Your favorite AM directional array patterns

[1L6E6VHF]

I'm asking all those out here who follow AM radio to post their "favorite" AM radio directional patterns, those that provide highly effective whilst doing their important task of protecting other stations from interference.

Sadly, my candidate for favorite was razed more than 20 years ago (the station still lives on 92.7 FM, and one tall tower stands holding their FM antenna high in the sky, on the same land that once held five smaller ones: CHYR, 710, Leamington, Ontario (now CJSP with country**)

http://fccinfo.com/CMDProEngine.php...bSearchType=Appl&sAppIDNumber=495266&sHours=D

note how this array effectively protects everything from dead west, though all southerly directions, all the way to just north of East, whilst delivery 90% or more of its peak power (about the equivalent of 30 kW using a 10 kW transmitter) over more than 70° beamwidth and at least 25% of peak power over a 115° swath.

I grew up on Detroit's East Side and received an excellent signal from "Cheer", never knowing that its signal was near nothing anywhere south of Detroit.

Compare this to the pattern of the six-tower night pattern of WWJ (950)

http://fccinfo.com/CMDProEngine.php...SearchType=Appl&sAppIDNumber=1155695&sHours=N

Of course, the beam is narrower, necessarily so, but peak power is only in an infinitely small point right around 353° - it's actually weaker at 352° and 354°!

**contrary to what you may have read, CHYR did not move from 710 to 96.7, where the CHYR call is currently heard. CHYR moved from 710 to 92.7, still with an AC format, but switched to country later. Today's CHYR (96.7) came on many years after CHYR 92.7 went country. Its call changed to CJSP around the same time 96.7 CHYR was lit.

 

[Schroedingers Cat]

"Now, turn your radio to 730 and listen for this sound." "Beepity Beep Beepity Beep Beepity Beep." "You're back on the beam with Cheer!" BEAM is the operative term. Probably without the use of computers, they were able to design a highly directional multitower pattern that had not only a wide beamwidth, but a central beam that did not fall off much for 30 degrees either side of the axis of the towers. There are so many patterns that I regard as my favorites, I don't know where to start. Many have advantages that I never knew about until all the parameters were available on the internet. I'll try to think of some. Anybody know how to post images here?

CHYR Day Pattern

https://transition.fcc.gov/ftp/Bureaus/MB/Databases/AM_DA_patterns/305316-26504.pdf

 

[Schroedingers Cat]

I've asked this question before on various boards, but history seems to be lost. Does anyone have access to very old databases for AM, and even very early FCC DA records?

One that I am particularly interested in is the 1000 watt daytime pattern of WBBC 1330 (now WTRX) Flint, MI. At the time it came on the air in 1947, the only daytime consideration was WEXL 1340 Royal Oak, which was 250 watts nondirectional from the now WOMC tower, which is between 1/2 and 5/8 wavelength. WILS (now 1320) Lansing was on 1430 at about that time with just 500 watts daytime only. WLEW (now 1340) Bad Axe was on 1500 at the time with 250 watts nondirectional daytime. WBBC could well have protected WEXL with just two towers (a near cardioid), allowing better coverage with just 1000 watts in the Western Genesee County areas. A whole lot of stations upgraded from 1000 to 5000 watts in the late 1950s. Unfortunately, by the late 1950s, WILS had moved to 1320 and WLEW moved to 1340 to allow WJBK (now WLQV) to upgrade from 250 watts on 1490, eventually to 50000 watts on 1500. WEXL and WLEW were required to directionalize in the daytime when they increased from 250 watts to 1000 watts to protect WTRX as a newly licensed 5000 watt three tower daytime facility. This did allow the benefit of WEXL to greatly increase its signal toward Detroit proper, and WLEW to be received better on the shore of Lake Huron way up as far as Harrisville. But WTRX was left squeezed in on all sides by WILS, WLEW, and WEXL. This also required a sacrifice of Western Genesee County to protect WILS. I'm sure this happened all over the place, but I've often wondered what the parameters of the two tower day pattern were. It also could probably have been 5000 watts with three towers with a wide open pattern except WEXL protection. Many stations have upgraded to a three tower near cardioid with much increased power, the type of pattern used by many of the former Class I-B stations that protect each other with 50000 watts nighttime with just three towers.

 

[davideduardo]

There are so many patterns that I regard as my favorites, I don't know where to start. Many have advantages that I never knew about until all the parameters were available on the internet. I'll try to think of some.

I am most fond of patterns that enhance the coverage of a station so the power is not wasted.

