My transmitter works!

Thread Starter

powzoom

Joined Jan 18, 2009
41
Well I'm glad to say that I just built my first AM transmitter and it actually worked. If only for about 6 inches away... but it's not finished yet.

2 questions:

Does it make a difference if I use the tiny variable capacitors that you turn with a mini screw driver or if I used a larger one with plates that I see in all the transmitter pictures?

Also, where can I learn how to make a proper antenna? I've heard loop antennas are good but how do I go about making one and attaching it to my circuit?
 

KL7AJ

Joined Nov 4, 2008
2,229
Well I'm glad to say that I just built my first AM transmitter and it actually worked. If only for about 6 inches away... but it's not finished yet.

2 questions:

Does it make a difference if I use the tiny variable capacitors that you turn with a mini screw driver or if I used a larger one with plates that I see in all the transmitter pictures?

Also, where can I learn how to make a proper antenna? I've heard loop antennas are good but how do I go about making one and attaching it to my circuit?

For the minuscule power levels you're using, the "trimmer" capacitors are just fine. If you start getting up to the 100 Watt level, you'll want some "bread slicer" capacitors.

The antenna you'll need depends on the frequency you're using. Need a few more details to answer that one!

eric
 

Thread Starter

powzoom

Joined Jan 18, 2009
41
It's an AM transmitter from 500 - 1000 KHz or so.

Also, what factor determines the distance that the radio can be heard? Voltage, Current, or Power? My output right now is about 1Vpp. Current in nanoamps I think but don't have an accurate measurement for that. I'm running it off a 9V so I cant see the voltage going more than 3or4Vpp but I can probably up the current.
 

Audioguru

Joined Dec 20, 2007
11,249
The antenna on an AM radio station (1MHz) is about the size of a football stadium.
The antenna on an fM radio station (100mHz) is about the size of a refrigerator.

Your frequency is very low so the antenna must be very long for good efficiency.
 

Wendy

Joined Mar 24, 2008
22,239
In the USA there is a maximum length for unlicensed radios of 10 feet, no more.

Antenna efficiency is a function of wavelength, or transmitter frequency. A resonant antenna in the FM band is around 4-5 feet.
 

KL7AJ

Joined Nov 4, 2008
2,229
In the USA there is a maximum length for unlicensed radios of 10 feet, no more.

As well as a transmitter power of no more than 10 mW. At least under the old Part 15 rules. :)

In my innocent, yet mischievous childhood, my experimental activities in the above vein, but in ignorant violation of said restrictions, merited me a "visit" from our friendly local FCC field agent.

Nuff said.

eric
 

KL7AJ

Joined Nov 4, 2008
2,229
In the USA there is a maximum length for unlicensed radios of 10 feet, no more.

As well as a transmitter power of no more than 10 mW. At least under the old Part 15 rules. :)

In my innocent, yet mischievous childhood, my experimental activities in the above vein, but in ignorant violation of said restrictions, merited me a "visit" from our friendly local FCC field agent.

Nuff said.

eric

P.S. Don't tell anyone!
 

italo

Joined Nov 20, 2005
205
The lengt of the antenna for low frequency is LONG. However if you cut it to the right lenght you may get an additional benefit. Like all antenna at some lenght no matter at what power the the emission is zero just like 120 at some point the power is zero. keep that in mind when cutting the lenght.
 
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