[sdiy] voltage-controlled AM radio tuning

[cs e]

Cool idea! We were just discussing this sort of thing in class today.
We're designing/building an FM transmitter and receiver (centered at
100MHz, etc).

Anyways, we've been looking at the VCO section of the transmitter -
and we're going to use a varactor for tuning.  (A simple pot/voltage
divider going to the varactor.)
The varactor I looked at had about a 15-45 pF range, using our voltage
levels.  Like Mr. Perry said, you can get a greater capacitance range
with larger voltages, depending on the varactor.

So, determine what range of capacitance you need (or will work) and
start looking around.  Maybe you'll find something?

On 3/13/09, rdrake <rdrake at data2action.com> wrote:
> i've done it w/ FM... found a kit w/ variactor tuning and just jammed in a
> CV.  as cheater sed, CAF.
>
> bbob
>
>>----- ------- Original Message ------- -----
>>From: cheater00 at gmail.com
>>To: synth-diy at dropmix.xs4all.nl
>>Sent: Fri, 13 Mar 2009 15:11:09
>>
>>The idea sounds cool as fuck though.
>>tuning into and out of a radio station in sync with
>>tempo? hell yeah
>>or better yet, 'choppers', 'blippers' and utility
>>bands!
>>
>>On Fri, Mar 13, 2009 at 9:46 AM, Paul Perry
>><pfperry at melbpc.org.au> wrote:
>>> The cap ratio has to vary as the square of the
>>frequency range ratio, so
>>> that means a ratio of about 10 to 1.
>>> You might find that to get a range like this, the
>>max applied voltage will
>>> bewell over 10 volts.
>>>
>>> What is worse, is that you will need to have at
>>least two tracking systems -
>>> the RF preamp and the local oscillator.
>>>
>>> paul perry Melbourne Australia
>>> _______________________________________________
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