# Tag Info

## Hot answers tagged satellites

16

The primary factor to consider is the directivity of the parabolic antenna. It is given as: $$d=\frac{(\pi D)^2}{\lambda^2} \tag 1$$ where D is the diameter of the dish and $\lambda$ is the wavelength of operation, both in the same units. To convert frequency to wavelength in meters, we use: $$\lambda=\frac{300}{f} \tag 2$$ where f is the frequency in ...

15

The earliest Soviet satellites, like Sputnik 1, transmitted what amounted to a CW stream -- just pulsed RF at pretty low power (later Sputniks transmitted data by pulse width modulation, still essentially CW). In order to hear it, you needed a Beat Frequency Oscillator -- a BFO -- and with a common radio receiver, the signal generator was standing in for ...

13

They don't always do that, but the reason for it is simply separating the transmitted RF from the received RF. A ground-based repeater uses a fairly large duplexer to make sure that its transmissions don't feed back into its receiver; with a satellite, size and weight are at a premium, and having two widely separated frequencies requires much less hardware ...

12

Free space loss is the power lost because it doesn't reach the receiving antenna. An example using an analogy is your eye, looking at the light from a light bulb. If you stand 10 metres away from a light bulb, and your pupil has a diameter of 2 mm, then you can see that only a tiny fraction of the power radiated from the light bulb actually enters your eye. ...

11

The specifications from AMSAT for the SO-50 are: The repeater consists of a miniature VHF receiver with sensitivity of -124dBm, having an IF bandwidth of 15 KHz. The receive antenna is a 1/4 wave vertical mounted in the top corner of the spacecraft. The receive audio is filtered and conditioned then gated in the control electronics prior to feeding ...

11

Many of the amateur radio satellites are built, owned, and operated by various AMSAT organizations around the world. They typically get their funds from donations and organization membership fees. They're able to keep their costs low by using commodity hardware when possible, utilizing volunteer labor, and sharing launch vehicles with other payloads (...

10

Satellites can and do use HF for communications. The first example would of course be Sputnik, which transmitted at 20 and 40 MHz. Amateurs use HF to communicate with satellites. According to Amsat, mode A: This mode requires a 2 meter SSB/CW transmitter and a 10 meter SSB/CW receiver... Mode K; This mode requires a 15 meter SSB/CW transmitter and a 10 ...

9

I'm going to make an educated guess and say no. Here's my reasoning: Consider the difficulty in just communicating with a satellite. See What is a link budget, and how do I make one? or What gain do I need to talk to SO-50 with my HT? Geostationary orbit is much farther away than SO-50 and thus requires more gain, or more power. Now if we are using this ...

9

First, consider that everywhere, there is an electric field. For every point in space, this field defines a vector that describes the direction and magnitude of force that would be experienced by a mobile test charge at that point. In practice, the mobile charges are electrons in our antenna. Radio works by creating waves in the electric field.1 These waves ...

9

I'm guessing many those signals are just noise. A fixed tone carries no information, so there would be no reason for a satellite (or anything else) to transmit it intentionally. The noise could be from an oscillator in some nearby electronics, or even from within the receiver itself. The noise may not even be at the frequency it appears in the waterfall: ...

9

Satellite engineers tend to use circular polarization for two reasons: When a linearly polarized signal travels through the atmosphere there are anomalies, such as Faraday rotation, that alter the polarization of the EM wave. The geographic reference of the satellite polarization changes for a non-stationary satellite as it traverses its path above the ...

8

The simplest might be to use an app. On Android, Heavens Above, a product of the 25-year-old website of the same name, stores the orbital elements of the satellites of interest, and does the pass calculations on your phone. The app uses the GPS to find your location. It likes to get fresh elements from the Internet on startup, but it caches them, so as long ...

7

The doppler shift $\Delta f$ is function of the relative velocity $\Delta v$ (a scalar quantity) and the emitted frequency $f_0$, see the relevant wikipedia page. If you know how the relative velocity (either at one instant in time or as a function of time), it's just a matter of using the formula: If you don't known the relative velocity, then you need ...

7

Take the simplest case of a VHF dipole receiving antenna on board a spin stabilized satellite. -----------O------------- Here is the satellite now. \ \ \ \ \ O and here is is a bit later \ \ \ \ \ As the satellite spins, the dipole rotates, and the resulting polarization ...

6

According to the ISS Fan Club's Frequencies page, for FM voice transmissions the downlink (your listening) frequency is 145.800 MHz and the uplink (your transmission) frequency is 144.490 MHz, when covering ITU regions 2 and 3, including North America. In ITU region 1 the corresponding frequencies are downlink 145.800 MHz and uplink 145.200 MHz. There are ...

