The Original WA6TDD Repeater on Mount Wilson!

The number of Op's that have QSY'ed here sense 2-10-07

HOW I DID IT

The repeater grew out of my interest in broadcast engineering. As you will see this was no ordinary repeater. It was most likely that my ego had run amok and was satisfied by doing a job well. Over the years it evolved from home-brew, military and two-way radio surplus to surplus radio and television station stuff. It grew from a single rack to more than three racks full and a transmitter that took up just as much floor space as well as taking over the top of the broadcast station's tower - with the owner's blessings.

It did a lot more than just repeat audio and it was a lot more than just a receiver and transmitter connected together. The more it did the more I wanted to build. I could turn on a mic listen and to noises inside the building - and we certainly did hear some unexpected things. I could also mix in audio from the control link that allowed me to do silly things such as mix in the sound of a cricket underneath a particular station resulting in people commenting on the cricket that must be in their microphone only to be met with a reply of "What Cricket???!!!"

Through the link we could run multiple carted ID's that fit the season. There was a cart that ran repeater ID's in every possible language in which we could get them recorded. Kelly Layng of Channel 4 News fame was the "Repeater Lady" although she never knew it until after the fact and then asked, "What peter on a mountain???. She had been asked to record an I.D. for something that made no sense to her but graciously did it anyway.

It could do a lot of things and do them well. Two of the people who found a way to take advantage of the capabilities of the repeater were Jim "Woody" Wood, K6BXW and Bill Butler Sr, W6BFA. Along with the help of many Hams that worked with them so unselfishly they put together Operation Santa not only on the WA6TDD repeater but also the K6MYK repeater. Woody and Bill found a way to make the two repeater's separate and combined coverage and penetration do a good thing to bring a smile to a lot of kids that might otherwise have had a sad and lonely Christmas. I know that Art Gentry and I shared in the feeling that the intent was for us all to have a good time together and learn from each other at the same time.

The repeater went to Mt. Wilson in early 1962. Although not involved in Amateur Radio, Bill Accord, KPFK's Chief Engineer was very supportive and instrumental in making it happen. Bill helped put together the agreement between K6OQK and Pacifica Radio that is in effect to this very day. Bill also helped me in applying for the Forestry Permit for the repeater. Don Wilson who later became KPFK's Chief Engineer helped in getting our agreement modified to give us the additional space we needed for the neat stuff to come along. John "Skip" Benedickson, the local ranger in charge of Mt. Wilson was also very helpful in getting around governmental bureaucracy and was able to make things happen for us. These are great people who went out of their way to help accomplish a good thing.

        Burt Weiner, K6OQK

This is a picture of the original repeater. The equipment in the rack starting from the top: the greatly modified ARC-4; the 35 mm film loop MCW ID loop; a monitor speaker and amplifier; the repeater logic including a Veeder - Root "Beep" counter"; the audio mixer and early AGC audio processing; the remote control relay interface strip; the ARC-1 receiver and it's power supply.

The ARC-4 was modified for higher fidelity using UTC wideband audio input and modulation transformers. The transmitter output was about 9 Watts. The 35 mm film loop ID had holes that were punched in the film using a standard single hole paper punch. The pickup was a piece of silver solder. The film rode between the silver solder and a grounded block of silver from an arc projector carbon clamp that was donated by a Ham/projectionist at a local drive-in theater. The logic for the repeater was a combination of relays, diodes and capacitors for the transmitter carrier control, delays and "Beeps". The audio chassis mixed the beep level, the MCW ID level, the local mic level and the receiver level. The AGC was pretty much a copy of Art Gentry's K6MYK repeater audio processor.

The remote control used a D.C. pair from the phone company. A long D.C. pulse on the line would cause the repeater to come to come on the air. Short pulses after that would cause the audio to toggle or transfer to... well, nothing. There wasn't anything for it to transfer to but it would do it anyway - basically muting the audio. A reverse polarity D.C. pulse would cause the system to go off.

