E-656: Communications Receiver RA-1772; manufactured by Racal Engineering Ltd., GB - Bracknell.
A few units of Racals digital frequency display all wave receiver RA-1772 has been acquired by the Swiss Army. The receivers got the designation E-656, I have no further informations about their use.
The E-656 / Racal RA-1772 is a communications receiver in a 19 inch rack design, it's dimensions are 48,3 x 17,8 x 41 cm and it's weight 21 kg. It comes with an integrated power supply for a great variety of voltages.
In the upper dark grey coloured part of the front panel, a small monitor speaker is hidden behind a small speaker grille in the left upper part of the front panel. In the middle, you find the switch for the thirty 1 MHz ranges, the LED display for the kHz digits of the reception frequency (the frequency is indicated with an accuracy of 10 Hz) and the signal strength meter at the right hand.
Below, the big well balanced main tuning knob is located in the middle of the front panel. On the left side, the control for the manually tuned preselector RF TUNE is located. Under certain conditions, it can be bypassed in the WB (wide band) position, this will result in a certain loss of dynamic range. Next to it, you find the rotary controls for the two AGC speeds and the tuning speed; for fixed frequency operation, the main VFO can be locked. Below next to the headphones jack, the I.F. gain to control the amplification gain of the intermediate frequency stages and the BFO control.
The reception modes switch is located at the right of the main tuning knob. The AM position is used for the reception of standard AM / A3 signals and the position USB+BFO for all A1 / CW signals. Only in this position and the USB position for single sideband reception, you can select from all I.F. bandwidth filters, there is only one I.F. filter available for LSB (lower sideband) reception. In the positions ISB-U and ISB-L you can select one of the sidebands of an independant sideband mode signal.
The suffix numbers and letters behind the model designation on the typeplate give information about the installed I.F. filters and options, you find the explanations in the user's manual or at the www.radiomuseum.org website.
The measuring instrument can not only be switched to act as signal strength indicator, but also as an aid to tune the receiver exactly to the carrier frequency, etc.
In the bottom row of controls, you find the main switch, the volume control AF GAIN, a switch for automatic frequency correction, which will lock the receiver on the carrier of a transmitted signal, plus another headphones jack.
On the rear face, you find the voltage selector and the mains fuses, the connectors for the I.F. and oscillator signal outputs (the receiver can also be operated locked on the input of an external high stability oscillator) and the ISB intermediate frequency. The antenna jacks for 50 Ohms and long wire antennas are BNC connectors.
The operation scheme is uncomplicated: just connect the receiver to the mains outlet and connect a random wire at the long wire antenna input. Adjust the AF gain control for a slight noise to be audible from the monitor speaker.
The RF TUNE switch should be on WB, so you don't have to bother with preselector tuning, set the AGC speed to SLOW, reception mode to AM. Use the switch at the left of the frequency display to select the desired MHz segment (e.g. „6“) and use the main tuning knob to tune to 0 7 5.0 0. Now, the receiver should be tuned to Radio Deutsche Welle from Cologne. In case, the reception frequency is not changing when you turn the tuning knob, make sure, the TUNING RATE control is not set to the LOCK position…
For single sideband reception, select the sideband with USB or LSB, use the position USB+BFO for CW reception and adjust the pitch of the morse code signals with the BFO control. The set offers excellent narrow I.F. bandwidth filters to „cut“ that signal out of interfering stations.
The set is completely solid state.
The purpose of use of the E-656 receiver in the Swiss Army is unknown.