PDA

View Full Version : Solved Bell 202 Modem Object



g3cwi
04-03-2012, 05:37 PM
Hi

I am using Phil' Pilgrim's Bell 202 modem object. I need to send some slowly alternating tones to equalise levels. Sending 1200Hz is easy using the "transmit" routine but I have no idea how to send the other tone (2200Hz). Have anyone else solved this poblem?

I have not e-mailed Phil directly as his profile asks for no PMs.

Regards

Richard
G3CWI

Phil Pilgrim (PhiPi)
04-03-2012, 06:00 PM
Richard,

There really isn't a good way to send long periods of 2200 Hz with the object in its present incarnation. I suppose I could add a break method if it's important to be able to do that. But first, I need to understand better your need for "equalisation." Can you explain, please?

-Phil
AD7YF

g3cwi
04-03-2012, 07:15 PM
Hi Phil

I need to be able to compensate correctly for the pre-emphasis and de-emphasis of the TX/RX set up so that the tones appear at the correct levels at the demodulator. An easy way of doing this would be to send each tone through the system to see what compensation (if any) might be best. However, if it's tricky I can live without it!

73

Richard
G3CWI

Phil Pilgrim (PhiPi)
04-03-2012, 07:34 PM
Have you tried using the Windows monitor program that I wrote for that purpose?

-Phil

g3cwi
04-03-2012, 08:05 PM
Err no. Is that in the OBEX?

73

Richard
G3CWI

Phil Pilgrim (PhiPi)
04-03-2012, 08:33 PM
Yes. It's in the zip file that you downloaded with the object and demo programs.

-Phil

ke4pjw
04-04-2012, 08:26 PM
I think you should only have to deal with de-emph if you are getting audio directly from the discriminator on the rx side and are feeding the transmitter via the mic input. From the mic input, audio is pre-emphasized and "clipped" on FM transmitters.

If you are directly feeding an FM modulator, you have bypassed the pre-emph and clipping circuity. You would then be able to take audio directly from the discriminator without any de-emph. The downside to that is you can splatter noise into the adjacent channels if you are not very conservative in your audio levels.

If you are feeding audio into a Phase Modulator, there is no way to bypass it's inherent pre-emphasis.