[Milsurplus] Mercury Comms

[Scott Johnson]

I have some interesting pictures somewhere of the UHF comms for Mercury 
and Gemini, which were, as stated earlier, single channel UHF AM.  They 
are hybrid, with a small disc seal tube for the PA.  The Gemini radios 
were similar.  If someone is REALLY curious, I have contacts that worked 
at the former Motorola Govt. Electronics (now General Dynamics) that 
worked on these programs (many of the boxes were actually built by 
Motorola for Collins under contract)  I even have a few early Apollo 
engineering brassboards.  I can probably dig up some info from them, or 
perhaps from the curator of the Motorola Museum in Schaumburg.  The 
bottom line is, all of the flight hardware was purpose built for the 
manned flights, and very little information exists outside the walls of 
the original manufacturers, and most of that is gone and forgotten. (The 
shuttle, on the other hand , carries a large amount of conventional 
military avionics).

73,
Scott W7SVJ

David I. Emery wrote:
> kOn Sun, Sep 10, 2006 at 04:53:35PM -0400, jjhaggerty01 at excite.com wrote:
>   
>>  > What communications systems were carried on the flights?
>> (designators, etc., communications training of the "Mercury Seven"?)
>>     
>
> 	The early Mercury flights carried two voice communications
> systems. One was UHF AM via what I have read was a fairly vanilla
> miniturized  crystal controlled Collins UHF AM Aircraft radio of the late
> 50s era designed for light weight, small size and low power consumption
> (couple of watts output) and adapted for space flight.   Frequencies
> were 259.7 and 296.8 (which remain in use with the shuttle to this day).
> There may also have been a homing beacon on 243 mhz.   And there were
> one or two UHF (P-Band) FM telemetry transmitters operating around
> 230-250 mhz.
>
> 	The other Mercury communications system was a single channel AM
> HF radio tuned to 15.015 mhz in the HF band.   Crystal controlled and
> very low power output.
>
> 	Antennas for the UHF stuff were mounted on the top (small end)
> of the capsule and were a little wire heart shaped loop - I guess giving
> omni RHC polarization.    HF was accomplished by feeding the bottom cone
> of the capsule and the upper part (with the UHF antennas on it) as a
> short dipole - apparently the two halves were isolated enough so this
> was possible.   A couple later flights had deployable HF booms as well.
>
> 	The HF never worked all that well and most all actual comms were
> UHF AM line of sight.   But a few folks (including me as an 8th grader)
> were able to copy some of the occasional HF AM traffic even though the
> orbit did not provide much visibility as far north as Boston for the
> UHF.   The ground stations used much more power on HF and were very
> strong at considerable distances.
>
> 	Interestingly the Russians, our fierce competitors in the space
> race in that era, used voice comms a few khz plus and minus around
> 20.000 mhz for many years during this era and seemed to make much more
> use of HF than the US did.
>
> 	It should also be noted that much of the global NASA tracking
> network for Mercury and Gemini was linked together either via primary HF
> circuits or backup HF for undersea cable circuits.   Many of these
> circuits were ISB HF SSB mux transmissions with RTTY on one sideband and
> a voice circuit on the other.    Communications satellite based
> international circuits only came in about the time of the early Apollo
> flights, so much of the tracking network overseas used HF to link back
> to the US and many of these circuits were very strong in the US, so one
> could overhear lots of traffic associated with the flights.   A lot of
> reports of signals "between 4 and 8 mhz" were no doubt reception of
> ground based circuits as part of the tracking network or recovery ship
> communications.
>
> 	As for communications training, the original 7 astronauts were
> military pilots and trained in use of communications systems of the era,
> probably including some CW though there was no actual CW gear on board
> the spacecraft AFAIK.
>
> 	Gemini used only the UHF AM, and I think may have later had some
> higher frequency than UHF telemetry.  No HF.
>
> 	The spacecraft used a fixed call sign like "Freedom 7", and the
> various ground stations used call signs like "Cape" or "Tannarive". For
> the Mercury program the primary communicators, at least for the overseas
> ground stations, were located at the ground stations and not remoted
> from Houston as was the case later on.  So the astronauts actually
> talked to various local folks as they made passes over the world wide
> network of ground stations - they weren't talking to one person in
> Houston designated as cap com as they have been ever since.
>
> 	And all the spacecraft of that era carried C band (5.9 ghz)
> radar transponders for tracking purposes.
>
> 	Apollo introduced S band (2.2 ghz) communications with the UHF
> AM only serving as backup.
>
> 	Ground equipment for the Mercury links was a GRC-27 (the ground
> version of the ARC-27).   I am not sure what was used for the HF.  
> Someone might know...
>
>   
>> Was any HAM activities involved in flights during these two programs 1960's?
>>     
>
> 	Not that I remember.
> __
>    Dave Emery N1PRE,  die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
> "An empty zombie mind with a forlorn barely readable weatherbeaten
> 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
> celebration of what could have been, but wasn't and is not to be now either."
>
> ______________________________________________________________
> Milsurplus mailing list
> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Milsurplus at mailman.qth.net
>
>