Jim:
Sorry I was not clear:
2 transmit ports could output processed audio for monitoring and 2 could
output 11025 KHz for sending to the radio. It will have the hookup we
currently use for the Delta 44 but we are sending the same thing to both
ports, one has AF gain control on it for monitoring and the other has
PWR control on it. Otherwise, it is the same audio.
This will move us away from the 1/f, DC mixing components, etc we
currently get (at a low level but present nevertheless) and it will move
the image from (say) a few Hz to 20+ Khz away making image rejection
more easy on TX.
Bob
Jim Lux wrote:
At 05:38 PM 12/16/2005, Robert McGwier wrote:
We are not using our 4 port cards correctly. We should have audio for
monitoring and 11025 KHz for the TX/IF. This would fix the tx spectrum
from the QST article and it moves the TX signal into a more stable part
of the soundcard filter. This will do nothing for the 2 port folks.
Bob
I'm not sure what you mean here..
I assume that if you have a high performance audio card, you'll use 2
of the inputs for the Rx and 2 of the outputs as the Tx.
But that won't allow you to calibrate the Tx side (unless you assume
the Tx and Rx responses are the same, which might be true for the
audio side on the card, but is almost certainly not true for the audio
side on the SDR1000). On the other hand, it might be "good enough".
It's conceivable that you could "loop back" the Tx into the Rx; they
actually join at the 4:1 transformer, after all. That's a convenient
calibration plane, at least for the image rejection issue, because
it's on the RF side of the QSE/QSD. Unfortunately, even though you
could calibrate the receiver, and then use that to calibrate the Tx,
it looks like the Tx/Rx control line disables and enables the
detector/encoder, with no way to defeat this (short of changing the
board).
For that matter, it might be "good enough" to calibrate/equalize just
the audio card with an audio loopback.
James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875
--
Laziness is the number one inspiration for ingenuity. Guilty as charged!
