Re: fm transmitters

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"Curtis Johnstone" <curtisj@magma.ca> writes:

> I dealt with the same issue about 1 year ago (PC upstairs and stereo
> downstairs). I initially was going to build my own solution but ran across a
> "MP3 Anywhere" product by X10.com [1]. It basically has an FM transmitter
> that hooks to your PC and transmits to a FM receiver that hooks into your
> stereo with RCA jacks. It also comes with a remote control that, with the
> appropriate software (a.k.a. BOOM -- free download from X10), allows you to
> remotely control your MP3 jukebox software from anywhere in your house. The
> whole package retails for $79.00 US.

I saw a similiar fm transmitter and custom fm receiver device pair,
which suggested to me a regular fm receiver couldn't pick up the
signal?  Biggest drawback would be only 1 to 1 capability.  

[]

>> I'll give a review of this device after it arrives

So my fm transmitter circuit arrived this weekend.  I was away so I
had to go to the Post Office to pick it up as it was sent registered
mail.  Actually this was advantageous as the PO it was at was near my
favorite, although overpriced, electronics store.  They're 10x better
than Radio Shack and I like giving them the business.  The Radio Shack
slogan "you've got questions, we've got answers" is entirely false as
most RS employees have been clueless to most questions I've ever
asked.  This other shop painfully reminds me of my ignorance from
not going through with a major in engineering.

It had a regular 9v battery connector attached to it and I replaced
that with the jack type for ac/dc power converters and added a little
power switch.  This device is suppose to take registered (non-varying)
12-16vdc power.  I grabbed a 12vdc power converter at this shop
although I likely have several here from regular consumer devices.

So far I'm impressed with the signal and sound quality.  They have
~70cm of regular insulated wire as the antennea and I may replace that
after a little research on antennea designs.  I may also exchange the
ac/dc converter I bought for a 16vdc one to further boost the signal.

Besides the frequency there are some jumpers for Pre-Emph (whatever TF
that means) measured in uS (u==micro symbol that resembles u) which
they recommend setting for 75uS in the United States, 50uS anywhere
else in the world (FCC regulation??).  That requires a little bit of
investigation and expirementation.  There are also audio level
correctors for both left and right channels so I can boost and balance
the signal slightly that way.  I started off in the middle range as
they suggested and do most audio signal boost setting on the computer
with linux's aumix and volume control in my mp3 player [5].

I decided to still have the sound card connected to the upstairs
stereo receiver inputs and the transmitter to some output jacks and I
can choose what sound source (another radio station, cd, mp3) to
transmit.  

Making an enclosure should be easy, especially if I forget about
trying to add dials to the little controls since I shouldn't need to
mess with the settings.  The on-board dials are tiny and hard to fine
tune.  I did crude tuning into uncrowded frequency space on the
transmitter while the receiver was on so I could hear when I got close
and fine tuned on the receiver.

I had downstairs stereo, boom-box on the back porch, clock radio and
car stereo all tuned to my mp3's.  I was able to drive a several blocks
away before losing the signal to static and signal from another
station on a nearby frequency.

> 3. http://www.veronica.co.uk/lpskit.htm
5. http://www.gentei.org/~yuuji/software/mpg123el/

--
Ted Guild <ted@guilds.net>
http://www.guilds.net

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