Diplexed Directional AM stations

Pictures and story sent along by occasional reader John.  I worked on diplexing an AM station in 2003, it was a 5 KW and a 10 KW on a single tower.  Those power levels require using some pretty large components, however, the setup was pretty straightforward.  Each station had its own ATU (antenna tuning unit) which was then fed into bandpass filters to isolate the other station and coupled to the tower.  The ATUs were set up as low-pass and high-pass filters respective to their frequency.  The whole thing had something like 45 dB isolation, which worked(s) very well.

Doing this with a directional antenna system is another problem altogether.  Add to that the tight filter networks required as the station are only 100 KHz apart.  One saving grace, the power levels are relatively low.  The higher the power gets, the more the magnetic fields build up around the coils and mutual coupling becomes an issue.

As John notes:

1560 (WGLB) owns the site and has been there for about 8 years. Originally WGLB was in Port Washington, WI with a BTA-250M running into a 2-tower array. The city of license was changed to Elm Grove, and this necessitated a move about 30 miles south to the site shown. A 6 tower combination array was needed to protect 1550 in Lake Geneva, WI, 1550 in Madison, WI, 1550 in Morris, IL, 1540 in Hartford, WI, 1570 in Appleton, WI, 1530 in Cambpellsport, WI and 1530 in Elmhurst, IL. A 4-tower in-line array is used on 1560 during daytime, and a 4-tower parallelogram with the two south towers switched in and the North two in-line towers switched out (floated) for 1560 nighttime operation.

WGLB WJTI combined directional antenna system
WGLB WJTI combined directional antenna system

Looks interesting.  Fortunately, the towers are not required to be painted or lighted, that is a big maintenance headache.

WGLB WJTI antenna field
WGLB WJTI antenna field

Another thing to note; the site looks well maintained, the grass is mowed, no trees growing up by the transmitter building, the building is painted, etc.  Likely these stations are locally owned and making a modest profit, not some abandoned afterthought.

Antenna Tuning Units
Antenna Tuning Units

Each tower has separate ATU’s for each station.  The ATU’s then feed what is likely a very tight bandpass filter for each station, which then combines the two signals and feeds the tower.  John continues:

An arrangement was designed when 1460 approached 1560 about leasing tower space for moving 1460 (ND-D) from Racine, WI north to West Allis, WI. This design is ingenious in that the array tower usage between the two stations is reversed for day-night operation! In other words, the 4-tower in-line array is used for 1460 nighttime, and the 4-tower parallelogram array consisting of the four south towers is used for 1460 daytime operation.

WJTI Phasetek antenna phasor
WJTI Phasetek antenna phasor

The 1460 pattern is pretty tight to protect 1470 at West Bend, WI approximately 30 miles north, and nighttime also to protect 1460 in DesMoines, IA. The friendly folks at Phasetek (Quakertown, PA) did the 1460 phasor and notch traps at each tower to prevent cross-modulation (inter-modulation) of the two signals feeding the towers, and after assembly on-site tuned up like a dream!

And that is saying something.  I have dealt with phasor manufacturers before, sometimes they nail it, sometimes they don’t.  Tune up can be a real challenge, which tends to put everyone on edge.

I might add that the high-tension electrical transmission towers nearby were de-tuned at 1560 years ago, and upon checking were broad enough to not require any further de-tuning at 1460! Another attribute of this design is that if something ever changes in the future, the deal can be easily be dissolved, because there is no mutual ownership of any equipment on site! It is truly one of the best “Win-Win” instances of AM station directional antenna combining I have ever seen!

It is good to see stations taking advantage of co-location these days.  It is a great way to save money on real estate and hassles with the zoning boards, who all see dollar signs when someone talks of putting up a tower.  With the amount of computing power and the lessons learned in the past 90 years or so, we are beginning to get this medium wave broadcasting thing down.

The first radio station licensed to Albany, NY

Although not the first station in the area, that honor goes to WGY. In fact, RPI licensed WHAZ in 1923, which makes it the second regional station.  Starting on 1430 Khz as WOKO in New York City in 1923, the station made a few stops along the way.  One of those was on Mt. Beacon from 1928 until 1930.  The original transmitter building is still there, although the tower was taken down in 2005 to make way for the DTV stations that moved in.    I always wondered why an FM tower on the top of a mountain had a base insulator.

WDDY towers
WDDY towers, Bethlehem, NY

In 1930, WOKO was sold and moved to Albany, NY, becoming the first station licensed to that city.  The transmitter site is located off of Kenwood Avenue in the town of Bethlehem, about 4 miles south of downtown Albany.  It first signed on with 1 KW, increasing to 5 KW in 1947.   This is the original transmitter site, but the towers were redone in the mid-1970s.  The towers themselves are 130 electrical degrees (235 feet) tall.  Like all AM stations, for years it serviced the community until it was gradually reduced to a satellite repeater, now owned by Disney.

WDDY transmitter site
WDDY transmitter site

The original transmitter building is in the back, the front was added in the 1970s when the studios and offices colocated with the transmitter.  Prior to that, they were in downtown Albany.

Nautel XR6 Medium wave broadcast transmitter
Nautel XR6 medium wave broadcast transmitter

The Harris BC5H transmitter was replaced with a Nautel in 2006.  The Harris AM H series transmitter has a pair of transistors on the audio driver board that were unique to that transmitter and no longer manufactured.  There are no equivalent replacement parts.  Once those transistors fail, the transmitter is done.

