How well can Voyager 1 separate Earth signals from Solar noise these days?

Question

This is a follow-up question to Can Voyager 1 receive signals from Earth? this and this answer. UPDATED: see additional information and discussion below.

As it continues to move farther from the Sun, the angular separation between the Earth and Sun continues to decrease, can it's antenna actually resolve the two and limit the noise from the sun? (seems to be about 0.4 degrees at opposition now) For that matter, how strong IS the noise from the sun relative to earth transmissions, considering the passband of Voyager's electronics - is is it a serious issue to begin with? As earth oscillates in its orbit - is there a seasonal effect?

Besides the mind-boggling large distances an weak signal, the problem I'm talking about here is that - as seen from Voyager 1 (and 2), the earth is only a small fraction of 1° away from the sun, which is a powerful and noisy radio source.

Voyager receives at around 2 GHz¹, so its 3.7m diameter dish can not separate the two. Even a quiet sun is almost $\text{10}^6$ Jy. The electronics is circa 1970, if it has an input bandwidth presented to the front-end of 10MHz, the sun will be a million times stronger than the 20kW Deep Space Network DSN signal.

above: data for the Sun, planets, Pluto, Voyager 1 and Voyager 2, from January 1, 1969 (a good year to start things) until now. Dots are now. Data is from NASA JPL Horizons.

above: Angular separation between the earth and the sun in degrees, as seen from Voyager 1 (heavy, blue) and Voyager 2 (light, green). The dips to near-zero stop happening once the spacecraft left the plane of the ecliptic.

above: example of the type of settings I used to get the data in ecliptic coordinates.

above: Partial screen shots from DSN Now: https://eyes.nasa.gov/dsn/dsn.html, just for fun because this is downlink at 8 GHz rather than uplink at 2 GHz.

¹ from All About Circuits' Communicating Over Billions of Miles: Long Distance Communications in the Voyager Spacecraft (a fun read!):

The uplink carrier frequency of Voyager 1 is 2114.676697 MHz and 2113.312500 MHz for Voyager 2. The uplink carrier can be modulated with command and/or ranging data. Commands are 16-bps, Manchester-encoded, biphase-modulated onto a 512 HZ square wave subcarrier.

from DESCANSO Design and Performance Summary Series Article 4: Voyager Telecommunications as discussed in this answer.

Answer 1

I was fortunate to have worked on Voyager, and other projects at JPL from 1970 to 1975. I was also fortunate to have had Solomon Golomb, PhD, as my advisor and mentor in Electrical Engineering graduate school at USC in the late 1960's. I wanted to study communications theory, and Dr. Golomb was the only professor at USC who was involved in that area. According to information from USC published at the time of his death, Dr. Golomb's research when I was his research assistant is the reason NASA can separate faint radio signals sent from spacecraft from much stronger background noise. (Incidentally, this research is given the credit for us having CD's, DVD's, and cell phones.) I really did not and do not really understand the research that I helped this reknowned mathematician who was a full professor of Electrical Engineering perform. I do know that without him, we would not be able to decipher Voyager's signals.

Answer 2

According to this source, the quiescent Sun produces about 10^-20 Watts per square meter per Hertz at 2 GHz at Earth's orbit. At a distance of 152 AU, it will be a factor of 152² weaker or about 4 x 10^-25 W/m²/Hz. Collected with a 12 foot dish (~10 square meters) gives 4 x 10^-24 W/Hz for solar noise.

Thermal noise in the front end is kT W/Hz. Assuming a noise temperatue of, say, 250K, this is 1.4 x 10^-23 x 250 = 3.5 x 10^-21 W/Hz

So the solar noise is much less than the thermal noise from Voyager's front-end amplifier. The fact that the antenna provides no discrimination doesn't matter.

The radio noise from the Sun can be over 1000 times larger during a solar storm. It would then be comparable to the front-end noise and could be a problem.

Answer 3

I believe that the Voyager receiver uses a PLL, phase locked loop to acquire the signal and filter out the solar noise. Also, the solar radiation is different to the transmitted signal which Voyager can use to differentiate between the noise with a band pass filter and some other electronics.

Answer 4

Since you "modified" your question: The purpose of an antenna is to receive a signal not to filter noise. The Power voyager receives, could be sun + earth, earth - sun, sun - earth or only sun. The Modulation used is still unknown, so i cant calculate the needed SNR for it to work.

But the normal radiation level shouldn't be a problem for the voyager probe. Think of the sun as a constant emitter. Only flares create spikes. The spectrum of these radio waves will have a Gaussian bell curve (Watts/ Hz). The Engineers of Nasa will probably have picked a Frequency spectrum that is on one of the lower ends of this bell curve. The radio power of the sun decreases faster per Meter away from its origin then that of earth. Since earth uses directional communication and the sun is just a big ball of energy. So the true problem will be, to always point at voyager correctly.