Big Dish Telescope: Radio Receivers

Front-End Receiver Components

The front-end components of the radio receiver system are those at the "front end" of the signal path -- where incoming radio waves are initially received -- and which are often mounted in front of the dish in prime-focus telescopes like ours. These components include feeds and waveguides to receive the signal collected and focused by the reflector, active antenna elements in which the radio waves induce alternating currents, a low-noise radio-frequency amplifier, and, in many cases, a frequency downconverter that reduces the received signal frequency to a lower "intermediate frequency" that is more manageable by subsequent system components. Radio astronomy signals are incredibly faint, so the initial amplifier stage is vitally important for enabling their detection. In modern receiving systems, the front-end components are often combined in a single unit called a low-noise amplifier (LNA), low-noise block-downconverter (LNB), or LNB + feed (LNBF).

Most of the following system characteristics describe available front-end units. A few relate to the size of the reflector dish.

Band
(IEEE)
Front-End Unit(s) Received Spectral Range Intermediate
Freq. (GHz)
Bandwidth
(GHz)
Beam Width
(FWHM)
Gain (dB)
Brand Model Type Wavelength (cm) Frequency (GHz) Amp. Directive Total
X - Ku Chaparral,
Pauxis
Universal
Single
LNB 2.35 - 2.56 11.700 - 12.750 1.100 - 2.150 1.050 0.516 - 0.562° 58 50.6 - 51.4 108.6 - 109.4
X 2.56 - 2.80 10.700 - 11.700 0.950 - 1.950 1.000 0.562 - 0.615° 49.8 - 50.6 107.8 - 108.6
S - C Chaparral,
SmartSat
MicroPac LNBF 7.14 - 8.82 3.400 - 4.200 0.950 - 1.750 0.800 1.57 - 1.94° 65 39.9 - 41.7 104.9 - 106.7
L (line) NooElec SAWbird
+H1
LNA+
filter
20.82 - 21.80 1.376 - 1.441 -- 0.065 4.57 - 4.79° 40 32.0 - 32.4 72.0 - 72.4
L (wide) GPIO Labs Ultra+
GNSS
LNA+
filter
17.65 - 27.27 1.100 - 1.700 -- 0.600 3.88 - 5.99° 40 30.1 - 33.8 70.1 - 73.8

Notes on the front-end table:

Back-End Receiver Components

Back-end components of the receiver system are those toward the "back end" of the signal path, also usually located in back of the dish, or even at some distance from it. They accept the amplified and often down-converted signal from the front-end components, sent over a coaxial cable, and perform whatever additional operations on the signal are required. These operations would include additional amplification, demodulation, digitization, and display or recording of the resulting output signal. In many modern systems, all these functions are handled by a software-defined radio (SDR), which can be either a standalone unit or one connected to a computer running specialized software. Our system uses the latter. There are many options for this. Back-end configurations we have tested to date include the following.

Brand Model Frequency
Range
(MHz)
Maximum
Bandwidth
(MHz)
Bit
Depth
Software Platform Computer
RTL-SDR
Blog
RTL2832U
V3
0.5 - 1750 2.4 8 LabVIEW Raspbian Raspberry Pi
+ Macbook
SDR # Windows PC laptop
Airspy R2 24 - 1750 10 12 SDR # Windows PC laptop
SDRplay RSPdx 0.001 - 2000 10 8 - 14 SDRuno Windows PC laptop

Notes on the back-end table:

Signal Generators

Although the radio telescope is designed only to receive signals, not to transmit them, signal generators are still required for some functions.


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