Re: Digital FM transmitter

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I recall a design in the 70s that used a quad NAND gate. Even that's not
minimum, but you seem to want to use digital and "no RF components". What do
hope to gain with a DSP?

Bob



Re: Digital FM transmitter
Connect Microchips PIC10F200 to the control pin of a Fox RFV250.Just two
small parts (but might not constitute "all digital").

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId13%35&dDocName=en019863

http://www.foxonline.com/rfxoseries2.htm

Thomas

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Re: Digital FM transmitter
And then? It can not be possible to do all thats needed in this  part?

It has at least 16 ADC's that can sample at good freq to do good FM?

FM as in 106.7Mhz?

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Re: Digital FM transmitter
My point was that the original poster did not specify what kind of FM
transmitter was being mimicked.  Frequency modulation, in it's simplest
form, only requires an interface to the control voltage of a VCXO at the
appropriate frequency.

P.S. FM doesn't only exist at 88-108 MHz.

Thomas

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Re: Digital FM transmitter
Sorry, 88-108Mhz FM :-)

I thought it would give you better THD, SNR, stereo seperation

Thanks.

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Re: Digital FM transmitter

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Analog Devices has an app. note with a basic DSP dev. kit and one of their
DDS chips. They use a mirror/harmonic of the DDS signal to get to the 3m
band. May need some filtering to comply with FCC rules.

Wim



Re: Digital FM transmitter
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As the frequency setpoint is stepped at the audio
sampling rate (48 kHz or 44.1 kHz in the AN-543),
there will be extra sidebands at the sample rate
and its multiples. This is because there is no
audio signal reconstruction filter before the
modulation (and in this application there's no
way to include it). The only way out from this
problem is to change the frequency setpoint at
each RF sampling cycle which would need a
200 MHz+ audio sample rate.

The signal is crisp and clean on a FM receiver
on channel, but there is plenty of crud outside
the allowed bandwidth.

The trick used by the AD app note is to use
the aliased frequency (125 MHz clock - set
frequency) as the payload output.

The app not device is OK for a directly connected
FM receiver, but not suited to be connected to
an antenna.

--

Tauno Voipio
tauno voipio (at) iki fi


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