Propogation Question?

25th May 2008, 06:38
I was sitting in front of a VHF DSC system in the early hours of this morning and a certain received call has made me ponder. I offer this up for any inputs.

We received a VHF DSC call from a vessel at around 0120 GMT and acknowledged it as normal. Around 26 minutes later, our VHF DSC received a transmission which appeared to have been sent by ourselves (our MMSI number was listed at the "from" MMSI). It was received via a site on the North of Scotland coast, and was weak (QSA1) but without any errors.

We had definitely not sent it, and had sent to other signals since the acknowledgement transmission.

As I understand things, a ship cannot change it's DSC system's MMSI number without the use of a shore maintenance base.

High pressure centred over the Faeroes, with Norwegian and Faeroese shore VHF stations clearly received via ducting.

Our equipment has the capability of reacting to our own MMSI in VHF DSC calls sent by our own sites, for test purposes.

Receive aerials - vertically-polarised non-directional folded dipoles.

I stress that we had not made a call at the time of reception.

Any thoughts?