PRC-68 Series Specials & Prototypes

Brooke Clarke 2001 - 2014

Prototype PRC-68 with cut away modules
PRC-68 (RF Amplifier)
PRC-68L
PRC-68(X)
PRC-68 Single Printed Circuit Board Design
Magnavox Marketing Radios
Amplifiers & Vehicle Adapters
Motorola PRC-68 Prototype

   Prototype PRC-68 with cut away modules

This prototype has a panel machined from Aluminum and has the tops cut off all the modules so you can see inside them.

PRC-68 (RF Amplifier)

This is an add on amplifier for the PRC-68.  It appears to be a prototype.  The ANT connector in the top view uses two screws to attach to the top of the panel, it is not a screw in type like on all the other PRC-68 series radios.  The ANT connector is also tapered unlike the later versions.

There are two coax cables in the vertical extension, one takes the radio output and feeds the amplifier input and the other takes the amplified signal to the top ANT connector.

The RF AMP module in the radio has been replaced with a board with a few components.

The RF Amplifier adapter connects to both the battery snaps and the SVM connector on the bottom of the radio.  (Maybe the top plate of the RF Amplifier adapter is from a SVM?

In the images with all the housings in place you can see from top to bottom:

 
 

PRC-68L

This is a 2 module prototype but has the same frame and panel size as the PRC-68. Not the longer frame that later was used on the PRC-68A.
Maybe they could not fit everything in the same space and route all the lines to the two connectors so had to make the frame longer?
The ANT connector has a hex nut on the top rather than the round metal that's on all the production ANT connectors, this takes the 5/16-24 threaded PRC-68 antennas, not the small thread like on the PRC-68B.
 
 

PRC-68(X)

The label says: AN/PRC-68(X) Radio Set, N00264-78-0024  Ser DM-099, Magnavox Ft Wayne, IND.
It appears to be a stock PRC-68, I don't see what the "X" is for?
 
 

PRC-68 has a removable printed circuit board and a fixed board

Most of the PRC-68 radios use two printed circuit boards back to back with a small gap between them to hold the modules.
The PRC-68X (above) is a good example and the left photo below shows the two boards with 1/16" gap between them.  The press to tune switch can be seen between the boards.  You can see the green PUSH TO TUNE switch on the right has a printed circuit board about flush with it's topside.  Also the exposed face of the board is typically a brown color.  These are double sided boards.

When the board on the PTT side (holds the VCO, Synthizer, MOD/Mixer) is removed you see the fixed baord below it.
 
2 boards
removable Board
fixed Board

Magnavox Marketing Radios

These radios do not have a contract number on the label and instead say Magnavox Marketing.

Amplifiers & Vehicle Adapters

AM-7032/VRC

 eBay: "Here is an RF and audio amplifier/speaker adapter for the PRC-68B series military radio. Unit is in good overall condition and I measured 7watt output with a 1watt radio connected. Covers 30 to 88mhz and includes hard to find antenna and audio cables and an M-80 microphone." - KM6AB eBay photos: Front, Overall, in the upper right corner of the Side view you can seea speaker facing up.
This is very similar to the OF-185.  I wonder if it has internal amplifier and filter modules like the OF-185?

OF-185

Part of the Scope Shield PRC-128 system.

Motorola PRC-68 Prototype

This was probably the Motorola entry for the Marine's requirement.  The block at the bottom holds the internal antenna (no provision for an external antenna) and maybe 10 crystals for alternate channels, no synthesizer.  No provision for voice crypto.
Motorola PRC-68 Prototype
Motorola PRC-68 Exploded view
Motorola PRC-68 Block dia
Photos and diagrams courtesy of N3AJA

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Page created 8 May 2001.