Czech RF-10 Military Radio

Background

The MHz selector is allowing to set frequency in 1MHz step in between 44-53MHz.
The kHz selectors has two knobs:

So ending frequency in range is 53.975MHz.

Regarding the lights on the top panel:
Left green light with yellow ring is indicating the transmission > in test mode (mode switch to test mode same icon).
Middle white light with white color ring is indication all the time that PLL synthesizer is locked correctly.
Right upper side red light with red ring is indication of the discharged battery pack.

I had a friend translate the Czech web site on the RF 10 radio set. Here is his translation for anyone interested in Czech radios.

Bill Howard

CZECH RF-10 Radio Set

For some time I have looked for info on this set which is serving in our army. What I could find was very general and for me insuficient. After half a year I was lucky to buy a pair of units and I started getting practical experience.I started to write a short summary on RF-10 and later I wrote this essay. Lately there was a large increase in apearance of those sets on the air. In this section I would be glad to introduce this communication device made by Company TESLA from Pardubice.

In the 70's there was planned a replacement of obsolescent R-105 and R-109 which were large, heavy, and used obsolete electronics which produced loud continous noise during reception. Constructors from TESLA produced an item of real quality. The technology employed significantly outdistanced other competitors. For example our enemy USA in the 70's used PRC-77 which the RF-10 greatly surpassed in smaller size, usefullness, lower weight, etc. In those days Czech Army used RF-10 mainly for communication on company level, but the utility did not end there, thanks to its adaptability they were mounted in the vehicles, served as telephone relays,allso they found use in fire fighting.

In storage and for transportation RF-10 is stowed in polyester boxes, and that fits into a waterproof container provided to keep out moisture fe. during descent in a helicopter or during immersion in water. In the boxes the parts of the set include radio set propper, microphone and head set, short and long antennas, hanging and directional antennas bags and harness for the set, spare bateries, cables and a box of spare parts. In some cases a charger box was provided to alow keeping batteries in fully charged state for battle readiness, the weight of the charger was on the order of 3 to 4 kg. Operating the set is simple and error free, if however the operator still did not understand something there is onthe side of transmitter short manual of operating
instructions.

On the top pannel of the set there are 2 connectors, one is for 0.5m or 1.5m Whip antennas, the other a BNC for a 5 m. hanging or 30m directional antennas. By the whip antenna connector there is an eylet connection for a grounding wire to provide image plane for the antennas.  Care should be taken that both whip and long wire antennas are not connected to the set at the same time. The whip antennas are very stiff so their ends have a plastic ball with a white line for safety of people working around the station.  Hanging antenna consists of two gold colloured wires connected to a coil assembly in the center, from the coil assy. a green colour coax connects to the antenna connector on the set. For the installation of the long wire antenna the gold single conductor wires should be stretched vertically to ground, the green coax may be routed as convenient.  Directional antenna provides for sending in a specific direction, its whole length is stretched in a backward direction at a height of 1 meter above ground.

Under the antenna conectors there is a 6 position operating mode selector switch. One position marked with a triangle activates the "Noise Compressor" stage. This is usefull if the operator has to send a message in whisper, compressor than increases the gain of microphone input circuit for small signals. The listener hears the message as if transmitted with normal loudness. In this mode operator has to watch thattransmitting loud messages and orders is not attempted as that can lead to overloading of transmitter stages which leads to modulation dropouts. Next two positions give two levels of loudnes in the headphones, the microphone sensitivity is set for standard voice level.  Sensitivity of "Noise Gate" is set for a quiet location. Proper functioning of the noise gate (squelch) is in RF-10 is a great improvement in comparision with previous equipment. In the fifth position of the selector switch the noise gate is disabled, this is preffered when receiving a very weak signal, headphone volume is set high Sixth position is test, a green light lights on the front pannel, and noise is heard in the headphones. For this test it is not neccesary to connect an antenna as the set input is routed to a dummy antenna.

Next three sellectors set operating frequency. First sets from 44Mhz to 53Mhz in 1Mhz steps. Next sets Kiolohertz in 1Khz steps. Last Hertz with values 00, 25, 50, 75 Hz (probably meaning 000,250 500 750 hz). In addition on the front pannel there is an discharged batteries alarm (red light), a headphones and microphone connectors, and two pushbuttons for adjusting the call tone which may allso be used for sending morse.

Now some info about power supply. Battery consists of 5 rechargeable NICD D size cells of 1.2V at 4 Ah. Charging may be provided in a number of ways: Most common method is thru use of "konzervatory", a trickle charger designed for maintaining 30 units in readiness for immediate use. Another is by using a field charger called "one hour charger" which indeed can completely charge a flat battery with high current in about an hour. Third method is by using box A of the RF-10 complet, this will provide a charging current of 450 mA. The Transmitter has an output of 1 W, which is not that much, so for a weekend practice sessions battery discharging is no problem.

Note from Bob:  The mic audio gain (deviation) control is the trimpot on the small PC  board just behind the audio connector.