VHF squelch question

[chubby]

I have a SH VHF a few years old, my understanding is that the squelch controls receiver sensitivity and when the knob is turned clockwise until the static just stops on an empty channel the receiver is most sensitive, but what this set does which others didn`t seem to is when a weak signal comes in it produces a burst of static but no speech, very irritating! whereas a strong signal gives speech, fine. If you turn the squelch further clockwise the set rejects the weak signals and no static bursts but is that not making the set less sensitive to signals that it might be important to receive?

I am sure there are plenty of electronics or radio experts who will tell me if my understanding is correct and whether I am risking rejecting important signals if the squelch is too advanced?

I am sure there will be someone who will tell me not to worry and we should all be self sufficient and not rely on VHF, perhaps just burn a barrel of tar if you need to attract attention!

A sub question is do any other sets make a better job of rejecting weak signals and not produce static bursts, are ICOM any better, an old but quite upmarket and now replaced Furuno VHF never seemed to have this problem.

 

[lw395]

If the squelch is set exactly at the margin, an incoming signal will overcome the squelch and still be very noisy.
A lot of modern sets have crappy digital squelch controls with not many steps, these often seem to shut out weak signals.

The only way to be sure about your VHF's sensitivity is to measure it or compare it side by side with another set.
Some radios do get noisy in their old age.

 

[Birdseye]

The squelch does not know whether the signal coming in is noise or talk. You can best imagine the squelch as a step and the signal has to get over that step to come through the speaker.

 

[Lon nan Gruagach]

Think of it not so much rejecting noise as rejecting signals that are unreadable. Then you can happily set it to reject a real signal that is so weak that you wouldnt be able to hear it over the noise.

So.. set it such that occasionally there is a burst of noise, it might correspond to a weak signal (that you couldnt hear anyway) or it might just be a freak "loud" burst of noise. That way, if there is a transmitter just too weak to be heard you will squelch it out, if there isnt one you will reduce the setting so that you wont miss the signal that is only just legible.

 

[skyflyer]

There is a common misunderstanding that the squelch is like a volume control in that only signals above a certain level will be heard.

A better analogy than thinking of it as a step which the signal needs to 'get over' is to think of it as a gate, with a spring keeping it shut. The little lambs can't push the gate open but the big sheep can. Once the big sheep has gone through the gate, it springs shut again.

But whilst the big sheep is pushing past the gate and its open, the little lambs, rabbits, geese and anything else that wants to, can also get through the gate.

So when a sufficiently strong signal 'opens' the squelch, until it closes again, you hear ALL transmissions within range, hence often a lot of noise!

 

[Burnham Bob]

I use the squelch as I was taught. Turn it down until you get noise, adjust the volume to what you want and then turn the squelch back up until the noise just stops. Sometimes you get noise when there is a really dodgy signal but that's only to be ecpected. I don't worry too much as its only occasional and i prefer to be able to hear weak signals.

 

[William_H]

The squelch circuit is actually a switch in the audio section of the receiver. It is turned on to give sound when it receives a signal. But you don't get the annoying background noise. So in setting the squelch control you are setting the amount of signal that is needed to open the squelch. At the most sensitive point it is the inherrent noise of the radio and atmospherics that are enough to open the squelch. Hence you hear the noise.
If you set the squelch control to just not open on inherent noise then any signal which arrives no matter how weak will open the squelch. This is good. So at least you know someone is trying to call even if you can't copy them. If that is annoying then advance the squelch control further to require a stronger signal to open the squelch. A stronger signal you can read.
So OP radio is working fine and in fact he is operating it correctly. good luck olewill

 

[Venus1]

Thanks olewill, I always find your posts useful.
Given these squelch issues etc, how much, if at all, does this affect AIS, which I believe operates on a VHF radio wave, but has no squelch adjustment? Sometimes AIS does not show all ships. Apologies in advance if this is a stupid question!

 

[mlines]

As has been said, the squelch switches on and off the audio part of the receiver, think of it as a switch on the loudspeaker that is controlled by the signal coming in the aerial. Therefore whilst the speaker is "off" all the rest of the radio is still working underneath. So any AIS receive function and any scanning etc. is still looking at the received signal even though you cannot hear it.

As for the AIS not showing all ships:

1. The ship may not be transmitting
2. You may have not waited long enough for the ship to transmit
3. The signal from the ship may be too weak (too far away, your receiving system could be insensitive etc.)

 

[chubby]

Ah now I understand, so the big sheep of QHM and Southampton VTS push the gate open but the little lambs from distant CG aerials just creep through! Now is the gate spring any better between one make of VHF or another, say ICOM or SH and latest sets vs those a few years old or is the technology fairly standard?

There is a common misunderstanding that the squelch is like a volume control in that only signals above a certain level will be heard.

A better analogy than thinking of it as a step which the signal needs to 'get over' is to think of it as a gate, with a spring keeping it shut. The little lambs can't push the gate open but the big sheep can. Once the big sheep has gone through the gate, it springs shut again.

But whilst the big sheep is pushing past the gate and its open, the little lambs, rabbits, geese and anything else that wants to, can also get through the gate.

So when a sufficiently strong signal 'opens' the squelch, until it closes again, you hear ALL transmissions within range, hence often a lot of noise!

 

[skyflyer]

to extend my analogy, the squelch sets the strength of the spring; presumably the settable 'range' of very-weak to very strong varies from manufacturer to manufacturer?

Also bear in mind that a nearby low strength signal may have more energy than distant powerful one, so radio interference from (say) your alternator might open the gate.