Part 101, Private Fixed Microwave Service

I have been tasked with installing one of these systems for a sixteen channel bi-directional STL.  This system was first mentioned here: The 16 channel bi-directional STL system.  As some of you pointed out, the unlicensed 5.8 GHz IP WLAN extension was the weak link in this system.  It was not an interference issue, however, which was creating the problems.  The problem was with layer two transparency in the TCP/IP stack.  Something about those Cambium PTP-250s that the Wheatstone Blade hardware did not like and that created all sorts of noise issues in the audio.   We installed the Wheatstone Edge Routers, which took care of the noise issue at the cost of latency.  It was decided to go ahead and install a licensed link instead of the license free stuff as a permanent solution.

Thus, a Cambium PTP-820S point-to-point microwave system was purchased and licensed.  The coordination and licensing took about three months to complete.  We also had to make several changes to our network architecture to accommodate the new system.  The PTP-820 series has a mast mounted radio head, which is the same as the PTP-250 gear.  However, for the new system, we used three different ports on the radio to interface with our other equipment instead of the single port PTP-250 system.  The first is the power port, which takes 48 VDC via a separate power cable instead of POE.  Then there is the traffic port, which which uses Multi-Mode fiber.  Finally, there is the management port, which is 1GB Ethernet and the only way to get into the web interface.  The traffic port creates a completely transparent Ethernet bridge, thus eliminating all of the layer two problems previously encountered.  We needed to install fiber tranceivers in the Cisco 2900 series switches and get those turned up by the IT wizards in the corporate IT department.

Andrew VLHP-2-11W 11 GHz microwave antenna
Andrew VHLP-2-11W 11 GHz microwave antenna

The radios mount directly to the back of the 24 inch 11 GHz Andrew antenna (VHLP2-11) with a UBR100 interface.  The wave guide from the radios is a little bit deceptive looking, but I tried not to over think this too much.  I was careful to use the O ring grease and conductive paste exactly where and when specified.  In the end, it all seemed to be right.

Cambium PTP-820S mounted on antenna
Cambium PTP-820S mounted on Andrew antenna

Not wanting to waste time and money, I decided to do a back to back test in the conference room to make sure everything worked right and I had adequately familiarized myself with the ins and outs of the web interface on the Cambium PTP-820 radios.  Once that was done, it was time to call the tower company.

Cambium PTP-820S on studio roof
Cambium PTP-820S on studio roof

One side of these are mounted on the studio building roof, which is a leased space.  I posted RF warning signs around the antennas because the system ERP is 57.7 dBm, which translates to 590 watts at 11 GHz.  I don’t want to fry anybody’s insides, that would be bad.  The roof top installation involved pulling the MM fiber and power cable through a 1 1/4 inch EMT conduit to the roof.  Some running back and forth, but not terrible work.  I used the existing Ethernet cable for the management port.  This will be left disconnected from the switch most of the time.

Cambium PTP-280S 11 GHz licensed microwave mounted on a skirted AM tower
Cambium PTP-280S 11 GHz licensed microwave mounted on a skirted AM tower

The other side is mounted at about 85 feet AGL on a hot AM tower.  I like the use of fiber here, even though the tower is skirted, the AM station runs 5,000 watts during the daytime.  We made sure the power cables and Ethernet cables had lighting protectors at the top of the run near the dish and at the bottom of the tower as well as in the transmitter room rack.  I know this tower gets struck by lightning often as it is the highest point around for miles.

PTP-820S RSL during aiming process
PTP-820S RSL during aiming process

Aligning the two dishes was a degree of difficulty greater than the 5.8 GHz units.  The path tolerances are very tight, so the dishes on each end needed to be adjusted in small increments until the best signal level was achieved.  The tower crew was experienced with this and they started by panning the dish to the side until the first side lobe was found.  This ensured that the dish was on the main lobe and we were not chasing our tails.  In the end we achieved a -38 dBm RSL, the path predicted RSL was -36 dBm so close enough.  This means the system has a 25 dB fade margin, which should be more than adequate.  While were were aligning the transmitter site dish, a brief snow squall blew through causing a white out and the signal to drop by about 2 dB.  It was kind of cool seeing this happen in real time, however, strangely enough, the tower crew was not impressed by this at all.  Odd fellows, those are.

