32

On voice, use "Mayday Mayday Mayday" at the beginning and end of the transmission. This is only for life-threatening emergencies. http://en.wikipedia.org/wiki/Mayday_(distress_signal) For other emergency situations, like reporting a wildfire that does not directly threaten you, use "Break Emergency" at the beginning of the call. This is a good guide to ...


23

Assuming that you have an amateur radio license makes this easier, but it's quite possible that the UK legal language includes provisions that may be applicable and allow transmission without a license. It depends on the specifics of the emergency in question. I would strongly recommend familiarizing yourself with the relevant definitions in the legal code ...


15

If you don't know what a frequency is, you need to read up on waves-in-general and radio waves. But the other two terms can be defined in terms of frequency; frequencies are the “natural” thing and everything else are things people invented on top of that. A frequency band, or band, is a range of frequencies with a specific least frequency and greatest ...


11

$$ \frac{c}{ \text{frequency}} = \text{wavelength}$$ $$ \frac{c}{ \text{wavelength}} = \text{frequency}$$ The above relation is a fact of physics. It's true unconditionally (provided you are using consistent units, e.g. wavelength in meters and $c$ in meters per second); it's how you convert between two different ways of measuring a wave. The frequency ...


11

Line A Part 97.303 section m states: (1) No amateur station shall transmit from north of Line A in the 420–430 MHz segment. See §97.3(a) for the definition of Line A. The definition of Line A in part 97.3(a) is: (29) Line A. Begins at Aberdeen, WA, running by great circle arc to the intersection of 48 deg. N, 120 deg. W, thence along parallel ...


11

Normally in amateur radio when specifying a frequency you specify the nominal carrier frequency. For SSB and other suppressed-carrier transmission modes, you specify the frequency to which the BFO needs to be tuned to re-insert the suppressed carrier. For this to work, you also need to specify which sideband you are transmitting on; lower, upper, or both. (...


10

"Shortwave" means roughly the same thing as "HF": 3 to 30 MHz. It definitely does not include the FM broadcast (around 90 MHz, too high) or AM broadcast (around 1 MHz, too low) bands received by a typical car radio. Shortwave frequencies have the unique property of supporting ionospheric propagation, which means under the right conditions they can ...


9

This is called operating "split" and it takes a certain amount of skill to work a DX operator working split and even more to operate split. The reason this is done is to help manage the pileup. If too many stations are calling and the pileup becomes unmanageable it takes longer and longer to complete an exchange. This is less fun for everyone. By ...


9

A pure tone is an unmodulated signal — it carries no data. Almost nobody intentionally transmits a pure tone — it would be wasteful. The exceptions are the time-and-frequency reference signals like WWV, but they have modulated time information in addition to the carrier which serves as a frequency reference signal. What you are receiving is almost certainly ...


9

Yes, very strong radio signals can be picked up by just about any device with a speaker and a transistor in it. The transistor acts as a rectifier, forming a crude envelope detector. Amplitude modulated voice can be heard quite clearly, single-sideband modulated voice is quite garbled but often still somewhat intelligible. No cause for alarm: it won't ...


9

It depends on the frequency range the termination is rated for, and the power handling required. High power and high frequency is very difficult. At HF, any old non-inductive 50 Ω resistor will do. For higher power, we'd put many resistors in series and parallel, perhaps on a heat sink or in a can of oil. At VHF and UHF I've made very good terminations ...


9

The signal is not at exactly one frequency. The only signal that exists exactly at one frequency is an unmodulated carrier, and such a signal contains no information. As soon as the carrier is modulated, the signal's energy is spread over a wider bandwidth. So to receive any signal containing information, the receiver must listen to some range of ...


8

Your frequency error is the difference between where your transmitter indicates you are transmitting, and where you actually are transmitting. The FCC does not regulate where you think you are transmitting. They only regulate where you are actually transmitting. Consequently, your frequency error can be whatever you want, as long as you keep it in the bands ...


8

Assuming that you're operating in the jurisdiction of the FCC, there should be no legal issue with you modifying your radio and using it to transmit on those two bands providing the following: Your modifications comply with good engineering practice, and You do not exceed the privileges (power or frequency) of your license Unlike other radio services in ...


7

If this is something you are interested in on an ongoing basis as a volunteer, then you should look into joining RACES and/or ARES in the US, and RAYNET in the UK: http://en.wikipedia.org/wiki/Radio_Amateur_Civil_Emergency_Service http://en.wikipedia.org/wiki/Amateur_Radio_Emergency_Service http://en.wikipedia.org/wiki/Radio_Amateurs_Emergency_Network ...


