Legalities of broadcasting in the AM range

mikeyb

Hi,

I want to buy a kit which will broadcast an AM signal. I want to be able to broadcast my iPod/iPhone podcasts to an old Pye radio I have. Something like this:

http://www.amazon.com/electronics/dp/B0002NRJCM

The spec. says:
100 mW output. Range up to 1/4 mile under optimum conditions. I only need to broadcast a couple of feet to be honest and I'm wondering if it would be in fact illegal to broadcast with this? I'm presuming yes is the answer. If this is the case, is there any way I could drop the power down with this circuit to keep within the law (I don't have an amateur licence either by the way)

cheers,
Mike

watty

It's illegal ANYWHERE in EU.

It's also pretty poor as are most Ramsey designs. many Ramsey products are not even legal in US.

There are designs which count as Test equipment and have radiation less than the CE EMC limits and certainly less than many SMPSUs.

Why don't you use PU/Gram input?

It's possible to adapt a €5 AM transistor radio. If you tune LW set (or a MW set lower than 1100kHz) you can pick it up on your Pye radio a metre away easily. L.O. = RF + 455KHz.

martinsvi

mikeyb, do you know the size of antenna they recommend to use for this kit? Are you happy to build an 8 foot loaded whip antenna just to get your ipod on air? If all you want is to get your old radio playing music, I would try to make an AUX input for the Ipod.

Fuzzy Clam

mikeyb wrote: »

Hi,

I want to buy a kit which will broadcast an AM signal. I want to be able to broadcast my iPod/iPhone podcasts to an old Pye radio I have. Something like this:

http://www.amazon.com/electronics/dp/B0002NRJCM

The spec. says:
100 mW output. Range up to 1/4 mile under optimum conditions. I only need to broadcast a couple of feet to be honest and I'm wondering if it would be in fact illegal to broadcast with this? I'm presuming yes is the answer. If this is the case, is there any way I could drop the power down with this circuit to keep within the law (I don't have an amateur licence either by the way)

cheers,
Mike

That Ramsey kit is ok. If you want to just transmit a few feet don't use an antenna or use only a couple of feet of wire.
As regards the law, it's up to you, nobody here has the authority to tell you what you can or cannot do. However, you will not get raided for using it.

watty

Until someone complains.

If someone ask is a transmitter legal they are entitled to an answer. Also see charter. Please don't mislead people into deliberately breaking the law.

The Ramsey stuff is over priced poor designs too, though it works for a given definition of works.

mikeyb

Thanks a million for all those detailed replies! Re the aux socket. I know I can do that but I have a passing interest in electronics so that's why I wanted to broadcast. Also, I thought it would be nice to use the radio as it was intended - as a receiver. To be honest, if I could get myself a 1.000 mhz crystal anywhere I'd prefer to try and build a small transmitter from a circuit diagram online, but it's going to cost me the same to buy a crystal as it would a kit by the time P&P are taken care of.

The idea of the short antenna is a good one. I only need to place the iPod at the radio, I'm not looking to broadcast all over my house or anything and maybe just a small wire placed near the unit would work and not cause any interference to neighbours' radios. "Until someone complains" - I'd hate to mess someone's day up anyway so I'd be careful about that,

thanks for all the good info,

Mike

mikeyb

It's illegal ANYWHERE in EU.

by the way Watty, is that true even if you are only transmitting literally a few centimetres? Is there a wattage or distance limit or something?

watty

The loophole is interference levels.

You aren't allowed a transmitter on AM without a Broadcast Licence. But Electronic equipment can legally create "interference" if it is below CE limits for the type of equipment. Also no law against making (or buying) your own test gear including a signal generator to align an AM Radio. The usual "coupling" method is a loop (about 20 turns on 30cm diameter or 30cm square non-metal former) placed near the radio. About 30cm to 60cm distance (too close and it detunes the Radio built in ferrite rod or frame aerial). If the radio only uses an external aerial then about 2m wire is attached and the far end wound about the test generator loop twice.

Such an arrangement is below EMC limits. The power is about 1000 times less than the Ramsey with no aerial or about 500,000 times less than the Ramsey kit with a 3m to 4m aerial wire.

The Ramsey is too powerful even without an aerial.

A 30cm loop will "magnetically" couple a few feet / 1m easily to a frame aerial or ferritte rod. If the radio is the kind with no internal aerial (Many before 1955), then the power needed is even lower. The Aerial and Earth of radio can connect to a "dummy" aerial which is isolated and connects via BNC direct to a signal generator about 20dB lower power even than the loop.

The Ramsey kit is for illegally broadcasting to the entire neighbourhood.

An SAA612 is a cheap 8 pin DIL IC using 2.5mA off 4.5V to 8V, so can run off 5 x AA Alkaline cells for over 1000 hours. It's a combined Balanced Mixer and Oscillator.

It needs hardly any parts. By default it's got a built in oscillator (add aerial coil and capacitor from any cheap AM radio, or a resonator between 560kHz and 1500kHz. Unbalance the Mixer's balanced input on either pin with a 22k to 100K resistor (or a preset 47K in series with 27K) to 0V and carrier is inserted. Input impedance is under 1.5k so input can be a pair of 220 Ohm to 1K presets or stereo log pot 220 Ohm to 1K driving one IC input via 2 x 1k Resistors to sum stereo and a 10uF tantalum capacitor in series to pin (+ to pin). The other input pin gets decoupled to 0V with a 10uF tantalum capacitor (+ to pin), which has the carrier level adjust preset on it.
The two output pins drive the loop which is tuned by 10pF to 470pF capacitor depending on frequency and loop inductance. If you want to use an AM radio dual gang capacitor, then you only use one o/p pin. If you use an FM/AM type you can use Loop to both O/P pins and connect the two AM sections to the two pins and common to ground, then parallel the VHF sections and use a higher value inductor and tune the loop and oscilator together.

Get parts from a €10 radio and buy the SAA612 under €2. But if you are expert you can replace the MW aerial coil on even a €5 AM radio with Audio in and put the AM aerial ferrite rod instead of first IFT, pad the oscillator/ increase OSC inductor and it will tune 600kHz to 1.4MHz, no other parts needed. Range a couple of feet. If the cheap Radio has LW, then its LO is 605kHz to 755 kHz automatically and the audio connects in instead of LW aerial coil. The LW RF padding capacitor is removed or reduced and MW coil + RF tuning replaces 1st IF.

The Modified AM radio trick likely can only manage 40% modulation. The SAA612 can do 100% as it's a separate osc and doubly balanced mixer.

Capt'n Midnight

You could modify the radio by having another receiver connected to the volume control of the PYE radio. (assuming that they only have 1V or so there)