Currently brushing up on FCC part 101 rules, part C and H.  It is always good to know the regulatory requirements of any system I am responsible for.  As AOIP equipment becomes more main stream, I see many of these type installations happening for various clients.

The Gates Air FAX-10, Numero Dos

This is the second Gates Air FAX-10 that I have installed. This one is in the shipping container transmitter site from the previous post of the same name.  In this case, we dispensed with the equipment rack that came with the transmitter and installed it in a standard Middle Atlantic rack.   The Harris rack configuration wastes a lot of space and since space is at a premium, we decided to do it our own way.

Gates Air FAX-10 in Middle Atlantic rack
Gates Air FAX-10 in Middle Atlantic rack

The bottom of the rack has the transmission line dehydrator. The top of the rack has the Dielectric A60000 series 1 5/8 inch coax switch, a Tunwall TRC-1 switch controller and the Burk ARC-16 remote control.  I cut the rack panel top to accommodate the coax switch.  The racks were removed from an old studio site several years ago and were in storage since that time.

Gates Air FAX-10
Gates Air FAX-10

The Gates Air FAX-10 transmitter on the air, running a sports-talk format.

Dummy load and Broadcast Electronics FM10B transmitter
Dummy load and Broadcast Electronics FM10B transmitter

View from the other side showing the test load and BE FM10-B transmitter.  This transmitter had a problem that I have run into before with BE FM transmitters.  The jumper between the exciter and IPA had the wrong phase rotation causing reflected power.  I added a foot to it’s length and that problem disappeared.

Shipping Container transmitter site

Shipping container transmitter site from the early 1990's.
Shipping container transmitter site from the early 1990’s.

I do not particularly like these. I know, they are relatively inexpensive, easy to come by, easy to install, etc. However, a shipping container was not designed to house a transmitter, they have certain drawbacks. These are, in no particular order:

  • Air conditioning.  Using a traditional Bard type equipment shelter HVAC unit requires cutting through a lot of fairly heavy gauge steel.  What’s more, the steel walls are uneven, requiring filler.
  • They are by necessity, fairly narrow.  Arranging racks and transmitters along the length of the unit restricts access to either the front or the back of the equipment.  Meeting NEC clearance requirements for electrical panels, transfer switches and disconnects can pose problems.
  • They are not very tall.  Mounting overhead equipment can be problematic as one does not want to drill through the top of the container.  Crosswise unistrut is one solution, but it lowers the overhead considerably.
  • Electrical work is slightly more dangerous.  Doing any kind of electrical work, trouble shooting, repairs, etc is a little more nerve-racking when everywhere around you is a metal surface at ground potential.
  • They are difficult to insulate against cold and heat.
  • The door latching mechanisms bind, wear out or otherwise fail over time.

All of those things being said, I am now rebuilding a transmitter site in one of these shipping containers.

Inside view of shipping container transmitter
Inside view of shipping container transmitter site

Fortunately, the original electrical work was not bad.  The transmitter is a twenty year old BE FM10B, which will be retained as a backup.  The new transmitter is a Gates Air FAX-10.  We have installed several of these Gates Air transmitters in the last two years or so and they seem to be pretty solid units.  This is the second 10KW unit I have installed.

Gatesair FAX-10 transmitter in Middle Atlantic Rack

We decided to install the FAX-10 in a Middle Atlantic rack, since we did not have a whole bunch of extra room for a separate transmitter rack.  The 1 5/8 inch coax switch is installed in the top of the transmitter rack along with a Tunwall TRC-1 switch control unit. The other rack will have the STL and all other ancillary gear.  My idea is to have nothing in between the door and the FM10B so it can be easily removed when that day comes.  Something, something about planning ahead since it will be likely myself removing the FM10B.

