16 votes
Accepted

Can I build a radio telescope out of a parabolic TV satellite dish?

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 ...
user avatar
  • 18.2k
15 votes
Accepted

Why would you need a signal generator to receive early satellite transmissions?

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 ...
user avatar
  • 3,891
12 votes
Accepted

Why does Free space have the highest loss compared to other losses like atmospheric loss, feeder loss etc?

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 ...
user avatar
  • 8,235
11 votes
Accepted

Who funds amateur radio satellites?

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. ...
user avatar
  • 1,013
10 votes
Accepted

Can there be (long range) propagation of HF from satellites?

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, ...
user avatar
  • 8,235
9 votes
Accepted

Identifying signals in the satellite exclusive band

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 ...
user avatar
9 votes
Accepted

Antenna polarization when dealing with satellite communications

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 ...
user avatar
  • 18.2k
8 votes
Accepted

Calculating satellite passes without an internet tracker?

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 ...
user avatar
  • 8,235
7 votes
Accepted

Are there any active ham satellites orbiting that use the 5cm band?

Yes! SatNOGS is a pretty cool crowdsourced satellite observation / recording system, and they have a database of known satellites. By the way, if you're using GPredict, the ...
user avatar
6 votes
Accepted

How to transmit images and video through a hurricane?

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 ...
user avatar
  • 18.2k
6 votes
Accepted

Who regulates ham radio satellites?

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 ...
user avatar
  • 1,099
6 votes
Accepted

What is the turn spacing on a Helix Antenna?

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 ...
user avatar
  • 18.2k
6 votes
Accepted

Help understanding this tweet about receiving images from satellite behind the Moon

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/...
user avatar
  • 669
6 votes
Accepted

Has an amateur radio communication ever taken a path outside the Earth-Moon system?

AMSAT-DL has heard their own echoes on an Earth-Venus-Earth path, on the 13cm band, with the help of the 20-meter dish at Bochum Observatory. It falls a little short of "communication", but ...
user avatar
  • 9,275
5 votes

Website for satellite down/uplink frequencies and live footprint?

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 ...
user avatar
  • 1,246
5 votes

Weather Imaging with NOAA satellites - legal?

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 ...
user avatar
  • 69
5 votes
Accepted

Weather Imaging with NOAA satellites - legal?

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 ...
user avatar
  • 136
5 votes
Accepted

cubesat turnstile antenna material selection

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 ...
user avatar
5 votes

Would the antenna described work?

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 ...
user avatar
  • 18.2k
5 votes

I would like to listen to a red roadster in space

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 ...
user avatar
  • 8,235
5 votes

What wireless communication technologies can travel long distances with a high bandwidth?

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 ...
user avatar
5 votes

Can I build a radio telescope out of a parabolic TV satellite dish?

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). ...
user avatar
  • 151
5 votes
Accepted

How do amateur satellites stay consistently in the amateur-sat bands acoss the globe?

A simple internet search turns up the IARU's Amateur Radio Satellite Frequency Coordination web page. There you will find an Amateur Satellites Short Info Paper that answers your question: ...
user avatar
  • 7,693
5 votes
Accepted

2 meter and 70cm OSCAR expected signal attenuation by topocentric elevation angle, chart?

It's close enough to zero at 2m and 70cm that I wouldn't bother computing it. Judging by ITU-R P.676 the attenuation due to the atmosphere is less than 0.01 dB/km for all frequencies below 1 GHz, and ...
user avatar
  • 9,275
5 votes
Accepted

Ham Radio and Space Communications

ISS has amateur radios on board. Sometimes they even work. Sometimes they're on. Sometimes when they are on, there is an astronaut talking on it. Details, schedules, frequencies, etc., can be ...
user avatar
  • 4,258
5 votes
Accepted

Receiving the ISS SSTV: dipole antenna configuration and orientation

reports it as "U: linear, V: linear" Satellites which transmit and receive at the same time frequently do one on VHF (2m) and the other on UHF (70cm), and they frequently have separate ...
user avatar
  • 9,275
5 votes
Accepted

what is the baseband for CATV?

Baseband video is the DC to about 6 MHz signal that encodes the brightness channel, and sync. If it includes colour too then it's called Composite video. Brightness and sync are truly baseband, a ...
user avatar
  • 8,235
5 votes
Accepted

How do phased array antennas work when they produce spot beams?

I'm doing this from a transmit direction, first, I find that easier to explain. You know that antennas work in transmit as in receive, so what you'll (maybe?) learn will work for reception as well. ...
user avatar
4 votes
Accepted

Can sub GHZ frequency can be used in space communciation?

Most cubesats communicate in a combination of VHF and UHF for both uplink and downlink. Advantages: Better link budget (lower free-space attenuation). Cheaper ground station (radio equipment, cables,...
user avatar
  • 1,099
4 votes

How much RF power should I expect to receive from a satellite?

You can calculate the answer with the Friis transmission equation. The great thing about space communications is that the path is very close to free space, so even highly idealized calculations are ...
user avatar

Only top scored, non community-wiki answers of a minimum length are eligible