June 2018
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Installing a satellite dish

This is a replacement dish for the Comtech dish destroyed in a downburst event a few weeks ago.  The first part of the job entailed placement of the new dish down on the ground.  The town code enforcement officer was much happier with this idea than mounting it up above roof level along back the building as the old one was.  Of course, this is possible due to the shift in satellites last year to AMC-18.

Finding a good spot on the radio station property was fairly easy.  The studio is located in a business district, thus the side yard requirements where zero feet, which is great.  The building inspector required that we dig a test hole to see what type of soil was there.  It turned out to be fill.  That required the footing design be changed somewhat and stamped by a licensed engineer.  Not a major problem.

Satellite mount pole, waiting pre-pour inspection

Satellite mount pole, waiting pre-pour inspection

The footing is 36 inches wide by 7 feet deep.

A little bit of water in the bottom of the hole

A little bit of water in the bottom of the hole

The mounting pipe has flanges welded to the side of it to prevent it from spinning in the concrete.

Footing poured and cured

Footing poured and cured

After the pour, we let the concrete set up over the weekend.

New dish bolted together

New dish bolted together

The dish is assembled and waiting for lift.  We used a back hoe to lift the dish onto the mounting pole, unfortunately, I was not able to take a picture as I was on a ladder attaching the dish to the pedestal with U-bolts.

Viking 1374-990 3.7 Meter R/O dish installed

Viking 1374-990 3.7 Meter R/O dish installed

Here it is installed and aimed at AMC-18. I used the Satellite Buddy, which makes the aiming job much easier. Once the signal is acquired, I like to peak the Eb/No on the West Wood One carrier, which seems to be the most sensitive to any type of change.

Viking 1374-990 3.7 Meter satellite dish, back view

Viking 1374-990 3.7 Meter satellite dish, back view

Register those C band satellite dishes!

UPDATE:The registration deadline has been extended to October 17th, 2018. Switch back to procrastination mode…

Satellite dishs, WABC transmitter site, Lodi, NJ

Unless you have been sleeping under a rock, you should already be aware of the FCC request to register the C band Receive Only (RO) satellite dishes. This development comes from the never ending drive for more bandwidth from the mobile phone/data networks (remember the desire to use GPS frequencies for mobile data a few years ago).  Normally, this type of registration would require a full frequency coordination study, however until July 18th, this requirement has been waived.  The registration is completed online with the filing of FCC form 312 and a $435.00 filing fee.  West Wood One has supplied and example form (.pdf) which shows the required information for each dish.  Schedule B of FCC form 312 requires quite a bit of technical information required for each dish:

  • Site Coordinates (must be NAD27 according to the instructions on the form)
  • Site elevation AMSL in meters
  • Dish height to top of dish in meters
  • Dish make and model number
  • Dish size
  • Dish mid band gain
  • Emission designator (WWO uses 36M0G7W other providers may be different)
  • Eastern and Western arc limits
  • Eastern and Western arc limit elevation angles
  • Eastern and Western arc limit azimuth angles

Most of this is intuitive.  There are several steps to getting the information in the correct format.  Google maps (or other mapping programs) will give coordinates in decimal format.  To convert to Degrees Minutes Seconds in NAD27 use NADCON.  Site elevation can be found using free map tools elevation finder.  To determine the arc, a smart phone app such as Satellite Finder or Dish Pointer can be used.  If not actually on site, then Dishpointer.com can be used to determine the arc.

My best suggestion is to include as much of the arc as possible for each location.  The future cannot be predicted with any degree of accuracy and it is entirely possible that the current satellite position may not be used forever.

AM station downgrade

I have been working on another formerly direction class B AM station, this one is in Rutland, VT.  WSYB has been on the air since 1931 with the same call letters serving the east central part of Vermont.  In 1931, it was operating on 1500 kc with 100 watts of power.  In March 1941 it moved to 1490 kc with 250 watts before settling, a few months later, on 1380 with 1,000 watts, directional night time protecting CKPC in Brantford, Ontario, Canada.

The transmitter site was first located at 80 West Street (now known as BUS US 4), in Rutland.  It was moved to its current Dorr Drive (Formerly Creek Road) location in 1938, when the station was requesting a power upgrade to 250 watts.  Whilst cleaning out the old transmitter building, a copy of an operating log, dated December 7, 1945 was discovered in the attic above the transmitter room:

WSYB transmitter log, 1945

Back from the time when readings were required every 30 minutes.

In 1956, WSYB was allowed 5,000 watts daytime non-directional with 1,000 watts night time directional.

