Characteristics of the AN/PRC-70

Type of Set                 Portable tactical transceiver
Type of Modulation          CW, AM, FM, SSB (also supports FSK for data
                             Communication)
Type of Emission            Voice, CW (morse code), data
Number of Channels          74,000
Tuning                      Continous
Frequency Coverage          2 - 76 MHz
Modes of Operation          FM - 40 km (VHF)- planning range
                            CW - 2400 km (HF) - planning range
                            AM and SSB
Power Output                FM, SSB, CW - 40 W
                            AM  - 10W
Power Source                NiCad or Metal Air Batteries
Antenna                     Whip - 6 feet
                            Whip - 15 feet
                            Doublet
Weight                      less than 25 lbs

Note: the weight is different than the one listed in TMP TM 1-1 which uses
39 lbs.

The characteristics of the AN/PRC-68A (from the orginal spec MIL-R-29401B -
USMC) are:

Type: Handheld VHF/FM radio 

Controls:
     Push to Talk Switch
     Volume Control
     Power Off/Power On/Squelch Disable Switch (Note: this swich will not
stay in the squelch diable position without being held there.  This radio
uses a 150 Hz tone to break the squelch on the receiving unit.  This means
that you will not hear static unless you manually disable the squelch and
hold it there)
     Phone/Mic/External Power Connector - a 5 pin connector compatiable with
the standard military handsets (ie H-250)
     Earphone Connector - for standard earphones (ie H-281) - this connector
disables the built-in speaker
     Built-in speaker
     Built-in microphone
     Channel Selector Switch (10 positions)

Frequency Range:
     Operating Frequency Range      30-80 MHz (in 25 kHz)
     Number of Channels             2000
     (Note: This unit will operate in one of four bands 30-40 MHz, 40-54
MHz, 50-64 MHz, and 60-80 MHz.  Each band has between 500 and 800 channels
each.  Out of these channels, the channel selector switch can select 10.
The band of operation and the ten channels are selected by programming
switches within the unit.  In my world, these ten channels are selected as 5
team channels and 5 guard (or regional wide) channels.  The four bands are
assigned to the four regional centers but the selected channels will be in
the operating frequency range of the PRC-70 (again my world - your world my
vary))

Planning Range
     With provided antenna     300 meters
     With long antenna (AT-892/PRC-25 (ie the VHF antenna for the PRC-70)
1.6 km

(Note - when we discuss planning range we mean the range where reliable
communications between two radios of the same type with the average operator
over a wide range of terrain types - for the PRC-68A this includes the
operator in the supine, kneeling, and standing position.  This explains to
some extent why the range is much shorter than that in the TMP TM 1-1.)

Hours of Operation
     36 hours with BA-1588/U (mercuric oxide battery) based on 1 minute
transmit - 1 minute receive and 8 minutes of standby (squelched): probably
much less with a NiCad battery (BB-588/U) but not stated

RF Output Power - 1W
Antenna - 12.7 to 19.7 cm long rubber covered - this antenna will be
removable to allow attachment of external units.

MTBF (mean time between failure)  1000 hours (at +65 degree C)
Operating Temperature Range  -40 to +65 C

This unit will accept the standard Secure Voice Module (KYV-2 or -2A)

Size: excluding the battery (as shown in TM 1-1) 23.7 cm by 9.6 cm (wide)
and 3.86 cm thick add 5 cm to the height for the battery.
Weight - 1.4 kg with BA-1588/U Battery

Okay there is the equipment so let's discuss the various possible
communication scenarios:

AN/PRC-68 - AN/PRC-70

Since the PRC-68 (sometime PRC is pronounced 'prick') is VHF, both radios
have to have "line of sight."  This means that, in the absence of blocking
vegatation, you should be able to see antenna of the unit to which you are
transmitting.  At these frequencies, vegatation does not cause a lot of
problems.  The range from the '70 to the '68 would be about 40 km while the
range back would be about 1 km (the longer PRC-70 antenna gives us a gain in
recieve with increases the range back).  If the foot team would go too far
from the vehicle, it could here the vehicle but not send back.

Another interesting item is that two AN/PRC-70 can be connected into a
retransmit mode (ie what is recieved by one unit is transmitted by the
other).  So two PRC-70 could be connected together and two nets of PRC-68
could be set up.  This would allow one group on foot to communicate to
another group.  Each group is on a different frequency (separated by 10
MHz).  This allows communications across blocking terrain (park the vehicle
on the crest of the hill and team can check out both sides).  It also
increases the operating range overall but the vehicle has to be in the
center of the area.

Finally, in my would I have added the following piece of equipment:
F2338 - Interlink Repeater System
weight: 1.6 kg
size 51mm high by 178mm wide  by 242mm deep
This links SSB HF and FM VHF/UHF radio for connecting nets.  Thus a PRC-70
can be connected to the PRC-68 through the handset connector.  This would
allow PB to listen in on the group's VHF net (PRC-68s).

AN/PRC-70 to PB

The planning range in the CW mode is 2400 km (note the change from my
previous post).  The 4000 km range in TM 1-1 is probably based on the
longest single bounce path obtainable on the earth.  From some first order
estimates (looking up the data and guessing the system performance at PB),
the PRC-70 could probably do this with voice (single side band (SSB)) but
this would require that the operator knew the best operating frequency for
that time.  I would expect that PB probably sent out the MUF (Maximum Usable
Frequency) predication using CW (which would go farther) one per week or
day.  With a vehicular amplifier and larger antenna, this would not be as
important.

AN/PRC-70 to AN/PRC-70 - both in manportable mode

It may be necessary for two teams each using AN/PRC-70s to communicate
without the vehicle goodes.  This can be done in HF in the heaviest terrain
using NVIS (nearly vetically incident sky wave) propagation.  The
frequencies that are use in this mode are not receivable with the AN/PRC-68.
Effectively we transmit up and receive the reflected signal.  The planning
range - pretty much without regard for the terrain - should be about 360 km
(longer with trained personnel making an effort - maybe as far as 500 km but
I don't have all the preformance information I need for the perdiction).

Hope this helps.

Bill

William R. Garmer, PE
Torrey Science Corporation
10065 Barnes Canyon Road  Suite B
San Diego, CA  92126-2777
Voice: 619/552-1052
Fax  : 619/552-1056
email: bgarmer@tst.com
