I recently looked up how weak the Voyager signals are when they get to Earth from the 22 W transmitters (as of September 2013, it was roughly -245 dBm). But that got me wondering how many watts of power the Deep Space Network (DSN) needs to send signals the other way.
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Any attempts at Google searching always resulted in how much Voyager throws our way..
TildalWave
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Check the DSN Now page when it will show any of its stations communicating with Voyager 1 (code VGR1) or Voyager 2 (VGR2), select that dish and then expand the side column on the right to show all the data. It will show transmit power under up signal section. I'll update this answer as soon as I see that happen (see below for updates), but it would be in the 20 kW range and more, depending on transmitter used to communicate with it.
I.e. pretty much at the peak power available to it and the transmitter can handle. For example, farthest range probe currently communicated with is New Horizons (NHPC) at distance of 31.86 AU from the Earth (round-trip light time of 8 hours, 49 minutes and 52 seconds), via the Madrid station 63 (their largest dish), transmitting at 20.63 kW:
Still a temporary fix while I update with exactly what you asked for, but since I Googled for images a bit, I also found this screen grab showing Canberra station 34 communicating with Voyager 2. It's not as far as Voyager 1 (see e.g. Where are the Voyagers at NASA Voyager), and the screen grab seems to have been made on March 21, 2014, so over a year ago, but it was then still over three times the New Horizons' current distance away from the Earth:
The station here transmits at the power of 19.08 kW. To compare, this same station is currently communicating with SOHO (Solar and Heliospheric Observatory) that is stationed at L1 Lagrange point between the Earth and the Sun (SEL1), about 1.5 million kilometers away from the Earth or ~ 1% the distance towards the Sun, and is transmitting towards SOHO with the power of 1.82 kW at frequency of 2.1 GHz.
Note that transmit power, unless you're already giving it all you can, does vary and depends on many parameters, including frequency, distance to target and angle to horizon, i.e. how thick of an atmosphere the transmitted signal has to go through, even wind, temperature and humidity in the lower atmosphere as those transmitters do get terribly hot when operating at near their peak power. And the lower the angle, the stronger the Earth's atmospheric effects, including diffraction, refraction and attenuation in general.
Thanks to OP's tracking of the Voyager's Space Flight Operations Schedule (PDF), we've now managed to capture Madrid station 63 (70 m dish, not the 30 m smaller ones) transmitting towards the Voyager 1 at the distance of over 131 AU away (Roundtrip Light Time from Earth of over 36 hours and 24 minutes). Temperature around Madrid, Spain was at the time of transmission over 31 °C at 11:36 p.m. local time (CEST), and nearly no wind (picking up from stall to only ~ 5 km/h), so it shouldn't be too surprising that its transmit power was under 20 kW (19.08 kW) to keep thermal noise down and the transciever below its peak TDP (Thermal Design Power):
Transmit power was slowly increasing as the environmental temperature dropped somewhat and the wind picked up on speed a bit. Dish's elevation is also increasing as it tracks Voyager 1's position, which will also lower atmosphere's attenuation of the radio signal.
For another comparison, here's Goldstone's same size dish giving it all it can (21.44 kW on image, going up to 21.6 kW) during transmission to New Horizons, but the temperature there was at the time of capture 15 °C and a nice breeze reaching 27 km/h:
For additional screen grabs see links in the comments below.
TildalWaveTildalWave
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I don't know how much they need, but they use a 20 kW S-band transmitter on a 70 m antenna at 16 bits per second for uplink.
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This document contains some technical details:
In page 12 you will see that the S-Band transmitter has a 400 kW maximum output power. Others have 20 kW max.
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RF Antenna input is typically used to connect a television antenna, cable TV wire, or satellite feed to a television, VCR, or other device that can process radio-frequency video signals, including some computers. Knowing when to use an RF signal and how it differs from other signals can be useful when setting up some computer and video systems.
RF Signals
A radio frequency (RF) signal is an electrical signal emitted as a radio wave. It travels from the broadcasting antenna to the receiving antenna. Different channels carry the signal at different frequencies. Depending on conditions, the signal can be received as far as 80 miles from the broadcast antenna. An RF signal can also be carried on wires that have been configured appropriately, either from a nearby broadcast antenna or as part of a cable TV distribution system serving an area ranging from a building to a city.
Appearance
The most common RF input resembles a short, thick bolt about one-quarter inch in diameter and one-quarter inch long. The cable cord screws into the bolt. Older television sets may have two screws side by side, designed to attach wires from a cable called a twin lead. There is an electrical difference between the two forms of connector. An adapter may be required to attach twin lead wires to a round RF input or vice versa. The adapters are inexpensive and widely available.
