# Tag Info

35

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 ...

24

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 ...

16

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 ...

13

The ITU bands are actually delineated along plain powers of ten! They're just hiding a bit. From the description above a table of all the bands on Wikipedia: As a matter of convention, the ITU divides the radio spectrum into 12 bands, each beginning at a wavelength which is a power of ten ($10^n$) metres… So the HF band is from 100–10m, or the UHF band ...

12

$$\frac{c}{ \text{frequency}} = \text{wavelength}$$ $$\frac{c}{ \text{wavelength}} = \text{frequency}$$ 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 48 deg. N, ...

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. (...

11

"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 ...

10

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

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 ...

9

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 ...

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

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 ...

8

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.

8

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 ...

8

These were common abbreviations in use for Components, Radio equipment, and Printed publications in the 19th and most of the 20th century. Mfd = microfarad or μF kc = kilocycles or kHz. 1,000 cycles per second. μμf or mmf = pF (picofarad) Frequency The change from kc to kHz and mc to MHz were done because someone though that Heinrich Hertz ought to be ...

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

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 ...

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 ...

6

None. Basically, aside from a few ISM bands, none of which are covered by your radio, you can transmit nowhere without a license, unless you're using hardware that restricts you to legal usage (e.g. DECT phones; you don't need a license to operate a wireless indoor phone, but the phone has to be built in a way that prohibits any other usage).

6

That's an expected phenomenon: Real-world physical systems tend to be frequency-selective (i.e. not constant over frequency), and "at large scale" low-pass systems. This applies to amplifiers, mixers, oscillators, and even transmission lines and connectors. So that's normal. Ettus even publishes exactly such measurements at https://files.ettus.com/...

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