Morse code key questions

draft

Mike Everette, 5 September 2000 Forum.

After I made my posting last night I took another look at the WE-13C transmitter schematic... something I said last night wasn’t quite right. I stated that it would have been no problem for AE to leave the telegraph key behind if all she wanted was voice transmission; just unplug it and remove it from the cockpit.

Well... that’s not right.

Indeed, it is not possible.

The "key" in this setup was more than just a morse key. It was part of a subassembly, a control unit. The unit contained the key and a switch. The switch, a double-pole double throw type, had two positions, labeled "CW" and "PHONE." Like I said last night, throwing the switch to "CW" closed the push-to-talk line (like the mic switch would do on voice) and made the rig READY to transmit. The "keying" was through an added relay. This relay actually followed the operator’s key.

To RECEIVE on CW, it was necessary to throw the switch on the controller containing the key BACK to "PHONE." Potentially confusing.

I had forgotten one more important function of that switching circuit, last night.

That switch, when thrown to "PHONE," also closed the CW keying relay circuit. The keying relay, therefore, was energized continuously when the rig was switched to "PHONE."

That way, the radio was ready to transmit on voice. It was NOT "keyed" on voice until the mic switch grounded the PTT circuit, energizing the dynamotor starter (and therefore applying high voltage) and antenna relays. The CW keying relay had to be closed to enable the tubes to function, by grounding the blocking-bias that kept them from drawing current (as well as applying screen grid voltage to the multiplier and final amplifier stages).

To summarize: Since the transmitter operated in Push to Talk fashion (PTT) on voice, the CW keying relay had to be closed on voice. It did not operate with the PTT circuit. The ’CW-PHONE" switch closed this relay on voice. The key closed it on CW, AFTER the "CW-PHONE" switch was thrown to CW mode. The switch had to be returned to "PHONE" to RECEIVE ON CW, in order to de-energize the antenna relay and dynamotor.

The transmitter DID NOT operate in "break-in" style on CW (the equivalent to push-to-talk operation on voice).

But here is a thought, and an important one:

If TWO ANTENNAS were used (one transmit, one receive) it would not have been necessary to have the antenna relay de-energized in order to receive; so returning the switch to "PHONE" would not have been a requirement.

The bottom line:

IT WOULD HAVE BEEN IMPOSSIBLE FOR AE TO USE THIS RADIO AT ALL, EVEN ON VOICE, WITHOUT THE TELEGRAPH KEY UNIT CONNECTED TO THE TRANSMITTER. The switch in the key unit had to be in the circuit....

UNLESS, and we may never be able to completely resolve this... some sort of modifications were made to the radio in Miami, to bypass this switch. All it would have taken, was a "dummy" connector plugged into the transmitter where the key unit was connected... if Pin 4 of this connector was jumpered to ground, that would complete the keying relay circuit. Of course, an internal mod to the transmitter’s wiring could have accomplished the same thing.

How hard is the evidence that she left the key behind? Anecdotal? It may be worth the paper it is printed on.

We have been through this before... wonder if there are any scraps of paper anywhere detailing the work done on that radio in Miami? Did Pan Am techs do it? Anybody search the Pan Am files that closely? (Chances are none to slim, right? Probably the document retention schedule was not that long and any such paper was tossed out with other routine stuff....)

A lingering question from earlier postings by others:

Would it have been possible to "key" this radio on CW, using the mic button?

Yes. BUT... It would have produced a very ragged, awful signal. The keying speed would be very slow. And the radio would have been damaged quickly because of heavy current circuits being made and broken, which were never intended to be so operated.