Video Introduction: As part of the 2021 virtual Four Days in May (FDIM) event, Tim Snodgrass KC0DN made a presentation about the accuracy and limitations of the VOACAP programme. KC0DN along with Charley, KC0CD and Mike, AC0HB set up an extensive listening station to monitor the signals from the time standard stations WWV, WWVH and CHU.
The experiment which ran from November 2020 to February 2021 monitored all three time standard stations on a wide range of frequencies from 2.5 MHz to 25 MHz and compared the reception results against what was predicted by VOACAP.
The receive station was set up in Cedar Falls, Iowa while the time standard stations are in Fort Collins, Colorado / Ottawa, Canada & Kauai, Hawaii.
WWV Ft. Collins Colorado: Transmitting 10KW on 5, 10, 15MHz; 2.5KW on 2.5, 20 & 25MHz
WWVH Kekaha, Kauai (Hawaii): Transmitting 5KW on 2.5MHz & 10KW on 5, 10, 15MHz
CHU Ottawa, Ontario, Canada: 3 kW on 3.33MHz, 5KW on 14.67 MHz, & 7.85 MHz
The presentation is aimed at a US audience as it uses it uses outdated MILES for distances which mean very little for an international audience.
I have prepared a map shown below which shows the distances in kms which makes things clearer as you watch the video.
Presentation notes in PDF format can be found HERE
Findings: My own summary of the findings...
1) Like any propagation software tool, VOACAP suggests what the conditions might be like and what paths might be possible. It shouldn't be taken as fact.
2) VOACAP predictions can be too pessimistic.
3) Openings on the higher HF bands (14 MHz and above) happen more often than VOACAP predicts.
4) Lower frequencies like say 80m & 60m are underrated. They can be used 24 hours a day with modern digital techniques.
5) The 30m band is often open at night when VOACAP says it should be closed.
6) The 5 MHz band (60m) was nearly always open 24 hours a day over a 1600km path.
7) By using two bands e.g. 3.5 OR 5 MHz AND the 10 MHz band, a reliable link can be maintained over a 1600km path.
8) KC0DN advocates the use of two bands for the use of 'Store & Forward' digital traffic.
9) Circular polarization on HF can result in a significant advantage.
In Conclusion: This video by KC0DN is the summary of a significant amount of work and should be of interest to anyone with an interest in propagation on the HF bands. It's a bit unfortunate that it uses the title "Breaking Free of the Solar Cycle" on YouTube as that really doesn't describe to the casual observer what the video is about.
It should be remembered that the results are for someone in the United States and at a particular latitude. The results may not apply so readily to say someone at a more northerly latitude.
However, there is still plenty of material in the video of interest and it's worth watching.
1) VOACAP online tool
1 comment:
At the end of the day, this video was not about the limitations of the VOACAP prediction software. The measurements they did are really a nice achievement indeed, and they deserve our thanks. However, the input values chosen for running the prediction (e.g. the sunspot number) and visualization of the VOACAP results (the threshold for SNR values) considerably skewed the interpretation of the predictions, and you may have been left with the impression that you cannot at all trust VOACAP predictions. We all know that VOACAP have its limitations but they are not as pronounced as the author wants us to think.
It would have helped if they have shown us the exact VOACAP input values they had used. Now I am basing my thoughts only on the output screens I saw glimpses of in the video.
These are the predictions I ran with my VOACAP Online service, and they tell a totally different story:
- https://www.voacap.com/pics/wwv.jpg
- https://www.voacap.com/pics/wwvh.jpg
73 Jari OH6BG
Post a Comment