[ARC5] [Milsurplus] Interesting ARC-3

[DSP3]

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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20171127/c0f5c016/attachment.html>