Detection of Earth's radio broadcasts at interstellar distances

[Pagan Harpoon]

I'm trying to understand the entry labeled 1.2.3 on this page - http://setifaq.org/faq.html#1.2.3

The main point of confusion, for me, is what they mean by Tsys. At first, I assumed it referred to the temperature of the telescope, but in the table of results, its value changes depending on the frequency being considered and it ranges from millions of kelvin to 40-50 kelvin.

What does Tsys mean?

Thanks.

 

[davenn]

I'm trying to understand the entry labeled 1.2.3 on this page - http://setifaq.org/faq.html#1.2.3

The main point of confusion, for me, is what they mean by Tsys. At first, I assumed it referred to the temperature of the telescope, but in the table of results, its value changes depending on the frequency being considered and it ranges from millions of kelvin to 40-50 kelvin.

What does Tsys mean?

Thanks.

no you are NOT looking at millions of K that's surface/core of the sun etc temps

Tsys = is the system temperature (Kelvins)
All electronics generate heat and this has an undesirable effect on the sensitivity of a receiver. For very sensitive receivers, like used in radio astronomy, the receiver system is encapsulated and cooled with (usually) liquid nitrogen. This has the effect of bring down the temperature of the receiver components and therefore substantially decreasing the noise they produce... the less noise, the more sensitivity. Temps of less than 20 Kelvin are achieveable.

If you do a bit of reading, you will discover that in radio astronomy signal level is usually measured in its temperature above the backgrond noise
there is masses of info on google.

cheers
Dave

 

[Pagan Harpoon]

Here is the contents of the table I was referring to:

Table 1 Detection ranges of various EM emissions from Earth and
the Pioneer spacecraft assuming a 305 meter diameter
circular aperture receive antenna, similar to the Arecibo
radio telescope. Assuming snr = 25, twp = Br * Tr = 1,
<eta>r = 0.5, and dr = 305 meters.
-------------+-------
Source -----| Frequency | Bandwidth | Tsys | EIRP | Detection |
------------| Range ------|---(Br) ----|(Kelvin)|-------| Range (R) |
-------------+--------------+-----------+--------+--------+-----------+
AM Radio | 530-1605 kHz | 10 kHz | 68E6 | 100 KW | 0.007 AU |
-------------+--------------+-----------+--------+--------+-----------+
FM Radio | 88-108 MHz | 150 kHz | 430 | 5 MW | 5.4 AU |
-------------+--------------+-----------+--------+--------+-----------+
UHF TV | 470-806 MHz | 6 MHz | 50 ? | 5 MW | 2.5 AU |
Picture | | | | | |
-------------+--------------+-----------+--------+--------+-----------+
UHF TV | 470-806 MHz | 0.1 Hz | 50 ? | 5 MW | 0.3 LY |
Carrier | | | | | |
-------------+--------------+-----------+--------+--------+-----------+
WSR-88D | 2.8 GHz | 0.63 MHz | 40 | 32 GW | 0.01 LY |
Weather Radar| | | | | |
-------------+--------------+-----------+--------+--------+-----------+
Arecibo | 2.380 GHz | 0.1 Hz | 40 | 22 TW | 720 LY |
S-Band (CW) | | | | | |
-------------+--------------+-----------+--------+--------+-----------+
Arecibo | 2.380 GHz | 0.1 Hz | 40 | 1 TW | 150 LY |
S-Band (CW) | | | | | |
-------------+--------------+-----------+--------+--------+-----------+
Arecibo | 2.380 GHz | 0.1 Hz | 40 | 1 GW | 5 LY |
S-Band (CW) | | | | | |
-------------+--------------+-----------+--------+--------+-----------+
Pioneer 10 | 2.295 GHz | 1.0 Hz | 40 | 1.6 kW | 120 AU |
Carrier | | | | | |
-------------+--------------+-----------+--------+--------+-----------+

(I hope that's readable, it didn't really copy well.)

In that table, the value for Tsys is varying depending on the frequency being examined, and they are indeed using a temperature of 68 million kelvin for one of them. The reason I started the thread is to see if anyone knows why they would be using such a temperature?

I'd also be interested in any other comments that people have on this calculation.

 

[davenn]

I really don't see why they are mixing Tsys into a transmitter situation
Tsys is purely a function/feature of the receiver sensitivity as I stated in my previous post.
In any normal transmitter, system temperature is only a factor of making sure the transmitter is as efficient as
possible... ie. its not overheating

I am well versed with Tsys of a receiver, as it is important in a number of activities I undertake both at work
and in my radio activities at home.also awaiting any other comments

Dave