At some point in the early 1990’s, the original towers were replaced with solid leg Pirod towers, each 195 feet tall.

After that, things went the way things do; AM steadily declined in favor of FM, local programming was mostly replaced by syndicated satellite stuff, there were several transfers of ownership, etc.

A translator on 100.1 MHz was added in 2016; the two bay Shively antenna was installed at the top of the South West tower.   There is local programming on the station from 6am to noon on weekdays.  There may also be some gardening shows and other such programming on weekends.

The current owner has decided, like they have done in other markets, that AM directional antenna systems are a maintenance nightmare, the risk of FCC sanctions are high for an out of tolerance antenna array, the ratings and income from the station do not justify the risk/cost.  Thus, non-directional night time operation was applied for and granted.  The station is now a Class D with 25 ass kickin’ night time watts.

WSYB had a two tower night time antenna system.  The tower closest to the building (SW) was also the daytime, non-directional tower and it now holds the FM translator antenna and STL antenna.  Thus, it was decided to ground that tower and keep those antennas in service.  The far tower (NE), which was the second tower of the night time array would become the AM antenna.  The night time ATU was built for less than 1,000 watts input power, so several components needed to be upgraded for 5,000 watt operation.

WSYB rebuilt ATU

WSYB rebuilt ATU

I had available these nice vacuum capacitors that came out of another decommissioned antenna system.  The vacuum capacitors are great because the voltage/current ratings are much higher than the mica capacitors that were in the circuit before.  You can see black goop where one of the Sangamo mica capacitors on the input leg failed several years ago.  These vacuum capacitors are rated at 15 KV and the current rating at 1.38 MHz is probably in the 70-80 amp range.  I had to move the base current meter from the former daytime (SW) tower out to the NE tower.  The day night switch was taken out of the circuit.  The transmission line to the far tower was replace with 7/8 inch foam dielectric cable.  A slight touch up of the coil on the input leg of the T network was all that was required to bring it into tune.

The electric lines to the tower have been temporarily disconnected.  As soon as they are reconnected, I will vacuum out all the mouse crap and other debris.  The ATU building also needs some work sealing in up against the elements.

The tower base impedance is 75 ohms, +j95 making the base current 8.6 amps daytime and 0.58 amps night time.

WSYB radiating element

WSYB radiating element

For me, the magic of radio exists at that boundary between the real objects (towers and antennas) and the ether.  The transference of electrical voltages and currents into the magnetosphere is something that still fascinates me to this day.  Coupling a 5,000 watt medium wave transmitter to a tower and watching it work is something that I will never grow tired of.

Fixing another AM station’s antenna system

I have done several of these posts in the past, but it always seems to be of some interest, so it bears repeating.  AM antenna systems are not black magic.  They are actually pretty easy to understand if the fundamental knowledge is in place.  Medium Wave frequency wavelengths are fairly large compared to other broadcast frequencies.  Thus, the components are larger.

The three basic components of an AM antenna system are the tower, the ATU (antenna tuning unit) and the transmission line (AKA Coax).  The tower is the radiating element and they come in a variety of flavors; uniform cross section guyed, self supporting, series excited, shunt excited, etc.   A series excited tower has a base insulator and is fed directly from the ATU.  A shunt excited tower has a grounded base and uses a skirt or folded monopole design to transfer the RF to the main radiating element.  This design has an advantage as the tower can be used for other wireless and broadcast services.

The antenna work in question for this project is WINE, 940 KHz, Brookfield, CT.  The skirted tower is used for WRKI.  It also has two way and cellular clients.  The issue is instability of the WINE antenna system, which is likely due to improperly attached shorting wires between the skirt at the tower.  Over the years, the impedance of the skirt has gone way up.  The tower itself is 152.1 meters (499 feet) tall, or 170.3 electrical degrees.  The skirt length is about 82 electrical degrees and it is shorted at about 72 degrees.  There have been several papers written about folded monopoles for Medium Frequency (AKA AM or Standard) broadcast service.  The recommendations state that for best performance, the short to the tower should be between 62 and 90 electrical degrees.  Since the existing system falls in that range, there must be other problems with the antenna skirt and or shorting wire to the tower.

WINE skirted tower diagram

WINE skirted tower diagram

If one looks at this diagram, that configuration should look something like a gamma match, often used on dipole and yagi type antennas.  A gamma match can be thought of as a stub of transmission line which is bonded to the radiating element at some favorable wave length corresponding to the desired radiation resistance.  This is one of several configurations for folded monopole antennas and this type is most often seen on towers that support other wireless service antennas such as cellular and two way systems which are installed above the skirt.

