Does the methods of taking dark frames or bias frames or even flats also apply to Radio Astronomy ?
Like in optical astronomy, where we are hampered by electronic noise of the sensor chip and also stray light within the optical train,
in Radio Astronomy we got similar problems.
The ambient noise (temperature, yes Radio Astronomers talk about temperature "black body radiation") and also the
noise figure of all active elements ( e.g. LNA, filter) including the local processor needs to be removed as much as possible,
otherwise the very faint radio signals we want to receive are not detectable.
I experimented with various methods of noise elimination, known for a long time :
a) switching between two antenna feeds, one in the direction of the target, the other on the back of the mirror
b) two complete antenna systems in opposite of each other
c) switching the gain (amplification factor) of the receiver
d) use two different frequencies, the second frequency some MHz lower to higher.
Thanks to Frequency regulations for Radio Astronomy there should be no emitter within as certain limit
this approach in fact includes all noise cancelling methods at once (dark,bias,flats).
all version subtract the two signals, like using dark, bias or flat frames in the optical telescope image processing.
I experimented with a) c) and d), but I got the best results using d)
The switching time between the alternate signals is in the range of seconds, so switching in a),b) could be done by using a (UHF) relay.
c) and d) is done by the software which controls the SDR dongle.
Both signals are added up (integration) and subtracted from each other after a desired time.
Based on the earth's rotation and the Antenna opening angle, a few minutes of integration is feasible.
I n my case the Antenna is fixed at AZ and EL during a measurement : drift-scan methode.
I choose 5 minutes.
If the Antenna is steerable and tracking, integration time can be as long as you need to detect the desired signal ( pulsars etc.)
My question is : Does someone have other experiences or may be suggestions how to minimize noise temperature of a Radio Telescope ?
b.t.w. I am self taught in this field, all I know is coming from searching the internet for publications / examples and making my own experiments.
cheers
Wanni
Like in optical astronomy, where we are hampered by electronic noise of the sensor chip and also stray light within the optical train,
in Radio Astronomy we got similar problems.
The ambient noise (temperature, yes Radio Astronomers talk about temperature "black body radiation") and also the
noise figure of all active elements ( e.g. LNA, filter) including the local processor needs to be removed as much as possible,
otherwise the very faint radio signals we want to receive are not detectable.
I experimented with various methods of noise elimination, known for a long time :
a) switching between two antenna feeds, one in the direction of the target, the other on the back of the mirror
b) two complete antenna systems in opposite of each other
c) switching the gain (amplification factor) of the receiver
d) use two different frequencies, the second frequency some MHz lower to higher.
Thanks to Frequency regulations for Radio Astronomy there should be no emitter within as certain limit
this approach in fact includes all noise cancelling methods at once (dark,bias,flats).
all version subtract the two signals, like using dark, bias or flat frames in the optical telescope image processing.
I experimented with a) c) and d), but I got the best results using d)
The switching time between the alternate signals is in the range of seconds, so switching in a),b) could be done by using a (UHF) relay.
c) and d) is done by the software which controls the SDR dongle.
Both signals are added up (integration) and subtracted from each other after a desired time.
Based on the earth's rotation and the Antenna opening angle, a few minutes of integration is feasible.
I n my case the Antenna is fixed at AZ and EL during a measurement : drift-scan methode.
I choose 5 minutes.
If the Antenna is steerable and tracking, integration time can be as long as you need to detect the desired signal ( pulsars etc.)
My question is : Does someone have other experiences or may be suggestions how to minimize noise temperature of a Radio Telescope ?
b.t.w. I am self taught in this field, all I know is coming from searching the internet for publications / examples and making my own experiments.
cheers
Wanni
