Communicating with space

At your risk.


If there is a faint electromagnetic signal from a far away solar system carrying information for the purpose of communicating with us...


What would be a good receiver to capture such a signal taking so many years to arrive to earth?


Would a bipolar or a JFET transistor or an electron tube front end be the best?


If it is JFET or electron tube would open gate or open grid (grid at space potential) be best?


If it is an electron tube open grid would a Pleiades V6 circuit impementation be best as it operates with clean battery power and low anode voltage minimising secondary emission effects. Would it be better having such an amplifier in space powered by a small solar panel?


If signal is coupled to grid through a capacitor grid is not disturbed. What desired is getting as much information from as few photons coming from space translated to as few electrons arriving to the control grid.


What is the input impedance of an electron tube at open grid conditions?
If the grid is open grid current is zero.
Positive grid current and negative grid current are balanced.
Grid settles to a negative value since cathode is more positive with respect to it since cathode has lost electrons by thermo emmision.


If a pull up bias resistor, either connected to cathode or anode is used there is grid current because there is outside path for electrons to return to the positively charged cathode. Amplifier can operate with the minimum anode voltage, eg 2 volts.
At such condition the input impedance of the electron tube may be typically 100KΩ.


When grid is at space potential more anode voltage is needed for similar anode current, say 30V. What is the input impeadnce at open grid or grid at space potential?


If grid is biased negative typically more anode potential may be needed. If the grid is biased negative input impedance can be very large. But is it larger or smaller than open grid conditions?


If a LC tuned circuit is connected to almost infinite input impedance, the Q (quality or magnification factor can be very high) especially if the coil is made of silver wire which has very low resistance.


But a high Q means self ringing for a long time. Like an electric guitar string vibrating for many seconds. Or a steel tuning fork.


Ringing at the receiving end means the information transmitted must not change more quickly as ringing would mask the information. Ie only low bit rate can be sent, say slow morse code.


This is another way of looking at Heisenberg's uncertainty principle applied to signals. The more certain we are of frequency, (high Q or sharp frequency response peak) the less certain we are of time variations.


And we are neither certain of frequency as we do not know at which frequency a transmission would be.


But if we do not know the frequency at all taking the Heisenberg's principle in reverse we may know exactly when the event takes place. This means the transmission lasts for a very short time, like a short pulse, an impulse, what may approximate to a delta mathematical function.


If there is life outside of earth wanting to communicate, would they transmit extremely short bursts of electromagnetic energy?