There are a few interesting data points when looking at these type of antennas.  First is the ratio of the diameter of the skirt over the height of the tower, or D/H.  The larger this ratio is, the better the bandwidth characteristics of the antenna system are.  This makes sense, when you think about it. In this instance, the tower is 151 meters (495.4 feet) tall and the skirt is 3.3 meters (10.83 feet) wide, thus the ratio is 0.0218.

The licensed base impedance if 234 ohms with a good amount of inductive reactance. When Sprint and T-mobile changed their configuration on the tower, that impedance shifted dramatically.  The existing skirt is in fairly rough condition.  The bottom ring that connects to the ATU is made out of copper tubing.  It is attached to the skirt wires with steel saddle clamps, all are rusted and all of which are lose and can slide around.  At some point, the tubing filled up with water, then froze causing the tubing to split open.  At the top of the skirt, the jumper wire looks suspicious and the top ring does not go all the way around. The shorting stub to the tower looks like it is made out of battery jumper cable.  I purchased new cross wire clamps and found some spare copper weld skirt wire at another site.  Both the bottom ring and top ring were replaced as well as the shorting stub to the tower.

After the repair work was done, I had the tower crew reattach the short slightly below the last skirt to tower bonding point.  In that position, I found the impedance went way up.  Thus, going lower was going towards a resonance point.  I had them move the short up to the former shorting point and remeasured and found the impedance was 235 ohms, only 1 ohm off from the previously licensed values.

Initially, I thought it would be nice to find a better position for the shorting stub and get a lower base impedance.  This would make the whole antenna system work better (improve bandwidth, stability, etc).  However, there was a set of guy wires above the bonding point.  The tower crew would have had to disassemble the top ring to move above the guy wires.  We were running out of daylight and weather so I had them lock everything down where it was.  On a station running an all sports format that has no listeners and does not make any money, it does not make a lot of sense to spend gobs of money and time to rebuild the ATU for a new base impedance.  When I got the impedance back to within 0.11% of the licensed values, it was time to declare victory and go home.

Engineering Radio; the satellite reaiming tour 2017!

As previously discussed, the migration from AMC-8 to AMC-18 is in full swing. There is less than two weeks left to complete the re-aiming process.  All totalled, we have 24 of these things to re-point and all but two of them  are done.  Toward that end, I have this down to an art:

  • Go inside and make a note of the signal strength on the satellite receivers on AMC-8
  • Look up the elevation angle on dish align app for AMC-8 then compare that to what the inclinometer reads, note the difference between the calculated and actual readings
  • Look up the elevation angle on the dish align app for AMC-18, apply the difference noted above to the final value
  • Connect the XR-3 satellite aiming tool to the LNB, make sure LNB power is on and the unit is set to AMC-18, C-band
  • Elevate the dish to the AMC-18 final elevation angle calculated above
  • Note the azimuth on the dish align app, look at the satellite picture and pick out a land mark.  Swing the dish towards the land mark
  • As you start to see signal from various satellites, swing more slowly.  If the elevation angle is set correctly, when the dish passes AMC-18 at 105 degrees W, the XR-3 will lock on
  • Peak the signal (azimuth and elevation)
  • Rotate the LNB feed horn for maximum signal to noise ratio
  • Go inside, check satellite receivers, reprogram carrier frequencies as necessary

It is pretty easy. I can do the whole thing in about thirty minutes if there are no rusted bolts, etc. I wonder how many small station owners will wake up on July 1st with no satellite programming?

Comtech Satellite dishes, WABC transmitter site, Lodi, NJ

The Applied Instruments XR-3 (XR-S2ACM-01) VSAT-ACM  satellite signal meter with AMC-18 locked.  This hand held tool is great and makes aiming any dish a snap.  As the sky around AMC-18 is a wee bit crowded, it is easy to mistakenly find the wrong satellite.  With the Identify function, the satellite the dish is aimed to will be displayed, then the dish can be adjusted accordingly to the correct bird.

Applied Instruments XR-3 satellite signal meter

There are many different flavors of dishes; Comtech, Patriot, Prodelin, etc.

Prodelin 3.7 Meter satellite dish

These are all about the same to work with, the only difference is the degree of rust and deterioration on the mounting hardware, the age of the LNB and number of bees nests that need to be removed.