7

Part 97 doesn't have anything to say about frequency error or drift in particular. The question pool, however, does: T1B09 (D) [97.101(a), 97.301(a-e)] Why should you not set your transmit frequency to be exactly at the edge of an amateur band or sub-band? A. To allow for calibration error in the transmitter frequency display B. So that modulation ...


7

A calling frequency is a common channel known to all - this is the channel that anyone can jump onto and say Hi! Or a specific person you know may be monitoring this channel, you can call out to them. Should you wish to hold a longer conversation, you would use this channel to agree upon which channel you will be switching to.


7

There are some straightforward reasons I can think of which apply to all spectrum allocations, not just amateur radio: In a lot of cases, the bandwidth of a RF device is relative; if you are using the same physical principles, but change the dimensions/values to double the operating frequencies, everything scales up equally so you have a device with twice ...


7

There's more space at higher frequencies so the allocations can be bigger. Consider the difference between 15 MHz and 30 MHz, and the difference between 5,015 MHz and 5,030 MHz. It's a 15 MHz change either way, but in the first case involves a halving of wavelength, whereas in the later case the wavelength changes only by a factor of 0.997. Since the way ...


6

I'd agree with @user3486184's answer, that this is primarily an effect of tradition. However, what @DaveTweed answered hit the spot how that tradition came to be: In early radios, you really had not much of a notion of electrical fields doing something periodic at a fixed frequency; these were simple crystal radios, doing nothing but taking the envelope of ...


6

You can think of the frequency range specification as if you did have an ideal “every frequency” antenna but the signal passes through a filter before reaching the receiver. That is, any signal will be attenuated by some amount, depending on the frequency. This attenuation does not mean that the signal cannot be received; it means that it is weaker, and ...


6

This is an interesting question and while we may not be able to get to an exact answer, we can certainly explore the issues to consider. First we start by calculating a primitive link budget. The transmitter has an output power of 100 watts or 30 dBm. If we assume a 50 ohm input impedance receiver will have adequate reception (20 dB of quieting) with a 0.5 ...


6

I wish you well with the general test! The radiolocation services in question are defined in CFR 47 §2.106: NG92 The band 1900-2000 kHz is also allocated on a primary basis to the maritime mobile service in Regions 2 and 3 and to the radiolocation service in Region 2, and on a secondary basis to the radiolocation service in Region 3. The use of these ...


6

Detecting a signal is not a question of amplifying the signal: the problem is distinguishing the signal from the noise. Noise by nature is random: individual observations are unpredictable, but as more observations are made the average tends towards zero. By averaging more observations, the noise can be made arbitrarily close to zero. Signals are not ...


6

It may be easier to think of the receiver as receiving all frequencies. The job of the receiver is not to tune to a single frequency. Its job is to filter out everything that's not at that frequency, or in a band around it. So when you tune your FM receiver to 144.2500 with a 25 kHz bandwidth, you're telling it to reject all frequencies that are more than ...


6

I want to locate a small ball in the air 1000 times a second. The ball is thrown from the ground and then flies in the air for 0.5 seconds until it lands. Distance from the location instrument is 1 meter That probably means you're not satisfied with a range resolution of a couple meters – you need a much finer measurement. That means your system must have ...


5

SSB is, as you say, half of AM, without a carrier. That's the way to think about it if you are implementing it with traditional analog electronics. However, here's a simpler way to think about it: SSB is the baseband signal shifted up into RF. Human hearing works from about 20Hz to 20,000Hz. Human voice needs only up to about 4000Hz. So, take your voice ...


5

An antenna of the wrong size is just an antenna that is not resonant at the particular frequency — meaning that each cycle of the radio wave captured by and conducted in the antenna does not perfectly match phase with the preceding cycle, since that only happens at the specific length. (Incidentally, the length of 1/4 wavelength is appropriate for a ground ...


5

So, the bandwidth argument is the dominant one. You need to incorporate the full Carson Bandwidth in your channel spacing, not only the frequency deviation! As explained in my answer to your previous question, that must be significantly larger than the bandwidth of the same audio signal in AM. Aside from that, as always in Ham usage: historical reasons. If ...


5

In general for a given antenna evaluated on a given frequency, if whatever is changing the Q occurs uniformly or universally and does not result in a change to the effective aperture, phasing, or geometry of the antenna then the pattern will not be altered in a meaningful way. An example of a uniform change would be changing the wire gauge of a wire ...


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