Make your own free website on Tripod.com

The Original WA6TDD Repeater on Mount Wilson!

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 cold 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 and Bill Butler Sr. 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. Jim 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. 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. Both are great people who went out of their way to help accomplish a good thing.

         Burt Weiner, K6OQK

The Repeater rack

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 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.

If anyone knows the whereabouts of that receiver I'd love to find it. -K6OQK

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.

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

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

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

Some of the clip art is from Zed Zed.

Dan Saltzman wb6mvp Web Master