[ADXA] Propagation and VOCAP comments

Mon Oct 31 19:03:53 EDT 2022

Retirement is suppose to be fun, but I wish I was still working OT and was 20 years younger.  The Westark times were indeed the best for me.  Loved that Dan Page BTW, but he wasn’t a ham>>>> sadly.

73 de jay/w5jay..

From: Sandy Hutson <k5yy1 at cox.net> 
Sent: Monday, October 31, 2022 5:41 PM
To: Jay Bromley <jayw5jay at cox.net>; 'ADXA' <adxa at mailman.qth.net>
Subject: RE: [ADXA] Propagation and VOCAP comments

Good discussion Jay and great memories of the old days down south in Fort Smith.. HI

Hey, to each his own. We here on the ADXA chat forum enjoy other people discussing things of  interest, sometimes changing our opinions and sometimes just us chiming in with our opinions or giving data, etc.. TU again.   A hobby is not a business venture where you must be at the top of your game at all times. Retirement is fun, right Jay? 😊

San YY

Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986>  for Windows

From: Jay Bromley <mailto:jayw5jay at cox.net> 
Sent: Monday, October 31, 2022 5:11 PM
To: 'ADXA' <mailto:adxa at mailman.qth.net> 
Subject: [ADXA] Propagation and VOCAP comments

Hi Guys,

Mainly posting this to the new guys chasing DX hoping they might benefit.  VOACAP stands for Voice of America Coverage Analysis  Program.  It was developed when we were in the Shortwave business to predict HF propagation to various parts of the world.  If you were or are a shortwave listener, you may have heard of Voice of America?  As far as I know VOACAP doesn’t take into account various other modes of propagation like Sporadic E, TEP, etc.    In the beginning it was only HF with “F” layer propagation in mind.  I am sure the program has evolved over time, just not sure in what areas.  

These postings take me down memory lane before the U of A Fort Smith (UAFS) was called WestArk.  We had some remarkable professors during that time frame.  One I remember was semi-retired from Grumman Aerospace, Dan Page.  He would do special classes on Antennas, Feedline, Microwave, not normally offered in the coarse book, but mainly during the summer months for industries like the cable company, MaBell, etc.  Anyway I would always make a point to sign up if he offered one of those classes.  

During one of those classes we had to learn VOACAP as part of the class.  To show you how old all this is, we were given 5 ¼ inch floppy disks for the program!  This was well before online web pages using the VOACAP engine.  Heck this was before the internet as we now know it.  The time frame was the late 70s to early 80s.

What I have found over 40 years of using the VOACAP program is it can be very accurate if you understand the limitations.  Like with most things in the DXing Toolbox, the more you use it, the more knowledge can be gained from it.  Remember it is just a “guide” for HF skywave propagation.  Most of the trusted propagation experts that we see on YouTube or at CTU forums I would be willing to bet use or are currently using forms of the VOACAP program.  

Without belaboring the topic, here is where I find VOACAP most useful.  Run it when there is going to be a marginal path or during the bottom of the solar cycle.  Then other propagation modes are rarely seen on the higher bands.  Instead of putting the best case scenario for my power and antenna I will use something less, like a dipole and 100 watts.  Noise floor residential.  On an all time new country (ATNO), I will look to see what if “ANY” chance or the best chance of hearing them.  Then make sure I am watching out for them on that band during the best time, but I will continue to check every band I see them spotted on to see what part of the world they are working.  Including bands that spots showing EU or Asia only!  Usually off spins of the program will show MUF of starting with 10% of confidence and go as high as 90% confidence.  I look very carefully at 10% vs 50% vs 90% to get a feel of best chance of working them.  You can also look at Long path vs short path, plus the time of day that gives your best shot of working them.   

Like I mention before VOACAP is just a another tool to use.  Please notice that good DXexpeditions will use VOACAP or similar programs before they leave home to know when to run certain continents over another.  Does that always mean you can rely on the results, no!  VOACAP is just a good guide to use, not the bible.  I have seen some unreal propagation (no paths predicted) from 160m through 10m where nothing adds up if you hear them or are lucky enough to work them when you shouldn’t.  However like with any software, for it to work you must have good data.  Sort of like antenna modeling, if your antenna doesn’t work like the model, you will go back and look at the measurements on the antenna.  If it works better than the model you will go back to the program to see what is missing, hi.  During the expedition I was on we also used DX Atlas to spotlight what areas of the world had the most likely propagation.  That is another neat program!

The last time I really used VOACAP was for the VU4W’s expedition.  That was an ATNO for me and I had been 3 time loser in last couple of decades.  So I was trying to do everything I could to maximize my chances with my current BB gun antenna system along with the higher than usual noise floor.  I didn’t work him a lot, but got him in the log on two modes and bands.  The break down for that expedition by Continent was only 4.4 percent for North America.  EU was 56%!

So if you don’t have an antenna system like Joel, Rick, or Earl, it can pay to try and get as much info as possible.  Even though I had the VOACAP charts for VU4W I was there the whole time chasing him with the DX cluster spots provided at the time.  Still in the end, I only heard him on two bands.  Which BTW, matched VOACAPs prediction engine in DXLabs exactly!  

I don’t rely too much on the SFI numbers once they go over 100 unless they go above 180, but I do watch the “K” index all the time.  Still nothing beats a great antenna system like Joel has and listening aka chair time!    

73 de w5jay/jay..

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