The ARC-1 receiver was pretty broad. As I result I used the BC-348 receiver that's sitting on the shelf to the left as the second I.F. The BC-348 was tuned to the ARC-1's I.F. of somewhere around 9 MHz. The BC-348 also had a TNS (Twin Noise Squelch) combination noise limiter and squelch. The ARC-1 is sitting on it's side and you can see an adjustable shorting stub sticking out to the right past the edge of the rack. This was the only protection the receiver had from the transmitter other than the transmit and receive antenna's 100' of vertical separation. In spite of it's lacking anything closely resembling State of The Art for the time it worked quite well.

The sign on the side of the rack had nothing to do with anything. I found it in the road one day and it just seemed like a good place to put it. The large EICO VTVM sitting on the shelf and a Heathkit Signal Tracer where the only two pieces of test equipment that I owned. I still have them.

Burt, K6OQK

These pictures are of the original repeater antennas. The left picture is of the 4 element Cushcraft J-Pole that was used for the transmitter. The receive antenna was an upside down groundplane at about the 100' level on the tower. Even though the J-Pole had much higher gain than the groundplane considering the shorter coax run and higher antenna gain, the groundplane did a better job of hearing due to the fact that it was higher and cleared surrounding terrain. The picture of the J-Pole was taken several months after the repeater first went on the air and shows the addition of the 420 Skeleton-Slot antenna used for the control link. -K6OQK

This picture shows the J-Pole that replaced the grounplane antenna. The groundplane was located where the top of the J-Pole is mounted to the tower but because of the FM antenna we could not go above that point. The J-Pole's center is about 75' above ground level. A few weeks after this picture was taken all of the elements of the J-Pole were rotated in line towards Long Beach and a downward tilt of about 1.5 degrees was added by moving the top bracket forward. This was a big improvement in receive capability over the groundplane but nothing compared to what would take place a few years later. -K6OQK

This is a picture of the control system and link transmitter that was built and put in operation about 1964. The transmitter is a modified G.E. Pre-Progress unit that was modified to direct FM. You can see where the modification was done just to the right of the crystal oven in the transmitter. The transmitter ran about 5 Watts into a Skeleton Slot antenna. We were always on the look out for usable 2C39 tubes for this transmitter.

The control system used 4 super-sonic tones which controlled Step/Reset, Raise/Lower (Increase/Lower) and Audio Transfer. The reset signal was a 1 second long step pulse. The stepper relay at the Mt. Wilson end was a 5 bank, 26 position Automatic Electric stepping switch. Each control channel had a raise and lower function associated with it so that you could either turn on or off a function or in some cases run a motor one way or the other such as the receiver squelch or the transmitter modulation level adjustment. The reset button just below the phone dial would send the stepper to the home or zero position. The fail-safe switch turned the link transmitter on or off. To meet FCC requirements the system fail-safe was such that if the control link receiver lost signal the repeater transmitter would shut off.

The repeater's Plate On/Off function actually controlled a Minor stepping switch. There were 4 modes of operation of the repeater. 1, automatic with delayed drop off which was the normal operating mode. 2, Direct Key which caused the transmitter to go on and off following the incoming signal without the delayed drop off. 3, Continuous Carrier where the repeater's carrier was always on. I can't remember what the 4th mode was. Anyway, each time you sent a raise pulse this would send the minor switch up one position to one of the modes. Lower would send the minor switch to it's zero or off position turning the plates off.

Audio transfer was an interesting and fun thing. The audio transfer button actually operated an Automatic Electric OCS Binary switch in the repeater's audio deck. This sounds like a fancy switch but it was really a gazillion pole two position switch that would toggle from one position to the other with each command pulse. Position # 3, raise on the remote control operated the transfer function the same as the audio transfer button. Position 3, lower toggled "Duplex" mode on and off. Duplex mode mixed the link audio in instead of hard switching it. This allowed the control operator to work duplex through the repeater but even more fun was that it made possible the ability to mix in sounds such as the endless cart of the cricket in with certain stations. I remember one station that almost tore his house apart looking for the cricket based solely on reports that it was only on when they were on. It was obviously being picked up by their sensitive microphone. I remember my Grandmother one time telling me not to mix in.