Commercial Radio Networks changing Satellites

Lockheed Martin A2100 series satellite
Lockheed Martin A2100 series satellite

Westwood One, Premiere, Skyview Networks, et al. will be changing their satellite from AMC-8 at 139° W to AMC-18/SES-11 at 105° W longitude.  More from There are several considerations for this move:

  • Dish design and two degree compliance
  • Obstacle clearance
  • Transponder frequencies
  • Timing

Two degree compliance is going to be an issue for many stations.  Those old 2.4 and 2.8 meter mesh dishes are going to have issues with 105º West because that is a very crowed part of the sky.  From New York, it looks something like this:

Satellite Longitude Inclination Azimuth Elevation Distance
TELSTAR 12 (ORION 2) 109.21° W 0.491° 227.46° 31.09° 38596.91 km
TELSTAR 12 (ORION 2) 109.21° W 0.491° 227.46° 31.09° 38596.91 km
MSAT M1 107.72° W 7.430° 231.14° 38.16° 38011.55 km
ANIK G1 107.33° W 0.013° 225.25° 31.96° 38518.62 km
ANIK F1 107.31° W 0.020° 225.22° 31.95° 38513.76 km
ANIK F1R 107.28° W 0.052° 225.22° 32.02° 38510.37 km
ECHOSTAR 17 107.11° W 0.019° 225.01° 32.08° 38503.29 km
AMC-15 105.07° W 0.025° 222.76° 33.28° 38400.67 km
AMC-18 104.96° W 0.027° 222.64° 33.34° 38400.16 km
GOES 14 104.66° W 0.198° 222.21° 33.38° 38394.57 km
AMSC 1 103.44° W 9.810° 228.37° 43.31° 37616.42 km
SES-3 103.01° W 0.041° 220.41° 34.42° 38307.12 km
SPACEWAY 1 102.90° W 0.032° 220.25° 34.43° 38299.87 km
DIRECTV 10 102.82° W 0.017° 220.17° 34.51° 38292.86 km
DIRECTV 12 102.78° W 0.035° 220.12° 34.50° 38292.93 km
DIRECTV 15 102.71° W 0.009° 220.05° 34.56° 38290.50 km
SKYTERRA 1 101.30° W 3.488° 219.07° 36.33° 38131.32 km
DIRECTV 4S 101.19° W 0.011° 218.24° 35.35° 38228.26 km
DIRECTV 9S 101.15° W 0.014° 218.18° 35.36° 38228.57 km
SES-1 101.00° W 0.016° 218.02° 35.45° 38217.56 km
DIRECTV 8 100.87° W 0.036° 217.88° 35.54° 38211.02 km

Generally speaking, dishes need to be 3.7 meters (12.14 feet) or larger to meet the two degree compliance specification.  For many, this means replacing the current dish.  This is especially true for those old 10 foot aluminium mesh dishes that were very popular in the 90’s because of the TVRO satellite craze.

If the existing dish is acceptable, then the next issue may be obstacle clearance.  Generally speaking the 105 degree west slot (south of Denver) will be easier to see that the 139 degree west slot (south of Honolulu) for much of the United States.  Still, there may be trees, buildings, hills, etc in the way.  Site surveys can be made using online tools ( or smart phone apps (dishalign (iOS) or dishaligner (Android)).  I have found that I need to stand in front of the dish to get the best idea of any obstacles.  While you are there, spray all the dish holding hardware with a penetrating oil like WD-40, Rostoff or something similar.  Most of these dishes have not moved since they were installed, many years or decades ago.

Transponder frequencies will not be the same, so when the dish is aligned to the new satellite, those frequencies will need to be changed.  The network satellite provider will furnish this information when it becomes available.  This generally requires navigating around various menu trees in the satellite receiver.  Most are fairly intuitive, but it never hurts to be prepared.

The window of opportunity is from February 1, 2017 (first day of AMC-18) until June 30, 2017 (last day of AMC-8).  Of course, in the northern parts of the country, it may not be possible to install a new dish in the middle of winter.  It may also be very difficult to align an existing dish depending on how bad the winter is.  Therefore, the planning process should begin now.   A quick site evaluation should include the following:

Network Satellite Receive Location Evaluation


Satellite Location:

Dish is 2°compliant? (Y/N)

Distance to receiver location:

Dish Latitude:

Dish Longitude:

Dish Azimuth (T):

Dish Azimuth (M)

Dish Height AGL:

Dish Elevation:

Observed Obstacles:

(permanent or removable? Owned or not owned?)


A .pdf version is available here. Based on that information, a decision can be made on whether or not to keep the old dish or install a new one.  We service about 25 studio locations and I am already aware of three in need of dish replacement and two that have obstructive trees which will need to be cut.  This work cannot start too soon.