
New WUPE-FM and WNNI Shively 6810 antenna
Tower climbers rigging tower for new antenna
Tower climbers rigging tower for new antenna

Prescott Tower from Rutland Vermont was on site to do the tower work. They were the primary contractor for installing the new tower and did a really nice job of it.

New North Adams tower ice bridges to various shelters
New North Adams tower ice bridges to various shelters
Hanging the top two bays of new antenna
Hanging the top two bays of new antenna
Lift of bottom two bays and first tuning section
Lift of bottom two bays and first tuning section
Securing bottom section and bolting bays together
Securing bottom section and bolting bays together

After that, there was twenty feet of rigid line, another tuning section, then the 1 5/8 inch helax into the transmitter room. The antenna was tuned and the load looks very good. We are waiting for the electrician to finish wiring up the new racks and we will move both stations into their new home.

Winter! Is upon us….

What better time to take the gondola to K-1? None, none at all.  We do work for the two radio stations that are on the peak of Mount Killington, near Rutland, Vermont.  In the summer, usually we can drive up there in a four wheel drive truck.  In the winter, the gondola is the way to go.  On this day, there was a 48-56 inch base, light north winds and air temperature around 10° F (-12° C) .

This is not my video, I did not have enough memory on my SIM card to film a video and I didn’t bring my expensive camera. However, this is a good example of the ride:

Not a bad way to get to a transmitter site, all things considered.

Ride up to Killington Peak
Ride up to Killington Peak
View from Killington Peak
View from Killington Peak
View from Killington Peak
Transmitter buildings on Killington Peak
View from Killington Peak
View from Killington Peak
View from Killington Peak
Tower from Killington Peak
Killington STL dishes
Killington STL dishes
ERI antenna, WZRT/WJJR Killington VT
ERI antenna, WZRT/WJJR Killington VT

The reason for the trip today; repair work on the Nautel VS2.5 transmitter. All three power supplies and the power supply summing board needed to be replaced.