Studio Buildout, Part III

I have been so busy that I forgot to post the pictures of the completed studio build out.  Overall, I would say that I am pretty pleased with the end result.  Of course, this is not Manhattan but rather an unrated market in central New York, and the budget reflected that.  Overall, the radio stations are in much better technical condition than before.  They are now located in the center of their community within walking distance of the town hall, other civic locations and activities.

There are five radio stations broadcasting from this new studio space.  Two stations are simulcast using the Westwood One Classic hits format from the satellite.  The only AM station is a Fox Sports Radio affiliate from the satellite with a local morning show.  Another one is a “we play anything” computer juke box and final station has a country format with quite a bit of local content.  Any station can go on the air from either studio.  In addition, all stations can simulcast the mother ship from Oneonta, which comes down via a Barix Exstreamer 1000.

Walton TOC

The Technical Operation Center consists of four racks containing the Ethernet routers, switches, a patch panel, automation systems, audio routing switchers, air monitor receivers, audio distribution amps, Barix units, Wheatstone Blade IP 88A STL, etc.  The equipment racks came from a disused site in New Jersey.

The satellite dish and receivers are located at the transmitter site, audio and closures come back via the Wheatstone Blade IP 88A.

Everything in this room is backed up by a STACO 2.5 KVA UPS.

TOC wire terminations

The wire termination from the studio are mounted to Krone LSA-PLUS blocks.  Studio trunk wiring consists of connectorized 25 pair CAT 5 cable.  There are also six runs of shielded CAT 5e cable for Ethernet and extended KVM from the TOC.

There is a manual transfer switch with a NEMA L14-30 input receptacle on the bottom.  A twenty for 10/4 SOJ cable will reach the ground from the window in the left hand side of the picture.  This is the standard NEMA plug/receptacle set for a moderate sized portable generator.  That feeds a 100 Amp sub panel which in turn feeds the racks and studio equipment.  Thus the entire facility can be run on a 5000 watt (good quality) portable generator in the event of a prolonged power outage.

The ground buss bar is connected to the main building ground at the service entrance.  All racks and studio consoles are grounded to this main ground point.

The air monitor receivers feed both studios.  There is also a provision to connect audio silence sensors up to each air monitor DA to notify the station staff in the event of an off air situation.  Believe it or not, this type of system has never been installed for these stations.

Studio A is the main studio.  The AudioArts Air4 console is a good fit for this type of operation.  These consoles have USB outputs, so the console can act as a sound card for the digital editing computer.  Each studio is equipped with an air monitor switch that can select any station to feed the external monitor input on the Air 4 console.  This allows the guy on duty to keep an eye on all the signals coming from the facility.

Studio A

The counter tops were custom made at a local kitchen place on trade. The microphone are Heil PR-22 with shock mounts, which are better than the Realistic mics in the old studio.  This is the first time that the main studio has had more than one microphone. The morning show guy has already pressed those guest mics into service with a few on air interviews.

The monitor speakers are JBL LSR305 mounted on home made speaker stands consisting of 18 inch black iron pipe and floor flanges.

Studio A

The small equipment rack is on casters and can roll out from under the studio furniture to get at the back of the equipment.  A used Gentner DH3 TELCO hybrid is used to get phone callers on the air.  Adobe Audition is used for editing and production on the left hand computer monitor.  That CPU is in the bottom of the roll around rack.

Studio A

The office chair and other furniture was also acquired on trade.

Studio A

What the operator sees. STORQ computer on the left for music, Scotts SS32 on the right for automation. Both are extended from the TOC. Unless the morning show guy is live on the air, the console is bypassed and the audio stays in the TOC.

It all works pretty well.

Studio B

Studio B is the same as Studio A except fewer microphones.

Studio B

Studio B operator view.  This studio can be used for one of the other stations or production.

Again, this is not a Fancy Nancy installation, but it does get the job done.

VOA Site B, Greenville, NC

I took a brief vacation last week along the coast of North Carolina. It was relaxing and fun to be sure. I was also aware of and slightly curious about the Voice Of America shortwave site, a slight distance inland in Grimesland, NC.  Thus, I made arrangements visit the facility on my way home.  Chief Engineer, Macon Dail, was gracious enough to give us the guided tour.  The facility is an engineering marvel.  The scale and complexity is enormous.  The entire facility is scrupulously maintained.  Many of the transmitters and other equipment have been upgraded to make them more functional.   I tried to take meaningful pictures, but in many cases, they simply do not to justice.

