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CW pumps out the full carrier but has a better SNR. On the other hand SSB suppresses the carrier, and one side-band but this suppression demands additional circuitry. There are probably additional considerations with SSB - poor SNR, operator dialect but these are not part of the question here.

When the available options to transmit are CW, and SSB in ARES - which of the two will conserve the battery more?

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CCW (Coherent CW), SSCW (Slow Speed CW), QRSS etc. integrate signals from bellow noise levels. This means very low power usage at the transmiter end, not unlike NASA uses on Mariner. –  Optionparty Jan 14 '13 at 14:38
@Optionparty - yes, though the phrase "integrate signals from below noise levels" is a bit of a mischaracterization. Noise power must be measured over a bandwidth - what can be done with a narrowband (or even its code hopping dual) mode is to have a filter which passes only noise which is extremely similar to the desired signal. This much smaller noise bandwidth has a total power which is less than the signal, and it is that SNR improvement which lets the signal be decoded. The signal is not actually below the final noise; only below the noise of an earlier stage of the receiver system. –  Chris Stratton Jan 14 '13 at 19:56

5 Answers 5

Your question suggests an actual use (that is, "pass a message on ARES"), so you've got to consider bandwidth as well. Not so much how much band space you will occupy, but how long you'll be on the air. How long does it take to send a message on CW vs. reading it on SSB? Transmit time will affect the battery as much as the indicated power level.

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The power output of an SSB transmitter is not constant - if properly aligned, it exactly tracks the power of the input audio signal, as the RF emission is literally the input audio image-reject-mixed up to RF. –  Chris Stratton Jan 14 '13 at 20:04
Well, and the output of an CW transmitter isn't constant either..assuming you're keying it on and off per A1 emissions. –  gbarry Jan 14 '13 at 21:52
Yes, keyed CW is also not constant, but if you follow the formal spacing rules it's less variable than voice and probably has a higher power-duty cycle within a message. –  Chris Stratton Jan 14 '13 at 22:02

It should be noted that this question assumes HAM (amateur) radio jargon/conventions and in that context it is strange to compare CW (a "digital" communication modality used with morse code) to SSB (an "analog" strategy used with voice communication).

If you transmit a monotone signal (like morse code) using SSB modulation the effective signal in the air consists of only one frequency as well (assuming SSB-SC -- carrier suppression). That signal is offset from the carrier by its tone frequency, but there is still only one tone in the air.

Therefore, at a theoretical level this question is silly since you are talking about a single tone and whether you On-Off key (OOK) the carrier (CW), or offset a single frequency from this magical carrier (SSB-SC) and OOK that, is completely irrelevant. The same energy is in the air.

That is to say, if your CW carrier is 1MHz, the equivalent carrier for SSB-SC transmission of a 3kHz tone is 1.003 MHz assuming you use the lower side band. Both strategies result in an airborne transmission at 1MHz. So from physics, energy is proportional to frequency (given constant amplitude), the signal energy is exactly the same.

If you now expand the question to include the radio hardware that is generating/receiving the signals, OOK (CW) hardware is typically simpler and, therefore obviously, requires less quiescent and operational power.

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"energy is proportional to frequency" is a reference to the energy of individual photons. Nobody talks about photons in the context of radio communcation, and this has nothing to do with the total power in the siganl. –  Dave Tweed Jan 14 '13 at 12:27
@Dave -- No. (1) Not just a reference to photons, it also covers the energy to generate the signal, the resistive losses in the antenna, dynamic and switching losses, etc ad infin. (2) Bringing focus to the underlying principles avoids "technician syndrome" where people talk in protocol and jargon rather than seeing through it to the what's actually happening. -- I know you don't have that problem, but just to explain my thoughts... –  DrFriedParts Jan 14 '13 at 18:22
"most HAM radios don't suppress carrier for connection recognition/auto-squelch purposes" On the contrary, almost all do - to not do so would be considered very poor and inconsiderate practice on crowded bands. There are some commercial systems however which do not, to support some of the automation mentioned. –  Chris Stratton Jan 14 '13 at 19:46
@Chris -- Fair enough. Revised. –  DrFriedParts Jan 14 '13 at 20:36

You can find here that CW uses up to 5W and SSB up to 10W, most of the time. This however does not mean that CW uses less battery power.

How much battery power you need (or how long the battery will last) depends on more than the output power. There might be circuits in CW generation that draw much current, so that it needs more power than SSB, while SSB has a higher Peak Envelope Power.

You cannot say which one conserves more power for you battery. We can only say that SSB may transmit more power in QRP operations, but that doesn't answer your question.

If you want an answer to your question, I'd recommend you to do some testing. You can simulate a battery with a regular power supply and measure the current in both modes, or you can test both modes in the field and measure how long a fresh battery lasts in that operation.

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You might be right (it is very likely!) but lets have this discussion on your answer, where we already have one. –  Camil Staps Jan 14 '13 at 7:24
Ehm.. this elmer..? –  Camil Staps Jan 14 '13 at 7:43
Okay, lol, I guess :P –  Camil Staps Jan 14 '13 at 8:04
I needed 15 characters to comment, and spaces at the end didn't work :-) –  Camil Staps Jan 14 '13 at 8:06
This is a a very poor answer, based on anecdotes rather than theoretical understanding. Given that the question posed here has a very well known answer, this is just pointless. –  Chris Stratton Jan 14 '13 at 19:37

CW communication carried out by highly trained operators is well known to be more power efficient than SSB voice for transmitting readily transcribable information. That's mostly because voice is not very efficient as a representation of information, requiring a relatively high signal to noise ratio for the amount of data carried, unless you include more nuanced things such as expressive tone in the total of information that is being transmitted.

However, CW does have the downside of needing more highly skilled operators with the benefit of a lot of experience.

The real answer today would be a digital mode, combining the spectral and power efficiency of CW (though probably not OOK modulation) with a fully automatic implementation - leveraging modern low power DSP instead of trained ears.

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+1 Also, see PSK31 regarding your last suggestion... –  DrFriedParts Jan 14 '13 at 20:31
For human-decoded signals, is the improvement in power efficiency sufficient to overcome the increased transmission time that would generally be required to send a message? I would expect that signals which are to be decided via machine could be sent more efficiently than those which are to be decoded by humans, since machines have the benefit of things like forward error correction and in some cases fine-grained negotiated retransmission. –  supercat Jan 14 '13 at 22:15

To answer your battery conservation question, CW will conserve battery more than SSB. That's why CW is QRP (Low Power). Hope this answers your question.

Some more information about QRP from wikipedia.

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QRP is about transmitting power, not about battery power. So the reason that CW is QRP isn't that it will conserve the battery more than SSB. It is true that CW most of the time is less than 5W Peak Envelope Power, and SSB less than 10W, but that doesn't mean CW uses less than SSB in the ARES. Since this is about battery conservation, other circuits influence the result as well. So a CW circuit drawing very much current might make SSB conserve more power, while the PEP is higher for SSB. –  Camil Staps Jan 14 '13 at 7:03
This answer is factually incorrect, as CW is by no means necessarily QRP! –  Chris Stratton Jan 14 '13 at 19:49

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