Receiving RF Signals
A television image encoded as an RF signal contains audio and video, both of which are decoded using a tuner. The key difference between a monitor and a television set is that a monitor cannot process an RF signal directly. Most televisions, VCRs, and cable TV boxes let you output the decoded audio and video signal to other devices. Separating the video and audio signals gives better quality than the integrated RF signal; S-video, component video, and HDMI outputs offer higher quality than RF. For a computer to process RF signals it must have a video card equipped with an RF input plug, as well as other hardware and channel-selecting software.
Sending RF signals
Using an RF signal to carry audio and video from one device to another is an option of last resort, as it is always the lowest-quality option. However, with older television sets and VCRs, or in complex setups, RF may the only option available. Most VCRs, legacy game consoles, satellite receivers, and cable descramblers can accommodate an RF signal, typically on channel 3. External RF modulators are available to generate an RF signal from the video and audio outputs widely used on computers and audio-video devices.
Other RF Antenna UsesRf Satellite Transmitter Power Supply
RF signals are used for FM radio signals and Wi-Fi computer networks. FM radios and audio/video receivers may have an RF input for the radio antenna, or a connection for a cable system carrying FM radio signals. Wi-Fi antennas usually connect directly to the wireless transmitter.
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An RF signal is an electromagnetic wave that communications systems use to transport information through air from one point to another. RF signals have been in use for many years. They provide the means for carrying music to FM radios and video to televisions. In fact, RF signals are the most common means for carrying data over a wireless network.
RF Signal Attributes
The RF signal propagates between the sending and receiving stations' antennae. As shown in Figure 3-2, the signal that feeds the antenna has an amplitude, frequency, and phase. These attributes vary in time in order to represent information.
Figure 3-2. Amplitude, Frequency, and Phase Are Basic Elements of RF Signal
The amplitude indicates the strength of the RF signal. The measure for amplitude is generally power, which is analogous to the amount of effort a person needs to exert to ride a bicycle over a specific distance. Power, in terms of electromagnetic signals, represents the amount of energy necessary to push the signal over a particular distance. As the power increases, so does the range.
As a radio signal propagates through the air, it experiences a loss in amplitude. If the range between the sender and receiver increases, the signal amplitude declines exponentially. In an open environment, one clear of obstacles, the RF signals experience what engineers call free-space loss, which is a form of attenuation. The atmosphere causes the modulated signal to attenuate exponentially as the signal propagates farther away from the antenna. Therefore, the signal must have enough power to reach the desired distance at a signal level acceptable that the receiver needs.
The ability of the receiver to make sense of the signal, however, depends on the presence of other nearby RF signals. For illustration, imagine two people, Eric and Sierra, whom are 20 feet apart and trying to carry on a conversation. Sierra, acting as the transmitter, is speaking just loud enough for Eric, the receiver, to hear every word. If their baby, Madison, is crying loudly, Eric might miss a few words. In this case, the interference of the baby has made it impossible to effectively support communications. Either Eric and Sierra need to move closer together, or Sierra needs to speak louder. This is no different than the transmitters and receivers in wireless systems using RF signals for communications.
The frequency describes how many times per second that the signal repeats itself. The unit for frequency is Hertz (Hz), which is the number of cycles occurring each second. For example, an 802.11b wireless LAN operates at a frequency of 2.4 GHz, which means that the signal includes 2,400,000,000 cycles per second.
The phase corresponds to how far the signal is offset from a reference point. As a convention, each cycle of the signal spans 360 degrees. For example, a signal might have a phase shift of 90 degrees, which means that the offset amount is one quarter (90/360 = 1/4) of the signal. A variation in phase is often useful for conveying information. For example, a signal can represent a binary 1 as a phase shift of 30 degrees and a binary 0 with a shift of 60 degrees. A strong advantage of representing data as phase shifts is that impairments resulting from the propagation of the signal through the air don't have much impact. Impairments generally affect amplitude, not the signal phase.
RF Signal Pros and Cons
As compared to using light signals, RF signals have the characteristics defined in Table 3-1.
Table 3-1. Comparing the Pros and Cons of RF Signals
These pros make the use of RF signals effective for the bulk of wireless network applications. Most wireless network standards, such as 802.11 and Bluetooth, specify the use of RF signals.
RF Signal Impairments
RF signals encounter impairments, such as interference and multipath propagation. This impacts communications between the sender and receiver, often causing lower performance and unhappy users.
Interference
Interference occurs when the two signals are present at the receiving station at the same time, assuming that they have the same frequency and phase. This is similar to one person trying to listen to two others talking at the same time. In this situation, wireless NIC receivers make errors when decoding the meaning of the information being sent.
