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Old 29-07-2017, 21:04   #1
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Why are SSBs so susceptible to noise?

Why are SSBs so susceptible to noise when other radio devices seem to have dealt with it. Power supply noise, radiated noise, cross talk from other cables all seem to impact SSB in a profound way, and people spend enormous amounts of time cleaning it up to get good SSB performance.

In contrast, VHFs just plug in and work unless there are awful problems, so the radio design seems to be immune to external noise. The same is true for cellular devices. Immunity to external interference appears to be dealt with in the design of the device. Even a satellite device that it is communicating back and forth to space has no trouble with the electrical environment on a boat.

So why are SSB radios so different?
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Old 29-07-2017, 21:12   #2
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Re: Why are SSBs so susceptible to noise?

oversimplified but....

ssb is kind of like AM radio where as VHF is FM

think of listening to your radio in your car FM=clear AM=noisey

But at night you can listen to AM stations from far away.

SSB lets you talk much farther just like AM

I know I really dumbed it down but that should give you an idea of what's happening...

Bob
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Old 29-07-2017, 21:46   #3
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Re: Why are SSBs so susceptible to noise?

Like Bob said it is the modulation technique. AM/SSB (amplitude modulation) noise prone, FM (frequency modulation) less noise prone. FM because of the wide spectrum requirements is only practical at higher frequencies. Higher frequencies yield short ranges (basically LOS on earth). Lower frequencies can travel around the world.

Semaphore gets around the noise problems but then there is fog.

Just no free lunch.
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Old 29-07-2017, 22:39   #4
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Re: Why are SSBs so susceptible to noise?

It's OK to get technical. Actually, I prefer it.

Why is AM more susceptible to noise?

Why can't the radio have power input filtering sufficient to filter out power supply noise, as opposed to me needing to do it all externally?

Actually, I might have answered my own question... external noise of all sorts will cause the strength of the received signal, and the background noise to shift, and to shift in amplitude. So the modulated signal is moving all over the place while you are trying to extract out what matters. With FM, all that external stuff changes amplitude, but not frequency. So even though the amplitude of the signal is moving all over the place, the frequency remains stable. Does that sound more or less correct?
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Old 29-07-2017, 22:57   #5
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Re: Why are SSBs so susceptible to noise?

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Originally Posted by tanglewood View Post
It's OK to get technical. Actually, I prefer it.

Why is AM more susceptible to noise?

Why can't the radio have power input filtering sufficient to filter out power supply noise, as opposed to me needing to do it all externally?

Actually, I might have answered my own question... external noise of all sorts will cause the strength of the received signal, and the background noise to shift, and to shift in amplitude. So the modulated signal is moving all over the place while you are trying to extract out what matters. With FM, all that external stuff changes amplitude, but not frequency. So even though the amplitude of the signal is moving all over the place, the frequency remains stable. Does that sound more or less correct?
Yes, more or less spot on!
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Old 30-07-2017, 10:48   #6
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Re: Why are SSBs so susceptible to noise?

And don't forget your (am/ SSB) receiver is amplifying a very very very weak weak far away signal (10 million x or so!) while your local noice is 1000s x stronger. All in all AM/ SSB do a pretty damn good job... considering!
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Old 30-07-2017, 11:56   #7
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Re: Why are SSBs so susceptible to noise?

I think SSB is somewhat of an old technology. I feel sure some Hams will jump me on that. It has a hell of a range as compared to AM and more so FM. A skip can get you around to world if you don't care who you get.
Todays technology has made it more of a hobby. Even as long as close to thirty years ago my phone rang and my son was calling SC from a longliner someplace off Norway.
Turn the squelch up on the SSB.
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Old 30-07-2017, 12:11   #8
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Re: Why are SSBs so susceptible to noise?

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Originally Posted by tanglewood View Post
Why are SSBs so susceptible to noise when other radio devices seem to have dealt with it. Power supply noise, radiated noise, cross talk from other cables all seem to impact SSB in a profound way, and people spend enormous amounts of time cleaning it up to get good SSB performance.

In contrast, VHFs just plug in and work unless there are awful problems, so the radio design seems to be immune to external noise. The same is true for cellular devices. Immunity to external interference appears to be dealt with in the design of the device. Even a satellite device that it is communicating back and forth to space has no trouble with the electrical environment on a boat.

So why are SSB radios so different?
SSB radios are a version of amplitude modulation, but was developed to allow only the amplification of intelligence as opposed to a carrier and both side bands like the AM radio in your car. Noise in the environment is a form of amplitude modulation. If you think about the radio in your car the AM side is noise and the FM side is not. Same on a boat with SSB as opposed to Marine VHF. While noise comes into FM radios it is also a form of amplitude modulation, but that is not what the radio is looking for. It is looking for (demodulating) the frequency changes and most radios actually clip off the AM part.

While Marine VHF is quiet, it only allows communication to ~ the horizon. HF SSB can talk thousands of miles and even around the world, given ideal conditions.

