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18

NO CARRIER, said the modem. SSB has no carrier, and the transmitter does not transmit anything when the operator is not speaking. There is no way to transmit the presence of silence to the receiver. Instead, you'll hear atmospheric noise, local and remote electrical noise (arcing in relays, remote thunderstorms and all that), RF hash from computers and ...


15

Amateur Radio operators use this rule of thumb for historical technical reasons. SM0AOM on the QRZ forums writes: The changing of ISB sideband positions at 10 MHz actually has an engineering background. In the earliest ISB exciters, it was found appropriate to change the final mixer scheme from subtraction to addition mixing at around 10 MHz due to ...


14

CW signals are not “transmitted on the upper sideband”, nor the lower one. A CW signal is approximately at a single frequency (with only the additional bandwidth required to allow the key-up and key-down transitions). However, the standard method of receiving a CW signal is identical in structure to a single-sideband receiver. The local oscillator (LO) of ...


11

Microphone technique has a good bit to do with clarity. Talk across the mic, not directly into it, unless it is a noise canceling type designed to be used that way. Speak no more than 2" away from the mic, even if it is a desk mic or a boom mounted type; many people make the mistake of thinking that just because they have a desk or boom mounted mic that ...


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

In the US, the FCC prohibits this type of operation if the purpose is to obscure the meaning of your transmission. 97.113 Prohibited Transmissions (4) ... messages encoded for the purpose of obscuring their meaning... In response to filings on this topic, the FCC has made it clear that this prohibition includes encryption. The FCC has also ...


11

It depends on what you mean by "stronger". Ignoring actual limitations of your hardware and just considering the theory of communications, if you have 25 W of transmit power, then you can spread that over as much bandwidth as you want, and you're always transmitting 25 W of power. The quantity which is 25 times higher in the 100 Hz case than the 2500 Hz ...


8

First of all, you're not 100% right that SSB will reduce transmit power. I often keep talking on SE about power spectral density. So let me start with that again and first assume that we have a radio that has fixed output power of 100 W. So let's first take a (simplified) look at AM: We have a carrier and two sidebands. One sideband, the part in red on ...


8

The short answer is "absolutely!". :-) I started out using Digipan on Windows, but other software such as Fldigi has been released since then. Audio from the sound card to the mic input --and from the transceiver's audio out to the sound card's input-- is usually used. To prevent hum from a ground loop, it is recommended to use 600:600 ohm isolation ...


7

(This is a purely theoretical answer; I have no experience in repeater building. Sorry.) The components of a repeater are: an antenna, a duplexer, a transmitter and a receiver, and a repeater controller. The antenna and duplexer are passive devices and aren't affected by what modulation you're using. The repeater controller is on the audio side of the ...


7

I could imagine a class D pwm system doing the Envelope and the phase modulated carrier getting clipped and fed into a class E amplifier and then you could run 100Watts with no heatsinks allowing smaller cheaper equipment .ZL4TIY We have demonstrated a system very much like this. See: The Polar Explorer: You may never look at your “linear amplifer” the ...


6

No, the receiver does not try to determine a carrier frequency, you do. When receiving SSB, you must adjust the VFO (main frequency control), not just until you hear a signal, but also to adjust to match the suppressed carrier frequency by ear. Slightly-off SSB signals have a distinct sound, which is not just being too low or high in pitch, because the ...


6

To put it simply, a balanced modulator is a mixer which has two inputs and two outputs. The outputs are (input1 + input2) and (input1 - input2). So, if the inputs are 100kHz and 1kHz, the outputs are 101kHz and 99kHz. For transmitting: If the inputs are 1MHz and (voice), the outputs are the lower sideband of the voice and the upper sideband of the voice, ...


5

If you are using (or building) a vintage radio that does not have a narrow CW audio filter, the audio bandwidth above and below a listenable CW audio side-tone frequency can be quite unsymmetric. By flipping the side-band, one might be able to move an interfering signal down close to 0 Hz audio frequency (inaudible), even if the audio is not bandpass ...


5

It looks like you are confused about what these graphs represent. Here's the diagram you used in the question: Probably, this diagram is intended to be interpreted with the horizontal axis being time, and the vertical axis representing voltage or current. Using that same representation, then SSB looks like this: For comparison, AM looks like this: and FM ...


