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38 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 ...
Kevin Reid AG6YO's user avatar
  • 24.6k
15 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 ...
Marcus Müller's user avatar
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 ...
Marcus Müller's user avatar
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 ...
Phil Frost - W8II's user avatar
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 ...
Kevin Reid AG6YO's user avatar
  • 24.6k
8 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: $...
Phil Frost - W8II's user avatar
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 ...
Phil Frost - W8II's user avatar
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?...
Phil Frost - W8II's user avatar
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, ...
Kevin Reid AG6YO's user avatar
  • 24.6k
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 ...
Phil Frost - W8II's user avatar
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 ...
tomnexus's user avatar
  • 11.3k
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 ...
Scott Earle's user avatar
  • 4,599
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 ...
WA9ZZZ's user avatar
  • 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 ...
tomnexus's user avatar
  • 11.3k
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 ...
webmarc's user avatar
  • 4,234
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 ...
Chris Short's user avatar
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 ...
Kevin Reid AG6YO's user avatar
  • 24.6k
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 ...
AG5CI's user avatar
  • 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 ...
Phil Frost - W8II's user avatar
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 ...
Marcus Müller's user avatar
5 votes

GMRS not transmitting within a half mile

First, the legal issue: in the US, it's not legal to transmit on GMRS frequencies on a radio not type-accepted for GMRS. Having an FCC ID doesn't mean that a radio is type-accepted for GMRS; UV-5Rs ...
rclocher3's user avatar
  • 9,242
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 ...
rclocher3's user avatar
  • 9,242
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 (-...
tomnexus's user avatar
  • 11.3k
5 votes
Accepted

I am trying to get the 800.00 frequencies on a Baofeng UV-5R

It doesn't do that. Depending on the revision of UV-5R you have, the highest receive frequency is either 470 MHz or 520 MHz. Either way it doesn't go up to 800.
hobbs - KC2G's user avatar
  • 12.5k
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 ...
Edwin van Mierlo's user avatar
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 ...
Gregory R. Sudderth's user avatar
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 ...
Hamsterdave's user avatar
  • 1,844
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 ...
natevw - AF7TB's user avatar
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 ...
Mike K6ML's user avatar

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