The squelch setting on your VHF is a way of rejecting background static. It improves safety by helping navigators concentrate, reduces VHF power consumption, and improves the experience of using VHF in general. It is important, however, to make sure your squelch is properly adjusted to get the most benefit.
- Turn the volume and squelch all the way down
- Increase the volume until you hear background static loud and clear
- Increase the squelch until the point where the static stops
- Increase the volume again slightly to make sure transmissions will be heard clearly
What is the Best Squelch Setting?
Squelch is a radio control that lets you mute the sound of background static coming out of a VHF speaker. Consequently, the best setting for your squelch is just above the level of that background static.
High Squelch – Strong transmission needed to break the threshold
Low Squelch – Weak transmission needed to break the threshold
It is impossible to put an exact figure on the best squelch setting because it will vary depending on local conditions. The only way to properly adjust your squelch is to follow a step by step process to get it right.
Step 1: Turn the Volume and Squelch to Minimum
You start off my turning both the volume and squelch down to minimum. Always turn the volume down first because you will hear static when you turn the squelch down. If the volume is too high, you could damage your hearing or your speaker when lowering the squelch.
With the squelch right down, your radio speaker will emit every sound it receives. Unless there is a transmission in progress, this should just be any background static.
As your volume is right the way down, you shouldn’t hear anything just yet.
Step 2: Increase Volume
Now that your radio is playing all the static it is picking up, you want to increase the volume.
The static gives you enough sound to work with so that you set your volume correctly.
You want a level that is comfortable to listen to, if you imagine the static is replaced by a human voice. You’ll probably set the volume a little low at this point because constant static can be quite uncomfortable to listen to.
Step 3: Increase Squelch
Now that you have background static giving you an indication of your radio’s volume, you can increase the squelch. Turn it up until you reach a point where the static only just disappears.
At this point, the radio is rejecting signals that are below the strength of the background static. Theoretically, any voice broadcasts will be more powerful, so they will break through the squelch threshold.
Step 4: Final Volume Adjustment
As I mentioned in step 2, you may find the static was uncomfortable to listen to. The final step, therefore, is to increase the volume again.
You don’t want to go too loud, but you want to make sure you’ll be able to hear every transmission loud and clear.
Remember, you may have been adjusting your set with your ear close to the speaker. If you are on a sailing boat with the radio in the cabin, you still want to be able to hear it from the cockpit. Likewise, on a large ship, you want to hear the radio from across the wheelhouse.
How Does Squelch Work?
The squelch control is just a noise gate that acts to reject weak signals. You set a threshold, and signals below that threshold are suppressed.
With marine VHF, the idea is that it suppresses the background noise. Background noise is normally a relatively weak signal compared to another VHF transmission. The squelch control just tells the radio to remain muted until a signal of sufficient strength is received.
When a signal breaks the squelch threshold, the radio unmutes itself and plays everything it can hear.
The VHF then normalises the sound to make it a consistent volume. Assuming a transmission is significantly stronger than the level of background noise, you will only hear the transmission. If the signal is only marginally stronger than the background noise, normalising will amplify the noise as well as the transmission. The result is that the transmission sounds broken.
How Often Should You Adjust the Squelch?
You should always adjust the squelch regularly. It is a threshold setting that rejects background static, so you need to frequently check that it is correct. The level of background static is likely to change depending on any number of variables including:
- Time of day
- Work occurring on board
There could even have been a consistent, weak broadcast taking place when you first adjusted the squelch. That would result in your squelch threshold being set too high.
A good rule of thumb is to adjust it every time you turn the radio on, and at least once per watch thereafter. If you have any reason to suspect a transmission is not coming through, it is a good idea to check the squelch again too.
Does Squelch Affect Transmission?
No. Squelch only affects the signals that your VHF radio receives, not the transmissions that you send.
When you make a transmission, your radio broadcasts the same signal, regardless of your squelch setting.
The only way your squelch setting will appear to affect your transmission is if you do not receive a reply. When you don’t receive a reply that you expect, you should always check both your volume and your squelch. If your squelch is set wrong, you may be rejecting the reply.
Likewise, other vessels receiving your transmission may not have their squelch set correctly either. If their squelch threshold is set too high, they may not hear you. The only way to break through is to increase the power of your transmission. Normally that is not possible, but it is worth checking that you are not on the “low power” setting.
Squelch in an Emergency Situation
When you hear any emergency broadcast, or see any distress signal, you should turn your squelch right down immediately.
The idea of squelch is that it keeps your VHF muted until a signal of sufficient strength is detected. If you know there is an emergency in progress, you need to be able to hear every transmission.
A Mayday broadcast from a handheld VHF in a life raft could be a very weak signal. You don’t want your VHF rejecting it just because it is weak. You might see some flares and not realise someone is calling on VHF because your squelch is rejecting their call.
When you turn the squelch down, the only difference you will notice is that there is no silence on your radio. At the times when your radio should be silent, it will be playing background static instead.
When any signal comes over the top of that static, it will come through your speaker. As it is now sensitive enough to play static, it will also be sensitive enough to pick up the weakest broadcasts.
Does Automatic Squelch Work?
Automatic squelch control (ASC) works by continuously analysing the signal / noise ratio. As background noise is fairly consistent, it just sets the threshold according to that consistent level.
In my experience, automatic squelch does work quite well. Its biggest limitation is when there are very weak radio transmissions in the area. The threshold will be set according to the background noise, but a weak transmission could still exceed that threshold. Even if the transmission is so weak that it only sounds like noise, it will still be played.
I hear this quite a lot on my handheld VHF. Other people on handheld radios produce enough signal to exceed the ASC threshold, but not enough to hear their transmission clearly. The result is that my radio sometimes cuts in, just playing noise through the speaker.