RadioBanter - View Single Post - Question about Frequency Shift Keyed signals

September 5th 04, 02:06 AM

(Jim Haynes) wrote in message link.net...
In article ,
M. J. Powell wrote:
In message , James
writes

Now, my question. If you send this signal into a standard FM Rx it
will produce a tone.

Why? The two frequencies do not exist at the same time in the receiver.

But if the shifting, the pulse repetition, is taking place at a high
enough frequency it will be heard as a tone. And, yes, the information
is still there because the waveform of the tone should be that of the
modulating signal.

I do not know the answer to why. All I know is that you in fact do
get a tone if you run this signal through a FM Rx.

Maybe I was not specific enough in terms of the RF signal. Let me try
again.

The low frequency pulse is 2 milliseconds long every time at the start
of a sequence. This 2 millisecond pulse is the start signal.The
higher frequency pulse (higher by 5 KHz) ranges from 1 to 2
milliseconds long. If it is under 2 milliseconds enough of the low
frequency pulse is sent to get to 2 milliseconds. Each consecutive
high frequency pulse controls one and only one channel of information
(and in general each of the nine channels will be different in
information and thus pulse length) up to the ninth high frequency
pulse. Then the information is either repeated or modified in one or
more channels depending on the inputs to the transmitter.

So, I repeat my question. What is the nature of the tone from the FM
Rx and does it still contain the timing information sent on the high
frequency pulse?

Thanks