15 votes

How do PTT buttons work?

The basic PTT (push to talk) button on the HT is a simple switch that is normally open and when it is pressed, the switch is closed (conducting). Internally to the radio, this applies power to the PA (...
Glenn W9IQ's user avatar
  • 18.6k
11 votes
Accepted

Is my low-power VHF transmitter dangerous?

Electromagnetic hypersensitivity does not exist. There is no confusion. It has been rigorously refuted by science. One watt is orders of magnitude below safe exposure limits, and indeed probably less ...
Phil Frost - W8II's user avatar
11 votes

How To Join Packet Radio BBS

A summary of requirements: Licensing: Technician - very minimal requirements Equipment: Transceiver, Terminal Node Controller and terminal Transceiver - traditionally a VHF/UHF FM radio Terminal ...
JSH's user avatar
  • 590
11 votes
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What does the spark-gap do in a spark-gap transmitter?

The spark gap is a simple, low-tech way of generating high frequencies. It was the only way of generating them before valves and transistors were invented. As C1 charges up through R1, eventually the ...
tomnexus's user avatar
  • 10.9k
9 votes
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What replaces the T/R switch in modern transceiver

Receivers and transmitters are still separated today, they are just in the same box. There is still a T/R switch too, integrated in the box. In many radios, it's a relay, same as they have been for ...
Phil Frost - W8II's user avatar
8 votes

Share wide band antenna with multiple transceivers

The basic concept is to use RF bandpass filters for each frequency range. This is frequently done by hams for VHF and UHF applications. The common term for a grouping of these filters is diplexer, ...
Glenn W9IQ's user avatar
  • 18.6k
8 votes
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How to calculate power transmitted by monopoles?

10⁻⁴ which I think is too low power. Why? Gut feeling says that is actually pretty good a transmission for such a distance. Notice how your free space path loss is $$\left(\frac{\lambda}{R}\...
Marcus Müller's user avatar
7 votes
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Detecting the listeners

No, that's not possible. There is no practical way to determine whether the transmitted power is usefully received by an antenna, or just absorbed by the ground. It is possible to detect that a ...
rclocher3's user avatar
  • 9,182
7 votes
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Share wide band antenna with multiple transceivers

A wideband antenna is not what you're looking for – you really don't care about anything between 900 and 1500 MHz, or between 1600 and 2400 MHz. Wideband antennas are inherently hard to make, and ...
Marcus Müller's user avatar
7 votes

How to create a simple 1296MHz transmitter?

So, there's a bit of disappointment I'll have to spread here: Building microwave circuits like the one you need isn't per se as easy as just scaling up a circuit for, say 3 MHz or 100 MHz. Let's ...
Marcus Müller's user avatar
7 votes
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Where does this common spurious transmission come from? Is there a quality difference?

This is very likely to be be due to overload of the receiver. A quick, rough way to tell the difference: Tune your SDR receiver so the waterfall center frequency is not the same as the transmitter's ...
Kevin Reid AG6YO's user avatar
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7 votes
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Can these in-band spurs from rpitx be eliminated somehow?

I can't dig up my source for this, but I'm pretty sure these spurs are just the result of rpitx using a fractional-N PLL (that isn't in any way optimized for phase noise) to generate a square wave. ...
hobbs - KC2G's user avatar
  • 12.2k
6 votes

How far does a watt equal in range in the FM band?

This is a link budget question. Transmit power is just one factor: others are terrain, antennas, frequency, quality, noise, and so on. If we restrict the variables to typical values for FM commercial ...
Phil Frost - W8II's user avatar
6 votes
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How to transmit images and video through a hurricane?

In general, the HF bands (1.8 MHz through 30 MHz) do not have sufficient bandwidth to support live transmission of a video signal. In the US, the FCC does not authorize an emission mode for live video ...
Glenn W9IQ's user avatar
  • 18.6k
6 votes

Will I get cleaner keying by keying the oscillator, or interrupting the amplifier B+?

