by MARIO GALASSO - IK0MOZ

 HISTORICAL INTRODUCTION

 On  1939  in  the  Italian Army  came  out  the  irrevocable requirement  of  modernizing and standardizing the  medium  power field radio stations. In  that moment several types of them were in use  like the R4, the R4A and the R4D designed an the beginning of the thirties and by then obsolete.

The  Allocchio  Bacchini  of Milan (one of  the  oldest  and bigger Italian military rigs manufacturer) was appointed to study the  new  set  in cooperation with the  Officina  Militare  delle Trasmissioni (Signal Corp Establishment). The requirements were theoretically simple: - Modern set simple to be operated; - Set  able  to  cover the operative needs of  the  previous "Serie 4" stations - Possibility  to  use  the  same  systems  and  accessories because available in large quantities. In  a  short time the Allocchio Bacchini  proposed  the  new radio  station  that was approved by the Italian Army  under  the military  classification  RF4 which stands  "for  interdivisional communications (4) radio station (RF)".

The  RF4 is a combined radio transmitter and radio  receiver which  provides telephone and C.W. communications as  a  portable field set within the infantry regiments. The  station  is  built in four cases plus  two  chests  for batteries. The contents for each single case is 1) Wireless set;2) Power unit, charger and accessories;3),4) Antenna system parts;5),6) High capacity batteries.Each case is fitted with handles to allow the trasnportation  by two  men per case (for very short distances) or by mule (in case of bigger distances) fastening the set accordingly to a  special saddle. The  radio equipment is housed in a wooden case and consists of  the receiver unit,  the transmitter unit and the controì box.

The  front of the case is closed by an hinged panel that  can  be used as a table when the set is operating. A  second  case  similar in dimentions to the  previous  one includes  the 12 Volt Power Unit,  the battery charger  unit  and accessories plus spare parts. This case is usually used as a base for the radio set.

As  said  the radio set is divided in three  separate  units easily  removable  from  the  frame  in  case  of  servicing  and inspection.

TRANSMITTER SECTION

Located  on  the left side of the case it is of  simple  and tough  construction.  The tuning is possible by two commands with different turning ratio.  The calibrated dial is viewed througt a lens  that enlarge the diaì indications.  An instrument gives the aerial current.The main characteristics are:

Frequency range : 212 - 1,550 kHz in three switched bands

Band 1 : 212 - 410 kHz

2 : 405 - 820

3 : 800 - 1,550.

Accuracy : better than 1 kHz

Thermal stability : 40 Hz / degree on low frequency

250 Hz/ degree on high frequency with reference temperature of 20 deg/cent.

Electricaì  strability  :  for  variation of 10 % of  the  supply voltage better than 0.5%.

Facilities : Telephony and C.W.

Power reduction possibility in C.W.

Voice switch on R/T

Crystal calibrator.

Valves : Master Oscillator PC 05/15, Power Amplifier Two PC 05/15 in parallel.R.F.

Output : about 20 Watt in C.W. 10 Watt in R/T.

Range : 60-120 km in C.W. 10- 20 km in R/T.

Modulation : A.M. with depth of 70 %

Power consumption : Filaments : 12V 1.4 Amp. Plates : 500V. 0.15 Amp. Screen grids : 270V. 0.17 Amp

CONTROLL BOX

This  unit,  placed  on  the middle of  the  case,  contains  the modulator,  the  crystaì  calibrator and the voice  switch.  This circuits  are operated by three valves type 6R and  connected  to the  transmitter by a shielded cable and some connectors.  On the front  of this unit there are the controls and the instrument  to check voltages and currents of the set, the microphone input and the key. The  modulation system is by suppressor grid of the  final  tubes and   the   voice  switch  allows  to  pass  froí  reception   to transmission simply speaking in the micro (when the set is in R/T mode).

