Minion

Making an RF sine wave

9 posts in this topic

Anyone know a kit or bit of circuitry that could make a ~125khz sine wave and transmit it?

The circuit you posted is basically just a filter, removing the higher order harmonics of the square wave to produce a sine wave.

JimmyRidge's link gives the basic L-C concept.

What are you intending to do with the 125KHz? What accuracy do you need?

Munge.

0

Share this post


Link to post
Share on other sites
Anyone know a kit or bit of circuitry that could make a ~125khz sine wave and transmit it?

The circuit you posted is basically just a filter, removing the higher order harmonics of the square wave to produce a sine wave.

JimmyRidge's link gives the basic L-C concept.

What are you intending to do with the 125KHz? What accuracy do you need?

Munge.

I was intending to make an RF card reader/cloner.

0

Share this post


Link to post
Share on other sites
I was intending to make an RF card reader/cloner.

Check out the RF Guardian project:

http://www.rfidguardian.org/prototype.html

I've not played in the RFID sphere yet, but I assume that they are quite tolerant frequency variation.

I believe that the basic concept is that a burst of RF both powers and synchronises the tag, you may be able to work with something as simple as a square wave with some minimal filtering. Maybe start with a PIC or even a PC driving a serial RTS signal/parallel port.

A simple amplifier and tuned antenna should be enough to get some RF emissions.

Munge.

0

Share this post


Link to post
Share on other sites

been awhile since my last post on this thread thought i'd share something that is helping me understand fully, and not just be able to copy a schematic and create a circuit, i've had my ham license for a few weeks now and i have got to say the best source for circuit explanation and designs would be in the ARRL handbook for radio amateurs.

i just went to the library today got myself a shiny new library card/account walked out with ARRL 2005 handbook, Unix in a nutshell, beginning C programming FREE lol libraries are teh shiz! its probably been more then 5 yrs since i checked a book out and i end up walking out with the biggest fricken books they have lol phonebook size

but back to the ARRL handbook go to the lib or just pay 50$ for the most recent 2008 i find it especially enlightening on componets essential to circuit design; inductors, capacitors, resistors, diods, rectifiers, relays, oscilators you name it, pluss they have some nice example schematic

and if memory serves me right you are planning on interfereing with aircraft communications which is a big no no , go get your ham license and play within the sandbox given to us there are still pirate radio shortwave transmissions you couldplay with i feel so retarded not realizing the freq in question here

0

Share this post


Link to post
Share on other sites
been awhile since my last post on this thread thought i'd share something that is helping me understand fully, and not just be able to copy a schematic and create a circuit, i've had my ham license for a few weeks now and i have got to say the best source for circuit explanation and designs would be in the ARRL handbook for radio amateurs.

i just went to the library today got myself a shiny new library card/account walked out with ARRL 2005 handbook, Unix in a nutshell, beginning C programming FREE lol libraries are teh shiz! its probably been more then 5 yrs since i checked a book out and i end up walking out with the biggest fricken books they have lol phonebook size

but back to the ARRL handbook go to the lib or just pay 50$ for the most recent 2008 i find it especially enlightening on componets essential to circuit design; inductors, capacitors, resistors, diods, rectifiers, relays, oscilators you name it, pluss they have some nice example schematic

and if memory serves me right you are planning on interfereing with aircraft communications which is a big no no , go get your ham license and play within the sandbox given to us there are still pirate radio shortwave transmissions you couldplay with i feel so retarded not realizing the freq in question here

A 125kHz sine wave, without the megawatt transmitting power capable of interfering with aircraft, is a frequency needed to activate most RF proximity card circuits, thereby allowing one to record the AM band code response.

0

Share this post


Link to post
Share on other sites

It really depends on what components you have direct access too.

The Collpits oscillator requires only a transistor, resistances, capacitances, and a single inductor. The low part requirement makes it a favorite over other oscillator types. The disadvantage is inductors are hard to find unless you order online. Also, you'd probably have to use a special toridal inductor to keep your RFID transmitting coil from interfering with it.

You can also get a sine wave out of a square wave by feeding it through a lowpass filter. Sometimes, even a single RC lowpass filter will block the upper frequencies enough for RFID use. By putting 2 filters back-to-back, you'll get closer to a pure sinusoid. Personally, I'd go with this method because it works well microcontrollers and other digital devices.

0

Share this post


Link to post
Share on other sites
It really depends on what components you have direct access too.

The Collpits oscillator requires only a transistor, resistances, capacitances, and a single inductor. The low part requirement makes it a favorite over other oscillator types. The disadvantage is inductors are hard to find unless you order online. Also, you'd probably have to use a special toridal inductor to keep your RFID transmitting coil from interfering with it.

You can also get a sine wave out of a square wave by feeding it through a lowpass filter. Sometimes, even a single RC lowpass filter will block the upper frequencies enough for RFID use. By putting 2 filters back-to-back, you'll get closer to a pure sinusoid. Personally, I'd go with this method because it works well microcontrollers and other digital devices.

Ya could wind your own if you really really wanted too... http://www.arrl.org/tis/info/pdf/9708033.pdf

0

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now