Paths to Everywhere!

I have been play­ing with HFTA soft­ware from the ARRL Antenna Book to deter­mine the typ­i­cal take-​off angles needed to com­mu­ni­cate to DX locales. First step was to develop my ele­va­tion pro­file, which I did based upon the instruc­tions included using a pro­gram named Micro­DEM. While not the most intu­itive thing in the world, I did man­age to fol­low the Antenna Book direc­tions to obtain my DEM GIS file from a gov­ern­ment loca­tion and to cre­ate exportable FAN files needed for HFTA. A FAN file is a ter­rain height pro­file in a par­tic­u­lar direc­tion from my QTH “tower” location.

The false-​color map shows rel­a­tive height above sea-​level (ASL). I am at approx­i­mately 550 feet ASL, or 168 meters. I recol­ored the chart and added lines to areas of inter­est. I used Gimp (a Pho­to­shop clone) to dedit MicroDEM’s map out­put, reduc­ing the blue to add clar­ity to the river val­ley ter­rain nearby, and the lines cor­re­spond to the HFTA FAN files to obtain ter­rain pro­files in the areas of interest.

A FAN file is a very sim­ple data-​set: dis­tance from point and height at dis­tance. Here is mine toward Europe:

meters
0 158.0
30 158.43
60 159.22
90 159.88
120 160.98
150 161.90
180 163.29
210 164.45
240 165.00
270 164.73
300 164.37
330 164.10

(And so on out to 4410 meters from my antenna in the direc­tion to Europe.)

Once the FAN files are saved in a loca­tion that HFTA can read them, I ran ter­rain plots for each of the direc­tions of inter­est. Here is the one to Europe…

If you fol­low along the line to EU on my ter­rain map, the ter­rain pro­file is up and down (or hills and hollers as they say in Ten­nessee!) as it con­tin­ues to drop height toward the riverbed. The ter­rain plot in that direc­tion is out to 15,000 feet or so from my antenna loca­tion (about 3 miles or 4.5 kilo­me­ters.) Of course, the ter­rain illus­tra­tion is highly exag­ger­ated due the x-​axis scale. The exag­ger­a­tion high­lights the pro­file changes as you get more dis­tant from the antenna location.

HFTA pro­duces an Assess­ment Plot for anten­nas based upon the ter­rain pro­file. In the fol­low­ing exam­ple I have illus­trated a dipole mounted 30 feet high plot­ted over flat ground of medium conductivity.

The bar graph cor­re­sponds to the sta­tis­ti­cal aver­age of wave angles that sig­nals arrive at my loca­tion from Europe on 20M. Notice the pre­dom­i­nant angles are 3 degrees, 10 degrees and 15 degrees. Super­im­posed is the gain line at wave angles for a sim­ple dipole at a height above flat ground of 30 feet (9 meters). This antenna is pretty weak at 20M sig­nals arriv­ing at 3 degrees – too low – but becomes a bit more use­ful for sig­nals arriv­ing at higher angles up until about 35 degrees where it is strongest. A quick analy­sis is this antenna will play mod­er­ately well into EU at the higher wave angles.

Note also the dipole Max. Gain is listed as 7.4dBi. This is cor­rect for a dipole 30′ over real ground of medium con­duc­tiv­ity. A dipole in free space is 2.1dBi, but put it over con­duc­tive ground and the hor­i­zon­tal polar­iza­tion ben­e­fits from ground reflec­tion gain. This is NOT the case for ver­ti­cally polar­ized anten­nas how­ever (although I wish it were).

In the next analy­sis I have graphed the same antenna/​frequency except this time using my actual ter­rain pro­file pointed towards Europe.

The real ground slopes down towards the river in the direc­tion of Europe enhances the angles below 7 degrees. Sta­tis­ti­cally on 20M sig­nals do not arrive much at 4 – 7 degrees, but there is a few dB increase at 2 and 3 degree take-​off angles. It is a bet­ter illus­tra­tion to com­pare the antenna ref­er­enc­ing another, so I have made a prac­tice to always include the flat-​ground mod­els in my graphs. Here is the 20M dipole 30′ up com­pared to both flat and real ground.

My sur­round­ing ter­rain enhances sig­nals by about 3dB below 7 degrees on 20M. Still weak though but hey…gain is gain! Sim­ply due to slop­ing ter­rain a dipole will have the same gain as a Double-​Extended Zepp at this height for TO angles under 7 degrees. So what hap­pens if I go higher?

A higher dipole pro­duces pre­dictably bet­ter gain at all take-​off angles. Def­i­nite enhance­ment hap­pens at 40′ (12 meters) and even bet­ter at 50′ (15 meters). I could derive from this study that 50′ is a great place for a 20M dipole to be placed, but 40′ is not bad at all. In fact, 40′ might pro­vide slightly more util­ity for domes­tic sig­nals arriv­ing around 5 degrees.

Lets look at the same sit­u­a­tion to EU but this time on 40M. Here is where HFTA is really show­ing some inter­est­ing things!

Sta­tis­ti­cally, 40M sig­nals arrive from Europe at around 4 degrees and around 13 degrees. Also some higher angles sig­nals arrive at 24 degrees. There is sig­nif­i­cant ter­rain enhance­ment at around 4 degrees, but lit­tle dif­fer­ence between the mod­elled heights! Basi­cally, a low wire on 40M plays just as well as a wire at 50′ into EU for very low TO angles. The dif­fer­ence between a 30′ and 50′ wire is about 4dB at 14 degrees. From my loca­tion, a 40M dipole at 9 meters high should play just fine, but being at 50′ makes sig­nals come in that much louder at higher wave angles.

A model is only just that, but my expe­ri­ence val­i­dates this exer­cise. My low G5RV (9 meters above ground) plays very well into EU on 40M most of the time. I do not know enough about prop­a­ga­tion at 40M to know when higher or lower wave angles are sup­ported (but will inves­ti­gate) but seem to recall that gray-​line sig­nals seem to be loud­est on 40M. My suc­cess on 20M is gen­er­ally less sat­is­fac­tory. There I am com­pet­ing with yagi anten­nas on tow­ers, and as such my sig­nals are always down in the noise by an S-​unit or so. I con­sider 20M my worst band.

Some final thoughts…

I get out just fine on all ham bands. my G5RV at 30′ has been a great antenna. In less than 2 years of being active again, I have worked all United States on 80 and 40M. I was awarded WAS Triple Play Award #123. I cur­rently have 131 coun­tries worked, with 95 con­firmed via LoTW. My worked coun­try totals on 80M: 73, 40M: 95, 20M: 104, 15M: 57. You can work DXCC with one low antenna in a short amount of time!