The Boeing 707 HF antenna coupler

2. Antenna Couplers

The Automatic Antenna Coupler production provided cash flow to keep the plants open in the '50s and early '60s. Couplers were needed for long range over the ocean communications. As illustrated on the right for the KC-135, tail tops or wing tip installations were common.

2.1 The Antenna Coupler Program

Contributed by Marc Shoquist, Project Engineer on Antenna Coupler Development - 1951 U of M graduate, Electrical Engineering. Joined ERA in 1953 (34 years with ERA/Sperry)

     ERA took on many study contracts from the government during its early years and one of the most successful was the Antenna Coupler program which resulted in the production of over 12,000 units for military and commercial aircraft communication systems during the 1953 – 1970 period, after which the program was transferred to Sperry Marine Systems. It was the largest production program ERA had in the mid 1950’s and during the 1953 – 1956 period represented over 25% of the sales and most of the profits for the division. During the 1953 – 70 period, there were three generations of antenna couplers developed; the initial model which used vacuum tubes, an all solid- state unit for the Boeing Jet aircraft developed in 1955 and finally a high tuning speed unit for the General Dynamics B-58 Hustler Bomber developed in 1958.
    The coupler consisted of a variable vacuum capacitor and inductor coil, each driven by servo motors which were tuned to automatically match the antenna impedance to the coaxial transmission cable. The tuning elements were controlled by a discriminator which sensed the resistance and phase at the termination of the coaxial cable to the antenna. The coupler tuned wire, probe and tail cap antennas in the High Frequency (HF) 2-30 MHz range. The 707 used a probe antenna mounted on top of the tail fin so the coupler was exposed to the outside environment where temperatures were frequently below – 65 degrees F. Moreover, the coupler after being in a cold soak at this temperature had to start up an complete the tuning within 10 seconds, a no easy task. In addition, the probe antenna impedance was so miss-matched at low frequencies that the coupling voltage to the antenna was over 20,000 volts. The early units were pressurized with dry nitrogen and sealed with a soldered seal. Later a Teflon coated O-ring seal was developed which was able to hold a vacuum over a long period, which simplified maintenance of the unit.
    In the early 1950’s RCA won an Air Force contract for the development of the new ARC-21 Airborne HF Communication System which included an antenna coupler. During its development, RCA experienced problems in developing the antenna coupler and the Air Force gave ERA a study contract as a fall back. The ERA coupler proved to be superior to the RCA unit thus ERA became the sole source production supplier of the coupler for the system. Initially, it was sold directly to Boeing who sold it as “contractor supplied equipment” in aircraft delivered to the Air Force. Over 7000 units were sold to the Air Force during the 1953-70 period and were used on about 10 different aircraft.  The Coupler assembly line is shown at the right.
         I joined the company in 1953 at the time the first generation coupler was entering production. The coupler engineering staff at that time was small and headed by Fran Biltz under the Communications Group directed by Carl Swanson. Other staff engineers included Leon Sabine, Robert Einfeldt, Bruce Sifford, Manny Block, Howard Peterson, and two technicians, Morris “Pappy” Pappenfuss and Oscar Haymen. Carl Hiat, a development engineer had transferred to manufacturing to assist in the transition of the Coupler into production. Fred Hargesheimer headed marketing and Don Blattie did the contracting. Al Meuller led Customer service, which included the training of the supervisors and technicians of the foreign airlines maintenance shops. {Editor's note: Al was the first VIP Club President in 1980.}
      My initial coupler assignment was conducting the Qualification Test of the coupler and writing the report. Later I was the field test engineer for system tests of the Arc 21 communication tests on the B-47 aircraft at McDill Air Force base. This was followed by my supervision of a coupler field modification program at Smoky Hill Air Force base in Kansas. I returned in 1955 to head a development group and became the project engineer for the 2nd generation coupler which was developed for the Boeing 707 aircraft.     

      In 1955, Boeing developed the 707 Commercial jet aircraft and based on the performance of the ERA Coupler awarded ERA the contract to develop the coupler without a competition. This launched the development of the 2nd generation all solid-state coupler, which was the first of its type in industry. The Boeing 707 initiated Boeing’s return to the commercial aircraft business, which they continue to lead as the world’s largest supplier. The 707 was sold to over 40 airlines worldwide and there was an ERA coupler on every one of them. This was the model 3250 shown at the leftt. The tube-like unit was mounted either in the vertical stabilizer or at the end of a wing. The control unit (rectangular box) was mounted adjacent to the radio set.   

