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Antennas and Transmission Lines / Mystery of the DR2W Propagation Map Default Antenna
« on: May 04, 2021, 00:21:21 UTC »
While doing some research in confirming the degree of realism in the Hamsphere HS4 simulator I stumbled upon the default power level and antenna used in the DR2W Propagation Map which many HS4 users use on a daily basis. The DR2W Team Website states that the power level of the modeled transmission site is 100 watts and that the default antenna (actually the only available antenna) is a 3/2 WL Monopole (that's 1.5 wavelengths!). This information hit me like a flopping salmon in the bottom of the boat. Why would anyone pick such an antenna for this modeling purpose. Is there some fabulous gain for this antenna? Does it have a great Take-Off Angle??
I began to look at the maps very closely and started estimating the size of the skip zones and the size of the signal arrival zones for the 30, 20, 17 meter bands in North America. The transmission site appears to be in the geographical center of the US so I found out the distance from Lebanon, Kansas to San Diego, CA (frequently the inner edge of the signal arrival zone and that turned out to be 1,085 statute miles. I averaged the width of several arrival zones for the first skip and they averaged about 800 SM so the center of the first arrival zone of the distance of the first skip would be 1,485 SM. Going to page 17 of the 1974 edition of the ARRL Antenna Book I find that Figure 1-10 yields a result of 23 degrees Take-Off Angle if F2 is at 261 miles (the upper limit) for a single-hop distance of 1500 miles. So there does not appear to be anything special in the way of radiation elevation angle with this antenna .And then there is the height of this antenna.
For 80 meters, a 1/4 WL monopole is 20 meters high (about 66 feet). A 1.5 WL monopole is 120 meters high (or about 394 feet approx.). There is no advantage with the 3/2 WL antenna over the 1/4 WL antenna in terms of difficulty of construction or maintenance. Perhaps the advantage is on receive because of a larger aperture? But the only consideration in the production of the maps is a transmitted signal not a received signal.
Well, I thought there must be some advantage in the gain figure. I looked up the "HamCAP and Type 13 & 14 Antennas" article by Alex Shovkoplyas, VE3NEA and there in the listing of the parameters for the 3/2 WL Monopole there is 0.0 gain over a dipole listed. Alex is one of the authors of the "HamCAP User's Guide". (I have an email into him asking the above questions about this antenna.)
Elsewhere in Alex's article there are parameter inputs for this antenna with a listing of 0.00 db gain and listed as Max Gain dbi which I take to mean "against Isotropic". Even worse.
OK, I told myself, I'm going to get to the bottom of this. I emailed Winfried Kriegl, one of the DR2W Team members (DK9IP) and he told me that he did not know why that antenna was the default antenna for their model but I got the impression it was because this was a legacy antenna from the original VOACAP software that their model is based upon. The DR2W mapping application is more of a shell with the added adjustment of an emphasis placed on Sun Spot Number.
The final result? I only know this is the last antenna anyone would choose to pay for and erect and I still don't have the take-off number confirmed. Neither do I have an explanation for the original selection of this antenna for VOACAP purposes (you can still select this antenna...go to VOACAP Online for Hams and check out the vertical antennas!)
I would really appreciate any answers that other forum users might provide!
73 de AL7EN Russ
I began to look at the maps very closely and started estimating the size of the skip zones and the size of the signal arrival zones for the 30, 20, 17 meter bands in North America. The transmission site appears to be in the geographical center of the US so I found out the distance from Lebanon, Kansas to San Diego, CA (frequently the inner edge of the signal arrival zone and that turned out to be 1,085 statute miles. I averaged the width of several arrival zones for the first skip and they averaged about 800 SM so the center of the first arrival zone of the distance of the first skip would be 1,485 SM. Going to page 17 of the 1974 edition of the ARRL Antenna Book I find that Figure 1-10 yields a result of 23 degrees Take-Off Angle if F2 is at 261 miles (the upper limit) for a single-hop distance of 1500 miles. So there does not appear to be anything special in the way of radiation elevation angle with this antenna .And then there is the height of this antenna.
For 80 meters, a 1/4 WL monopole is 20 meters high (about 66 feet). A 1.5 WL monopole is 120 meters high (or about 394 feet approx.). There is no advantage with the 3/2 WL antenna over the 1/4 WL antenna in terms of difficulty of construction or maintenance. Perhaps the advantage is on receive because of a larger aperture? But the only consideration in the production of the maps is a transmitted signal not a received signal.
Well, I thought there must be some advantage in the gain figure. I looked up the "HamCAP and Type 13 & 14 Antennas" article by Alex Shovkoplyas, VE3NEA and there in the listing of the parameters for the 3/2 WL Monopole there is 0.0 gain over a dipole listed. Alex is one of the authors of the "HamCAP User's Guide". (I have an email into him asking the above questions about this antenna.)
Elsewhere in Alex's article there are parameter inputs for this antenna with a listing of 0.00 db gain and listed as Max Gain dbi which I take to mean "against Isotropic". Even worse.
OK, I told myself, I'm going to get to the bottom of this. I emailed Winfried Kriegl, one of the DR2W Team members (DK9IP) and he told me that he did not know why that antenna was the default antenna for their model but I got the impression it was because this was a legacy antenna from the original VOACAP software that their model is based upon. The DR2W mapping application is more of a shell with the added adjustment of an emphasis placed on Sun Spot Number.
The final result? I only know this is the last antenna anyone would choose to pay for and erect and I still don't have the take-off number confirmed. Neither do I have an explanation for the original selection of this antenna for VOACAP purposes (you can still select this antenna...go to VOACAP Online for Hams and check out the vertical antennas!)
I would really appreciate any answers that other forum users might provide!
73 de AL7EN Russ