33
votes
On which of these frequencies can I transmit without a license?
None of them.
You say you are in the United States. In general, all radio transmissions fall into one of three categories:
The operator is allowed to transmit on that frequency (amateur, "business ...
- 23.1k
14
votes
Moon->Earth 433MHz link achievable digital bandwidth
Short answer: Math says max link rate is 2Mb/s if you knew the perfect channel coding. Which is still an unsolved puzzle.
Long answer:
You're calculating a link rate. That is fine, and can be ...
- 13.4k
12
votes
World wide Radio Module
Your problem is that there's really but one globally usable unlicensed band, and that's the 2.4 GHz band.
But that doesn't sound so bad. People think "high frequency = short reach", stemming from the ...
- 13.4k
9
votes
Why is VHF better than UHF in this situation?
This is an ill-posed question, since "best" could mean so many things. If VHF is so plainly best, why does anyone bother with UHF at all?
If you mean what option has a lower path loss, then sure VHF ...
- 49.9k
9
votes
Accepted
Why aren’t emergency services using callsigns?
… Why don’t these unencrypted FM emergency services seem to use any call signs … ?
They aren't required to and don't find it useful in their procedures. Also, they don't have call signs in the sense ...
- 23.1k
8
votes
Why can't VHF / UHF be used with ionosphere reflection?
The ionosphere typically neither reflects nor absorbs waves with VHF or higher frequencies, but passes them through to space. There are no reflections back to the ground, so there is no useful ...
- 23.1k
8
votes
Accepted
VHF 50 Ω Antenna Over 75 Ω TV Coax
I will need a UHF/VHF diplexer on either end to suitably merge/split the signals from each antenna
Yes, this is correct.
A tangent: If you wanted to save some money by using mass-market parts, ...
- 23.1k
7
votes
Moon->Earth 433MHz link achievable digital bandwidth
Summary: Theoretical maximum in the neighborhood of 10s of megabits per second. Less than that in practice, perhaps a lot less depending on budget.
Let's start with the Friis transmission equation:
$...
- 49.9k
7
votes
Accepted
It it really useful to terminate unused 75Ω outputs on a coax splitter?
Terminating unused ports will never make things worse, and indeed is necessary to provide "ideal" behavior. Is ideal behavior really necessary? It depends on the application. Is your setup working now?...
- 49.9k
6
votes
What would be the easiest and most cost effective ground system for a startup UHF/VHF station
That statement is wrong on several levels.
The antenna is DC grounded so no lighting arrestor is needed.
A lightning arrester is needed, even if the antenna is DC ground. The arrester's job is to ...
- 49.9k
6
votes
Accepted
Where are the baluns for VHF and higher? How can one be made?
Let's clarify some terminology: a balun is any device used to convert between a balanced system (ladder line, dipoles) and an unbalanced one (coax, vertical monopoles). There are a lot of ways to make ...
- 49.9k
6
votes
Accepted
Do MRI machines use the ISM band, and do they generate audible CW signals?
Medical MRI looks for the nuclear magnetic resonance of hydrogen, at around 1 or 2 Tesla, at about 100 MHz.
NMR is a phenomenon of the nucleus, not the atom, it is different to anything involving ions ...
- 8,171
6
votes
Accepted
Is there any practical advantage to a parabolic reflector over a high-gain beam antenna?
The issue with using a parabolic dish antenna at UHF is one of size. The 60cm dishes you see on the side of people’s houses are picking up signals at 10GHz, and if you scaled them up for the 70cm band ...
- 4,329
6
votes
Why aren’t emergency services using callsigns?
Why don’t these unencrypted FM emergency services seem to use any call signs or ham codes?
They are required to identify periodically and they do. That is the Morse code you heard.
Emergency ...
- 276
6
votes
Accepted
Is testing SWR *practically* less important for 2m/70cm than HF bands?
I would say in practice it is less important because hams use different types of antennas for HF and for VUHF.
At HF, the same antenna is often used for many bands. The bands have large fractional ...
- 8,171
5
votes
Can RF work while it's in motion?
The effect of motion is to cause Doppler shift in the received signal. This changes both the carrier frequency and the symbol rate. However, because the speed of propagation of the wave — an ...
- 23.1k
5
votes
TV strong station has no signal when coax is connected
I'm not at all sure about the exact situation, but I predict that you will find that the cable between the distribution amplifier and this particular TV set is damaged.
In general, when you omit the ...
- 23.1k
5
votes
TV strong station has no signal when coax is connected
You may be overloading the front end of the "faulty" TV, creating adjacent channel interference or some other kind of distortion. The loss you introduce by only loosely coupling the receiver may be ...
- 432
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 ...
- 49.9k
5
votes
Why does signal power drop every night?
That's a GSM band. If there's still GSM service in that band, it's very common to see Mobile Network Operators (MNOs) turn of base stations at night, effectively enlarging the remaining cells. I've ...
- 13.4k
5
votes
Any reason not to choose a discone antenna over a Wide/ MultiBand mobile antenna for TX/RX operations
The discone antenna that you mention cites "effective" gain of 0 dBd. I don't know what they mean by effective gain, but dBd means decibels compared to a dipole; 0 dBd would mean that the discone has ...
- 8,922
5
votes
Failing to detect Hydrogen line with 105cm dish
The sawbird H+ looks like a nice LNA, do you have the H+ H1 version?
The plan version seems to be for 1542 MHz, "center frequency of the module is 1.542GHz with approximately 80MHz of bandwidth (-...
- 8,171
5
votes
What kind of soldering iron is best for PL-259 (UHF) connectors?
I'm going to answer a slightly different question to the one asked... I promise not to be offended if it's ignored or even downvoted (if it receives enough downvotes, I'll delete):
Crimping, with the ...
- 2,885
4
votes
BAOFENG UV-5R for cubesat communication on lab, does it work?
The usability of the Baofeng (or any radio with > 1Hz frequency step) will depend on the frequency and mode that you are using. If you use a 12.5kHz frequency step size you will never be able to tune ...
- 258
4
votes
What antenna on a BaoFeng UV-5R Pro will give me better reception?
I also have a couple of Baofeng HTs and little budget to work with, and I have 2 go-to antennas and a couple others I use on occasion.
The one I would recommend is a Comet SMA(in my case, BNC with an ...
- 716
4
votes
Accepted
Effect of night on VHF/UHF propagation
When we have a large temperature spread here (day/night) I start looking for new repeaters on vhf/uhf. The gradient will usually form a temperature inversion that is pretty efficient at scattering ...
- 56
4
votes
Which Frequency Band(VHF/UHF) is most useful for satellite in MEO?
Satellite communication works from around 30 MHz to 40,000 MHz. Once you are out of Earth's atmosphere, it doesn't really matter how much higher you get since there isn't anything out there to alter ...
- 49.9k
4
votes
Scanner radio for 433MHz locator beacon
I am looking for a recommendation of an inexpensive scanner radio that should be used to locate animals equipped with 433MHz locator beacons.
First, let me clarify some terminology: you don't need a ...
- 23.1k
4
votes
receiving AM radio station on UHF frequency
at 450.040 I picked up a local AM radio station
I am sure you picked up a transmission
just a Baofeng UV5R
But not with that radio, or at least not AM
You either:
Picked up a signal which is ...
- 2,077
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