RECEIVER SECTION

This  is one of the first superheterodyne receiver used  for field purpose in the Italian Army.  It uses 7 valves of the  same type  6R made by FIVRE according to a military specification.  It can receive AM and,  turning on the BFO, the CW. The dial is very large,  each band has a different color and it looks vaguely like the British R107. The electrical main characteristics are: Frequency  range  :  220 - 4,400 kHz in five switched bands and precisely:

Band 1 : 220 - 460 kHz

2 : 440 - 850

3 : 800 - 1,580

4 : 1,250 - 2,400

5 : 2,200 - 4,400

.Accuracy : 0,15 %Sensivity : better than 10 microVolt

Selectivity : 10 kHz at 60 dB down

Image rejection : in the worst condition not less than 22 dB

Thermal and Electrial stability similar to the transmitter;

Circuit : Superheterodyne with an RF stage and BFO

Facilities : R/T and C.W.

Valves : Seven type 6R

Intermediate frequency : 175 kHz

Power consumption : 230 V. 0.03 Amp.

All  voltages  necessaries for the  wireless  operation  are supplied from the power supply which is located on the left side of  the case.  This device consists of an interruption  dynamotor formed  by  an electril motor driving a three  sections  rotative switch.  The  battery  voltage  is lifted and rectified  by  this switch  and  a  suitable  transformer.  Some  filters  eliminate commutator ripples and RF interferences. The battery charger is located on the right.  This unit  has the  transformer with universaì primary winding and  can  supply, with a copper oxide rectifier, 12-20 Volt DC with a current up to 10 Amp. The output is controlled by a switch that is on the front panel. In  the center of the case there is the space for acessories and  spares.  The  standard equipment were  quite  rich  (compas, AVOmeter,  scissor,  pliers...)  but  for severaì reasons in  the reality the equipment came to be the strickly necessary like  the handmicrophone,  headphones,  pencils,  paper, log station, fuses and essential spare tubes.

Even  in  this  case the theoreticaì standard  equipment  is quite wide.  16 mast sections,  copper wires,  hemp guys,  reels, stakes,  hammer,  pulleys, counterpoise nets and other parts fill up completely two cases for a totaì weight of 96 Kg. The  RF4  was designed to use all types of antennas  of  the "Serie  4"  sets  but usually the favorite system  was  two  wires inverted  L with net counterpoise and sometime dipole in case  of fixed station.

In  practicaì use this station was easy to be  operated  and reliable in operation. The receiver controls are standard and the net operation is simple. Even  the transmitter P.A.  tuning was simple and could  be made  turning the knobs INDUTTANZA AEREO and than VARIOMETRO to obtain  the  maximuí on meter reads.  The dials  were  calibrated directly  in  kHz  and each band  had  indications  in  different colors. The  RF4 has been made in several series usually marked with the  year  of production.  The more common is the model  RF4/1940 used from Italian troops in North Africa and in the Balkan area.

There is a version marked RF4D (D=Difesa, Defence) where the R.F.  stage has been modified to work on the frequency from 1,270 to 4,300 kHz and used for Coastaì and Internal  defence.  Usually this  set  were  powered  directly by the main lines  and  had  a special tank to tune ground aerials. After the end of the war this set were again largely present in  the Italian Army and again used for some years up to when  it was  completely  replaced from the "Canadian" WS19 placed  in  a wooden  chest  (containing  complete radio  set,  variometer  and accessories), similar (or the same) to that used for RF4.

Up to 1960 the receiver were sold by many Surplus shops, the price was very chip, because if compared to the BC312 or the R107 the  frequency coverage and the generaì characteristics were very poor.  Sometime  they have been used like second converter  using like front end a Geloso converter. Today I guess that no more than 5 or 6 complete sets exist in Italy,  I have personally seen 4 of them in good shape. I even know  that some of these set has been captured from the  British and  taken in England for technical evaluation.  After this could be  the remote possibility to find an RF4 buried in  some  dusty military depot.