VHF & up WSPR overview
Glenn Elmore
VHF (and above) WSPR Overview
WSPR was not originally intended for operation at shorter wavelengths such as 144 MHz and above. Rather, it was meant to allow reporting of primarily ionospheric propagation at HF and below. On his home page, Joe, K1JT, writes: “This program is designed for sending and receiving low-power transmissions to test propagation paths on the MF and HF bands.“ He also has indicated doubts about its usefulness at VHF and above because of “Doppler spreading”.
However, in practice, many of us have found WSPR to be very applicable to propagation studies above HF and “Doppler”, that is single or multi-path components involving moving net path length such reflection from aircraft, have not been a significant problem. While particularly at 6 m and 2 m we often do see a lot of aircraft related components, to a large degree these signals do not spend more than a small portion of the 2 minute WSPR interval close to a “main” signal and WSPR's software does an excellent job of decoding in their presence. We also occasionally see what is clearly an aircraft scatter (ACS) component that is also stable enough over the entire 2 minutes that it decodes. Sometimes we will see double spots, one from a main, non Doppler, path and one from a stable-enough ACS path.
As we go higher in frequency the ACS components seem to be even less of an issue since they move through the critical few Hz either side of the WSPR signal so quickly that the error correction within WSPR can handle the self-QRM they represent.
As a result, WSPR at 2 meters and up has been very productive. Already we have found instances of types of propagation that were not widely recognized as useful for amateur communications as well as influences to propagation, particularly from powered commercial aircraft, that weren't previously recognized within amateur radio. We've also found some interesting attributes of common propagation in drastically non-LOS environments, that appear to relate to all amateur VHF-microwave communications and may provide direction for VHF & up Dxers, contesters and others as well as those who desire to study the physical characteristics of real-world propagation. In short, using WSPR at 2 meters and above has already been very productive.
VHF and above WSPR does present special problems though. While WSPR decodes based on differential symbols, that is, the change from one of the four FSK symbols to the next rather than the absolute frequency of each, it has some resilience to drifty signals. It appears that it can follow and decode signals that drift as much as 3 or 4 Hz in 2 minutes, depending a bit upon the nature of the drift. Beyond that, decodes are not likely to occur. This degree of stability is near or beyond the limit of many standard amateur stations, even some of those equipped with high-stability frequency references.
Because so much of the power of WSPR is in the large number of stations involved and located in various locations, we all benefit from increased activity. I hope we can discuss our experiences and solutions to the problem of providing both stability and absolute frequency accuracy from VHF to microwave with common amateur hardware.
Once more stations get on 2 meters and particularly as we increase activity at 432 MHz and above, I hope this group will provide a convenient forum for discussing our observations,experiences and for collaborating.
73,
Glenn n6gn cm88ok
Santa Rosa, CA
6 Oct 2012
Leigh VK2KRR
You mentioned microwaves in this post, from my limited tests on 1296 MHz WSPR, it would seem that the higher in freq you go the more the WSPR transmissions will spread (wider than intended) due to some sort of scattering or doppler. WSPR wont be able to decode these most probably. Though I would like to do some tests at 10 GHz band, im finding it very hard in VK to find anyone interested enough to even test 1296 MHz WSPR let alone 10 GHz. Hope to be able to do some more tests in future.
Glenn Elmore
At shorter wavelengths, 70 cm and above, we have not noticed any scattering or spreading of the signal that is inherently limiting WSPR to lower frequencies. At 23 cm, things look very much as they do at 70 cm, though with ACS components whipping through very rapidly, for the most part. We do see reflections from smaller surfaces. For the first time we have been able to see what is almost certainly "Vehicle Scatter" due to traffic on a busy roadway between N6GN and another local WSPR station. While some of these interesting propagation mechanisms may show spectral differences - WTV propagation is one example I can think of - there is nothing about shorter wavelengths that keeps WSPR from working fine.
WA6M and N6GN have very successfully run WSPR-15 on 70 cm. This is with an occupied bandwidth of about 1.5 Hz and symbol spacing of around 200 milliHertz. At 70cm, the associated WSPR spot and waterfall look completely clean. There is no evidence of anything getting in the way. Of course, this could change if antennas were blowing in the wind and putting phase modulation onto the total path, but so far we've not seen this.
On an associated topic, we've used the 43rd harmonic of very good 10 MHz GPSDO's, to transmit 70 cm across a couple of kilometers as a way to compare time standards. This technique actually is the best one we've been able to figure for comparing time bases of two physically spaced ham stations (apart from the GPS system we were using to generate them). If there were significant spreading or multipath problems, this would not have resulted in the kinds of accuracies and repeatabilities that we have measured.
I believe that 10 GHz WSPR has already been accomplished by two hams in Southern California. Perhaps Chris, N3IZN, may be able to comment. My 10 GHz transverter is the only one I have not yet integrated into my SDR so perhaps I should do this so we can try it here. But judging from what we've seen this far, WSPR is an excellent vehicle for examining propagation and amateur stations well into the microwave region, at least.
Nice to have you back and active on the list!
Glenn n6gn
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n3...@aol.com
You digging up old emails? :)
A few years back W6SZ and I ran WSPR on 10,368. We don't have a line of sight instead we bounced off a known hill between us. It has a beacon on it, we both peaked on the beacon then peaked on each other. Signal level was perfect for WSPR, just a strong trace on the waterfall. That method would hopefully mean others could peak on the same beacon and join in, but we had no takers.
This was several years a go so I didn't look for things I would now. We would get decodes from each other but if there was any precipitation we would not get decodes. You could see the traces but no decodes. Back then I didn't think to zoom in on the trace.
In a straight line we are 59 miles apart. With the mountain we used for the bounce maybe added another 20 or so miles to the path. We ran for a week or 2 and couldn't get any more station to join so we called it.
Chris
WSPRing form 1.8 to 10,368........
Leigh VK2KRR
Hi Glenn and Chris,