[Milsurplus] Mercury Comms

[David I. Emery]

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."