Headlines - Maintenance Department Report - Transmitter Keying Reverse Engineering
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Maintenance Department Report - Transmitter Keying Reverse Engineering
We're in the somewhat enviable position of having more transmitters in Bolinas (BL) than we have transmitter control switches at Point Reyes (RS). That's because for most of the station's life there was just one station to control: KPH. We're controlling two stations, KSM and K6KPH.
As many will know, during the last years of KPH operations at Bolinas/Point Reyes sister station WCC on Cape Cod was controlled from RS as a cost saving measure. That applied to both the CW and SITOR operations but it's the CW operations we're concerned with here.
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| KPH (blue) and WCC (black) transmitter control panels at RS |
The installation of control facilities for WCC was a big deal, involving a WCC control panel at each of the six operating positions at RS, a dedicated rack of WCC tone sets and a T1 line to connect the two stations. The receivers at WCC were also remotely controlled from KPH but with the closure of operations at Bolinas/Point Reyes that system disappeared. The control circuits for the WCC transmitters remain however and therein lies the subject of this narration.
Mr. Bill Ruck (RK) or the Maintenance Department has taken on the task of a> understanding the WCC control system and b> reverse engineering it so we can use it to control additional transmitters at BL. This is no easy task. There are multiple layers in the system, some added to correct problems with earlier layers, and the documentation is thin and sometimes unreliable.
We have an expression when we encounter a particularly puzzling or poorly executed system as part of our restoration: "Welcome to KPH", this coined by Warren Reese, last transmitter technician at BL. To this Bill now adds "Welcome to WCC". But we should really let him tell his own story, as he does in this report:
The next step in getting more transmitters controlled is to revamp the transmitter keying system at RS. The plan is to use the KPH system for KSM and the WCC system for K6KPH. This will give each operating position the ability to select 20 transmitters which is more than the tone sets can transmit. (The tone sets are limited to 16 frequencies; 2 of which are used for the order wire TTY.)
My first attempt at verifying the WCC system was not successful. To coin a new phrase, "Welcome to WCC". This may be just a special case of "Welcome to KPH". The issue is that some of the documentation is correct. We also do not have complete documentation. Which part of what we have is correct is always the problem. I read through the documentation that we have for WCC keying and based on that fabricated a test jig so I could test the CW Position 1 control panel on the bench. This is important because otherwise I'd drive Mike Payne (MP) nuts.
The WCC CW Position 1 control panel clearly has several layers of modifications after it was constructed. The first generation workmanship was OK. Then there are layers of poor workmanship with wires spliced in mid-air. The modifications are mostly all done with blue wire. It also has a row of miniature toggle switches at the top which does not appear in any documentation.
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| Bill Ruck hard at work at the bench at RS |
What I learned Saturday:
1. The control panel needs -12 VDC. The main schematic does not show this but after being unable to key the output lines I read through other schematics, including what are called "insert" schematics for the main schematic, I saw that the keying relays are powered from -12 VDC. Then in another schematic, "POWER AND SIGNAL DISTRIBUTION BOX" I saw hand corrected designations which puts -12 VDC on Pin 23 of the DC-37 connector. When I did that I could key all lines. Note that on most documentation Pin 23 is labelled "PK232". There are four relays: two for the wheel and two for manual keying.
2. Mercury wetted relays do not work upside down. I should know this but while trying to follow wires I had to look at the bottom of the panel. After some head scratching when things worked some of the time it was look, turn it right side up, and test.
3. The top row of miniature switches are in series with the DC-37S connector that goes to the FDM multiplex (tone sets). If the switch is down nothing happens.
4. The transmitter select toggle switches are mechanically sticky. At times you have to move the switch and wiggle it until it clicks. The red "busy" LED indicates if the switch hasn't clicked. I noticed this with other WCC panels at other operating positions.
5. There are two three-position toggle switches on the CW Position 1 panel that select "WX" / "WHEEL" or "PK-232" / "LIST". (The functions are labelled differently in different places.) Center off. The upper switch selects transmitters 2, 4, 6, 8, and 10. And transmitter 1 (MF) only in "PK-232" / "LIST" mode. The lower switch selects transmitters 3, 5, 7, and 9. One of these switches clearly was added later.
6. For some reason there is an interaction between the KPH and WCC keying system. If the CW Position 1 DC-37P and DC-37S are not connected to each other (either through the panel or directly) CW positions 2 through 6 KPH keying does not work. This was a surprise; I have not found anything in the documentation that explains this.
7. When I removed the WCC panel MP reported that he lost side tone. After studying the switches on the audio control panel I showed MP that he could get KPH side tone in either ear. The audio control panel had been left with WCC side tone. The CW Position 1 hand key is plugged into the WCC panel and then feeds the KPH panel. I had bypassed this with a 1/4" jack to phono jack temporary adapter but that did not allow WCC side tone to be generated. I have a vague notion of how local side tone is generated but will have to fully document the system as it exists. It may be likely that there may be more than one configuration; i. e. how CW Position 1 is configured may not be a model for other positions.
Now that I understand how the WCC keying works the next trip will be to learn how to connect this system to the 901 tone sets. The 901 tone sets are -8 VDC keyed to ground. The WCC FSM-76 FDM mux has a circuit somewhere that converts the FSM-76 positive voltage to ground to -12 VDC keying through a photo isolator. Exactly where that lives I have to find so that I can isolate the 10 keying lines from this circuit. Ultimately those 10 lines will terminate in the tone set rack. I will also transcribe my notes to a clean schematic and share that.
RK
This kind of thing can easily drive the best intentioned engineer 'round the bend. Luckily for us Bill enjoys reverse engineering the the feeling of triumph that comes with finally understanding what's going on.
Bill makes passing reference to the test jig to built to allow bench testing of the keying panel. With the modesty typical of great men, he fails to mention that the jig is a thing of beauty, better engineered and constructed than much of what it's testing, complete with rows of LEDs to confirm keying and power. If he had relied on the usual jumble of clip leads to analyze the keying panel he would have long ago been led off gibbering to the radioman's padded cell.
If you've been following these reports of our activities you know that all of us, including Bill, are volunteers. And Bill, yet to retire, is trying to make a living in between sorting out the arcane systems of KPH. He makes the trip from San Francisco to remote West Marin and even brings morning buns along to be consumed at morning Services of the Church of the Continuous Wave at Bolinas. It's really hard to ask for more than that.
Of course we all participate happily in this project and feel lucky to be involved with The Cause. But you know... a little assistance from our fellow True Believers would be a great help. It allows us to make purchases of needed parts and equipment that otherwise would have to be paid for from our personal bank accounts - which we are happy to do when needed.