Of course, not many stations can play "pick a pattern" but I know of three rather exotic ones.

Radio 10 in Buenos Aires, Argentina was a new station built in the mid-90s on 710 AM with a license for 100 kw non-directional. The site is to the NW of Metro BA, and there was concern for signal strength in the very dense central parts of the city. So a passive tower was built NW of the main to nudge a bit more power towards the city and less towards the rural areas and Paraguay. The result was the equivalent of about 130,000 watts towards the desired area. It worked beautifully.

Ecos de la Montaña in Quito was a 10 kw non-directional license on 660. In 1970, I installed it as a two tower directional to send the signal roughly north and south up and down the andean corridor where the population was concentrated. We sent less than 1 kw east and west, and enhanced the other directions significantly. The station had no phaser as we fed matched coaxials out of the transmitter to each tower from a tx building rather perfectly placed half way between the towers.

Finally, going back to the 60's the big Colombian network, CARACOL, had a 50 kw station on 820 in Cali. Cali is in a valley with the population extending up and down the valley which was much longer than it was wide. They built a directional system to optimize the signal in all parts of the valley, using the same "matched" line idea. But in this case, they had open line from a building near one of the towers. Two lines left the building in parallel, and traveled to the center of the array, where one folded back and one went to the farther tower. It worked marvelously and it was the inspiration for my system built about 10 years later in Quito.

 

[Schroedingers Cat]

Thank you David, for americanradiohistory.com, which allowed me to accurately reconstruct the timeline of the frequency changes and power increases, as people otherwise would express doubt as to whether the timeline was accurate. The FCC history cards are another excellent resource to supplement such timelines, but they are very limited in numbers so far. It seems like call letter changes and ownership changes have allowed some of these to be misplaced. I see one station where the folder is there, but no contents were found.

Some FCC engineers have gone so far as to rescue some old historical information and even technical treatises from dumpsters. These often contain the technical reasons why certain decisions were made, such as the terrain roughness factor for FM protection, and the actual construction of various engineering graphs and maps.

 

[Schroedingers Cat]

While many stations placed their directional antennas where they concentrate their signals over the Community of License, this was a double edged sword when suburbanization placed many people in the nulls of the DA. WCFL/WMVP is the ONLY AM station in Chicago to place a 25 mV/m predicted signal over the entire City of Chicago. However, when people started moving to the furthest West suburbs, the night pattern became a liability. Glen Clark designed their current dogleg night pattern, which allowed a slight increase in the IDF in one of the nulls, and also let out the shallow nulls in the day pattern further.

Another happy coincidence happened with WAMM 1420 Flint (now WFLT), which originally applied for a clear channel in the 1500s with just 250 watts. Due to some shifting to accommodate the increase from 10000 to 50000 watt WJBK, another channel was proposed, 1420 kHz, with 500 watts, but as you well know, was right up against the post with interference to WHK 1420 Cleveland, and fellow Malrite property WBRB 1430 Mt. Clemens, and had to be directional with a two tower array. This allowed them to concentrate the signal over the population it intended to serve, the African American population of Flint. The station was originally the dream of well known Detroit and Flint R & B Disk Jockey "Frantic" Ernie Durham. He was forced by the FCC to sell his share of the station when employed by competitor Booth Broadcasting, owners of WBBC and WJLB.

With the East central city TL, it had a strong signal throughout the city, as it was no further than 4-5 miles from the far corners. The nulls were to the SE toward Mt. Clemens and Cleveland, and generally fell over areas not demographically advantageous. Around 1980, they were awarded 142 watts PSSA, which they eventually were able to license fulltime. Even with a 27 mV/m NIF exclusively from WHK, most of the city receives an interference free contour. It also is in a creek bed that has conductivity equal to or exceeding M-3. On the clear channel, it would have been stuck as a strict daytimer on a Class I-B channel within the protected skywave contour.

 

[Schroedingers Cat]

Thanks again to David's site and the FCC history cards for reconstructing the above timelines.

 

[Kelly A]

Of all that I've had to deal with over the years, I can't think of one MW directional antenna system as a favorite. The ones I worked with were either messed up from years of neglect, incompetent technical staff, changing environment around the antenna system, or building a new design to put it on the air. Do I miss those days of AM directionals and all those damn measurements? Nope, no way!

 

[K.M. Richards]

Let me know when you're ready to hear about one of the stupidest directional arrays I ever saw, created only so the station could put "50,000 watts" on the advertising rate card. This one is a doozy.

