ASSA Radio Astronomy Group

Out of the Box operation

(from the manual)

The efficient simplicity of this and similar receivers is made possible by the Signetics NE612AN mixer-oscillator U1, functionally identical to the well known NE602. The NE612AN is used because it is standard Ten-Tec inventory.  L1, C1 & C2 form a tuned RF input circuit coupling the antenna to U1, Pins 1 & 2.  The dissimilar values of C1 and C2 are selected for impedance matching . Potentiometer R1 is an attenuator to minimise overload  by strong signals and nearby AM broadcasts, therefore serving as RF gain control.  The local oscillator frequency is determined by C3, C4, L2 and the varactor tuning network coupled through C5.  Voltage applied through tuning potentiometer R2 and R4 to the MV209 varactor provides coarse tuning or "band set".  The fine tuning or "band spread" by R3  is done by coupling the control voltage to D1 through R5.  As desired, changing the value of R5 will increase or decrease the fine-tuning rate.

Zener Diode D2 regulates the voltage to the oscillator's varactor circuit, supporting U1's never exceed Vcc limit of +8V.

The output from U1, Pins 4 & 5  is low level audio, the direct conversion result from mixing antenna RF input with the variable local oscillator frequency.  This audio output is coupled through the filter network formed by R6 thru R9 and C10 to the inputs of U2a.  The LM358 (U2 a,b) is a dual op-amp.  The voltage gain from the antenna input to U1 through to U2a output is typically 68dB. The other LM-358 op-amp (U2b) and its associated components serve as an elementary bandpass filter, with front-panel filter tuning done by potentiometer R16.

Initially, the Ten-Tec 1056 will be used in its 'out of the box' configuration for Jupiter emission observations until sometime in 2013 when it will become part of another Simple Interferometer.

A single Ten-Tec 1056 receiver

For the interferometer, note that there is provision for another receiver to be fitted to this enclosure as indicated by the additional set of pilot holes  for the controls on the enclosure's top panel.  The battery will have to be relocated to another enclosure and it's capacity increased to drive the second receiver and the incident/quadrature local oscillator common to both receivers.  The local oscillator will be one of the AD9854 Direct Digital Synthesiser boards detailed here.  The local oscillator will be housed in another identical enclosure (3 in all), these diecast boxes should provide sufficient shielding to suppress any digital interference/noise away from the receiver's front ends.

For future operation, receiver sensitivity will be enhanced with a low noise amplifier, to be inserted between the RF line behind the divider/prior to the receiver.  This LNA adds about 9.6dB gain at 20MHz, the additional gain may overcome the perceived lack of sensitivity for the Ten-Tec 1056 receiver noted in 2011.

It should also be noted that amplifiers often add more problems than they solve and they should be used with caution
to ensure that there is a tangible benefit obtained rather than just adding additional noise and interference.