Hello Mark:
I have purchased the SF100 and have not opened it to tryout
but I read your posting and was wondering if you could send me info on
how you modified it. If you can draw up a schemmatic and email or fax
me I would appreciate it. Also the cost of the modifications would be
helpful. Thanks.


Mark Malson wrote:
I'm glad you had good results with your SF120. I have an earlier
model,
the SF100 and though it has some more features, I had to modify it to

make the signal useful.

The SF100 plugs into the cigarette lighter and also has a switch and
a
power adapter so that you can supply power to a portable CD player
right
from the SF100. Pretty handy.

However, the SF100 is not a particularly stable transmitter. I am
constantly having to retune it and the signal is not very good. I
think
this is a design problem -- I had a knowledgeable guy look at it and
he
was just aghast at how unstable the thing must be. So we modified it
to
add an impedance matcher, an amplifier, and an external antenna. Now
it
sounds great and has a good range.

I also use the old Radio Shack Silent Play which has a pretty strong
signal and sounds OK right out of the box. Its only big limitation is
it
can only provide a signal between 88 and 92 MHz.

article , wrote:

SOUND FEEDER: Wireless CD Player Adapter SF120

This little FM transmitter costs about $20 and can be found
hanging
inconspicuously in the accessories rack in the radio-tv section of
Walmart. It is about 3 1/2" x 2 1/2" x 1" and was designed to let a
CD
or casette player be picked up on the FM band of a car radio thus
avoiding a lot of messy connections. It does well at this task with
good frequency response and stability powered by one AA cell.
However,
it can be modified to really put out to make it useful as a relay.
I
use mine hooked up to my base receiver. I can then listen to a
program
on a small portable radio as I work around the yard and garage.
The range can be greatly expanded by two simple mods:
(a) Increase the power supply to 3 volts. Long-term tests have
shown
no problem with heating or audio distortion. The audio starts to
clip
at 4 volts.
(b) replace the 3" stubby whip with a longer one from the Shack.
These mods will give about a 500' range. One can do wonders with
a
dipole FM antenna (Shack) if a larger coverage is needed for a farm
or
ranch but one doesn't want to attract attention by causing
interference
in an urban area or attracting a SWAT team. I wouldn't even think
of
adding an amplifier such as the ones found in the Ramsey FM-10
websites.


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Before you buy

--
-- Mark Malson