Radio recption prediction maps ???

[Mr Red]

Hi
I work at a community radio station www.stroudfm.co.uk

And they are considering moving the aerial.

The coverage map they have was totally unscientific and I would like to advise them on their chosen potential sites.

I have been driving around listening and got an idea of present limitations for some routes but I can only do this for the present location.

Community stations are limited to 12 watts ERP anyway and Stroud is characterised by 5 valleys

So - any ideas other than Google maps per se (no use AFAIK)

TIA

[Progenitor A]

Radio propagation characteristics are notoriously difficult to predict with any real accuracy. A 3dB error margin is good - that is an error margin of 50-100%.
I assume you are using a half-wave dipole - although you could be using others that limit the wasteful transmision of energy into the sky.

I also assume that you are transmitting in the range 80-110 MHz FM band.

The way this is done prfessionally is on a computer that scans the topography on a line of sight of maps over the countryside on a 360 degree arc. You will not have access to such maps and software, but you should seek the highest point in the area available to mount your aerial.
If you send me the data such as frequency, antenna type, ERP and minimum received power for satisfactory reception then I can calculate your theoretical radius of communication. That can be refined using an OS map of your area and drawing contours of the topography then applying in corrections to the basic equations.

It basically amounts to this - is there a line of sight between your antenna and the furthest point you wish to have solid reception? Lack of los does not mean that reception is impossible - just difficult - knife edge diffraction and refraction can enable reception in the most unlikely areas.

You also have to consider possible interfering stations so if you could also send me the transmission plan for your area that would be useful.

[carnyx]

A very rough idea of line-of-sight coverage could be obtained by using 'google earth'.

.. if you can get it to work ..

[Mr Red]

Yea 'praps I should have said I am an Electronic Engineer of many years standing and studied radio comms at Uni.

It is the Google Earth wotsit I found not as good as I remember it. Perhaps I needed to install the s/w on someone elses machine to even begin to see the tilt and topography.
Line of sight it may be (but it will bend a bit even at 107.9 MHz), but I have driven along roads that are definitely not on an eyeball profile, and Haresfield Beacon is definitely in the way. "Beacon" being a bit of a cluette.
One thing I can't get them to understand is the stereo burden, not just effective power but the stereo switch in the reciever - even if listeners could choose mono with their set, would they know how?
Maybe my dots on the map will suffice for the present location.
I just wondered if there was a website (free) that might help. And someone might know.

Now - anyone remind me of the Austen-Cohen formula? I long since forgot.

[Progenitor A]

Haven't used Austen-Cohen equations and haven't heard of them

I have used Plane Earth Model, Hata's path loss model, Parson's semi Empirical model, Walfish _Ikegama (limited to 5km radius), Rappaport Mohammed and Kapoor exponent values.

Unless you have an accurate dB of map profiles on a computer then you have no real option but OS to derive path profiles

If you know anyone in the GSM network field (3G will not do!) from Vodafone, Orange, Telekom etc, they could probably get someone in their radio planning department to run your parameters and OS co-ordinates through their radio path planning programme. They have a number of Path Loss models on board. It would take them half an hour or so and you'd get a pictorial printout - these machines are quite magical.

[Mr Red]

Austen - Cohen
most useful at sea.
Line of site includes 1/(r^2) for the near (transformer) field and 1/r for the radio field.
We have a radio controlled clock and PC receiver for same that suffer from being within 20 wavelengths of the transmitter. ie the 1/(r^2) field. Daylight hours are worse, but that may just be all the other electrical equipment being switched on in the shops area we inhabit.
Re-siting of the Tx has gone quiet just now.