On Jan 10, 2013, at 8:52 AM, Dave Greig wrote:
> Question. Is there a simple RF sampling device and software that will allow
> the RTTY RF signal to viewed?
Both K0SM and I have used a directional coupler for our separate work.
I think Andy uses some professional directional coupler. I myself use the
directional coupler kit from Elecraft. I wired my coupler for -30 dB. If you
want to take this route, the Elecraft CP1 kit is $40.
The loss of the directional coupler is small enough that you can keep it in
line all the time if you run low power (or wire it between your transmitter and
the amplifier). Think of it as a SWR meter without the meter :-).
You then send the tap through an attenuator to the receiver.
Remember that -30 dB of 100 watts is still 100 milliwatts, and will overload
pretty much any receiver but perhaps the Hilberling :-). So, you need to have
plenty of RF attenuation on hand.
I use a bunch of cheap F-connector attenuators that are used in the cable TV
world -- they are meant for 75 ohm termination, but works perfectly well for
this type of application. A couple of resistors in a T- or Pi topology will
work as well too as long as you take a little care to shield the input from the
output.
The most cost effective receiver ("detector") to use is actually the SoftRock.
It costs a couple of Happy Meals plus an evening of soldering and coil
winding), which you feed into a decent sound card.
If you are only watching your own signal, a stereo sound card that gives you 90
dB of dynamic range is sufficient. For monitoring your own signal, you also do
not even need a high sampling rate. 48000 samples/second will give you more
than 40 kHz of bandwidth. (If your signal spatters more than 40 kHz, you
really have problems :-) :-).
There are lots of software that will display wide and deep spectrum from an
SDR. A Google search for "SDR software" should turn up many.
73
Chen, W7AY
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