FM Radio Transmission Distances?

Question

I have two simple questions - But I fear there isn't two simple answers.

1) I would like to start a small, non-commercial, home transmitted FM Radio Station - mostly for fun and as a hobby. I have seen an 18W transmitter for a reasonable price. I live on relatively flat land in the country side with no buildings around.

What is the best case scenario for distance the 18W transmitter will transmit?

2) What is legal in Queensland Australia? Is an 18W home non-commercial transmitter legal? Or am I going to have to go find some licensing and pay huge dollars to DJ live on air to a small crowd?

Thanks in advance if you have the answers. I am looking forward to knowing more!

Cheers

Slim

Answer 1

Using an antenna on top of your roof, you'll cover line of site and a bit more perhaps.  If there really are no obstructions (including trees) and it's flat you could get 10km+ easy.  The higher and better the antenna is really makes the difference here.  This is just an estimate and varies largely upon local conditions.

As for legal implications, 18 watts is illegal without a licence.  In Australia, there's something called LPON -- Low Power Open Narrowcasting.  This is a licence offered by the ACMA which is relatively inexpensive.  There are two different power limitations depending on where you live.  If you live inside or within 20km of an urban area, you're limited to about 1 watt.  If you're in a rural area, you can run about 10 watts.  I say "about" because the rules don't state figures in watts, but in field strength.  A typical omni antenna with gain and coax losses figured in would yield transmitter output limitations at approximately 1w and 10w.  It costs $300 to apply.  There are 3 frequencies available.  If no one else is using them nor has applied to use them in your area, then you will pay the base price of either $250, $1000 or $2000 dependent upon whether you live in a low, medium or high density area respectively.  If there are others who have applied for this licence in your area, then whoever pays the most money gets the licence (turns into an auction).  There is also an annual "tax" which must be paid.  

The limitations for unlicenced transmissions (LIPD class) in the FM broadcast band are 10 µW (yes, that's .00001 watts!).  You'll go a couple of city blocks in the open with that.