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

Eric Scace, K3NA wrote a two part article for the NCJ a few years back on all the adjustments you can make to your audio chain to improve it's quality. While the article focuses on audio quality for contesting, I think most of the points are relevant "regular" phone contacts. He has 6 main areas that he addresses: Operator training — Things like ...


5

You need to add a carrier in order to perform envelope detection, which is the standard detector in most applications. If no carrier is added, the signal envelope is centered around 0, so the detected output is full-wave rectified. The carrier adds a DC component to avoid the zero crossing of the envelope.


5

Your description is not wrong, but your premise is. In the system you describe, both the receiver and the transmitter require oscillators at 1 MHz. They may be called different things in the two cases, but they are playing essentially the same role: defining the carrier frequency. In the transmitter, the oscillator's frequency is added (in the frequency ...


5

Firstly, FM is a constant-envelope modulation, meaning the amplitude is constant. SSB, being a kind of amplitude modulation, obviously does not have a constant amplitude. Consequently, FM can employ a non-linear amplifier which is more power efficient, and thus has a longer battery life in mobile operation. Secondly, SSB signals add with each other and also ...


5

Partial answer, because I don't know the actual electronics theory, but I hope which will help make progress towards a complete answer: A balanced modulator is a mixer with a particular feature. Basic analog mixer designs tend to include the carrier in the output, whereas a balanced modulator is one which is designed to "suppress" the carrier. Hence, if ...


4

Yes, this is a workable modulation. In fact, it's used all the time on HF; what you have described is precisely single-sideband (SSB) modulation. The usual choice of filtering is for an occupied bandwidth of 3 kHz rather than 4 kHz, but that's just a parameter; the principle is the same. The reason it's called single sideband is that if you use the ...


4

To understand better, I'd suggest you follow this: 1) If you have an AM transmitter at 10.000 MHz (let's use simple numbers). If someone whistles in the microphone, at, say, 1kHz, two sidebands will appear, at 9.999MHz and 10.001 MHz (and a carrier at 10.000MHz). 2) If you convert the AM tx into USB, and transmit at 10.000 MHz, the whistler will appear at ...


4

I am not sure I understand the question but I will attempt to answer a part of what you are asking. Thinking about this once, I said to myself: SSB is 3 kHz wide, so we can divide that neatly into XXX0000, XXX3000, XXX6000 Hz with only a little bit of waste. No one does that. When you choose a particular frequency for SSB, you usually will look for ...


4

Let's start with voice, just to show what it looks like. Voice doesn't have a "carrier wave". It simply contains the up and down level of the voice. Where the sound wave is 0 is effectively the carrier. Typical AM signals take this signal, and modulate it with the carrier wave. Thus, the signal has a large peak at the peak of the carrier wave, and a ...


4

As Juancho already mentioned, adding a carrier to the signal is needed for envelope detection, one particular demodulation technique (which can be seen as locally converting the signal to an AM, or more precisely vestigial sideband, signal). However, any SSB reciever, no matter how it is designed, must in some sense have a signal at the carrier frequency (...


4

In the picture there is only ONE frequency and the amplitude changes Ah, but this actually causes a second frequency component, the one that you wish to transmit: (Please excuse my rudimentary paint skills.) It is this second, implicit frequency which combines with the AM carrier to then form a strong carrier signal in the centre of the spectrum, and a ...


4

My current understanding from reading and looking at spectrum plots from SDR software is that the sound is modulated with the carrier, but only half the carrier wave. That's — not really accurate. A SSB signal uses half the bandwidth of a double-sideband (whether AM or DSB-SC) signal, but there's no sense in which it uses "half the carrier" in the ...


4

EDIT to be more specific about the input circuit per Phil's comment: The antenna (aerial) is connected to the the oscillator of the first transistor stage formed by VC, L and the self capacitance of T1. This forms a classic regenerative circuit where the oscillator essentially samples a portion of the signal from the antenna as the oscillator builds up its ...


4

There is no such specific legal requirement, because AM and double-sideband suppressed carrier (DSBSC) are allowed. Different emission types occupy different bandwidths, as the FCC clearly acknowledges below. § 97.307 Emission standards. (a) No amateur station transmission shall occupy more bandwidth than necessary for the information rate and ...


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