6

Strictly speaking, there are 3 categories of allocations for space missions, depending on what you are doing. And the laws never go away, although the enforcement might go away after a distance. The 3 categories are: Near Earth Communication- I can't find a specific definition, but this appears to be anything closer than the moon, or that orbits the moon. ...

6

In general, the HF bands (1.8 MHz through 30 MHz) do not have sufficient bandwidth to support live transmission of a video signal. In the US, the FCC does not authorize an emission mode for live video on HF. The lowest available band in the US that supports live video is 70 cm (~440 MHz). There are, however, options for transmitting pictures on HF. One of ...

6

When all the communications of a satellite qualify as amateur radio satellite communications, then the frequency coordination is carried out by IARU. ITU delegates this function to IARU. The link provides instructions and information for filing a coordination request. (Background: I filed a satellite coordination in 2013, launch was in june 2014.)

6

During his long career, J.D. Kraus studied, and experimented extensively with, helix antennas. There is a large body of published work in college text books on this subject. The following summarizes some of the key construction details. The ideal circumference of each turn of the helix antenna is given as: $$C=\lambda \tag 1$$ where $\lambda$ is the free ...

6

32-50 degrees EL -- all 11 decodes tonight on JT4G very strong , FT991A 17db LNA, 1/4 hardline 24ft ,Gulf Alpha 8 x 11 beam H-POLE. JT4G - digital signal mode, http://physics.princeton.edu/pulsar/k1jt/JT2_JT4.TXT FT991A - Yaesu FT991A radio 17dB LNA - low noise amplifier (with 17dB gain perhaps) 1/4 hard-line - the coax connecting the radio to the ...

5

There are at least 4 significant things that make satellites difficult to exactly determine: The position and velocity of a satellite is only known at any one time with a finite precision. Without a perfect knowledge of where the satellite is and how fast it's moving, it's impossible to know where it will be in the future. The atmosphere is quite uncertain, ...

5

The reason you don't need to shift one frequency is that the Doppler shift for the 144MHz band, for a satellite in this orbit, is only about 2-3kHz, which is within the range needed to make contact without adjusting. You can, and you'll get better results if you do, but to make satellite operation easy many do not. The 440MHz band, however, experiences a ...

5

n2yo.com is a wonderful resource for keeping track of all of the orbiting satellites. It has many resources for tracking info to enter into tracking software and other places. It also shows a live google map of the location of each satellite.: amsat.org also has a wealth of information about contacting and tracking the satellites including uplink and ...

5

Here in the US, it is perfectly legal for you to listen and "download" the satellite data. Since the data is created by a public agency, it is considered to be in the public domain and not subject to copyright. On this website at http://www.weather.gov/disclaimer, you can find the following: "The information on National Weather Service (NWS) Web pages are ...

5

Here in EU it's perfectly legal to receive transmission on any frequency. Additional restrictions may apply if the transmission is not mean to be public, for example encrypted Wi-Fi networks or government agencies radios. (source: Telekommunikationsgesetz (TKG) § 89).

5

As usual, for antennas, the better your material conducts, the higher your antenna efficiency. Hence, go for copper. It has an excellent conductivity per volume (which might or might not be critical in your application), and there's not many metals that will beat its conductivity at all. Steel really isn't good for that. If you're using suitable frequencies,...

5

The purpose of a turnstyle antenna for satellite work is to generate a circularly polarized radiation pattern off of its axis. By adjusting the phasing of the feed to the two crossed dipoles, the circular polarization can be switched between left and right hand polarization. In your diagram of the proposed antenna, one element is shown to meet at is end ...

5

Good find of all the frequencies and powers, it sounds like you have all the right basic equipment. But sadly for the roadster, you're too late, it's out of range. The video link is designed for a few hundred km, and it's probably half a million km away already. Assuming the batteries on the spacecraft are still OK. It's transmitting 44 dBm. The path loss ...

5

All kinds of digital microwave technologies can do this, including WiFi. It takes a good antenna location high from the ground, and good antenna gain / transmit power. Commercial wireless ISPs do it regularly. With a good antenna and cooperative terrain (no hills in the way), it could be done with consumer 802.11 equipment. Mind the link budget, and the ...

5

It's been done before. The University of Groningen astronomy department runs (ran?) a couple of 2.5 m dishes for radio astronomy exercises. IIRC they mainly observe our Sun (strongest radio source). So I'd say yes, that dish could be a good starting point.

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