I don't see this working-FM TX

[amdx]

Does this look like it has any chance of working, and if not
what is it supposed to be?

http://broadcasthardware.blogspot.com/2008/05/small-fm-transmitter-with-loop-antenna.html

Mike

 

[Tim Wescott]

On Sun, 25 Oct 2009 17:22:59 -0500, amdx wrote:

Does this look like it has any chance of working, and if not what is it
supposed to be?

http://broadcasthardware.blogspot.com/2008/05/small-fm-transmitter-with-
loop-antenna.html

Mike

The big strip around the outside is a coil, it's the "loop antenna" that
the author refers to. With that, the circuit forms a push-pull Hartley
oscillator, that's modulated by the input audio.

As a bonus, you'll get AM modulation as well as FM.

Work -- probably, at least sometimes.

Work well? Well...

--
www.wescottdesign.com

 

[amdx]

"Tim Wescott" <tim@seemywebsite.com> wrote in message
news:O5SdndOt1MAkSXnXnZ2dnUVZ_jJi4p2d@web-ster.com...

On Sun, 25 Oct 2009 17:22:59 -0500, amdx wrote:

Does this look like it has any chance of working, and if not what is it
supposed to be?

http://broadcasthardware.blogspot.com/2008/05/small-fm-transmitter-with-
loop-antenna.html

Mike

The big strip around the outside is a coil, it's the "loop antenna" that
the author refers to. With that, the circuit forms a push-pull Hartley
oscillator, that's modulated by the input audio.

As a bonus, you'll get AM modulation as well as FM.

Work -- probably, at least sometimes.

Work well? Well...

--
www.wescottdesign.com
Thanks Tim,

I didn't see any osc. but now I understand, Seems with that large tuning
coil the temp. stability would be poor. It is the simplest FM transmitter
I have ever seen though.
Mike

 

[Tim Wescott]

On Sun, 25 Oct 2009 18:53:45 -0500, amdx wrote:

"Tim Wescott" <tim@seemywebsite.com> wrote in message
news:O5SdndOt1MAkSXnXnZ2dnUVZ_jJi4p2d@web-ster.com...
On Sun, 25 Oct 2009 17:22:59 -0500, amdx wrote:

Does this look like it has any chance of working, and if not what is
it supposed to be?

http://broadcasthardware.blogspot.com/2008/05/small-fm-transmitter-
with-
loop-antenna.html

Mike

The big strip around the outside is a coil, it's the "loop antenna"
that the author refers to. With that, the circuit forms a push-pull
Hartley oscillator, that's modulated by the input audio.

As a bonus, you'll get AM modulation as well as FM.

Work -- probably, at least sometimes.

Work well? Well...

--
www.wescottdesign.com
Thanks Tim,
I didn't see any osc. but now I understand, Seems with that large
tuning
coil the temp. stability would be poor. It is the simplest FM
transmitter I have ever seen though.
Mike

Not just large, but low Q -- that big coil/antenna resonates _and_
couples energy to the aether, which means you _can't_ have high Q.

Of course, _any_ power oscillator is going to have this problem -- to get
efficiency you need a low Q, to get a really good quality oscillation you
need high Q. You can't have both with just one amplifying device.

--
www.wescottdesign.com

 

[Michael Black]

On Sun, 25 Oct 2009, amdx wrote:

"Tim Wescott" <tim@seemywebsite.com> wrote in message
news:O5SdndOt1MAkSXnXnZ2dnUVZ_jJi4p2d@web-ster.com...
On Sun, 25 Oct 2009 17:22:59 -0500, amdx wrote:

Does this look like it has any chance of working, and if not what is it
supposed to be?

http://broadcasthardware.blogspot.com/2008/05/small-fm-transmitter-with-
loop-antenna.html

Mike

The big strip around the outside is a coil, it's the "loop antenna" that
the author refers to. With that, the circuit forms a push-pull Hartley
oscillator, that's modulated by the input audio.

As a bonus, you'll get AM modulation as well as FM.

Work -- probably, at least sometimes.

Work well? Well...

--
www.wescottdesign.com
Thanks Tim,
I didn't see any osc. but now I understand, Seems with that large tuning
coil the temp. stability would be poor. It is the simplest FM transmitter
I have ever seen though.
Mike

That's the sort of equipment that was used to move up in frequency.

Modulated oscillators and superregenerative receivers, worked hand in
hand. They weren't very good, but they would get people on the bands so
there was activity. The instability of the modulated oscillator didn't
matter, the superregenerative receivers were broadband. These things
would move in, they were easy to build so many did, and then the band had
a certain level of population, which then caused others to get more
serious. Eventually, the modulated oscillators were prohibited as too
unstable, and better equipment had to take over. The modulated
oscillators and superregenerative receivers moved up to the next band and
started all over. Sometimes one tube was used for the modulated
oscillator and superregnerative receiver, merely making some fine
adjustments between transmit and receive.

FM broadcast band receivers are fairly wide, so they too can live with
unstable oscillators.

Michael