Edward R Murrow Transmitting Facility, (VOA Greenville Site B) Grimesland, North Carolina

Officially known as the Edward R Murrow Transmitting Station of the International Broadcasting Bureau, VOA Site B was constructed in 1961.  Six of the eight shortwave transmitters are original to the construction of the building.  The other two (BBC SK55 and AEG S4005) were added in 1986.  All of the dipole curtain arrays, rhombics, transmission line and the antenna switching matrix are also original.  A few brief statistics about this site:

  • Land area is 2,715 acres (1099 hectare).
  • Over twenty six miles (forty two kilometers) of 300 ohm open transmission line rated at 500 KW.
  • Sixteen dipole curtain arrays, average antenna gain 17 dBi.
  • Twenty rhombic antennas, antenna gain 15 dBi.
  • Two of the dipole curtain arrays can slew azimuth and take off angle.
  • Three Continental Electronics 420A 500 KW Doherty modulated transmitters.
  • Three General Electric 4BT250A1 250 KW high level plate modulated transmitters.
  • One Brown Boveri Company (BBC) SK55C3 500 KW PSM transmitter.
  • One AEG Telefunken S4005 500 KW PDM transmitter.
  • Antenna switch matrix connects any of the eight transmitters to any of the thirty six antennas

While we were there, both of the newer transmitters were on the air, running at 250 KW.  The GE transmitters are used as needed and the Continentals are rarely used due to age, difficulty to tune, change frequencies and gross power inefficiency.

The station staff has, out of necessity, fabricated some very cool upgrades to the transmitters and facility.  The first of which is the alarm annunciator, which is based on a Star Trek (Original Series) sound scheme.  Once or twice I heard the bridge general alarm go off, followed by a female voice stating the problem: “GB8, OFF AIR.”

Chief Engineer’s office.  NCC-1701; no bloody A, no bloody B, no bloody C, and no bloody D

The GE 250 KW transmitters have been retrofitted with a computer controlled auto tune system for frequency changes.  The antenna switch matrix controller has been replaced by a PLC based system.  As the transmitters are so old, many of the transmitter specific parts need to be machined or fabricated locally.  The rest of the transmitter parts are stocked in a large parts storage room, all of which is meticulously labeled and tracked.  The floors are waxed and spotless, there is no dust on the horizontal surfaces, the work shop is clean, tools are put away, grass and weeds are cut, etc.  All of these little details did not go unnoticed and indicate great pride by the staff in the facility itself.

The heart of the facility is the control room which consists of four rows of equipment racks and a central operating position elevated above floor level.  Arranged around that are the eight shortwave transmitters in two long transmitter galleries.

VOA Site B control room

From this point, the operator can view all of the transmitters in the two transmitter galleries.

Operating position

Around the control operator are arranged a series of computer monitors showing various station function status.

Transmitter modulation and status indicators

Antenna Matrix status and control

VOA transmitter control and status (center)

Audio monitoring router

The equipment is installed into the equipment racks by type; one rack contains the frequency generators for each transmitter, the next contains first stage power amplifiers, the next contains audio processors and modulation monitors, etc.

Equipment racks and Shift Supervisor’s  office

Transmitter frequency generators

Audio processors, modulation monitors and patch panels

Backup audio feeds

The audio comes from the VOA studios in Washington DC via satellite. There are Comrex Access links as a backup and the Gentner EFT-1000s are used as a backup to the backup.  Prior to 1995, an eight hop microwave system covering the 300 mile (483 KM) distance was used.

GE 4BT250A transmitter with computer controlled tuning system installed

The station staff has created a computer controlled tuning system for the GE transmitters. Each transmitter can change frequency several times a day, during each frequency change, all of the transmitter stages need to be retuned. When done by hand, this can take several minutes to accomplish. The computer system uses follow pots and micro controllers to set the tuning elements to specific values. They can be touched up by hand if needed. A frequency change can usually be done in less than one minute.

GE 4BT250A transmitter

Your humble author and CE Macon Dail discussing the auto tune system

GE 4BT250A auto tune modification

GE 4BT250A IPA tube and input tuning.

The 2nd IPA and PA input tuning work the same way. The copper sleeve slides up and down over the coil to change resonant frequency. The vapor cooled tube sits inside the tub at the top, anode facing down. These tuning sections are a mechanical nightmare according to Macon. One of the reasons why VOA site A was closed down was due to the frequent frequency changes at that site causing excessive wear and tear on the old GE transmitters. This particular transmitter was being repaired; the staff was rebuilding a tuning network bypass capacitor assembly

GE 4BT250A transformer vault

The GE transmitter transformers still contain PCB’s. The plate transformers are in the back, basically pole transformers, one for each phase. Primary voltages is 4,180 volts, secondary rectified voltages are 12 KVDC (PA plate supply)  and 15 KVDC (modulator plate supply).

