I was watching the tower crew measure the guy tensions on this tower the other day:
AM tower
The preferred method is to use a pulling force to move the guy wire slightly off of the turnbuckle or hairpin bolt then measure that force. Hydraulic rams with a pressure gauge are used more often then not.
hydraulic ram, showing 7,000 lbs pulling force
These guy wires are called “Bridge Strand,” the bottom wire is is 7/8 and the top is 1 1/8 inches. Normally, these are tensioned to around 5 – 10% of their breaking strength at 60 degrees F. In this case, it was slightly colder so the tensions are a little bit higher. If it would have been warmer, then they would be a few percentage points lower.
A couple of videos for your viewing enjoyment:
Lower guy tension 7,400 lbs, Upper guy wire tension 10,500 lbs. Both are well within their ranges.
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
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 installedDiplexor 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 is a broadband 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 backup for any of the three FM stations; WKBE 107.1, WNYQ 101.7, or WFFG 100.3. Two transmitter sites for those stations are mountaintop locations which are very difficult to get to in the wintertime. 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 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
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 transmitters are BW TXT-600 with low pass filters before the output connector. There are three frequencies of interest;
(F1 – F2) + F1 or (97.9 MHz – 96.9 MHz ) + 97.9 MHz = 98.9 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. Mobile 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 readings to fall back on is always the best course in case the “out of tolerance” condition gets reported 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 were 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 under test and measurement
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 (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 2-way star junction combiner
We are still doing some grounding and neatening work behind the 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
We share the room with Access Plus, which is a wireless internet service provider in western Massachusetts. Their stuff is in the open-frame racks to the right of WNNI.
Another view:
Transmitter racks for WUPE-FM, WNNI and W266AW
TL;DR: Tower collapses, and the facility is rebuilt better than before.
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 the groundNorth 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 a backup facility for both stations. The Shively Antenna went up in stages.
New WUPE-FM and WNNI Shively 6810 antennaTower 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 sheltersHanging the top two bays of the new antennaLift of bottom two bays and first tuning sectionSecuring the bottom section and bolting bays together
After that, there were twenty feet of rigid line, another tuning section, then the 1 5/8 inch heliax 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.