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32

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 band", aviation, military, etc.) The radio is allowed to transmit on that frequency (CB, FRS, MURS). The transmissions are very low-power ("Part 15": WiFi, ...


19

Every time I purchase a cheap HT such as the Baofeng you mention I also spend another $10 or so on an antenna, as the stock antenna is noticeably worse than even an inexpensive antenna like the Nagoya NA-771. There are still better antennas than this, but there are always tradeoffs. The stock antenna is one third to half the length of the NA-771, which is ...


15

There have been a number of good answers already, though I think there are a few additional points worth sharing. Answers would also be more relevant if we knew what situation(s) you were coming up short range wise. For portable use (out in the field): The stock Baofeng rubber duck antenna has been shown to be a poor performer. All of the stock rubber ...


14

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 answered using Shannon's Channel Capacity, which gives us the upper limit for bits per second that we can get across a given channel: $$ C= b\cdot \log_2\left(1+ \...


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

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 well-known Free-Space Path loss formula $$P_r = P_t \cdot G_t G_r \left( \frac{c_0}{4 \pi fd} \right)^2\text,$$ where the received power $P_r$ falls with the ...


11

Requirements: Less than $100 Commercially available Better reception than stock antenna Excellent portability Recommendations: Nagoya NA-771 Nagoya NA-701 Tram 1185 (Vehicle) Nagoya NA-771 Cost: $11 on Amazon.com as of March 2014 Length: 396mm Weight: 37g Nagoya NA-701 Cost: $10 on Amazon.com as of March 2014 Length: 211mm Weight: 40g Tram 1185 Cost:...


9

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 is the better option. But then HF would be even better. And why not go with ELF? As the frequency decreases, so do free space path losses. Well, an ELF antenna ...


8

For the most part, propagation for VHF/UHF (1280 MHz is UHF) is line-of-sight because it doesn't tend to get the benefit of ionospheric reflection like HF does. This will also apply to your mentioned 433 MHz transmission, which is in the UHF range. While there are occasionally atmospheric events that result in indirect UHF/VHF propagation (e.g. tropospheric ...


8

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 propagation between stations on the ground. Tropospheric ducting is a different propagation mode which does carry VHF signals well, and is actually sought and used ...


8

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, you could use 75 Ω power dividers (coax splitters) instead of diplexers. This has 3 dB loss because the signals are not directed exclusively to the intended ...


8

… 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 amateurs do — they may have names for different groups in a transmission ("Car #3" or whatever) which are call signs in the sense that they play the same role ...


7

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: $$ P_{r(\mathrm{dB})} = P_{t(\mathrm{dB})} + G_{t(\mathrm{dB})} + G_{r(\mathrm{dB})} + 147.6 - 20 \log_{10} (rf) $$ Insert the values you've given for ...


7

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? If so, terminators aren't necessary :-) A typical splitter has these properties: It has an input port and two output ports, which we'll call A and B. It has ...


6

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 limit the center conductor's voltage to be not very different from the shield. That the antenna is "DC grounded" isn't worth much. Lightning is not DC. In fact,...


6

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 or electrons moving in a magnetic field, like aurora and the ionosphere. Here is a table of NMR frequencies for somewhat higher magnetic field strengths. MRI ...


6

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 you would have a dish around 14m across. Those satellite TV dishes have a gain of around 35-40dB (source), which is very impressive - but you’re not going to ...


6

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 services (police, fire, EMS) along with taxicabs, tow trucks, anything else that moves on land, is licensed under part 90, Private Land Mobile Service, of the FCC ...


6

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 bandwidth. Antennas are often simple wire, very thin compared to wavelength. And finally, because the wavelength is quite long, they are often too short for the ...


5

The antenna included with the BaoFeng is notably bad, even for a rubber duck. To answer your question of what would be better: anything would be better. You'd have to switch to a dummy load to do worse. Whatever antenna you do select, it need not be anything specific to your radio. Any antenna suitable for whatever bands you wish to operate will be fine. ...


5

Ron points to the band plan and that's where you should start. I've redacted it somewhat to the bands most appropriate for simplex work. Note that depending on where you are, there might be large chunks of the repeater frequencies unused. Or you could live between two major metropolitan areas like me where there are NO unallocated repeater pairs...If they ...


5

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 electromagnetic wave — is the speed of light, this effect is very small for terrestrial conditions. A link between a fixed station and a vehicle moving at, let's say, ...


5

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 a balun, and a common-mode choke is one of them. A choke can also be used in balanced to balanced, or unbalanced to unbalanced connections where suppression of ...


5

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 shield connection to a coaxial cable, it starts operating more like an unshielded single wire — a monopole antenna, if the other end is disconnected. For ...


5

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 bringing down the signal level to a point where it is no longer impairing the receiver. The fact that a distribution amp is inline with your television probably ...


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

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 witnessed that very drastically in a German city center, where telefonica used to completely switch of one of their 3G base stations. This is done because power ...


5

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 the same gain as a dipole. That's OK gain, but certainly not great. Lots of other antennas would give you a few more decibels for not very much money. I ...


5

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 (-6dB rolloff). As such, it should be used for reception of frequencies between 1.50GHz-1.58GHz" but the H+ H1 has "65MHz bandpass region, centered ...


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