[Milsurplus] Tube Electronics Question

[k2cby]

Precision expectations.

The long and short of it is: (1) Are you talking date of manufacture or 60
years later? (2) When was the gear produced? (3) Who made it? (4) For what
purpose was it made and how good did it have to be?

First of all, amplitude is largely irrelevant to Loran A (and indeed to its
successors) except for the pedestal level inside the display unit. The
transmitters were pulse modulated. You identified the transmitter by its
carrier frequency and the pulse repetition rate. You determined the line of
position by the delay between receipt of the master pulse and receipt of the
slave pulse.

So the key specification is time.

At the transmitter end time was very accurately determined by crystal
oscillators and frequency-dividing multivibrators locked to them. 

AM Broadcast stations in the 1960s had no trouble maintaining a frequency
accuracy well within the ±20 Hz FCC limit using tubes. (The transmitter
crystals weren’t even oven controlled, although the frequency monitors
were).That translates to about 10 ppm, so I would guess that the
state-of-the-art limit for that era might be at least a factor of 10 better
than that.

Loran A, of course, operated just north of the AM broadcast band.

Loran A receivers, which until the mid-1960s had no digital circuitry,
basically used the oscilloscope technology of the era in which they were
made.  In other words, they depended on values of resistance and capacitance
to set the timing in the display unit (So did radar displays, for that
matter.). 

Using high quality components, trimming adjustments, and good circuit design
it was possible to get timing accuracies down to 50 ppm or better. Hence,
Loran A was good to plus or minus a couple of miles using ground wave.

Bay and large, the determinative factor was not whether tubes were used
instead of solid-state electionics, but whether the circuits were analog or
digital.

 

  

 

 

Miles B. Anderson, K2CBY
16 Round Pond Lane
Sag Harbor, NY 11963
Tel.: (631) 725-4400
Fax.: (631) 725-2223
e-mail: k2cby at optonline.net