Why are SSBs so susceptible to noise?

[TLSparks]

Originally Posted by IOM

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.

You are correct, you could use SSB on VHF frequencies, if it was legal. The issue is who would as there is no advantage. The range would remain the same, to the horizon, and the radio would be just a noisy as an HFSSB. Going the other way channel spacing for Marine FM is 25KHz where as HF SSB is only 3KHz. In order to get any fidelity from FM, you need wider channel spacing. FM detection is based on two factors. 1. The maximum frequency shift is proportional to the amplitude of the modulating signal. 2. The rate that the frequency is changed is equal to the frequency of the modulating signal. That is why FM is typically only used on higher frequencies. Trying to shift the frequency of lower frequencies to obtain a good signal at the other end would be difficult and would require international changes to frequency assignments.

[El Pinguino]

Originally Posted by Cadence

That is truly perplexing. I wonder if her charger isn't on it's way out.

When I am receiving WFM on 137MHz I have to unplug the charger from my Mac.

The mains to 18V charger that came with the Mac causes only minor problems... a third party one that I had... 12V to 18V .... was a shocker.... current 12V/18V has minor issues but still needs unplugging for the best picture.

[Frankly]

[/QUOTE]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.[QUOTE]

Accurate statement.

In a standard amplitude modulated transmission the original carrier frequency is transmitted (number on the dial), and an upper sideband, and a lower sideband are generated and transmitted. Just the nature of the beast (AM). All the necessary information is contained in either sideband but demodulating on the receiving end is more complicated for the SSB. The original carrier must be reinjected at the receiver and the phase of the carrier is critical so early on it was just simple AM. As technology moved along SSB became easier. It was first adopted by the Hams some 50 years back and then became the standard for all long haul communications. Expect if you nose around on the flight deck of a not too old long haul aircraft you will find a SSB set lurking somewhere. I have actually heard a few commercial pilots on the Ham Bands before.

Kind of like Archimedes Law, old but still works just fine.

[snokid]

Originally Posted by TLSparks

You are correct, you could use SSB on VHF frequencies, if it was legal. The issue is who would as there is no advantage. The range would remain the same, to the horizon, and the radio would be just a noisy as an HFSSB. Going the other way channel spacing for Marine FM is 25KHz where as HF SSB is only 3KHz. In order to get any fidelity from FM, you need wider channel spacing. FM detection is based on two factors. 1. The maximum frequency shift is proportional to the amplitude of the modulating signal. 2. The rate that the frequency is changed is equal to the frequency of the modulating signal. That is why FM is typically only used on higher frequencies. Trying to shift the frequency of lower frequencies to obtain a good signal at the other end would be difficult and would require international changes to frequency assignments.

SSB is legal for a HAM to use on VHF as well as UHF.

Line of sight is still the factor for the higher freqs. But there are ways to talk further.

I have talked quite the distance on 2meters pretty close to the marine channels we are talking about here.

I used to contest back in the day big antenna's high up 2 meter's, 6 meter's and 70cm were my favorite bands, I always kind of laugh when someone come's on the forums and says their marine radio is only good for x miles...

Bob

[Cadence]

The only SSB I've used was CB just to be able to have the range to tell the wife I was still going to be late. As happenstance I recognized a voice my father inlaw some 800 miles away. We chatted for some 15 minutes, Skip is something on 13 watts an antenna about a foot long on the car. Don't ask me the wavelength. But it is happenstance. So was Norway and South Africa.

[Paul Elliott]

Originally Posted by IOM

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.

Can you provide a product name, or a link for one of these devices? To be honest, this sounds like snake oil.

[snokid]

mfj 1026

[Lake-Effect]

Originally Posted by Paul Elliott

Can you provide a product name, or a link for one of these devices? To be honest, this sounds like snake oil.

The principle is easy: if on one receiver (A) you have desired signal plus local noise, and on an identical other receiver (B) you have mostly just local noise... when you subtract B from A, you should have the desired signal and less noise.

Of course the success is in the implementation...

[Paul Elliott]

Originally Posted by snokid

mfj 1026

OK, that unit can provide a directional notch at a particular frequency based on antenna phasing. While this is a potentially useful technique, it is not as described by IOM (at least the way I interpreted it). I doubt that it would work very well for in-boat generated noise, or for that matter, on most typical noise sources we fight with in the marine SSB environment.

[Paul Elliott]

Originally Posted by Lake-Effect

The principle is easy: if on one receiver (A) you have desired signal plus local noise, and on an identical other receiver (B) you have mostly just local noise... when you subtract B from A, you should have the desired signal and less noise.

Of course the success is in the implementation...

And what sort of antenna will pick up *only* the local noise and not the desired signal, in a phase-coherent manner? Perhaps you can use phasing to place the directional null on the desired signal, and then subtract that from the main signal path?

OK, that might work but I wouldn't want to be diddling with those adjustments when operating my SSB at sea.

[S/V Illusion]

The problem no one has mentioned which a major cause of noise in marine HF SSB radios is that they all universally lack the necessary noise reduction common in high end ham radios.

As example, my Icom 802 suffers from both conducted and radiated noise despite using all available 'stuff' to minimize both. By comparison by Elecraft KX 2 model ham radio easily eliminates virtually all noise.

Marine radios are inherently inferior in this respect, consequently, boaters have to compensate for the limitations in what is available to boaters unless we want to buy better equipment. And as a boater, I know we are generally too cheap to drive the market to produce better radios.

Regarding phase noise reduction, while the equipment exists, it's too complicated for most boaters and phasing the antennas is impractical on most boats so that discussion is pretty useless.

[Aswayze]

This video, although old and recorded via duck-o-phone, does ad excellent job explaining why FM is so much less noise prone:

https://www.youtube.com/watch?v=4Qgg_upU_5s

[Auspicious]

Originally Posted by tanglewood

Why are SSBs so susceptible to noise when other radio devices seem to have dealt with it.

Others have addressed modulation. VHF FM is not less susceptible. The noise floor still rises. The response of most operators is to just increase squelch. Signal-to-noise ratio is still down and communication adversely affected.

Frequency is also an issue. The higher the frequency the less external noise (external to the radio, internal to the boat) has an affect. On the other hand attenuation becomes a greater problem. Marine VHF FM is more susceptible than HF/SSB, and your cell phone worse yet.

Originally Posted by Cadence

Turn the squelch up on the SSB.

Squelch doesn't work well for AM or SSB. You can clean things up significantly with audio DSP. It still isn't squelch as it works for FM.

[El Pinguino]

Originally Posted by Auspicious

Squelch doesn't work well for AM or SSB. You can clean things up significantly with audio DSP. It still isn't squelch as it works for FM.

I have one of these and it works well https://www.bhi-ltd.com/noise-cancel...ers/dspkr.html

Reviews on another one of their products BHI Compact-In-Line Product Reviews

[trifan]

All of y'all missed the point with all the technical answers. The answer is "money" and is tied to one of the comments about being "old" tech. If one were to use a SDR (software defined radio) and that software included all the fourier transforms necessary to extract signals (and only valid signals) out of the noise (and all the other software tricks needed to put it all together), then there would be no noise to go to the speaker, only the signal.. That stuff costs big bucks. Why? Because they can. I have heard HF SSB radio that is absolutely silent unless a signal is present; it is like a squelch, in the way it is perceived but there is no control. Just quiet that is broken when a signal appears. It is like magic but I cannot afford it.