How AM Directional Antenna Proofs Were Done – 60 Years Ago!

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AM radio directional antenna systems go way back; into the 1930’s. The FCC evolved a very strict body of rules to govern every detail of the setup and adjustment of those antenna systems.

From the FCC archives comes this proof of performance done by one of the early and well-known broadcast engineers – Harold Rothrock. Active from the earliest days of radio, Rothrock was a broadcast pioneer.

 

Cover page – WJPR, Greenville, Mississippi

 

The cover shot is from the FCC file copy – notice the manual typewriter, onionskin paper, and crooked text. That’s how it was done back then. How old is this? All FCC to station correspondence was by telegraph!

 

Map for measurement point locations

 

Today we take finding AM proof measurement points for granted. Between GPS and high quality, up-to-date maps, its relatively quick and easy! In 1951, not so much. There was no electronic navigation and the sole source of “good” detail maps was the US Geological Survey 15’ quadrangles. If you were lucky there were more modern 71/2’ maps for your location Hundreds of locations had to be hand-plotted on maps that had to be ordered weeks before.

Getting around was miles of dirt roads and farm lanes. Interstate highway construction hadn’t started yet, and there were a few miles of four lane near cities. Aside from the occasional pay telephone, there were no communications with the site. A few broadcast consultants were experimenting with two-way radio, and others used primitive mobile amateur sets to clandestinely stay in touch.

Measurements went to about 20 miles in eight or more directions, two sets, or more, depending on day/night directional patterns. In our era, these measurements undertakings are measured in days. In Rothrock’s time, weeks or months! In fact, Harold’s wife Mary often traveled with him and set up temporary housekeeping at these sites. Many consultants took wives to measurement projects to assist.

 

Groundwave conductivity charts for WJPR

 

The results of the measurement activities, hundreds of values, were analyzed and hand-plotted on groundwave conductivity charts. These revealed the RF radiation of the antenna system along different radials or bearings. No Excel spreadsheets or graphing assistance here. What is done in the office today in a few hours took days of work with a calculator and slide rule. Just in case you’ve never seen these relics, see them below. By the way, all figures had to be copied off these devices onto paper. You were the working memory!

 

The radio engineer’s tools – 1950: Calculator and slide rule

 

When adjusting an AM directional antenna system, the radiation pattern predicted for the particular tower arrangement didn’t always emerge. That meant this whole, tortuous process often was repeated time and time again until the FCC pattern specifications were proven. Today, method of moments computer calculations allow the RF engineer to model electrical details of the towers and site, and AM reradiation objects, often achieving success on the first try.

 

“Proven” pattern of WJPS – end of the engineer’s rainbow

 

Many directional stations are still operating under the same licenses and configurations as they had many years ago. In the 1960’s and 1970’s, LBA engineered, supervised installation, and did FCC proofs for hundreds of stations. Because many of the station which must be considered in cellular AM detuning and AM collocation today, are of the old type, we are uniquely positioned to understand and help wireless operators deal with their idiosyncrasies.

If you would like to look at the whole 60 page, handcrafted 1950 WJPS proof, you can download the PDF HERE.

For assistance in AM colocation or AM detuning, contact Mike Britner at 252-757-0279 or mike.britner@lbagroup.com.

Since 1963, LBA has also supplied innovative AM and medium wave antenna systems to broadcasters around the world.

25 Comments on "How AM Directional Antenna Proofs Were Done – 60 Years Ago!"

  1. Alan Casebier March 20, 2012 at 4:14 pm · Reply

    LB, I just reviewed your AM proof article with interest and yes I’ve had a slide rule in my hands, but never had to seriously use it. Thanks for the articles and the network invite.

    ln

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  2. Yaacov (Jay) Goldma March 21, 2012 at 1:02 pm · Reply

    Wow, this brings back memories! In 1968/9, as a neophyte engineer, right out of tech school, I had the great learning experience of taking all the field strength measurements for an antenna proof of performance at WTTM, in Trenton, NJ. It was a three tower 1KW array, figure eight pattern. Not only did I learn a lot about RF field strength measurements, but also how to read a map and how to stay off of someone’s property without asking first if I could use their driveway or private road to set up my equipment.

    ln

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  3. William Burckhard March 21, 2012 at 3:51 pm · Reply

    I remember a proof for KMON in Great Falls, Mt. where i got stuck in the mud in the middle of a farmers field. He stuck his truck in there trying to get me out and both vehicles had to be pulled out with a very large tractor.