 

[Schroedingers Cat]

There are quite a few 50000 watt stations with multitower directional patterns, and a lot of them have less than great coverage. Where do you start? If you can concentrate your signal where you want it, and minimize it where you have to, you can gain from it. I suspect that most DAs today are not well maintained. Just looking at keeping monitor points below the specified value, and not at the overall coverage and large lobes, doesn't tell you much. It also has to be close enough to put a strong signal in the area to be served. Wasting strong signals over areas of low population density happens a lot these days, trying to comply with numerous regulative constraints, the the cost of land and land usage restrictions in areas closer to a city and surrounding area. I actually think the consulting engineers used to do better without all the extensive computer design and databases. But there were fewer constraints in the past also.

If FM DAs required regular proof of performance tests after installation, you'd find a lot of strange things also. And even nondirectional antennas on FM ARE directional, unless they have been extensively modeled to minimize directionality. And AM nondirectional patterns can be distorted by nearby towers in an unfavorable way.

Remember that WKRP in Cincinnati was 50000 watts in the pilot episodes? The last zero was dropped in subsequent episodes, leaving the "5000" off center in the mock up coverage map on the wall. Seems like you could see where the other zero was removed.

 

[davideduardo]

Let me know when you're ready to hear about one of the stupidest directional arrays I ever saw, created only so the station could put "50,000 watts" on the advertising rate card. This one is a doozy.

1520 Port Hueneme

 

[Schroedingers Cat]

I'm surprised David didn't bring up WJBK/WLQV. In the early 1950s, WJBK was a 250 watt Class IV on 1490. Eventually they moved to 1500, first with 10000 watts daytime, then to 50000 watts daytime with 9 towers day, and 1000 then 5000 watts night with 12 towers. They were actually only able to get 2500 watts input, and burned off another 2500 in an SLR. Between the 132 degree towers and the pattern gain, they met the 392 mV/m minimum efficiency for 5000 watts. They negotiated to get 10000 watts night, and also taking three towers down, in an interference agreement with WTOP and KSTP. It took many years to accomplish.

Because it is in good soil, uses somewhat taller towers, and has an endfire component that reduces fading, the signal is pretty good, all things considered. But Storer really wanted to be 50000 watts night also.

 

[xmtrland]

I help maintain 3 directional 50kw stations on Vashon Island. The favorite would be the KIRO 710 array. Non directional day, directional night protecting the east coast and down south to LA. From what I hear it was the first 50KW directional west of the Mississippi. Just two towers, original impedance was around 71 ohms, since been rebuilt to 50 ohms. It's just two towers and fairly simple design. Good night time coverage to all the western Washington area. Can run Directional during the day and no one notices. The transmitter site was built in 1941 and is a great place to store my antique radios and other old radio stuff. One of the real interesting points is the 1 year of program logs from 1946 that have been stored at the site since the late 40's. Very interesting reading.

The other two stations I work with are less than a mile away from the 710 site, and are directional day/night, 1090 and 770 share the same transmitter site and three towers. Both of those you know when the night pattern is on. 770 was originally a 1KW daytimer in Seattle with the call letters KXA, now it's KTTH.

It's interesting to note that when KIRO moved to their Vashon transmitter site in 1941, KXA moved to the old KIRO long wire antenna on the Arcade building in downtown Seattle and broadcast from their for a long time. Eventually the station also moved to the KING/1090 site on Vashon island to increase power to 50KW day and 5KW night (and less than a mile from the present KIRO 710 site). There is an engineering report that states the 5KW night pattern for 770 outperforms the 1090 50KW night pattern. This lead up to an onwnership swap between 770 and 1090 which was written into the original lease.

1090 was the original occupant of their site, moving to Vashon in 1946 (then know as KEVR latter as KING). 770 moved to the site in the 90's but had to agree to swap frequencies if 1090 wanted to. When the 1090 site was bought by Bonneville, they elected to swap 1090 for 770 so they would have the better night signal at only 5kw on 770 versus not as good night signal on 1090 at 50KW. 770 played better in places like Kent, Bellevue and Federal way. 1090 has a null in Des Moins/Federal way area where you can barley hear 1090 even though your less than 4 miles from the transmitter and can see the towers.

Both 710 and 1090 were built by Jim Hatfield senior in the 40's. I have his original hand written notes on the 1090 array, ironically written on 710 stationary from 1945. 1090 has had alot of work done on the day and night patterns since 1946. In looking through the logs and notes, it looks like they were changing things almost every 5 years from 1946 through 2013 when 1090 went to the mom proof system. We just did a mom proof on 1090 last week.

