R/T Transmissions
 

A few years ago I read Andrew Greig's novel "That Summer" about the Battle of Britain. A good read but something also intrigued me and I thought that I might ask here as someone may know.

In the book's introduction he mentions that some R/T transmissions from the Battle have become trapped between the ground and the Heaviside layer and they bounce back and forth endlessly because they don't decay. He further states that once in awhile a radio ham skimming the radio waves will suddenly stumble across these signals, hearing the Battle of Britain with controllers instructing and pilots communicating, shouting and cursing.

Ever since reading this I have been intrigued and wondered whether this is indeed true. So does anybody here know more about this phenomenon?

Cheers,

Tim.

Re: R/T Transmissions
 

Hi Tim,

HF transmissions skip off layers in the atmosphere (D and E - if I remember correctly) and so can bounce between these layers and the earth and cover great distances. HF communication can be a bit hit and miss as the propogation properties of the layers vary depending on the time of day. Nowadays an equipment called a Chirp Sounder can ascertain the best HF frequency to use.

VLF transmissions use the "ground wave" effect and can cover even greater distances. With ground wave transmissions the signal actually hugs the ground. The Omega navigation system uses VLF to receive signals from the eight Omega "beacons" around the world (of which it needs at least three to get an accurate position).

VHF (and above) transmissions are line of sight so are affected by the curvature of the earth, range being dependant on height and power.

All RF transmissions will eventually decay.

It's been a long time since I did comms theory so I might not be 100% correct but I think the basics are more or less correct.

Best Regards

Andy Fletcher

Re: R/T Transmissions
 

Tim,

Ducting can also cause the waves to bounce between layers making them travel a long way without losing much energy which they would if travelling by bouncing between layers and ground. Nevertheless the energy fades out in the end becoming more and more diffused with every bounce

K

Re: R/T Transmissions
 

Thanks guys! So Mr. Greig might have been painting it up a bit then!

And Kyrre, it's a bit strange seeing Sola in your signature now, long way from the North!

Tim.