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  4. anthony stewart March 21, 2012 at 5:21 pm · Reply

    I designed and tested the radiation patterns of antenna for sounding rockets at Bristol Aerospace Ltd ( now Magellan) about 40 yrs ago. and just used a CW transmitter with transmitter aimed fro one rooftop to another which had Rx Antenna under test.

    It was a stretched dipole that was spun in space after the nose cone was ejected and was coasting at 5 Hz spin rate for 15 minutes. the experimental data was collected during the whole time. The only dropouts were only when the axis of the antenna was pointing exacting at the ground stations. To verify the performance. my shop foreman (Ernie Hoplock) designed and built the test jig so I could rotate yaw and azimuth of the rocket nose with the relative angle marked .

    It was a manual jig built like a proverbial “brick s***-house” on teflon sliders. I put a biconical wideband antenna on the rooftop of building A and received with a spectrum analyzer on building B and measured the level , increment rotate by 10deg or enough to change 3 dB whichever was bigger and repeat. for a dipole made from a cold rolled 1/4″ braided wire and stretched out using string to a dipole to simulate being spun out by centripetal force of a spinning rocket at high altitude, I was able to map out the performance of the expected signal patterns with biconical notches when viewed from either end..
    The antenna length was optimally tuned to length by using a return loss bridge to measure the reflected power voltage on the RF diode. and hence the null point was the resonant frequency. Same could be done using a directional coupler and RF diode or spectrum analyzer or power meter.

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  5. Anthony Stewart March 22, 2012 at 8:22 am · Reply

    I designed and tested the radiation patterns of antenna for sounding rockets at Bristol Aerospace Ltd ( now Magellan) and the Shop foreman designed and built the test jig so I could rotate yaw and azimuth with an indicator marked.It was a manual jig built like a proverbial “brick s***-house” on teflon sliders. I put a biconical wideband antenna on the rooftop of building A and received with a spectrum analyzer on building B and measured the level , increment rotate by 10deg or enough to change 3 dB whichever was bigger and repeat. for a dipole made from a cold rolled 1/4″ braided wire and stretched out using string to a dipole to simulate being spun out by centripetal force of a spinning rocket at high altitude, I was able to map out the performance of the expected signal patterns with biconical notches when viewed from either end..

    ln

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  6. William Crunkhorn March 22, 2012 at 10:09 am · Reply

    Neat.

    That’s one application when you can be sure of a good line of sight with minimal multi-pathing.

    Bill

    ln

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  7. John Robson March 22, 2012 at 10:58 am · Reply

    I still have a slide rule, keep it as a reminder!

    ln

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  8. Mark Moss March 23, 2012 at 8:14 am · Reply

    @Yaacov (Jay) Goldma
    Wow Jay, I did WBUD’ bak in 83. Hope all is well with you.

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  9. Sam Virgillo March 23, 2012 at 10:17 am · Reply

    Wow. That brings back memories…

    I started in radio at the ‘Big BUD’ WBUD back in ’71.

    I too remember getting stuck in the mud at one of the monitoring points. What a mess. Also recall trying to time the day/night readings so the change over would occur just as I finished the day readings.

    I also remember being nearly attached by wild dogs when going to do tower base readings there. That was a bit scarey.

    Later when I worked at ‘CAU I remember doing a skeleton proof that took me into some neighborhoods that I was lucky to make it out of.

    Doing a lot of remotes these days. Different challenges now.

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  10. Gary A. Smith March 26, 2012 at 4:32 pm · Reply

    I did my first proofs with a round slide rule which I still have. At KLUB, Del Williams and I hand built a CPM based computer and modeled the array in basic. It would take abour six minutes to do the calculations and print them. Each change require a new data dump to the printer. Two years ago Ben Dawson and I did a MOM Super Model for KMVP. The setup of the ATU’s and the Phaser was extremely accurate and required minimal adjustment. Times have changed.

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  11. Gary A. Smith March 26, 2012 at 4:36 pm · Reply

    I might also add that my first field strength meter ran on a 12 volt marine battery and weighed as much as the battery. The antenna required several minutes to set up and the whole process was qute labor intensive. Since field strength readings were done several times a week, the introduction of the
    Nems-Clarke was a real time saver.

