[ARC5] [Milsurplus] Interesting ARC-3

[Peter Gottlieb]

I believe the portable URC-200 is standard 25 kHz and optional 8.33 kHz, covers VFH air, ham and commercial AM/FM and UHF air and military also AM/FM. These pop up on eBay here and there. 




Peter

> On Nov 27, 2017, at 3:48 PM, scottjohnson1 <scottjohnson1 at cox.net> wrote:
> 
> 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?  
> 
> 
> 
> Sent from my Verizon, Samsung Galaxy smartphone
> 
> -------- 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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