Whatever happened to VHF?

[Piers]

Re: Propogation modes in VHF

As you said in one of your posts, it's a really interesting subject.

Piers du Pré
MBM Cruising Club enthusiast
www.dupre.co.uk/fsPlaydeau.htm

 

[Twister_Ken]

Re: Propogation modes in VHF

Pleased to hear about Shetland/Ostend - means I can save money by not buying SSB!

 

[ParaHandy]

Re: Propogation modes in VHF

That being so (and many thanks) a HF ground wave, eg between 3.0 and 30 mhz, will follow the curvature of the earth *because* the wave is slowed by contact with earth's surface which causes the wave to swing into and follow the surface? The signal close to the surface is degraded by frictional losses which is why so much power needs to be radiated for a ground wave to be heard?

Presume that if you wanted a HF signal to be received with minimum attenuation over a very wide area (>500nm), you would try to transmit at sufficient power so that the point where the ground wave signal strength diminishes is where the first hop/skip/jump bounces down from the atmosphere. Got a feeling that might be very difficult to achieve unless the transmitter deliberately radiates power at low angles to the horizon (to get ground wave) and high angles to get as short a distance as possible between the transmitter and a hop.

 

[Bergman]

Re: Propogation modes in VHF

I can't beat it personally but a friend of mine has regularly worked trans continental distances on VHF by bouncing signals off the moon.

Just to add a little to the debate ionospheric reflection can occur at frequencies well above 30 megacycles (I'm that vintage too) peope regularly work long distance ( 1 - 3000 miles) on 50 Mc/s - given the right conditions.

Just to show my true vintage I remember VHF television, 405 line, used to occasionally transmit warnings of poor reception due to atmospheric conditions. Usually in summer during hot weather with high pressure predominant. Good ducting weather perhaps.

 

[Twister_Ken]

And Navtex too

Despite having some difficulties getting Navtex from Niton when in Hamble, in the early hours of Sunday morning we were receiving extremely readable Navtex messages from all over, including reports of ice around Greenland, and F7 in the Adriatic and Ionian.

 

[Bergman]

Re: And Navtex too

You clearly have a gift for this sort of thing, perhaps you should take up ham radio.

This would'nt be ducting like VHF just atmospheric conditions giving you some sky wave reception where signals are reflected from ionosphere.

Radio conditions have been very odd of late, funny sun spots or something.