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EI7GL....A diary of amateur radio activity

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Video on the limitations of the VOACAP HF Propagation Software ...by KC0DN

Posted: 10 Jun 2021 02:30 AM PDT https://ei7gl.blogspot.com/2021/06/video-on-limitations-of-voacap-hf.html


What is VOACAP?: VOACAP (Voice of America Coverage Analysis Program) is a popular and free professional high-frequency (HF) propagation prediction software tool originally developed for the Voice of America (VOA).
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The presentation is aimed at a US audience as it uses it uses outdated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.

The presentation which is 45 minutes long can be seen below…

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.Links...
1) VOACAP online tool

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