Re: [Discuss-gnuradio] fm_tx_2_daughterboards output 2nd board is AM!!

[Eric Blossom]

On Mon, Feb 26, 2007 at 11:33:22AM +0100, anmar wrote:
> hi,
> 
> when i load the fm_tx_2_daughterboards.py I see on the scoop that the
> output of channel 2 is AM modulated, why is that?
> and the output of the 1st channel is not modulated,
> what i'm doing wrong?

I don't think anything's wrong.  What do you expect the output to be?

The way you've got it set up, side A is modulating a 10 MHz carrier
with a 600 Hz tone.  Side B is modulating a 12Mz tone with the sum of
350 + 440 Hz tones.

As the comment at the head of the file indicates, it's generating SSB
(Single Side Band), a form of AM modulation.  Take a look in any comms
text or amateur radio book.

> Tuning side A to 10MHz
>   r.baseband_freq = 0
>   r.dxc_freq      = 10M
>   r.residual_freq = 0
>   r.inverted      = False
>   OK
> Tuning side B to 12MHz
>   r.baseband_freq = 0
>   r.dxc_freq      = 12M
>   r.residual_freq = 0
>   r.inverted      = False
>   OK
> why is there no baseband_freq and residual_freq?

There's a baseband_freq, it's equal to zero.  There's no problem with
that.  I'm assuming that you're using Basic Tx boards.  They have no
RF upconverter on them, so all the work is done in the digital up
converter.  That's why you have the two dxc_freq entries, one saying
10M, the other 12M.  There's almost never a residual_freq, and if
there is, it's on the order of 0.001 Hz.

I'm assuming you've got two Basic Tx daughterboards installed, right?
That means you have a total of 4 SMA connectors that you can probe on
the 2 Basic Tx daughterboards.

While this is running, have you looked at all 4 outputs, the two on
the A side and the two on the B side?  The two on the A side will be
related.  One of them is shifted 90 degress from the other.  Likewise,
the two on the B side are related.  One of them is shifted 90 degrees
from the other.

Eric