On Oct 27, 2006, at 11:10 AM, Doug Faunt N6TQS +1-510-655-8604 wrote:
> http://www.cliftonlaboratories.com/Z90.htm
>
> I've one on order.
Buy? Why not build your own?
A SoftRock SDR kit goes for less than $15 (write directly to
KB9YIG). I bought five kits for $70 (for phased array and diversity
reception experiments one day.)
Since the SDR provides an I and Q channel (complex analytic signal),
any stereo A/D converter will give you at least 40 kc worth of
passband to work with. Simple FFT will give you the rest. If you
want to be fancy, buy a DDS kit and you can be frequency agile (40 kc
is enough for a typical RTTY pileup, but not for a busy contest), or
use an A/D converter with a 96 ks/s sampling rate.
By the way, I have found that when looking for the QSX in a pileup
(or S&P in a contest for that matter), it is much easier to use a
"waterfall" spectrogram than to use a spectrum scope. Signals are
much, much easier to identify and the visual "history" that is built
into a waterfall allows you to see very weak signals that are right
at the noise level (as Project Cyclops demonstrated back in the early
1970s with respect to SETI signal detection -- very DX and very weak,
if they even exist :-).
The SoftRock is a circuit board that is 1.5 inch by 2 inches. That,
together with a USB A/D converter will hardly take up any space in
airline luggage in a DXpedition :-).
I had implemented a frequency agile waterfall in my software so that
clicking on it will not just move the mark/space tone pair of the
demodulator to where you've clicked, but it also sets your transmit
modulation tone pair to the same spot (this is what you cannot easy
do with FSK, only with AFSK). Filters, etc are recomputed on the fly
when you click on a different spot.
With something like the FT-1000MP, where the transmit audio passband
is not completely flat, you need to be careful with the audio level
so ALC don't show -- a future transmit audio equalizer function will
take care of that.
The software has two independent RTTY channels, each taken from an
audio signal from the stereo pair and each with its independent
waterfall and crossed ellipse display. I have wired my A/D
converter's left channel to the main receiver of my FT-1000MP and the
right channel to FT-1000MP's sub receiver. During a split DX
operation, I place the DX on one of the FT-1000MP's VFO and center
and tune the pile on my other VFO. When I see what appears to be a
signal responding to the "local" that is working the DX, I just click
on it and when I transmit, I will be on the DX' QSX.
You can see the simple user interface here
http://homepage.mac.com/chen/cocoaModemPage/UsersManual/rttyManual/
index.html#wideband
(when I captured that screen shot for the documentation, I had set up
a "Garry" macro to send a personal greeting to NI6T when he was on a
DXpedition, HI HI. K7C, I think?)
You can see the two long horizontal displays for the waterfalls. The
"restore" button places the tone pair into a default position where
my rig's narrow IF filters are.
The popup menu that says "60 dB" controls the dynamic range of the
waterfall (to handle different band conditions and large signals in
the passband).
The squares with a cross in them is the crossed ellipse display. The
"Normal" button is for switching to an inverted signal. There is not
much else -- just the bare essentials to catch an RTTY DX from my
humble setup (barefoot, wires and verticals). In fact, if you
notice, I have only set up just the bare essential macros for working
a DX :-) Less often used functions are brought up using the "Aux"
buttons -- stuff like different FSK shifts and baud rates and
bandpass filter characteristics.
Vy 73
Chen
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