Multiple FM frequency transmitter

Sun Aug 09, 2009 11:19 pm   

I am looking for investigating if it is possible to buy a multi
frequency FM transmitter. I want to broadcast a FM signal out on the
whole range of 87.5-108 MHz. i want the output to be limited to about
a couple of hundred meters of diameter, does anyone have a clue if
that is possible ?

Ive read about some PCI cards you can buy for your PC which should
have a really powerfull output (i think about 15 kW) does anyone know
if there are some cards which can broadcast on multiple frequencys'

Thx Nichlas

Mon Aug 10, 2009 7:17 am   

"Hans jkfa" <lortefirewallregler_at_gmail.com> wrote in message
news:31c4ee77-1c62-40d3-88e9-2b77d40e80f8_at_d34g2000vbm.googlegroups.com...

OFDM

Try picoChip (Bath, UK) for suitable processors to perform the IFFT


Near-field antenna


Trying to take 3000A from your PC PSU will melt it long before it gets to
your target output.

Mon Aug 10, 2009 1:58 pm   

Hans jkfa wrote:

Do you mean any frequency at a time, or ALL the standard frequencies
simultaneously. Ramsey Electronics has a couple of kits that do the
first. I don't even WANT to help you do the second

Mon Aug 10, 2009 3:49 pm   

"Computer Man" <invalid_at_invalid.invalid> wrote in message
news:h5ohin$l7m$1_at_news.albasani.net...


Ramsey Electronics has a line of AM and FM transmitters at
http://www.ramseyelectronics.com/hk/default.asp?page=amfm. Available in kit
form, but I think they are also available in assembled/tested form.

--
Dave M
masondg44 at comcast dot net

I went to a bookstore and asked the saleswoman, "Where's the
self-help section?" She said if she told me, it would defeat the
purpose.

Tue Aug 11, 2009 4:36 pm   

On Mon, 10 Aug 2009, Don Stauffer wrote:


Electronics (or maybe it had morphed to Electronics Now by the time he
covered this specific topic).

Apparently there was a need for a transmitter that output on multiple
channels. The example I remember was for real estate, where apparently
they used low power transmitters to send a recorded message to passing
cars, the sign saying something about turning on your radio, so they get
the sales spiel without even stopping or dropping in. And they wanted
multiple frequencies so nobody had to fuss over tuning to the proper
frequency.

My memory says the column mentioned commercial products that did that, but
it's been a while. He went into some ideas on how to do it, none of which
I can remember now.

Michael

Wed Aug 12, 2009 9:57 am   

In article <Pine.LNX.4.64.0908111233260.28909_at_darkstar.example.net>,
Michael Black <et472_at_ncf.ca> wrote:

An article I read somewhere (quite possibly the same article you're
referring to) described doing this by generating a comb using logic
gates to produce a sufficiently harmonic-rich signal, bandpass filtering
it to the FM band, and then either mixing it with a baseband signal or
varying the oscillator that produced the comb, in order to modulate all
the individual carriers with FM audio.


--
Wim Lewis <wiml_at_hhhh.org>, Seattle, WA, USA. PGP keyID 27F772C1
"We learn from history that we do not learn from history." -Hegel

Thu Aug 13, 2009 1:43 am   

In article <h5tskv$o44$1_at_underhill.hhhh.org>, Wim Lewis <wiml_at_hhhh.org>
wrote:


Generate the comb (200 KHz square wave fed into an ECL ff to divide by
two to get 100 KHz with really fast edges, which means plenty of
harmonics), bandpass filter that, amplify, and feed it into a mixer.
You'll probably want a 20 MHz spread above 200 MHz or so, to make the
bandpass filtering easier, and also so that the tilt on the comb
spectrum isn't that great over the 20 MHx band you want.

Rather than a fixed LO going into the mixer, you want to FM the LO, so
that the output of the mixer (bandpass filtered once again) is the FM'd
combs 100 KHz apart.

Amplify to taste (but you're going to need a very good amplifier).

The amps have to have a *lot* of headroom -- each comb is fairly small,
but you're amplifying all of them at once. That's a different
problem...

--
Namaste--