On Feb 17, 12:55 am, "Dave.H" <the19...@googlemail.com> wrote:
> On Feb 17, 12:52 am, default <defa...@defaulter.net> wrote:
>
> > On Sat, 16 Feb 2008 05:46:44 -0800 (PST), "Dave.H"
>
> > <the19...@googlemail.com> wrote:
> > >I've got a 10K audio taper pot. Will that also work.
>
> > It will
> > --
>
> OK. I hope to get this transmitter up and running today. I will post
> here with the results.

Built it and rebuilt it and it didn't work. I installed the 12 pF
instead of the trimmer cap, even took it apart and resoldered all
connections. Any suggestions why it doesn't work?

On Sun, 17 Feb 2008 03:52:10 -0800 (PST), "Dave.H"
<the1930s@googlemail.com> wrote:

>On Feb 17, 12:55 am, "Dave.H" <the19...@googlemail.com> wrote:
>> On Feb 17, 12:52 am, default <defa...@defaulter.net> wrote:
>>
>> > On Sat, 16 Feb 2008 05:46:44 -0800 (PST), "Dave.H"
>>
>> > <the19...@googlemail.com> wrote:
>> > >I've got a 10K audio taper pot. Will that also work.
>>
>> > It will
>> > --
>>
>> OK. I hope to get this transmitter up and running today. I will post
>> here with the results.
>
>Built it and rebuilt it and it didn't work. I installed the 12 pF
>instead of the trimmer cap, even took it apart and resoldered all
>connections. Any suggestions why it doesn't work?


What method did you use to build it? It is a 100 MHZ circuit so
layout can be critical -

The next question would be what is the transistor doing? What is the
voltage from base to ground? What is the voltage from ground to the
emitter? (and if it were oscillating, taking a reading there would
stop it).

Can you / have you measured current consumption of the circuit?

What steps have you taken to verify it isn't working and what steps
have you taken to fix it other than checking your connections?
--

On Sun, 17 Feb 2008 03:52:10 -0800 (PST), "Dave.H"
<the1930s@googlemail.com> wrote:

>On Feb 17, 12:55 am, "Dave.H" <the19...@googlemail.com> wrote:
>> On Feb 17, 12:52 am, default <defa...@defaulter.net> wrote:
>>
>> > On Sat, 16 Feb 2008 05:46:44 -0800 (PST), "Dave.H"
>>
>> > <the19...@googlemail.com> wrote:
>> > >I've got a 10K audio taper pot. Will that also work.
>>
>> > It will
>> > --
>>
>> OK. I hope to get this transmitter up and running today. I will post
>> here with the results.
>
>Built it and rebuilt it and it didn't work. I installed the 12 pF
>instead of the trimmer cap, even took it apart and resoldered all
>connections. Any suggestions why it doesn't work?

Two things come to mind assuming no mistakes in the construction.

I would disconnect everything west of the vertical 10K that joins with
the base of the transistor - it isn't necessary for oscillation.

Then I would replace the transistor with another type - I've always
had better results with the metal can version of the 2N2222 for FM
mics but change the transistor if you have another NPN good for high
frequency.

The other thing, assuming no oscillation, is the feedback cap. It
shouldn't be very critical but it can go a long way to getting a
transistor that won't oscillate to start. Too high and it won't work
and too low and it won't work . . .

Try a gimmick cap in there. If you have some wire wrap wire or cat 5
USTP those are probably ideal but any solid wire will work. Magnet
wire is another good choice. Vinyl insulation isn't ideal at that
freq so if you can get it to work with vinyl, change it for a lower
loss dielectric to get maximum range.

http://www.shol.com/kuggie/cttip/pix/gimmic.jpg

Two wires twisted together, but not connected, form a "gimmick" cap.

No magic formula for value of the cap - thinner insulation = greater
capacity, longer gimmick = greater capacity, dielectric constant of
the insulation determines capacity also, dissipation factor of the
insulation = Q (quality).

good insulations - Teflon, polyethylene, Tefzel, Delrin, enamel (low
dissipation factor)

Without modulation - it can be hard to hear the transmitter. It will
sound like a Thump when you tune through it on the receiver and it
should be able to kill the sound of a weak FM station when it is
tuned to the same freq.. On an analog TV with antenna, it will look
like wavy lines or a herringbone pattern.
--

On Feb 18, 2:24 am, default <defa...@defaulter.net> wrote:
> On Sun, 17 Feb 2008 03:52:10 -0800 (PST), "Dave.H"
>
>
>
> <the19...@googlemail.com> wrote:
> >On Feb 17, 12:55 am, "Dave.H" <the19...@googlemail.com> wrote:
> >> On Feb 17, 12:52 am, default <defa...@defaulter.net> wrote:
>
> >> > On Sat, 16 Feb 2008 05:46:44 -0800 (PST), "Dave.H"
>
> >> > <the19...@googlemail.com> wrote:
> >> > >I've got a 10K audio taper pot. Will that also work.
>
> >> > It will
> >> > --
>
> >> OK. I hope to get this transmitter up and running today. I will post
> >> here with the results.
>
> >Built it and rebuilt it and it didn't work. I installed the 12 pF
> >instead of the trimmer cap, even took it apart and resoldered all
> >connections. Any suggestions why it doesn't work?
>
> Two things come to mind assuming no mistakes in the construction.
>
> I would disconnect everything west of the vertical 10K that joins with
> the base of the transistor - it isn't necessary for oscillation.
>
> Then I would replace the transistor with another type - I've always
> had better results with the metal can version of the 2N2222 for FM
> mics but change the transistor if you have another NPN good for high
> frequency.
>
> The other thing, assuming no oscillation, is the feedback cap. It
> shouldn't be very critical but it can go a long way to getting a
> transistor that won't oscillate to start. Too high and it won't work
> and too low and it won't work . . .
>
> Try a gimmick cap in there. If you have some wire wrap wire or cat 5
> USTP those are probably ideal but any solid wire will work. Magnet
> wire is another good choice. Vinyl insulation isn't ideal at that
> freq so if you can get it to work with vinyl, change it for a lower
> loss dielectric to get maximum range.
>
> http://www.shol.com/kuggie/cttip/pix/gimmic.jpg
>
> Two wires twisted together, but not connected, form a "gimmick" cap.
>
> No magic formula for value of the cap - thinner insulation = greater
> capacity, longer gimmick = greater capacity, dielectric constant of
> the insulation determines capacity also, dissipation factor of the
> insulation = Q (quality).
>
> good insulations - Teflon, polyethylene, Tefzel, Delrin, enamel (low
> dissipation factor)
>
> Without modulation - it can be hard to hear the transmitter. It will
> sound like a Thump when you tune through it on the receiver and it
> should be able to kill the sound of a weak FM station when it is
> tuned to the same freq.. On an analog TV with antenna, it will look
> like wavy lines or a herringbone pattern.
> --

I have spaced the components too far apart, that could be the
problem. The only thing I've done other than rebuild it is check for
a signal on an FM radio, I will perform other tests later, I have
learnt to leave things like this for a few days then come back to
them.