Hallway and maintenance access to back of GE transmitters

AEG Telefunken S4005 500 KW transmitter on the air

While we were there, the newer transmitters were in operation transmitting Spanish language programming to the Cuba on 13,605 KHz and 11,930 KHz.  Currently, the Greenville site is broadcasting mostly Spanish language programming with some English, French and Bambara language programming for Africa.

A fact that does not escape the notice of the staff.

VOA transmitter gallery, showing transmitters GB8 through GB4

Continental Electronics 420A 500 KW Shortwave transmitter control and metering panel

The three Continental 420A transmitters (GB-1, GB-2 and GB-3) are essentially a pair of 250 KW amplifiers combined. As these are Doherty power amplifiers, frequency changes are very difficult to effect. These transmitters spend most of their time in backup service.

Electrical distribution panel

The antenna matrix building is very impressive. Routing eight 250 or 500 KW transmitters to 36 different antennas takes a bit of doing. Mechanizing that set up is no mean feat. The pictures I took of the antenna matrix building do not show the size and complexity of the system.

Transmission line between transmitter building and antenna matrix building

For that, we need a satellite photo:

VOA Site B antenna matrix building

Basically, the transmitter building is in the lower left hand side of the picture. The transmission line go over to the antenna matrix building (looks like rectangular duct work), then run all the way to the back of the building. Each antenna transmission line come into the building and runs to the other side. Pneumatic arms then couple the transmitter line to the antenna line. This is all controlled by a custom made PLC and controlled by the operator from the main operating desk.

Custom made antenna matrix control system

300 ohm open transmission lines

300 ohm open transmission lines

Some of these lines are very long but have low loss due to the air dielectric. The most used antennas are the dipole curtain arrays.

Dipole curtain arrays

These consist of a series of broadband dipole antennas arranged side by side and stacked three or four high. behind those antennas is a reflector screen. There are two curtain arrays that are slewable. The dipole antennas phase relationship to each other can be changed to adjust the take off angle and azimuth, thus giving optimum coverage to the targeted area.

Close up curtain array

In this picture, the dipole antennas are to the right. Behind them is the reflector screen, behind that is the antenna feed system. Each antenna feed goes through the reflector screen to the center of the dipole antenna.

Each array requires four towers to support it.

Curtain dipole array supporting towers

Curtain dipole array supporting towers

Remote Antenna Switch.  Allows two antennas to use one transmission line.

The entire antenna field is viewable from an observation platform on the main building

Observation room

Entrance gate and slewable curtains in background

Curtain arrays

The entire facility is very impressive. The truth is, I could have spent several more hours there, but I know that people have jobs to do and I felt that I had taken up enough time. We often forget in this country that not everyone in the world has access to the internet. Shortwave broadcasting has a long reach and is not subject to government controlled firewalls or other forms of electronic censorship. Currently, the Greenville site is broadcasting mostly Spanish language programming with some English language programming for Africa. There are many areas in the world that are in political tension right now, some startlingly close to home. Places like Brazil, Argentina and Venezuela have been in the news lately. I do not see a time when these long reach broadcasting services will not be needed. Becoming a welcome source of good information for those affected people is good for brand USA. It would be money well spent to invest in a couple of new Continental 419H (still made in the USA) DRM capable transmitters for this facility. While the old GE and Continental units are great, the time may come when they are really needed but unavailable due to being down for repair.

Special thanks to Macon Dail for his time, knowledge and patience.

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.


A pessimist sees the glass as half empty. An optimist sees the glass as half full. The engineer sees the glass as twice the size it needs to be.

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
~1st amendment to the United States Constitution

Any society that would give up a little liberty to gain a little security will deserve neither and lose both.
~Benjamin Franklin

The individual has always had to struggle to keep from being overwhelmed by the tribe. To be your own man is hard business. If you try it, you will be lonely often, and sometimes frightened. But no price is too high to pay for the privilege of owning yourself.
~Rudyard Kipling

Everyone has the right to freedom of opinion and expression; this right includes the freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers
~Universal Declaration Of Human Rights, Article 19

...radio was discovered, and not invented, and that these frequencies and principles were always in existence long before man was aware of them. Therefore, no one owns them. They are there as free as sunlight, which is a higher frequency form of the same energy.
~Alan Weiner

Free counters!