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  12. Roland Richter April 16, 2012 at 8:38 am · Reply

    Interesting reading! My first experience with field readings was at KBGO-AM in Waco, Tx in 1966 using a tube type field meter looking at monitor points on a 4-tower array. I think there were 9 or 10 points in the day and 12 at night. Later at KSPL San Marcos and KVOZ Laredo used an FIM-21 to do full proofs of a two tower and three tower respectively. Even in the 1980′s this was often interesting, particularly for the Laredo station where there are not many roads, just open ranch land. The KVOZ proof began in August with navigation by compass, USGS maps, sticks and rope and DF-ing the station…temps over 100 and one day with 17 miles of walking one radial, no gps and no cell phone. Done once non directional, then because adjustments from theortical had to be made, about three times on directional. There are many folks who have done this many, many times for a living. A true adventure every time.

    ln

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  13. Lawrence Behr April 16, 2012 at 8:39 am · Reply

    Roland, right you are. Every project was an experience. I remember once, near College Station, TX, wandering into a n A&M research pasture for some field points. I was amazed to see cows with plexiglass windows into their stomachs, wearing nuclear radiation hazard signs!. The proof ended up doing without those points!

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  14. Roland Richter April 16, 2012 at 8:44 am · Reply

    Lawrence:
    Heard the same story about the cows but without the radiation signs! What station were you measuring there? I worked at WTAW in the late sixties while attending A&M and some part time after transferring to UH later. WTAW was daytime in those days with a Collins transmitter. They have since gotten night time with a directional and an expanded band transmitter on 1620…I think they moved the WTAW calls to 1620 from 1150. A lot of history in that station!! I went from there to KRBE and KILT in Houston until Uncle Sam couldn’t finish his war without me in the seventies…

    ln

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  15. Henry Ruhwiedel April 16, 2012 at 8:45 am · Reply

    TIme for Older Than Dirt to weigh in again. My first regular field readings and proof was WGSB St Charles, IL. 1966. A DA2, I took the day pattern measurements during the day, and the night pattern at night. Mostly urban/industrial sites. I’m out at 3 AM and a cop stops me during a FSM measurement and asks waht I am doing. I Tell him I’m CE and doing field measurements and pattern adjustments because its a tiny bit out of tolerance. He asks where else do I do this so I name a few locations, he drives off. About an hour later I return to the station. The cop is there complaining he waited at one of the other locations and I never showed up. So I had to take him inside and show the photos of the original proof field points showing exactly where I was was the exact same place the original proof readings were done. It takes me an hour to convince this guy I am not casing places to rob. The idiot shows up later in the day and comploains to the GM about my “stalking around at night.” The GM tells him to take a hike. Besides I was the county comm officer for civil defense (yeah old enough to remember that?)

    Come May, I am up the towerrs changing lights, DuPage county airport is LOS a couple miles away. Suddenly I see 4 military jets at my 12 BELOW me. I never got down a tower so fast. I didn’t know a Chicago station had scheduled an air show at the airport. Well I did get a birds eye view of it!

    Henry Ruhwiedel

    ln

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  16. Henry Ruhwiedel April 16, 2012 at 8:45 am · Reply

    Another station was in SD 1000Khz. Had to do a radial proof after adjustment to get a null that happened to fall exactly along a HV wireline that ran for 50 miles. I had been sent another kid along to help, I would have him watch the field point while I cranked on the phasor. There was a dir road with a curve at the entrance to teh corn field array. The inside of the corner was a 6′ drop off. Yup, he backs out across the road and off the drop off. tow job #1 to put the exhaust back on. On another radial, the road turned to mud for 2 miles up and down a small hill. The Audi was front wheel drive. Yup up to the axels about a half mile in. OK, back out foot to the floor. Exhaust repair #2. Lesson, when the dirt roads of SD turn muddy, find another road.

    Henry Ruhwiedel

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  17. Henry Ruhwiedel April 16, 2012 at 8:46 am · Reply

    Another station: Gilda Radnor [Radcom} bought an AM NE of Detroit where Lionel makes trains. Pattern was way off and field strength was 20% of what it should be on daytime. DA2, towers in line on day and dog leg at night. Towers 2/4 are about 6 feet apart. Talk about coupling! Made an RF choke from some handy 1/2″ heliax to kill tower 4 to work on the day Night pattern tuned in on the first crank, radial checks showed all points near dead on. Went to non directional with tower 1. Got a half mile away and discovered tower 1 was not connected to RF. Drove back, tubular lead from antenna tuner to tower had fallen off. New bolts later, checked and RF field was as expected omni, first 3 points on one radial are through a cemetary, then its water of Lake St CLair. Measurements to 5 miles on 6 radials shows omni works fine.
    Back to day pattern. Cranking away for four days the pattern comes in but RF level is way low. Found the copper radial wires in the ground had been removed from the day pattern and used for the night towers. No ground system for day pattern!
    OK, hook up towers 2, 3 to nearest ground strap points on towers 4, 5. RF level now seems about right. Amazing what a little ground system will do. We are out driving the length of each radial. One happens to fall through a not so nice part of Detroit. As we get to the site, we notice a group of youths carrying bats, clubs and looking mean. We noted, reading not taken at this location due to local interference.

