Exceptional VHF reception this weekend

[Roberto]

Old thread but same phenomenon as of yesterday, AIS targets received from near Lorient


OpenCpn shows 530 targets, several with ranges in excess of 150nm. There is no signal from Class A transmitters all along the traffic lane Ushant/Finisterre (which runs 80-150 miles from there), the inversion was probably located only along the coastal area.

 

[Bilgediver]

AIS runs on VHF frequencies so when VHF R/T is being ducted over a long distance AIS will be similarly affected.

AIS is similar to Ham APRS. During lockdown I was playing around with APRS and received several mobile stations (cars) driving in the Stavanger area. These were directly received and not via relay stations. I also received the International Soace Station on several occasions.

It is not unusual to be able to contact stations on the other side of the North Sea at this time of the year using ham VHF which is close to the marine VHF band.

I am on high ground south of Edinburgh which helps.

 

[Daydream believer]

..

 

[Mark-1]

I didn't realize, but it's actually forecast!

https://www.dxinfocentre.com/tropo.html

 

[st599]

Atmospheric temperature inversion creates a layer that VHF/UHF can travel long distances. Radio Amateurs use this to make contacts.
Back in the analogue days the TV made announcements about disruption to TV reception.

Not just temperature inversion, the amount of ionisation also helps. It's also a problem for Digital TV, but it doesn't appear as on screen noise like it did with PAL

It can also cause issues for RADAR, you end up receiving from the previous pulses, but the receiver can't discern this so displays the far targets too close.

I didn't realize, but it's actually forecast!

https://www.dxinfocentre.com/tropo.html

Yep, it's useful for planning point to point links and knowing when people are going to complain about bad reception.