I had a portable control box that was on a 50 foot cable that I could drag around the apartment. This box had a speaker, a mic jack and duplicated the control functions complete with a dial. I still have the control unit safely tucked away. -K6OQK

This is a picture of the Audio Logger for the repeater. The basic unit was made by Soundscriber and donated by KFI Radio. It used 2" wide tape on 3" reels. Each 3" reel would last 24 hours and 15 minutes. It was decided that a method of recording longer time periods was needed. So in true Ham spirit proceeded to go overboard. The spindles from an Ampex 2" Quad Video Tape machine were obtained. Harry Wells, W6YLC machined and fitted the spindles to two washing machine motors and mounted them to 3/16" thick rack panels. Hold-back tension on the top, supply reel was accomplished by applying about 1 VDC to the motor. The take-up reel tension was accomplished by applying about 6 VAC to the bottom, take-up reel.

With 14" video tape reels we could record 30-40 days continuous. The problem was that how did you go back about two or three weeks to find something that someone thought happened about a certain time, maybe. We couldn't. It took to much time. On more than one occasion I invited the person wanting the audio to come and find it. They all ran away. If you look at about the 2:00 position on the bottom reel you can see where pieces of paper were slipped between layers of tape. These pieces of paper had dates and times written on them when interesting things took place. Even with that it was still a real headache to go and retrieve something. It finally came down to that if something interesting happened we would grab it out of the logger right away and dub it to cassette.

A humorous side story: In the process of trying to locate 14" reels of tape a call went out on the repeater. Shortly afterwards reels started to appear on my front door step. After a couple of months of this there was more tape than we could've ever used. I got on the repeater numerous times thanking whoever was delivering it and asked them to please stop. The mysterious deliveries increased. There were times I would get up in the morning and not be able to get out through the front door because of the reels stacked so high. There were no labels on the tapes that might have given a clue as to where they were coming from and they had been well bulk erased. Finally the midnight deliveries stopped just as they had started.

And yes, for some reason I still have the Soundscriber.

The unit just below the logger is one of the early 420 MHz control link transmitters. -K6OQK

This is a picture of the WA6TDD repeater circa 1968. The two racks are RCA type BR-84s The equipment from top to bottom in the left rack is the original remote control telemetry generator; the ARC-4 10 Watt AM auxiliary transmitter (with the two large meters); a converted G.E. Pre-Progress 420 MHz 1 Watt telemetry link transmitter; the remote controlled modulation level adjustment; the 100 Watt AM transmitter with a 4CX250-B final modulated by a pair of 807's; the power supply for the 100 Watt transmitter. The right rack starting at the top contains the Two-Meter AM receiver that had the 8 KHz Collins Mechanical Filter; the mic pre-amp for the "inside the rack" microphone; the audio processing and logic chassis for the repeater; the wide-band 420 control link receiver; the remote control containing a 52 position stepper and the super-sonic tone decoders for the Step, Reset, Raise and Lower functions and a 24 Volt DC power supply. Most of this equipment is presently stored in racks in my garage. Someone wound up with the AM receiver when the stuff from Dave Farone, WA6KOS was auctioned off in the early 80's.

1. The inside of the AM receiver. This was pretty much a copy of Art, W6MEP's K6MYK AM receiver. It had a DC Amplified AVC system that drove the very low impedance AVC buss that got rid of a lot of the mobile flutter. Near the top left you can see the bottom of the 8 KHz Collins Mechanical Filter.

2. A rear view of the receiver showing the two re-entrant cavities and the cavity trap on the mixer grid. The two relays are for the squelch control motor located near the center bottom. The receiver was originally a Wilcox Electric Aircraft receiver that was stripped down to the bare chassis. The unit just below the receiver is the pre-amp for the "inside the rack" microphone.

The repeater was constantly going through technical changes. This picture was taken in 1975 by JA1FQO who made a special trip from Japan to see the repeater.

