Q on multiple RX and on TX into dummyload

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kc9chg
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Joined: 2010/10/31 - 20:07
Q on multiple RX and on TX into dummyload

Hi everyone,

I'm pretty new to wspr but have made enough data runs to realize that getting information out of the data requires some care. In particular I have been struck by how much the S/N varies from measurement to measurement when I receive signals from around the world. I'm sure that is both because propogation varies a lot and because my local noise varies.

What I would really like to do is compare the "effectiveness" of two antennas. I have seen entries in the wspr forums about this and it is pretty clear that one cannot just make a long data collection run with one antenna and then with another. I would like to consider tilting at this windnmill by using two independent wspr systems (radio + computer) and look at effectiveness (for a given transmission location) by looking at my received S/N. To do this, though, I will need to have two "callsigns". I'd appreciate your advice about what I should use for a second callsign (the first of course is the one given to me by the FCC). I have a login on wspr.net using kc9chg. If I pick some random second callsign do I need to have a login with that name on wspr.net as well? If not, then would any text string that the wspr program doesnt think is too long be ok?

I have done a quick study without uploading my data to the website (since I feel like I need to know about the second callsign before I do that). I have seen that if I use a single antenna and a splitter to feed the two systems I get "pretty much" the same S/N values for the two systems, but they vary from eachother in what seems to be a random way typically by about 1-2 dB. I went to some care to make sure my clocks are well synchronized and I did the test on 40m where I would have thought that the noise would be dominated by noise from the antenna.

I also did a short study in which I transmitted into a dummy load from one system and measured that local signal using the second system. Here as well I saw S/N values that varied, but I expected that since my locally picked up noise from the antenna is not expected to be a constant. It struck me that I could use this setup to effectively cancel out my local noise when looking at a remote signal. By subtracting the local S/N from the remote S/N, I am basically looking at S(remote)/N(local) / S(local)/N(local). Since S(local) is a constant, the result is a relative measure of the remote signal strength with the local noise cancelled out. This seems like a neat way to measure the change in propogation effeciency as a function of time without being impacted by time variation of local noise. But to do this, I transmit into a dummy load. If I do this and others on the wsprnet see my signal, I'd like to have a power level in the transmitted data that makes sense. Can anyone suggest what I ought to put? Seems to me like setting the power level to the power that is being put into the dummy load is misleading.

Really love seeing what everyone else is doing and will very much appreciate any responses folks have to my questions. Of course any thoughts about my plans would also be very much appreciated

73, Barrett, kc9chg