[TMC] Optimistic but clueless seller

[Robert Nickels]

has listed a Northern 153 dual frequency shift keyer with some 
entertaining comments:

https://www.ebay.com/itm/265133627883

The manual can be found on the TMC History site;  custom plug-ins 
determine the tone frequency and the module that can be read is for 
2167.5 Mark and 2082.5 Space, i.e. 85 kHz spacing.   The front panel tag 
shows another pair to be 2337 and 2252 Hz, also 85 Hz spacing.   So that 
would translate to 153Z12 and 153Z13 modules in this unit.

Frequency-determining modules were sold by center frequency which is 
shifted +/- 42.5 Hz  and recommended 170 Hz channel spacing at 100 wpm, 
and the output of up to 18 channels can be combined. Eighteen keyers 
would fill one rack, then of course you'd need a couple of racks full of 
demodulators on the other end, which is why Northern came out with the 
transistorized version that put all 18 tone keyers and converters in 
less than 16" of rack space:

http://tmchistory.org/NorthernRadio/Manuals/northern_230_235_tm.pdf

It would be interesting to hear what 18 FSK tones would sound like over 
HF but according to the manual, these 18-channel systems were intended 
for use on microwave or wireline circuits.

73, Bob W9RAN