The equipment in the left rack from the top: The auxiliary transmitter, a Motorola 30-D that was modified for direct FM; The 140-D main transmitter also modified for direct FM and it's power supply; A panel containing a 5 KHz low-pass audio filter that pre-ceeded the transmitters; a G.E. Pre-Prog 420 receiver that was used as a link receiver from somewhere; the FM Sensicon-A main receiver and just above that is its metering panel; the Sensicon A's power supply and motorized remote squelch control.

The equipment in the right rack from the top: A CBS FM Volumax that limited the peak deviation to 4.5 KHz without clipping; The audio processing and logic controller; the control link's super-sonic control tone decoder and control logic; the 24 VDC power supply; A strange drum recorder from the telephone company that was modified for voice ID's that could be recorded up the link; the interface for the drum recorder; A 247-B touch-tone decoder that was tuned to odd frequencies to control via telephone. -K6OQK

Picture 1

This picture is when we first got the TVM-1 microwave receiver going. It was inside the transmitter building on Mt. Wilson looking through the wall of the building. Scott, WB6QFR was at the bottom end of the link and we were tweaking our hearts out. It was not a problem to get the transmitter well down into the 5650-5925 MHz Ham Band but the receiver was a different story. The microwave equipment was complete with cavity type frequency meters. We could not find a Klystron that would take the receiver down into the Ham Band but we discovered that a transmit Klystron running on the lower voltage of the receiver would jump modes and land at the desired 130 MHz above the receive frequency. The signal was so strong that the 0-500 Signal meter on the receiver was pinned. In this picture you can see the Klystron and down converter mounted to the back of the dish. Later, Fletch W6DEO built a platform located just inside and above the door of the building. This became the home of the dish (and storage) for many years. -K6OQK

Pictures 2 and 3

Back in 1976 I acquired a RCA TVM-1, 1 Watt television microwave system for the repeaters control link or STL which in this case stood for "Shack-Transmitter-Link. With the help of Al, W6ILL Klystrons were found to put the transmitter well into the 5650-5925 Ham Band. The microwave transmitter and receiver both had the cavity type frequency meter so we were able to confirm operating frequencies. The problem was the receiver. No Klystron could be found that would work as the receiver's L.O. for the Ham Band. Finally we discovered that a Klystron intended for transmitting would work when installed in the receiver. Apparently the Klystron would jump mode with the lower voltage of the receiver and we were able to get the proper L.O. injection of Fc+130 (MHz). The 130 MHz I.F. presented another problem. With the receiver's I.F. 20+ MHz wide and centered on 130 MHz the receiver was seeing the 146.40 MHz output of the repeater. This was quickly resolved by installing a spontaneously crafted 146.40 MHz series resonate to ground notch filter in the output BNC connector of the microwave's down-converter. This filter totally removed any sign of 146.40 signal in the 130 MHz I.F.

Another interesting problem arose when we discovered that if the receiver lost signal the AFC would drive the Klystron around looking for signal and would drive it to where it quite. In the beginning this meant a trip to Mt. Wilson to turn the AFC off and then back on. I built a carrier operated relay that sensed when the carrier dropped to a pre-determined level and would disable the AFC returning the receiver to its' nominal center. This totally resolved the problem which was a very good thing.

The wide baseband bandwidth opened up new possibilities. I was now able to add two 15 KHz audio channels, a 6.2 and 6.8 MHz subcarrier to the STL as well as having 5+ MHz of space for video. On the 6.8 MHz subcarrier I added a 185 KHz subcarrier that contained the primary control system for the repeater.

The remote control system graduated to a Moseley PBR-15 and later to a PBR-30 with return metering consisting of a low frequency tone of 20-30 Hz applied to the buffer stage cathode of the main and auxiliary transmitters. This caused the transmitters to deviate about 50 Hz with the low frequency tones and with a high gain amplifier and low-pass filter installed in the G.E. ER-1 monitor receiver at home I had full telemetering. In order to calibrate the metering system I had a small surveillance type TV camera looking at the receive end meter and was able to look at it at the mountain and calibrate the metering system. Talk about cheating!!!