Highest frequency stability is generally achieved when the oscillator is kept running while some following stage (or stages) is (are) keyed. However, the very high Q of a crystal-controlled oscillator ...
Brian K1LI's user avatar
  • 7,828
6 votes
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How does one know how a signal has been modulated

Yes, you'll have to look at it. I can't go into detail about every possible modulation, because there's just too many. But typically, a look at the spectral representation gives you an idea of ...
Marcus Müller's user avatar
6 votes
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If i transmit on the same frequency using two separate transmitters joined together will they both add up in a reciever to produce a stronger signal?

You certainly can, in theory, use multiple transmitters together to produce a signal of higher total power. However, there is a catch: the signals must be in phase with each other. Otherwise they will ...
Kevin Reid AG6YO's user avatar
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6 votes
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Is this "floating" output single-ended or differential and against GND or VCC?

The other part of me thinks that the DC blocking capacitor will be a low impedance at RF so that the RF is actually "pushing against" GND or VCC but I don't know which one. This appears to ...
Phil Frost - W8II's user avatar
6 votes

Reasons for an antenna tuner at the transmitter other than transmitter protection?

Just because the finals don't go up in smoke when driving a mismatched load, doesn't mean they're working well. They will probably deliver less power to the antenna than they would in a matched ...
hobbs - KC2G's user avatar
  • 12.2k
6 votes
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How do businesses develop and test amateur radio products in the US if you cannot be paid for amateur radio use?

Two parts to this answer: First, most testing would be done against dummy loads, looking at the results on spectrum analyzers. Such tests should not propagate. Secondly, there's a fine line here. As ...
user10489's user avatar
  • 5,959
5 votes

Weird Harmonic Issue on Raspberry PI FM Transmitter

There are many articles which describe how to use a R-Pi to emit (=transmit) a signal. However what most, if not all, articles fail to describe is that this signal is a very rough signal, usually not ...
Edwin van Mierlo's user avatar
5 votes

Weird Harmonic Issue on Raspberry PI FM Transmitter

You are observing a practical example of harmonics. Harmonics of a Square Wave You do not mention how you are generating the signal with your Pi but it probably uses a simple square wave generator. ...
Glenn W9IQ's user avatar
  • 18.6k
5 votes

Unlicensed TV broadcasting power limit (Band I)

Since you mentioned part 15, I'm guessing you're asking about the rules in the United States. If you look at part 15 subpart C in detail, you'll see that the frequencies in the VHF I band (44 - 87.5 ...
mrog's user avatar
  • 1,023
5 votes

Long range communication with just 1W of power?

At 27 MHz and a distance of 1000 km, propagation will be the main determinant of the possibility of communications. Propagation will primarily be a factor of time of day and the sun spot conditions. ...
Glenn W9IQ's user avatar
  • 18.6k
5 votes
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What happens when you directly couple the transmitter antenna to the receiver antenna?

If your transmitter emits enough power to be heard more than a few meters away, the likely result will be destruction of components in the receiver and possibly in the transmitter as well. Receivers ...
Zeiss Ikon's user avatar
  • 4,097
4 votes

How To Join Packet Radio BBS

A Technician Class license or better is required. What equipment you need very much depends on the solution or solutions you pursue. There exist well-baked schemes for creating relatively long ...
Tadd KA2DEW's user avatar
4 votes
Accepted

What is the output impedance of a typical solid state ham transmitter?

Inside the output of a transmitter is often a PA, consisting of a transistor and a matching network. The output impedance of the transistor is easy to define during small-signal operation. From the ...
curtis's user avatar
  • 176
4 votes

What is the output impedance of a typical solid state ham transmitter?

Strictly speaking, the output impedance of most amateur transmitters is not specified. The specifications instead state what the output power of the transmitter will be into a 50 ohm load. Often the ...
Glenn W9IQ's user avatar
  • 18.6k
4 votes
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Ettus B210 USRP Is it possible to transmit on both Tx Ports either with same or different application?

UHD requires a USRP to be owned by one process only, so no, you can't share the same USRP across two flow graphs, but you could use for example the ZeroMQ PUB/SUB sink/source pair to stream data in ...
Marcus Müller's user avatar

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