The Federal Communications Commission (FCC) regulates the use of most frequency bands and modulation types to avoid the possibility of signal interference between systems. However, radio interference can still occur, especially with systems operating in license-free bands. Users are free to install and utilize license-free equipment such as wireless LANs without coordinating usage and interference.
Figure 3-3 illustrates various forms of interference. Inward interference is where external signals interfere with the radio signal propagation of a wireless network. This interference can cause errors to occur in the information bits being sent. The receiver eventually discovers the errors, which invokes retransmissions and results in delays to the users. Significant inward interference might occur if another radio system is operating nearby with the same frequency and modulation type, such as two radio LANs operating in the license-free bands within close proximity.
Figure 3-3. Radio Signal Interference Can Be Inward or Outward
Other sources of inward interference are cordless phones, microwave ovens, and Bluetooth devices. When these types of RF devices are in use, the performance of a wireless network can significantly decrease because of retransmissions and competition on the network for use of the medium. This requires careful planning and consideration of other radio devices that might interfere with the wireless network.
One of the best ways to combat RF interference is to eliminate the sources of interference. For example, a company could set a policy for not using cordless phones that fall within the same frequency band as the wireless network. The problem, however, is that it is often impossible to completely restrict the usage of potential interferers, such as Bluetooth devices. If interference is going to be a big issue, consider choosing a wireless network that operates in a frequency band that doesn't conflict.
Outward interference happens when the signals from the radio signal system interfere with other systems. As with inward interference, significant outward interference can occur if a wireless network is in close proximity with another system. Because wireless network transmit power is relatively low, outward interference rarely causes significant problems.
Multipath
Multipath propagation occurs when portions of an RF signal take different paths when propagating from a source?such as a radio NIC?to a destination node, such as an access point. (See Figure 3-4.) A portion of the signal might go directly to the destination; and another part might bounce from a desk to the ceiling, and then to the destination. As a result, some of the signal encounters delay and travel longer paths to the receiver.
Figure 3-4. Obstacles Cause the Signal to Bounce in Different Directions
Multipath delays cause the information symbols represented in the radio signal to smear. (See Figure 3-5.) Because the shape of the signal conveys the information being transmitted, the receiver makes mistakes when demodulating the signal's information. If the delays are great enough, bit errors in the packet occur, especially when data rates are high. The receiver won't be able to distinguish the symbols and interpret the corresponding bits correctly. When multipath strikes in this way, the receiving station detects the errors through an error-checking process. In response to bit errors, the sending station eventually retransmits the data frame.
Figure 3-5. Smearing of the Signals Because of Multipath Causes Confusion and Bit Errors in Receivers
Because of retransmissions, users encounter lower performance when multipath is significant. As examples, 802.11 signals in homes and offices might encounter 50 nanoseconds (ns) multipath delay while a manufacturing plant could be as high as 300 ns. Based on these values, multipath isn't too much of a problem in homes and offices. Metal machinery and racks in a plant, however, provide a lot of reflective surfaces that cause RF signals to bounce around and take erratic paths. As a result, be wary of multipath problems in warehouses, processing plants, and other areas full of irregular, metal obstacles.
What can you do if multipath is causing problems? Aside from clearing desks and chairs from your building, diversity seems to be the best solution to combat the perils of multipath. Diversity is the use of two antennae for each radio NIC to increase the odds of receiving a better signal on either of the antennae.
Diversity antennae have physical separation from the radio to ensure that one will encounter fewer multipath propagation affects than the other. In other words, the composite signal that one antenna receives might be closer to the original than what's found at the other antenna. The receiver uses signal-filtering and decision-making software to choose the better signal for demodulation. In fact, the reverse is also true: The transmitter chooses the better antenna for transmitting in the opposite direction.
In radio transmission, transmitter power output (TPO) is the actual amount of power (in watts) of radio frequency (RF) energy that a transmitter produces at its output.
This is not the amount of power that a radio station reports as its power, as in 'we're 100,000 watts of rock 'n' roll', which is usually the effective radiated power (ERP). The TPO for VHF-/UHF-transmitters is normally more than the ERP, for LF-/MF-transmitters it has nearly the same value, while for VLF-transmitters it may be less.
The radio antenna's design 'focuses' the signal toward the horizon, creating gain and increasing the ERP. There is also some loss (negative gain) from the feedline, which reduces some of the TPO to the antenna by both resistance and by radiating a small part of the signal.
Marathi movie download torrent. The basic equation relating transmitter to effective power is:
Note that in this formula the Antenna Gain is expressed with reference to a tuned dipole (dBd)
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