The latest block diagram is here:
< http://www.hamsdr.com/dnld.aspx?id=139 >
Since the board is 100mm (~4") wide then we are a little tight for space.
I suggest 3.5mm jack sockets for the microphone and headphones. A bias
voltage is available for Electret microphones.
I also suggest using 3.5mm stereo jacks for the high speed A/D inputs.
Since all the A/Ds we are considering can take a balanced input a stereo
plug will provide a balanced input and a mono plug will earth one input
for use with unbalanced inputs. This does mean that we will need two
leads
from the radio as apposed to the single stereo jack at present.
We can either use 3.5mm jacks for the remainder of the sockets or
consider
RCA's.
Is it worth going to gold plated RCA sockets - what experience do the
audiophiles have with these?
Some of the options are:
1.. Don't mount the connectors on the PCB but use a breakout box like
the
D44
I really, really prefer the connectors to be part of the PCB.
2.. Don't provide balanced inputs for the high speed A/D converter
For high performance, balanced is better :-)
3.. Don't fit line in on the Tx A/D - do we need this for digital
modes
now we have VAC?
If the board's only purpose is an accessory for running the SDR-1000 on
Windows, then perhaps not. But if it is to support other
experimentation, then fit the connections if there is space on the board.
4.. Don't fit line out, use the headphone out to drive external
speakers
etc
If there is room, add the connectors.
5.. Use stacked RCA sockets - but that will increase the height of the
board
Bulky.
6.. Use smaller alternatives to RCA sockets - DIN perhaps?
At the moment my preference is to use 3.5mm jacks for all connectors.
I have to agree with this. Such connectors are readily available in
right-angle PCB mount configuration, low cost, and have a small footprint.
Comments and suggestions welcome.
If the board is intended to be used with the SDR_1000, then having a
mating connector such that you can use a readily available patch cable
is a plus. On the other hand, the connection between the QSD and the
audio sampling system exposes one of the most vulnerable parts of the
radio's signal path. Since the SDR-1000 already uses 3.5mm jacks, Janus
is no worse in this respect. For people who want to make their own QSD,
it might be interesting to provide an alternative, perhaps in the form
of a male header on 0.1" pin spacing (OK, 2.54 mm spacing) so a daughter
board could be stacked onto JANUS and bypass the 3.5mm jacks entirely,
at least on the Wolfson ADC. This also allows one to more easily adapt
his or her connector of choice in lieu of the 3.5mm jack.
73,
Lyle KK7P
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