Mounting a new satellite dish

Something that almost every radio station has but no one really thinks about; the satellite down link. I think radio stations began installing satellite down link 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
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 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 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.  Re-using the old pad and part of the old mount seemed to make more sense.  I did some rough calculations on paper regarding wind forces, this was the results:

WDCD satellite dish mount design
WDCD satellite dish mount design

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, 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
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
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 so that it was 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.

New mount for Prodelin dish
New mount for Prodelin dish

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.

Prodelin 1374 dish about to be lifted
Prodelin 1374 dish about to be lifted

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.

Prodelin 1374 dish, installed
Prodelin 1374 dish, installed

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
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.

The XDS satellite receiver

I remember, back in the day, when we all used Scientific Atlanta 7300 satellite receivers. There were two flavors of decoder cards; DATS and SEDAT.  Starting about 1982 or so, satellite distribution of network audio was a quantum leap over the old TELCO circuits used previously.  The use of satellite downlinks allowed radio stations to receive an almost unlimited number of programs from every network under the sun.

The SA 7300 receivers gradually gave way to the SA 3640, which gave way to the Starguide, Starguide II and Starguide III series which finally lead to the XDS and MAX receivers used today.

XDS satellite receivers
XDS satellite receivers

The newest generation satellite receivers are yet another quantum leap over the last, with on board hard drive storage that allows time shifting of entire shows.  Another nice thing is the web interface.  Before you know it, everything in the broadcast plant will have a web interface.

The one issue I have had with nearly every single XDS receiver is the fan going bad.  The manufacture must have laid into a supply of defective fans.  A bad fan is noted with the fault light turns red and the unit will return a “Fan stopped” error message.  The network will send a replacement fan if you let them know.  I have carefully replaced several of these fans without turning the receiver off.

Otherwise, the web interface is pretty intuitive.  Drop down menus allow for programming the audio ports on the receiver and setting up the delayed recording and playback function.

XDS satellite receiver weekly programming grid
XDS satellite receiver weekly programming grid

Any required network closures are configured in the relay screen.  The programming clock provided by the network will specify which relays are used for each show.

XDS relay maping screen
XDS relay maping screen

Each receiver has two DB-37 connectors that have 16 relays each for a total of 32 output closures.  That should be enough to cover almost any programming situation.

Finally, the receiver’s overall operating condition can be monitored via the health screen:

XDS satellite receiver health screen
XDS satellite receiver health screen

Something like this can greatly speed up any remote diagnostic trouble shooting by eliminating (or pinpointing) a satellite system failure as the reason for a station being off the air.  I also make sure that all automation systems have some type of remote access like VNC so that I don’t have to needlessly drive to the studio to fix a silly computer problem.

Then there is one more neat tool, for those XDS receivers that do not have any front panel user controls (one certain network uses these), called the “XDS discovery tool.”  I have found this bit of software to be very helpful from time to time.

Center of Box, AMC-8

Satellite dishes have been a part of radio station technical equipment for years. I am surprised at the number of broadcast engineers that do not consider center of box when aiming dishes. As dishes get larger and focal points get smaller, center of box aiming is not a nice thing to do, it is a necessary thing to do.  The latest generation of satellite receivers, (AKA XDS) have a somewhat less than lively RF front end, they require higher E/B than the previous generation Starguide receivers to stay locked.

For years, the majority of commercial radio networks were carried on AMC-8 or its predecessors living at 139° W.  On the east coast, particularly in the Northeast, that makes aiming points relatively low to the horizon, anywhere between 8-10° elevation.

3.2 meter comtech dish
3.2 meter COMTECH satellite dish

This all means that precise aiming the satellite receive dish is critical for satisfactory performance. SES Americom owns AMC-8 and thus they have a web page about all of there satellites and important operating information. SES Center of box for AMC-8 is available in one month blocks, which makes scheduling the aiming chore fairly easy.

Large satellite dish aiming diagram
Large satellite dish aiming diagram

I have always used a spectrum analyzer though a 3 dB splitter to look at the 950 MHz  LNB output.  This aiming setup allows the best combination of Azimuth/Elevation/polarization.  Using the satellite receiver to confirm and maintain signal lock, peak the wave form that the  receiver is locked to.  It is pretty crowded up there, so there will be lots of signals on the spectrum analyzer trace.

It is a pain in the rear end to lug all that equipment out to the satellite dish, especially if it is on the roof.  That is why it only need be done once; the right way the first time.

Any shortcuts will likely lead to those annoying chirps and drop outs or complete loss programming, particularly when the weather turns bad.

Satellite dish wasp fade

More bee related RF stories. This happens often this time of year, the paper wasps have worked hard all spring to build their nests up in size and during July, they become large enough to block the aperture of the antenna mounted on a satellite dish. As the nest fills up with eggs and larva, it becomes denser and blocks more RF from the antenna. Soon, the signal on the satellite receiver drops and audio dropouts occur.

I have noticed that the newer generation satellite receivers are not as good as the older Starguide III and II units.  The Starguide receivers were pretty light duty when compared to the Scientific Atlanta 7300 or 2300 series units.  Those things were build like tanks, took up a lot of rack space, and so long as one replaced the power supply capacitors every so often, never failed.  The newer satellite receivers are very intolerant of phase shifts or any carrier disruptions.  Many times, the signal strength might look to be above the drop out threshold (usually 4.5 to 5 dB), but the audio still occasionally cuts out.  That symptom is almost always bees in the feed horn.

3.2 meter comtech dish
3.2 meter COMTECH satellite dish

This dish is mounted up high above the roof of the building on 6 inch well casing.  In order to service the feed horn, one has to either rent a cherry picker or loosen the azimuth bolts and spin the entire dish around so the feed horn is over the roof area.  Then an eight foot step ladder is need to get to the feed horn.  Luckily, it is a flat roof.  Needless to say, I made sure the feed horn had the proper cover over it so that no bees could get in.

satellite feed horn with insect cover
Satellite dish feed horn with insect cover installed

Bee fade is best cured with a can of Raid hornet and wasp spray.  The culprits are almost always paper wasps, which, I can tell you from experience, have a nasty sting.  Once the nest is cleaned out of the antenna aperture, a proper cover must be installed.  If one finds that they don’t have a proper cover, I have found that a top from a spray paint can will work as a temporary cover until a proper one can be installed.  I would not call a spray paint can cap a permanent solution because the sun will eventually degrade the plastic and it will fall apart.