One of the best investments I made many years ago was a *Bird 4431
Wattmeter*. It looks like the standard Bird 43 which uses
interchangeable 'slugs' to measure different power levels and frequency
ranges. The 4431 also includes a 'sampling port' which picks off a
variable amount of RF and presents it on the BNC connector. You can hook
up a scope, spectrum analyzer, detector, or other device and 'sniff' the
RF passing through the Wattmeter.
I don't think they offer this particular model anymore, but you might
snag one at a hamfest or on eBay.
73 de Bob - KØRC in MN
------------------------------------------------------------------------
On 1/10/2013 4:07 PM, Kok Chen wrote:
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
_______________________________________________
RTTY mailing list
RTTY@contesting.com
http://lists.contesting.com/mailman/listinfo/rtty
_______________________________________________
RTTY mailing list
RTTY@contesting.com
http://lists.contesting.com/mailman/listinfo/rtty
|