[pups] PDP-11 / vacuum tube interface

Kevin McQuiggin mcquiggi at sfu.ca
Wed Dec 10 15:02:08 AEST 2008

How about using the pdp-11 to decode Morse code transmissions that you  
receive on your vintage radio?  This would eliminate any issues with  
interfacing to HV circuits, as you could simply run the radio's audio  
output through a PLL circuit to detect tone/no tone and then read this  
single bit signal on the pdp-11.  You decode the Morse code in  
software.  I have code for you (in an old version of Pascal) if you'd  
like.  It adapts to the Morse code speed automatically and "catches  
up" to changes in Morse speed in about 5 letters maximum, as I  
recall.  From an undergrad project I completed in the late 1970s!  I  
could also dig out the hardware info.  Then again you might have more  
fun reinventing this yourself!


On 9-Dec-08, at 4:00 PM, Ross Tucker wrote:

> Dear all,
> (This has got to be the strangest cross-post I've ever done.)
> I have just taken a bet from a friend to challenge my geekiness. I was
> telling him about my love of Vintage Technology and he proposed that I
> combine two hitherto separate hobbies and see what happens. The
> topics: the DEC PDP-11 minicomputer (vintage: 1970s) and vacuum-tube
> ham radios (vintage: 1960s). I do sincerely apologize for
> cross-posting, but I am rather younger than either of these
> technologies (vintage: 1984) and this seems like a monumental
> challenge.
> My question for y'all: how could I possibly design+build a project
> that uses both of these technologies? My thought is to port some radio
> receiver Digital Signal Processing (DSP) application into PDP-11
> assembler, compile and run it via emulator on my PC, then use it with
> the vacuum-tube regenerative receiver that I built a few years ago...
> Does anybody know if PDP-11 UNIXes even had the capability for a
> "sound card"? Or, to get ambitious, I would LOVE to design some
> interface circuitry between PDP-11 digital circuitry and vacuum-tube
> electronics... The challenges are legion: the tube side of the circuit
> operates around 350V DC levels with radio-frequency (RF) signals at 7
> MHz (almost the clock rate of some PDP-11s!) and I don't have the DEC
> Handbooks, but I'm pretty sure that even those ancient pre-TTL
> circuits operate below 350V!
> So... any, er, "ideas"?
> Best regards,
> Ross Tucker
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