[ARC5] [Milsurplus] Interesting ARC-3

[scottjohnson1]

I believe the US standard for GA is now 760 ch.    I also think Europe is contemplating 8.33 kHz, wheras the US is Going 12.5.  All the newer mil stuff supports all the above and 50- 512 MHz AM and PM.  Anyone have a spare ARC-210?  


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-------- Original message --------From: DSP3 <jeepp at comcast.net> Date: 11/27/17  10:48  (GMT-07:00) To: arc5 at mailman.qth.net Subject: Re: [ARC5] [Milsurplus] Interesting ARC-3 

    Jack,
    That is a very good question.  I have a set of
        Proceedings from an RTCA symposium in the mid-early 50's and I
        will pull them out and have a look.  They cover comms and
        navigation.  I know that by 1958, 90 channels was the
        gold-standard for light, general aviation operating in the
        low-altitude structure.  The mid-50's Narco Superhomer had only
        5 tx channels but they were on the new spec spacing.  The 1960
        ARC catalog lists their T-25 transmitter with 360 channels, so
        we're getting close.  What I do not know is where/when the ICAO
        got involved and how that may have affected the RTCA issue(s). 
        Right now, Europe has 12.5 kHz VHF channel spacing (1440
        channels) , vice our 25 kHz spec (720 channel) , right now.  The
        old Mark 12B and the KX-175B are soon to goners if we go that
        way, too!!  I assume the two-letter carriers, at least, already
        have the ICAO standard, by now.  As far as the 3 MHz HF, I will
        have to look.  That frequency may have survived a lot longer as
        did HF AM for aeronautical use.  AM didn't sunset until the late
        60's in the US. In the third world, a lot later...   Your
        question of why all this?  There was a huge demand for
        additional frequencies.  With that was the requirement for
        narrower receivers and closer freq. tolerances.  In 1963 when I
        first started flying, and speaking of VHF only, one could squeak
        (and I mean squeak) by with 5 channels if using small airports,
        only.  They still had tower and ground common channels as well
        as a few FSS frequencies.  When I got out and bought my first
        airplane in 1966, 90 channels was fine.  But, by about 1970, the
        FAA slowly started commissioning facilities that used channels
        above 126.9 in the low altitude structure, which precipitated
        the need for 180 or 360 channels.  180 channels never really
        caught on and most went to 360.  Then, by about 1985-90 or so,
        if you didn't have 720 channels, you couldn't play ball. 
        Before, if you didn't have a channel, ATC might give you another
        one of the lower split, so to speak.  This ability went away
        fairly quickly.  I remember the old stand-by was to have you
        come up on GUARD to establish contact.  Now... you simply must
        have dual 720 channel comm to get around.  Most, if not
        virtually all, of the older stuff with 360 channels, or less, is
        not even on the FAA/FCC accepted list.  As an aside, the  UHF
        channel spacing is now also 25 kHz.  The old ARC-27 and VRC-24s
        won't hear it all.  

      
    Jeep - K3HVG

    
    

    On 11/27/2017 10:59 AM, Jack Antonio
      wrote:

    
    On
      11/27/2017 10:32 AM, jeepp wrote:
      

      Particularly interesting.  A lot, arguably
        tens of thousands, of xtals went obsolete when the RTCA and
        ARINC first instituted 100 kHz VHF comm channel spacing.  I
        remember that the USAF tower common freq.  in the 40s and 50s
        was 126.18.
        

      
      

      Out of curiosity, when did this happen, and also, *how* did it
      happen. Was it a gradual phase in of the new plan, or
      

      was there a hard cut off date when the transition occurred? Did it
      happen at same time in military and civilian service?
      

      Was it driven by the military, or by the civilian side of the
      aviation community?
      

      

      Along the same lines, was there a "drop dead" date after which the
      tower LF(278kc), aircraft HF(3105/3023.5kc) system
      

      would no longer be used?
      

      

      Jack Antonio
      

      WA7DIA
      

    
    

  
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