I hope that helps
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Old 30-07-2017, 12:45   #9
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Re: Why are SSBs so susceptible to noise?

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I think SSB is somewhat of an old technology. .
Maybe, but SSB is an integral part of GMDSS which means it will be around for quite a while longer
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Old 30-07-2017, 12:50   #10
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Re: Why are SSBs so susceptible to noise?

[QUOTE]I think SSB is somewhat of an old technology[QUOTE]

A pretty accurate statement (50+ years M/L).

Keep in mind if you are the only station on the air then frequency/modulation techniques might be different, but a lot of people like to talk at the same time.

A single commercial broadcast FM channel uses the bandwith of a hundred Hams all talking on 80 meters using SSB. There are some digital modes used by Hams but most still like to talk. SSB is an efficient way to do this.

As cell usage/ coverage/ modes have exploded some pretty sophisticated modulation schemes have shown up. Now we are talking about frequencies that are not only LOS but also subject to significant range attenuation. The reason we see cell towers everywhere. Sending text messages must be the most efficient comm technique since Samuel Morse came up with his code. Morse code is a probably faster though.
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Old 30-07-2017, 13:14   #11
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Re: Why are SSBs so susceptible to noise?

I don't know why anyone would be comparing SSB with FM. SSB is am with no carrier just an envelope and the carrier put in at the receiver. If some can explain that in so many words I would appreciate it.
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Old 30-07-2017, 13:30   #12
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Re: Why are SSBs so susceptible to noise?

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Originally Posted by Cadence View Post
I think SSB is somewhat of an old technology. I feel sure some Hams will jump me on that. It has a hell of a range as compared to AM and more so FM. A skip can get you around to world if you don't care who you get.
Todays technology has made it more of a hobby. Even as long as close to thirty years ago my phone rang and my son was calling SC from a longliner someplace off Norway.
Turn the squelch up on the SSB.
Old technology, yes, but a staple in the Marine industry. Read the rules for GMDSS. SSB is a cruisers link into that extensive infrastructure. That assumes you have a DSC capable radio and not an old technology marine or heaven forbid an illegally modified Ham rig to allow some use in the marine bands. VHF range about 12 miles when off shore, possibly 20 miles to shore installations. The ground wave on HF SSB can extend out 150 miles on the MF 2182.0 frequency. GMDSS vessels are required to monitor the 2 MHz DSC frequency. They can easily be your closest help at sea.
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Old 30-07-2017, 13:56   #13
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Re: Why are SSBs so susceptible to noise?

SSB and FM are just modes of operation. It is possible to use SSB on the same frequencies as the VHF radios, and FM on the frequencies of the normal “SSB” (if the radios are designed for both modes), BUT, the advantage FM offers in noise reduction has made it very popular for general short range communication. That being said FM has disadvantages, and is not used in Aviation because of them (or so I was told when I queried it).
But despite popular belief, FM radios like Marine VHF still suffer from the noise generated by modern electronics. Have you never noticed you can run a lower Squelch level in an isolated anchorage, compared to a busy marina?
The higher noise levels force you to turn up the squelch level, which forces the radio not to receive any but the strongest signals, so the weaker ones will be cut off. The fact that you are not hearing the actual audio from the noise, does not mean its not there. Because they don’t hear the noise, most people just never worry about it, and so they are also unaware of the effect on the range it has on a VHF radio. On the so called "SSB" radios you are mostly receiving weak signals, so you never set the squelch up to kill the noise, but killing the noise at the source will help both radios actually.

There are devices that you can use to actively kill the noise at your boat, but they take a little skill to use The basic operation is, you receive noise off a small antennae, mix it with the noise from the normal antennae, and adjust the amplitude and phase so. the result is very low noise at the radio, despite there still being quite a lot of RF noise. Its not perfect, but certainly makes a “SSB” radio more pleasant to listen to.

As a final comment.
I find it amusing to see how many diss the old technologies as inferior and useless, only to come looking for them when the new technologies fail them on a passage.
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Old 30-07-2017, 14:05   #14
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Re: Why are SSBs so susceptible to noise?

Don't think your VHF is immune from noise. My VHF started with static could not transmit or receive. Swapped it out with spare same thing. Started to look at the antenna. Make this short my wife had a12V phone charger and had plugged it in to charge her phone, as soon as I unplugged it the Radio worked as usual. Won't say how long it took to find the problem but phone was at 100%. Other 12V charger didn't cause a problem.
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Old 30-07-2017, 14:18   #15
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Re: Why are SSBs so susceptible to noise?

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Don't think your VHF is immune from noise. My VHF started with static could not transmit or receive. Swapped it out with spare same thing. Started to look at the antenna. Make this short my wife had a12V phone charger and had plugged it in to charge her phone, as soon as I unplugged it the Radio worked as usual. Won't say how long it took to find the problem but phone was at 100%. Other 12V charger didn't cause a problem.
That is truly perplexing. I wonder if her charger isn't on it's way out.
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