How do you actually make a transmitter TRANSMIT?!?  I have made many kits
in my time, but never understood this.

Suppose there is an oscillator running at say 100MHz, which you modulate
with your input signal...

Now how you convince the high frequency signals in your circuit to just
shoot off into free air?  I mean, HOW DO YOU TRANSMIT?!?

At 09:27 PM 3/17/00 +1100, you wrote:
>> Can anyone tell me some websites with good introductions to PLLs on them?
>
>And for a purely hypothetical practical example, let's say that you wanted
>to design a FM Broadcast transmitter kit which covered from 88 to 108
>MHz.......... :-)
>
>You first design a nice stable Voltage Controlled Oscillator which covers
>the required band and is tuned via DC onto a vari-cap diode.
>
>You decide on 100 kHz channel spacing, so you arrange to divide a convenient
>crystal down to generate a 100Khz reference (say divide a 4Mhz Xtal by 40).
>
>Next the VCO is divided down to 100Khz through a Programmable Divider chip
>(to Transmit on 88 MHz you divide by 880 and on up to 1080 to get 108 MHz).
>
>The two signals are then compared in a phase/frequency comparator, which
>generates an error voltage which steers the VCO onto exactly the right
>frequency (and phase).
>
>The only tricky bit is getting the time constants of the control loop
>correct. The maths of this can get nasty. It is basically a PID, with just
>the right amount of leading and lagging phase to overcome the mechanical and
>thermal instabilities in the VCO.
>Most people cheat and tweak the values empirically.
>
>Oh yes, and to Frequency Modulate this beast you could feed a little audio
>into the control line to waggle the VCO frequency.
>
>These days all the divider chains and comparator etc are available in a
>single tiny SM chip which you control over serial lines via a PIC. The PIC
>Xtal probably also generates the original 4 Mhz reference. The PIC picks up
>the channel number from a dip switch or rotary encoder, etc.
>
>See I just knew that we would get back on topic eventually!!!!!
>
>
>.................................... Zim
>
>