     One of the highlights of the military business was supplying the couplers for the Presidents Air Force One planes. There were six couplers including spares on every aircraft and their installation received special treatment by our engineers and field service staff. Robert Brown, who led our field service group made the initial installation in 1956 at Boeing before they were delivered. The system was upgraded in 1965 and Ernie Griffith a lead engineer on the coupler did the installations at Andrews Air Force Base near Washington DC where the fleet of Presidential aircraft and helicopters are based. I went along to chat with the Boeing representatives and just touring this specially equipped aircraft was worth the trip.
     I was project engineer for the 3rd generation coupler for the Air Force B-58 Hustler Bomber. By the time the B-58 Coupler contract was won in 1958, the engineering staff which then included drafting had grown to 70 people and engineers which were added for the 707 project development included John Moe, Charles Class, Allen Anderson, Mick Alsop, Al Sorenson, Paul Richardson, Howard Chen, and Bob Rife. By this time, the division had become recognized as a specialist in the development of this product to the extent that when Hughes won the contract for the development of the new ARC-68 HF Communication system, they selected us as the coupler supplier, rather than develop it themselves.
     While the initial coupler business was with the Air Force and Boeing, in 1967 the company was successful in displacing Collins Radio as the supplier of the Coupler on the Lockheed P-3C Patrol aircraft for the Navy. Winning this contract was a milestone in extending the airborne coupler business to other services. In 1984, I visited Sperry Marine systems 15 years after they the Coupler Business had been transferred to them and supplying couplers for the P-3C was the major source of their revenue for the coupler military business. The P-3 coupler is shown here. [Marc Shoquist] 

    The antenna coupler is very much a part of the military history of ERA/Univac/LM. I think that the first one was designed for the KC130 "flying filling station", the prototype of the Boeing 707. The USAF let Boeing build three 707s on government tooling and then made Boeing build their own tooling for the commercial plane. This gave Boeing several years to test fly those planes. In the early 1930's Boeing had built a few prototype B-17s. The depression stopped the production. A Dr. Reynolds invented modern flight testing and spent years working on those prototypes. That is why the B-17 was such a good plane. Dr. Reynolds designed the B-29 at the start of WW II. The first prototype killed him. His niece worked for Remington Rand Univac about 1958. I met her because her parents lived across the street from my parents in Tegucigalpa, Honduras. It's a small world. At one time Margaret might have been the most knowledgeable person in the plant on transistor physics as a result of her programming in that area. [Harry Wise]

The photo at the left was taken in the 1950s at the then ERA plant 3, located on University Avenue between the Cleveland and Raymond intersections.

Αυτή είναι η ιστορία του αυτόματου κάπλερ για κεραίες αεροπλάνου της ERA. Στο διάστημα 1953-1970, κατασκευάστηκαν 12000 κομμάτια σε τρεις βελτιώσεις της βασικής ιδέας. Το κάπλερ αποτελείτο από έναν μεταβλητό πυκνωτή κενού κι ένα μεταβλητό πηνίο, τα οποία μεταβάλλονταν με σερβομοτέρ για να επιτύχουν τον κατάλληλο συντονισμό και να προσαρμόσουν την σύνθετη αντίσταση της κεραίας με αυτή του ομοαξονικού καλωδίου. Το κάπλερ αυτό μπορούσε να συντονίσει την όποια κεραία τύχαινε να έχει το αεροπλάνο στην μπάντα των HF 2-30MHz. Επί του προκειμένου το 707 χρησιμοποιούσε κεραία ακίδας στην κορυφή του πίσω πτερυγίου κι έτσι το κάπλερ ήταν εκτεθειμένο σε εξωτερικές θερμοκρασίες της τάξης των -53° Κελσίου. Έπειτα το κάπλερ θα έπρεπε να ξεκινήσει να συντονίζει μέσα σε 10 δευτερόλεπτα από την εντολή ενώ ταυτόχρονα ήταν παγωμένο απ΄ τις εξωτερικές θερμοκρασίες. Επιπροσθέτως ήτο και το γεγονός ότι στις χαμηλές συχνότητες ήταν τόσο μεγάλη η δυσπροσαρμογή έτσι ώστε εμφανίζονταν τάσεις της τάξης και πάνω των 20.000 Βόλτ. Οι πρώτες μονάδες συμπίεζαν ξηρό άζωτο και σφράγιζαν τον δακτύλιο με κόλληση και κολλητήρι. Αργότερα χρησιμοποιούσαν στεγανοποιητικό δακτύλιο από τεφλόν, πράγμα που απλοποιούσε την συντήρηση αφού το κενό μέσα στο κάπλερ διατηρείτο για πολύ διάστημα.

Αυτό είναι σε γενικές γραμμές το σκεπτικό και η λειτουργία του κάπλερ και της τότε κεραίας των αεροσκαφών αφού σήμερα χρησιμοποιούν το κάθετο τμήμα του πίσω πτερύγιου ως κεραία. Έψαξα και βρήκα φωτογραφίες στο διαδίκτυο με κεραίες αεροσκαφών αλλά σας εφιστώ την προσοχή σε δύο βασικές λεπτομέρειες. Οι κεραίες είναι πολύ μικρές ως προς το μήκος κύματος και "πετούν" πολύ ψηλά στην ατμόσφαιρα μακριά από εμπόδια και παρεμβολές! 

Ίσως η ανάρτηση αυτή να δώσει το κέντρισμα σ' έναν φίλο ραδιοερασιτέχνη και τεχνικό της ΟΑ να μας γράψει μερικές αράδες περισσότερες γιαυτό το θέμα.

Αεροσκάφος 707 της ΟΑ με την probe antenna.

Fin tail antenna.

A modern version of fin tail antenna.