Despite a lot of people denying the existence of such a link it continued to be quite reliable for many years. The STL receiver consists of the two green units in the bottom half of the left rack. The top green thing is the receiver's back end and video. The bottom green thing is the receiver's power supply. Between the two units are the two audio channel diplex-demodulators and the AFC control carrier operated relay. The PBR-30 remote control can be seen about a 3rd way down in the right rack sticking part way out of the rack. When this picture was taken I was in the process of getting the remote control up and running. The "Shack" end of the Moseley PBR-15 is sitting on the table to the left of the racks. In studying the pictures on this site I don't know how I managed to squeeze all of this stuff into the two racks without removing any of the other stuff. However, if you could see my garage you would understand how I would find a way to do this. -K6OQK

Picture 4

This is a picture of K6OQK on the tower making adjustments to the 4' STL transmit dish. The dish was just high enough to clear trees about two blocks away. The path length was 38 miles. Alignment of the dish was easy to accomplish. Since the remote control system was able to bring back the microwave receiver signal strength reading it was a simple matter to take that reading out of the remote control and feed it up a spare pair in the transmitter control cable. While aiming the transmit antenna we could see the receive signal at Mt. Wilson on a meter located in the back of the transmitter head. More cheating of the first magnitude!!! -K6OQK

OOps! I almost forgot to put in the pictures of the two helpers that help Burt move the STL Transmit dish to his tower. So here it is!! -WB6MVP

They are Bill WA6ITF and Al W6ILL! Sorry Guys!

This is a picture of the WA6TDD/WR6ABE repeater and the 1 KW RCA BTF-1C Broadcast Transmitter that was on line for a while. The RCA is immediately to my back in this picture. The RCA was feeding 1200 Watts up the 1-5/8 inch line to the single bay, center mounted Jampro Circularly Polarized antenna located about 8 feet above the top of the tower. The Jampro Antenna Company in Sacramento had built this antenna specifically for the repeater and it's center frequency was 146.40 MHz. The exciter that was driving the RCA's parallel 4-125-As 1st RF stage was a modified Marti RPT-40 RPU transmitter. The RCA's final was running a 5762 Triode in grounded-grid configuration.

Due to the high power we could not use the duplexer so the receiver was connected to an auxiliary antenna with the duplexer acting as a bandpass-notch setup. The RCA was running straight into the transmission line to the Jampro. -K6OQK

This is the first account of a WA6TDD event from a users. I hope it wont be the last. This one is from Steve Jensen, W6RHM. (Ed.)

I thought you might be interested in the story of how the repeater split (146.400/147.435) came about. Today of course it seems a bit odd but all of this happened long before the 2 Meter band plan came out. At the time of the installation on Mt. Wilson, (sometime in 1962 I think) the only other repeater on the air was Art Gentry's K6MYK machine. Its input was 145.180 and its output was 146.980 (I still have the crystals). This one was all AM at the time.

As FM was just starting to become popular, Burt wanted to accomodate that as well and he had an idea to have two inputs, AM and FM for the Mt. Wilson repeater. I was involved in a survey of frequencies on Mt. Wilson using a Stoddart NM-30 receiver in conjunction with a my Heathkit Pawnee as I recall to find a repeater pair for Burt that was relatively free of intermod. We decided on 146.400 for the output and 147.425 for the input. Then it was decided that there should be two inputs centered around 147.425 at +/- 10 kHz which gave rise to 147.435 for the AM input and 147.415 for the FM input. At the time all of this conversation was going on, the repeater was put on the air as an AM repeater using the two frequencies idendified for the AM operation with the plan being to implement the FM operation later. The output was always on 146.400. Well, as FM grew rapidly in popularity during those days and AM diminished, what actually happened was the old AM pair became the present FM pair and the other pair was never used. When the repeater changed hands after Burt gave it away, the input and output was later reversed to its present configuration using 147.435 as the output and 146.400 as the input. (The reason for that is unknown).

73, Steve Jensen, W6RHM

This page is under construction, we are looking for material to add to this site. If you have any pictures or interesting stories about the WA6TDD AM repeater or the early WR6ABE FM repeater at Mount Wilson Please send them to WB6MVP

Last up date was 2-18-05

Some of the clip art is from Zed Zed.

Dan Saltzman wb6mvp Web Master, Editor