Saturday, February 11, 2017

WSPR and Antennas

Last fall I purchased an Ultimate 3s WSPR/QRSS transmitter kit from QRP Labs. I bought the U3S, GPS module, receiver module and case, for the 30m band. Recently I got around to finishing the transmitter half and set it up for WSPR. Watching the spots come in is a lot of fun, seeing how far I can get with only 23dBm (thats 200mW for those who aren't engineers). Looking at the map of spots, it appears that my antenna might have nulls pointed at New England and the Carolinas. Maybe that's why I've yet to work any states in those regions. I have not seen many spots from Asia or the pacific, and have seen none from Europe, South America or Africa.
24 hours of spots of KB1KXL, ending 0020 UTC 2/8/2017.

I think that my antenna is to blame for the lack of results in those directions. It is a low (~15 feet) doublet, cut for 40m, and in an inverted-V configuration. I'm feeding it with 300 ohm twin lead, which has to pass through a metal window frame. I also have to keep the feedline low in some rose bushes until it gets to the antenna tree so that it can pass under the power lines. Also, one of the legs passes through a few trees. The tuner in my KX3 is able to match it on all bands 80-6. My guess is the low height and all of the compromises I had to make in order to get it up are limiting the range and ability to hear dx. To upgrade I'm going to try running some small coax through the window to a balun outside, under the theory that it will reduce losses while going through the window. A more difficult upgrade is to get a tall pole to support the center of the antenna.
Using the online VOACAP modeling for coverage area, it looks like I can get some improvement from going from a dipole at 5 meters to one at 10 meters.
Dipole at 5 meters (17 ft)

Dipole at 10 meters (33 ft)
 These plots were generated on 2-3-2017 at 0100 UTC, location Sacramento, 5W, CW, on 40m. All others settings were left at the defaults.

At some point I'll switch the Ultimate 3S over to QRSS and see how that does. I'll post an update with some results when I do. Next I need to get the Raspberry Pi set up with a sound card so I can have my own WSPR/QRSS grabber...

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