It is set by a relay on the post amplifiers and the preselector in or out. Also
the third setting is a resistive pad. I think these 3 settings are manual
operator input.
The rest of the story is the dynamic range of the sound card. The three gain
settings put the dynamic range with the bottom setting at the noise floor of
the frequency in use.
KD5NWA <[EMAIL PROTECTED]> wrote:
Flex implements the AGC in software so it can be finely controlled
and maintain accuracy of the input signals.
With SDR the philosophy being that as much as possible to be moved
from fixed hardware to a DSP, PC, or FPGA so it can be controlled and
changed by software. The second you put in a traditional AGC then you
have no clue of the system gain and your S-Meter is no more accurate
than your typical receiver where it's basically and approximation of
signal strength.
Also to be noted on a SDR radio the largest signal in the band-pass,
not the one you are listening to must not be allowed to saturate the
ADC's with hardware that is difficult do, with software it's simple,
you look through the FFT bins for the largest signal and set the
receiver gain accordingly.
The SoftRocks series is meant to demonstrate how simple the hardware
needs to be to create a quality receiver. All the "traditional things
like AGC, Filtering, Demodulating, and Noise reduction is carried out
in software not in hardware. But to keep them inexpensive Tony had to
use a fixed crystal frequency, and do not they have a front end
pre-amp, and that is the main limit of them. Within their range and
limits they work remarkably well for such simple piece of hardware
again demonstrating how most of the hardware feature can be moved to
the software side and they should so you have more control over the radio.
As little hardware as possible, and as much software as possible is
what makes a SDR radio a superior and extremely adaptable radio.
Because a QSD mixer is so clean, the LO becomes a critical part( it's
always been in any radio) of the radio, and the individuals who
pursue creating variable clean LO's will be rewarded with a high
performance in the little radios.
At 11:32 PM 6/12/2006, you wrote:
>Francis Carcia:
>
> Yes there is that problem of agc acting on all of the spectrum
> coming into the sound card over 96 kHz. So I propose that as a
> standard when desired to be use that any agc applied needs to be
> both switcable on and off and also adjustable. Even adjustable in
> time constant which mere capacitors can accomplish.
>
> My first view of agc was to sample the output from the sound card
> of the desired signal level and use that. A better idea then, to
> use the audio output of the sound card to control itself going into
> the final audio amplifier section external to the PC in the monitor
> system. This way only the desired audio will have agc applied.
>
> Sometimes however it might be desirable to have some agc in the
> receiver and so as I mentioned above that can be switchable. Again
> the better idea for that is to use only the sound cards output as
> the signal that controls the receiver as well as the external monitor gain.
>
>ka9rza
>
>
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>Yahoo! Groups Links
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>
>
Cecil Bayona
KD5NWA
www.qrpradio.com
"Windows, the most successful software virus ever" Don Seglio Batuna
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