[MilCom] UHF Space shuttle frequencies?

Wed Jul 13 09:04:41 EDT 2005

The UHF system is used as a backup for the S-band PM and Ku-band voice
communications primarily during extravehicular activity. For communications
with the STDN ground stations, the UHF system operates in a simplex mode,
which means that the orbiter flight crew can only transmit or receive, but
cannot do both simultaneously. The UHF transceiver takes the voice signal
from the audio central control unit and transmits it through the external
UHF antenna on the bottom of the orbiter forward fuselage. The incoming UHF
signal goes through the external antenna to the UHF transceiver, which sends
it to the ACCU for distribution in the orbiter.

UHF transmission is controlled through the UHF mode control knob and the
three two-position toggle switches on overhead panel O6 labeled xmit freq,
splx pwr ampl and squelch . The xmit freq switch selects one of the two UHF
frequencies, 296.8 MHz primary or 259.7 MHz secondary, for external
transmission. The splx pwr ampl switch selects the UHF antenna on the
external skin of the orbiter's lower forward fuselage or the airlock
antenna. The UHF antenna on the lower forward fuselage is covered with
reusable thermal protection system. The airlock antenna is used by the EVA
astronauts, in extravehicular mobility units, to check out their
transceivers before exiting the airlock; it is also used for air-to-air
communications during EVA.

The squelch switch permits on or off selection of UHF squelch. A
five-position rotary knob on the UHF control panel activates power to the
UHF transceiver and selects any of the following modes of UHF transmission.
When the knob is positioned to EVA , EVA transmissions are made on one
frequency selected by the xmit freq switch, and the message is received on
the other frequency. The off position removes all electrical power. When the
UHF mode rotary contral knob is positioned to simplex, transmission and
reception are both on the frequency selected by the xmit freq switch.
Positioned to splx + g rcv, transmission and reception are the same as in
simplex except that reception of the UHF guard (emergency) frequency (243.0
MHz) also is possible. In the g t/r position, transmission and reception are
both on the UHF guard (emergency) frequency.

Access to transmission and reception of UHF signals is controlled by
two-position toggle switches located on the bottom of the audio center panel
on panel A1R at the aft station. The switches are labeled t/r for
transmission/reception, off for blocking UHF signals to or from the UHF
transceiver, a/g for the air-to-ground channel and a/a for air-to-air
channel. All three of the UHF frequencies (296.8 MHz, 259.7 MHz and 243.0
MHz) are preset in the UHF transmitter and cannot be altered by the flight
crew.

The UHF system is used for EVA operations. The EVA astronaut's UHF
communication are through the orbiter UHF airlock antenna. The two existing
UHF frequencies of 296.8 MHz and 259.7 MHz are used; an extra UHF of 279.0
MHz is added to the EMU backpack. The 279.0-MHz frequency can transmit or
receive only among the two EVA astronauts and the orbiter, not the ground
stations.

One EVA astronaut operates in mode A, transmitting data and voice to the
orbiter on 259.7 MHz, transmitting voice to the other EVA astronaut on 259.7
MHz, receiving voice from the orbiter on 296.8 MHz and receiving voice from
the other EVA astronaut on 279.0 MHz. The other EVA astronaut operates in
mode B, transmitting data and voice to the orbiter on 279.0 MHz,
transmitting voice to the other EVA astronaut on 279.0 MHz, receiving voice
from the orbiter on 296.8 MHz and receiving voice from the other EVA
astronaut on 259.7 MHz. The orbiter then communicates through a switch in
the orbiter via the UHF EVA relay mode by retransmission over air-to-ground
through its S-band system to the STDN ground station, its S-band system to
the TDRS or its Ku-band system to the TDRS. As a backup procedure only when
the shuttle is over a UHF ground station, the EVA astronauts, orbiter and
ground can switch to the 259.7-MHz UHF, simplex. During EVA, the EVA crew
members' biomedical data also are transmitted to the airlock antenna and
separated from voice signals in the orbiter instrumentation system for
transmission to the ground.

The UHF system may be used after entry during the approach and landing phase
of the mission. Air-to-ground voice communications take place among the
space shuttle, the landing site control tower and chase planes (if used).

http://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/comm/orbcomm/uhf.html

Found by searching NASA web site

----- Original Message ----- 
From: "Stavro Giovani" <mykonos21 at adelphia.net>
To: <MilAirCommsChat at yahoogroups.com>; <flacom at yahoogroups.com>; "MilCom"
<milcom at mailman.qth.net>; "Scansavannah" <scansavannah at yahoogroups.com>;
<MilGovMonitoring at yahoogroups.com>; <ScanNorthAmerica at yahoogroups.com>;
"ScanJax" <ScanJax at yahoogroups.com>; <CSFRC at yahoogroups.com>
Sent: Wednesday, July 13, 2005 7:49 AM
Subject: [MilCom] UHF Space shuttle frequencies?

> These are listed. But are they any good and if so what can we expect to
> hear on them if anything?
>
> UHF Frequencies
>   259.700 Air-to-Ground voice downlink (AM) (Primary)
>   279.000 EVA voice orbiter only, no ground link (AM)
>   296.800 Air-to-Ground voice downlink (AM) (Secondary)
>
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> http://groups.yahoo.com/group/ScanNorthAmerica/
> Scanners ham radio and more.
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