I really think that AM could make a comeback, but the following conditions need to be met:

  1. Kill AM HD radio.  Kill it dead.
  2. Cut away the dead wood.  Those stations that are not making money, have not made money and have no hope of ever turning a profit again.  Most of these are owned by large consolidators that cannot yet afford to write off the bad investment.  More and more will be spun off and given to MMTC and others.  If they can make a go of it, good.  If not, then the stations will go dark and eventually surrender their licenses.  We have one like that around here that basically turns its transmitter on one day a year to avoid license forfeiture.  That should stop, either they use it or lose it.
  3. FM radio will continue to be the investment bank darling, in spite of lower and lower listeners and revenue.  This will lead to more and more translators, HD radio, LPFM, and other things being shoehorned into an already crowded band, creating AM-like conditions on the FM band.
  4. Those that can take on the challenge of an AM station should immediately begin looking at reducing maintenance costs.  Directional antennas are money holes, if at all possible, get rid of the DA in favor of a single tower closer to town.  Duplexing with another AM is a great way to save money and the costs of building a new tower.  Using a taller tower, up to 190 electrical degrees, will daytime signal and reduce the radiation angle (vertical) of the tower, thus permitting better PSSA, PSRA, and or nighttime operation.
  5. Local programming.  Local sports, local politicians, local bands, local church services, local events, etc.  Local.

But anyway…

Where will they put a radio station this time

In the time that I have been working as a broadcast engineer, I have seen some pretty unique transmitter sites. The aforementioned power plant, with the antenna mounted on a smoke stack. The more traditional AM station, is located in a swamp. Other stations both AM and FM combined into one antenna, etc.

WGDJ AM transmitter site
WGDJ AM transmitter site

This is WGDJ, 1300 KHz, Albany, NY.  It is located in what might be a swamp if we were not experiencing marginal drought conditions this summer.  The transmitter is located along route 9J.  It is a four-tower directional daytime, 10 KW, and a six-tower directional night time, 5 KW.  Nothing spectacular, 90-degree towers, spaced 90 degrees apart.  Since they are below 200 feet, they don’t need to be lit or painted, which is nice.

WGDJ directional antenna towers
WGDJ directional antenna towers

The building and all the towers are on 20-foot-high steel stilts.  The area is right next to the Hudson River and often floods in the springtime.

Back of WGDJ transmitter building
Back of WGDJ transmitter building

The transmitter site sort of reminds me of something I once saw at coastal radio stations WCC and KPH.  They were located along saltwater bays.

Phasor with Nautel XR12 transmitter
Phaors with Nautel XR12 transmitter

The station signed on the air in 1963. Initially, it was a 5 KW daytimer only.  They added night operation sometime in the seventies. Around 2006 or so, they went to 10 KW day, 5 KW night.  The phasor is gigantic for a 5 KW station, or even a 10 KW station.  I’ve seen smaller phasors on 50 KW directionals.  It has a “Quakertown, PA” nameplate on it, which may be the forerunner of Phasetek.  There is a rare art form to creating a functional, yet space economical phasor.  Harris could sometimes pull it off, RCA did well, Kintronics seems to be the one of the top phasor makers today.

The main transmitter is a Nautel XR12, which has a very similar look as the V series FM transmitters.  The backup transmitter is a MW5A, which, quite frankly scares me.  The site was just recently air-conditioned, which means the MW5A transmitter was sucking swamp air through it for 25 years.  I do not want to turn that thing on under any circumstances.

Nautel XR12 medium wave transmitter
Nautel XR12 medium wave transmitter

All in all, the station has a pretty good signal into the capital city of New York.  It nulls to the west, somewhat.  Being on 1300, it doesn’t carry as far as some of the other class B AM stations like WROW 590 kHz, but it does alright.

After years of neglect, the station is making a bit of a comeback in the Albany market.  They do a lot of local talk radio, which, when the other station is carrying almost all satellite syndicated talk, is making an impression.  Being the state capital, there is a lot of fodder.

Downgrading AM stations

One of the AM stations around here that I am familiar with is considering a downgrade, which is to say reduce power and get rid of a directional antenna system in favor of a non-DA antenna.  In this particular case, it makes sense, as the station can co-locate with another AM that is closer to the COL by a good distance.  The coverage from the new site at reduced power looks to be a good fit.  If this can be arraigned, the AM station in question would lose a multi-tower AM antenna system that is 50 years old and all the attendant headaches, expenses, and labor that goes with it.

five tower directional AM tower array in a tidal swamp

Many AM stations that are DA-2 or even DA should consider downgrading to a lower power level and getting rid of their DA system.  Directional antenna systems on AM stations are maintenance nightmares.  Unfortunately, in the ’50s, 60s, and 70s, it was often thought that adding power, and extra towers to an AM station would give them great swaths of extra coverage.  Sometimes it worked out, sometimes it did not.  Often what happened was some area was added, but in areas that were nulls toward protected stations, signal strengths went down.  What the station ended up with was more towers, more maintenance, monitor points, a sample system, and more expense.

Taking an AM station in the other direction might actually make more sense.  Go back to one tower non-directional 1 KW or whatever power can be used in the daytime.  Time was when the FCC would only allow certain power levels; .5, 1, 5, 10, and 50 KW.  Those were what a new station had to work with.  No longer is that the case, any power level can be used so long as it meets interference contours and the city of license contour coverage requirements.

Presunrise authority is normally 500 watts and is available at 6 am, post-sunset authority varies but often a PSA extends the on-air time to 9 pm in the wintertime.  For a local radio station, which is what all but the class A AM stations are destined to become, this will be adequate.   For a losing station, it may be that, or turn in the license and sell the land to a developer.

Diplexing on another AM station’s tower closer to town is also a good way to get out of maintaining an expensive antenna array with diminishing income.

Something to think about.