surfernan
Member
If you turn the squelch up I wonder if it it affects the range of receiving DSC alerts .
Is channel 70 totally separate in this case?
Is channel 70 totally separate in this case?
Dsc and Squelch
- Thread starter surfernan
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Sandy
Well-known member
No.
Squelch is a filter to remove 'noise' (that horrid crackly sound) from the signal and does not affect the signal.
Squelch is a filter to remove 'noise' (that horrid crackly sound) from the signal and does not affect the signal.
Dellquay13
Well-known member
The squelch is a gate that opens when signals of a desired strength or above are received.
It is probably built into the vhf that it has no effect upon ch70, but if it does cut out any ch70 dsc data packets, it is likely that the originating ch70 dsc call is so weak and distant to be of no consequence to you anyway.
It is probably built into the vhf that it has no effect upon ch70, but if it does cut out any ch70 dsc data packets, it is likely that the originating ch70 dsc call is so weak and distant to be of no consequence to you anyway.
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Sandy
Well-known member
Just to add. Think of a CH 70 transmission as a text not a voice message. The range will always be greater.
lustyd
Well-known member
Range is actually identical (within the bounds of different frequencies doing slightly different things), that's just physics. What is different is reliability due to built in error checking (basically fancy checksums) which means that the full message can still be understood when broken because the missing parts can be reconstructed, unlike voice where you get what you get because there is no "spare" information.
Sandy
Well-known member
Burst transmissions always travel further. One explanation on why I can get a WhatsApp message 10nm offshore, but not a mobile signal. From your post you have an understanding of data transmission, entropy and error checking, thus will understand what can be 'unpacked' from 'noisy message' (one reason satellites can pick up an AIS packet from space).
A couple of examples, I do love examples, friends we coming back from Cuba at the start of COVID - Marine Traffic showed them 150 miles off Ushant for 15 mins on their return to the UK - perhaps an atmospheric fluke, but I can 'see' up to 50 miles on AIS and have sat in the semaphore station on the Ile de Batz and heard Falmouth CG as well as I can hear them in Falmouth! OK, I know that they had military grade kit, but it shows what is possible.
lustyd
Well-known member
That WhatsApp message appears in the brief time you're connected, it's not because it travels further somehow. The actual signal travels the same distance but you're right that short transmissions may have a better chance of not getting interference. Satelites get AIS because they have line of sight, VHF frequencies will travel infinite distance if not interfered with or obstructed, and in certain circumstances can be bent or reflected to travel further than expected. In the case of AIS to space, it'll be hit and miss because the time multiplexing is designed for surface use and cannot cope with enough targets to allow them all to get through.