Interesting to see how these three stations have interacted over the years reading through the engineering logs at the 1090 site and the 710 site. I also have access to the engineering records for the KOMO transmitter site on Vashon which was built in 1943. Having access to the past engineering of three 50KW sites on Vashon gives a unique picture on how certain stations engineers worked together and others did not. It's great to be able to have hands on reading of some of the engineering history and the stories. Today I'm off to mow the grass at both sites and make them look good as you drive by.

 

[K.M. Richards]

Let me know when you're ready to hear about one of the stupidest directional arrays I ever saw, created only so the station could put "50,000 watts" on the advertising rate card. This one is a doozy.

1520 Port Hueneme

That's the one.

Went from 10kW DA-D to 50kW DA-D and threw most of the extra wattage due west into the Pacific Ocean to protect KOMA in Oklahoma City. Spent tons of money on the directional array and an RCA Ampliphase, plus the electric bill for that beast from the mid-1960s to the early 2000s, before downgrading back to 10kW. (All the while, night service was 1kW with a different DA using an old Collins transmitter, meaning the switch at sunset was an incredibly noisy affair, shutting down the RCA, switching to the night pattern, and firing up the Collins. Never accomplished without a few seconds of no carrier. The switch to day pattern and power usually went smoother.)

When I worked there briefly in 1978, one of my tasks was to trudge out to the towers and take base current readings while we were at high power. It took the better part of a half-hour, which is why it wasn't done by the operator signed onto the log (the station was a live top-40).

Back in 2011, they discovered one of the night monitoring points was out of tolerance and dropped night power to 650 watts on a STA. Six months later, they discovered that an employee of the agricultural concern using the adjacent property crossed over the boundary line and tore up about half the ground radials for one tower (as described here). That necessitated a further reduction in night power to 136 watts and day power to 4.6kW.

The STA has been renewed regularly, with each application providing a progress report on investigation and actions taken by the licensee, including a bet hedge in 2014 that they were also exploring a new transmitter site because the landowner wants to sell the site and has no interest in a long-term lease for the towers (they did eventually get their lease, as noted in the STA extension application last August). In the meantime, they have flipped formats and call letters between 1520 and co-owned 1590, and again between co-owned 1400.

The latest paperwork was filed in February of this year, for a silent STA because the array was not tuned to match their Harris 10kW transmitter, which blew out most of the 54 RF amplifiers in same (Read all about it here).

They've spent a lot of money trying to get that 10kW array functional, when it probably would have been fine if kept at 10kW in the first place.

 

[1L6E6VHF]

I'm surprised David didn't bring up WJBK/WLQV. In the early 1950s, WJBK was a 250 watt Class IV on 1490. Eventually they moved to 1500, first with 10000 watts daytime, then to 50000 watts daytime with 9 towers day, and 1000 then 5000 watts night with 12 towers. They were actually only able to get 2500 watts input, and burned off another 2500 in an SLR. Between the 132 degree towers and the pattern gain, they met the 392 mV/m minimum efficiency for 5000 watts. They negotiated to get 10000 watts night, and also taking three towers down, in an interference agreement with WTOP and KSTP. It took many years to accomplish.

Because it is in good soil, uses somewhat taller towers, and has an endfire component that reduces fading, the signal is pretty good, all things considered. But Storer really wanted to be 50000 watts night also.

But the falloff in the 12-tower pattern when one was not right in the center of the lobe (17° true) was drastic. At night where I used to live (EN82mj), WDEE was weaker than WLAC 1510 at night most of the time, with all those 1490s running on the channel below squeezing "Big D" from both sides (the 1490s would become four times the trouble in the mid-1980s). WSM actually had the best country signal at night! In Grosse Pte. Farms, right where Jefferson Ave met Lake St. Clair and became Lakeshore Drive, the signal would drop in in the daytime!, while it absolutely boomed along parts of I-69 in St. Clair County about 80 air miles out! It was stronger up there than in the Amy Joy Donut Shop on the other side of Dix.

I forgot the name of the broadcasting pundit who said (about 1500): "You can hear it in Norway, but not in Ann Arbor".

 

[semoochie]

That's the one.

Went from 10kW DA-D to 50kW DA-D and threw most of the extra wattage due west into the Pacific Ocean to protect KOMA in Oklahoma City. Spent tons of money on the directional array and an RCA Ampliphase, plus the electric bill for that beast from the mid-1960s to the early 2000s, before downgrading back to 10kW. (All the while, night service was 1kW with a different DA using an old Collins transmitter, meaning the switch at sunset was an incredibly noisy affair, shutting down the RCA, switching to the night pattern, and firing up the Collins. Never accomplished without a few seconds of no carrier. The switch to day pattern and power usually went smoother.)

