36
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 ...
- 24.4k
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 ...
- 15.5k
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 ...
- 15.5k
10
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 ...
- 51.6k
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 ...
- 24.4k
8
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 ...
- 51.6k
8
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?...
- 51.6k
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, ...
- 24.4k
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:
$...
- 51.6k
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 ...
- 51.6k
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 ...
- 10.5k
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 ...
- 4,539
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 ...
- 286
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 ...
- 10.5k
6
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 ...
- 3,905
6
votes
UHF 70cm unlicensed use
The likelihood that your radios are being operated legally is small in my opinion, at least if you're in the US. The only entirely unlicensed frequency in that section of the spectrum that I'm aware ...
- 61
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 ...
- 24.4k
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 ...
- 542
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 ...
- 51.6k
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 ...
- 15.5k
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 ...
- 9,162
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 (-...
- 10.5k
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 ...
- 24.4k
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 ...
- 51.6k
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 ...
- 2,137
4
votes
On which of these frequencies can I transmit without a license?
There are lots of "radios" for sale on places like EBAY that are not legal to use in the U.S.
There are lots of radios of recent manufacture for sale in many places that include the ability to ...
4
votes
Can 433 MHz amateur bands be used for ISM purposes?
There is a very narrow sliver of bandwidth at 433MHz that is designated as an ISM band that overlaps the ham band, however the power limitations are quite severe, as are antenna and bandwidth ...
- 1,834
4
votes
Accepted
How does VHF/UHF propagate beyond the expected (radio) horizon?
Turns out that, after turning to discussion of HF propagation for a number of intervening pages, this Antenna Book ends up getting back around to its own answer for this question!
From the "Scatter ...
- 7,269
4
votes
Troposcatter: really all that bad?
Troposcatter is the common mode for beyond line of sight on the 10 GHz ham band when the band is not otherwise open, good for 100's of miles. A radio with just a few watts output power and a ...
- 41
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