    Henry Ruhwiedel

    ln

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  18. Lawrence Behr April 16, 2012 at 8:46 am · Reply

    Roland – It was WTAW. In the early ’70′s we designed and supervised the build and proof of a directional array for higher power day, and night time operation. WTAW was on 1150 kHz, but has subsequently changed call sign frequencies. At the time, it was owned by my good friend (after all this time!) Bill Watkins.

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  19. Roland Richter April 16, 2012 at 8:47 am · Reply

    I remember Bill! He was GM when I worked there beginning in ’68! He had a lot of “interesting” advise for a young guy going to college! At that time if memory serves me right, they were next to a mobile home park..or maybe it was around them. They had a Sparta console in the control room and simulcast mono FM at the time. I became good friends with a sales guy named Mike Wisnieski at the time who was interested in FM-DX…One night after sign off we hooked his FM tuner to the FM transmitting antenna to do some listening. He lived in one of those mobile homes next to the station. At that time I was living in Leggett Hall at A&M…had the ham rig in the room with a long wire stretched to the water tower behind the parking lot behind the dorm…but that’s another whole story!! I mostly wrote copy and cut spots between classes and evenings at the station. They kind of let me come and go as needed and it was a good job for a college kid.

    ln

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  20. Tim Sawyer April 30, 2012 at 9:15 am · Reply

    Oh war stories, aka life in the field? Fun times. Worst possible area? Meadowlands New Jersey. Re-radiation nightmare. 40 years in the field? Yeah I’ve seen it all.

    ln

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  21. Lawrence Behr April 30, 2012 at 9:16 am · Reply

    Hi Tim! You’ve had your share of field “fun”. Maybe even a story to contribute?

    ln

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  22. Bob Groome April 30, 2012 at 9:16 am · Reply

    Lawrence

    A good read indeed. I worked one summer for Carl E Smith. That would be in the early 70′s. We still ‘ran radials’, plotted on graph paper, calculated every thing wild slip sticks, and Carl Would submit to FCC. Lots of work and yet gave me a good over view on how all this works. That fall if I remember right, the first scientific calculator (an HP with a thermal printer and magnetic strips for your ‘programs’ came out. That would have really speeded things up. Had my first 1-2-3 spread sheet a couple more years later and that was hot sh**.

    Thanks for the good history lesson!

    ln

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  23. Dick S. Pickens May 7, 2012 at 2:33 pm · Reply

    Three comments: (a) I never saw an “irradiated” cow, but did meet a few “irritated” bulls when I climbed over a gate with my FIM-41 to take a point about 40 yards inside. The bulls thought my FIM was a food container. It and I barely made it back over the gate before the horns got there. They were very irritated that there was no food left behind. (b) As an ABIP inspector I have been into many of those AM-DA sites that are just as they were 50 years ago sans some of their ground radials and licensed parameters. (c) And I still have my old Nems Clarke meter and some good spare batteries for it. It matched up very well recently against a new PI-4100. As the old saying goes, “They don’t make ‘em like they used to!”

    ln

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  24. Lawrence Behr May 7, 2012 at 2:33 pm · Reply

    We still have several of the old Nems-Clarke and RCA monitors around, including one I purchased in 1962, along with the FIM-21 and 41 meters. Because Potomac is not particularly helpful on service to the FIM-21 and 41, we graduated our field engineers to the 4100-meters. They are pricey at $16K a copy, and not nearly so convenient as the predecessors. They do have a few useful features, but I can scratch notes in a notepad for a whole lot less money!

    We would like to restore the old NC and RCA units for old times sake. Any suggestions, manuals, etc. would be welcome.

    ln

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  25. Dick S. Pickens May 7, 2012 at 2:34 pm · Reply

    I DO have a pretty good copy of the Instruction Book for Model 120-D.

    Dick

    ln

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