When I worked there briefly in 1978, one of my tasks was to trudge out to the towers and take base current readings while we were at high power. It took the better part of a half-hour, which is why it wasn't done by the operator signed onto the log (the station was a live top-40).

Back in 2011, they discovered one of the night monitoring points was out of tolerance and dropped night power to 650 watts on a STA. Six months later, they discovered that an employee of the agricultural concern using the adjacent property crossed over the boundary line and tore up about half the ground radials for one tower (as described here). That necessitated a further reduction in night power to 136 watts and day power to 4.6kW.

The STA has been renewed regularly, with each application providing a progress report on investigation and actions taken by the licensee, including a bet hedge in 2014 that they were also exploring a new transmitter site because the landowner wants to sell the site and has no interest in a long-term lease for the towers (they did eventually get their lease, as noted in the STA extension application last August). In the meantime, they have flipped formats and call letters between 1520 and co-owned 1590, and again between co-owned 1400.

The latest paperwork was filed in February of this year, for a silent STA because the array was not tuned to match their Harris 10kW transmitter, which blew out most of the 54 RF amplifiers in same (Read all about it here).

They've spent a lot of money trying to get that 10kW array functional, when it probably would have been fine if kept at 10kW in the first place.

Most of the extra signal may have gone into the Pacific Ocean but they also covered parts of Los Angeles fairly well.

 

[davideduardo]

Most of the extra signal may have gone into the Pacific Ocean but they also covered parts of Los Angeles fairly well.

I don't recall it getting farther to the SE than the Conejo Grade, although it may have had a bit of a signal in the Malibu/Pacific Palisades/Santa Monica area... but when it was operating at 50 kw I don't think I ever got out to that area.

The period when they had 50 kw was one of less man-made interference, so I guess anyone in the NW part of LA County who wanted badly to hear them listen if they tried.

 

[Schroedingers Cat]

I remember finding out that WJBK was 50000 watts in about 1967. A Junior High schoolmate had built a Heathkit AM/SW radio, and an add on product was a copy of WRTH. I was surprised, since their signal was weak near Flint, and had not yet seen their pattern or the groundwave curves in the NAB Engineering Handbook. I knew that lower frequencies carried better in the daytime than higher frequencies, but it was not quantified until I saw those graphs. Also, in my neck of the woods, WKMF 1470 had a 100 mV/m signal and splatter for 30 kHz either side pre NRSC. When we'd go to Tiger Stadium, I'd bring the transistor radio in the car and try to put the radio next to the pillar between the back window and rear window riding in the car. All the way through Detroit and somewhat beyond "Eight Mile" on I-75, I noticed that while WJR would fade out in many underpasses, WJBK did not fade out in the underpasses. With the AGC you could barely notice. Now some of that may have been due to the frequency difference in attenuation of the underpass and the radio peaked at the top of the band, but I was impressed with the signal. Is there something that would absorb the signal or shadow it in Grosse Pointes?

 

[semoochie]

1520 Port Hueneme

Hueneme? Hue not a different place?

 

[1L6E6VHF]

@Schrodinger's Cat:

Yes, the loss of signal strength encountered when going under an overpass is less severe with increased frequency (hence you can see visible light, 450-700 THz, as easily under the overpass as below it). It is noticeably not as severe at the top of the AM dial as as the bottom, and far less severe in the international shortwave broadcasting bands.**

I-75 in SE Oakland County and the northern edge of Detroit was right in that super-powerful lobe. When the 12-tower array was still up, their major lobe just may have had the most powerful beam of any AM BCB station in the Americas (I wouldn't know how to investigate that now).

There did not need to be anything to absorb or shadow the signal in GP Park and GP city. There was hardly any signal to shadow. GPP and GPC were at about a 45° azimuth from the WJBK et al array. In that direction they were more like 500 watts day and 50 watts night.

**You would not believe how many people insisted that a shortwave broadcast could not be heard under an overpass. People who actually worked in the engineering field and hams with extra class tickets would insist that since the modulation used was AM, that the modulation would be "captured" by the overpass. Of course, FM easily gets under the overpasses as it has waves about 1/100 as long. An AM signal at 100 MHz would get under the overpass, as an FM signal at 500 kHz will be blocked, as the AM video signal of a lowband TV station would be carried with the same station's FM audio when sporadic-E skip was in.