An introduction to low power FM transmission (or pirate radio basics...) part 2

What equipment do I need?

The portable set up:

This is a quick review on what you need. Make sure to browse the internet for further detailed information.

Tape player

We advice you to go for a reliable professional cassette player
with a good rca or xlr output.

like the Sony tcd5 pro2

A Sony Pressman may do the trick as well.

"Townies iPod and MP3 players won't give you any satisfaction!"

Preamp

Assume every portable transmitter you can find is not intended to compete with professional broadcasters, a preamplifier will be handy to strengthen your signal. We are using a Nagra IV.2 for this. The main inconvenient is its weight. Walking in fields to the broadcasting location or climbing up stairs with the bastard on your back will make you consider getting its hard to find but well efficient pocket-sized little sister: the Nagra SN.

the Nagra SN:

You may also skip the Nagras and go for a home made portable console.

Here is a starting point then:
These people know the ropes on Telefunken, Siemens, EMT, Neve equipment.

http://www.danalexanderaudio.com/
http://www.marquetteaudiolabs.com/

Transmitter

This is the core of your system. May we suggest you to make a search on the interweb for "portable fm transmitter"?

We don't want to put you on the screw too much ladies but don't make us plough the sands. Does it mean anything??? ... Hahaha (from a book of English idioms)

Look for something you like with similar specifications to a Bext P10.

Bandpass filter

This is all about harmonics (multiples of your tranmissions frequency).

Let's say you're broadcasting on nine-o-nine Mhz, your aerial will send harmonics of this frequency as well. In that case 181.8, 363.6, 727.2, etc… Mhz, which are not inside the 87-108 fm band anymore.

You'll be a pain in the neck for emergency services (police, ambulances, firemen) without even noticing it… which means they'll put the DTI on your case without any delay. You may loose half a dB using it, although the loss of that dB might save somebodies life!
or help somebody get away :)

Power supply

Your power requirements will depend on your rig. 12v is the normal requirement, so a car battery is suitable (without the car running! or use a regulation circuit). Car emergancy starters are good (dont be tempted by the crap strobes on it though). Deep discharge battery will last longer and give better performance, electric wheelchairs use these, so they are easy pickings!:)

The more you spend, the more power you get, also it's easier to carry.
cheaper > more expensive: lead acid, Gel Lead acid, NiCads, Lithium Based batteries.
The more efficient (and expensive) the battery technology is, can also mean it's more difficult (expensive) to charge safely.

If you are going to be located in one place for some time, you may be able to use the forces of nature to keep you powered up i.e., solar or wind can trickle charge your batteries in time for your broadcasts.

Here's some links:

http://electronics.howstuffworks.com/battery.htm
http://www.vonwentzel.net/Battery/00.Glossary/
http://www.batteryweb.com/
http://www.exideworld.com/
http://www.mdsbattery.co.uk/defaultuk.asp
http://www.homepower.com/
http://www.americansolarchallenge.org/event/asc2005/
http://www.rain.org/~philfear/how2solar.html
http://home.earthlink.net/~fradella/green.htm

Mast

Unless you can find a location atop of a high building, a mast is a must!
Go for an air-operated 10 to 12 meters high mast which is the best value for weight, strenghtness and minimum retracted height.

http://www.alphalink.com.au/~gfs/Clark/clarkp30.htm

You can also go DIY with aluminum tubes and guy wires.

Antenna

The other key part of your radio station. It is similar to a loud speaker in a stereo system.
Again, we advice you to have a deep look on the internet on different models and manufacturers.
http://www.ac6v.com/antprojects.htm

Cable

It brings the signal from your transmitter to the aerial. Keep it as short as possible.
Any unnecessary meter will weaken your signal and then the signal/noise ratio.
To get it, have a quick look at some electricity basics here.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmlaw.html

Quality RG213 cable is a good choice.

Other

Don't go out for a broadcast without appropriate clothing! It's too late to think about your missing top when you're on air. Double check batteries and that you take any tools you need for mast erection, rope, gloves and flashlight. A sweety may be welcome and a glass of Merlot as well! You may be in a rude environment; it doesn't mean you have to get rid of pleasures of life.