[Elecraft] Sloping Terrain vs Feedline Losses

Fri Jul 15 22:32:02 EDT 2016

Agree with your points.  I've said for a couple of decades now that one 
of the least expensive ways to improve a modest station (assuming one 
has at least a decent antenna) is to add an amplifier.  Lots cheaper 
than a bigger tower and a bigger antenna.

Also, to your point about arrival angles ... HFTA calculates a "figure 
or merit" for several common paths.  N6BV (the author of HFTA) ran a few 
thousand simulations in VOACAP between various parts of the world for 
the parameter TANGLE ... the optimum takeoff angle for that path. He ran 
it for every month of the year over a full sunspot cycle (typical solar 
fluxes) for each path to generate a statistical profile of the 
normalized signal strength for each takeoff angle.  I believe the data 
for those profiles is included with the ARRL Antenna Book.  HFTA's 
"figure of merit" for a particular antenna over a particular terrain 
overlays the calculated radiation pattern over that VOACAP statistical 
profile of takeoff angles and sums the combination for each angle.

For example, N6BV ran 121 TANGLE calculations (12 months and 11 years) 
from W7 to Europe, compiling the signal strength at every degree of 
elevation for each of the 121 runs.  Adding up the strengths for each 
angle and dividing by 121 gives the statistical profile for the TANGLE 
calculation.  Overlaying the HFTA radiation pattern for the terrain 
profile pointing from W7 to Europe onto the TANGLE profile, and then 
adding up the result for each degree, gives the HFTA Figure of Merit.  
The net result gives an interesting assessment of the antenna/terrain 
for a particular path taking into account an entire sunspot cycle.

That being said, TANGLE is an empirically generated projection based 
upon actual data taken during the International Geophysical Year and 
other times, and one of the key scientists who worked on VOCAP and 
adapted it for general use (Greg Hand) has pointed out that of all the 
20 or so parameters that VOACAP can produce, TANGLE is probably the 
least rigorously substantiated.  Still, I think that HFTA Figure of 
Merit offers a useful assessment of the combination of horizontally 
polarized antennas and terrain for a desired path. I've used HFTA quite 
a bit, and my on the air results subjectively correlate quite well with it.

73,
Dave   AB7E

On 7/15/2016 12:16 PM, brian wrote:
> Guys,
>
> There is another issue here.
>
> That is :
>
> Just because ones antenna pattern is inferior to an optimum one by 5 
> or even 20 db at the best arrival angle, that doesn't mean there is 
> zero energy at the most important arrival angles.  It just means there 
> is less.
>
> QRPers often work the same stations as QRO guys. You see it all the 
> time in contests. Likewise guys with high radiation angle antennas do 
> work DX. Maybe just not always the really rare ones, or as many or as 
> quickly.
>
> ---------------------------------------------------------------------
> It might be more interesting to discuss something like $/db to get to 
> closer to optimum.  Going from low dipole to a higher one might cost 
> zero to a couple hundred and gain 3 db at about $10-$100/db. Going 
> from that higher dipole to something directive that picks up 4 db more 
> might cost a couple kilobucks - $200-500/db.  Going from this 
> directive array to something that picks up another 3 db might cost 5 
> to 10 kilobucks. Now you're at > $1000/db.  Diminishing returns can 
> happen quickly.
>
> Desktop dB are near the cheapest. One can pickup 10 db (from 100 w) 
> for about $100-200/db by buying a used amp.  Desktop dB can be easier 
> to keep "in the air" too.
> --------------------------------------
> So what is that extra db worth to you?  Real world constrains besides 
> money often limit what's possible too.
>
> Paper and electricity is cheaper than hardware.  Learn how to use 
> EZNEC or another antenna modeling program. Spend pennies/per bad new 
> antenna design rather than big bucks.  Go after the cheap dB first.  
> Debunk the myths about magic or folklore antennas that waste time and 
> money.
>
> Don't forget feedline loss.  One example was a local who was trying to 
> work satellites using 50' of RG58 feedline.  Switching him over to 
> LMR-400 doubled his uplink radiated power and improved reception by 
> even more.
>
> Read all you can. For example, K9YC's paper referenced in this thread 
> illustrates how difficult it is to make a vertical work as well as 
> even reasonable height dipole on the higher frequency bands. The 
> ground reflection gain of a horizontal antenna (event a zig zag one) 
> is hard to overcome.
>
> 73 de Brian/K3KO
>
>
>
> On 7/15/2016 18:02 PM, Jim Brown wrote:
>> On Fri,7/15/2016 10:07 AM, Wes Stewart wrote:
>>> shows an example where IONCAP says there is no (usable) path between
>>> two stations, yet QSOs are made.
>>
>> Wes,
>>
>> There are exceptions to every generalization, even when the
>> generalization is good most of the time. I recall some well known person
>> who had come up poor but was no longer saying "I've been poor and I've
>> been rich, and rich is better." :)
>>
>> Sure, there are times when a higher angle path is better than a low
>> angle path (or exists when the low angle path is not present). But
>> N6BV's statistical data for paths to various locations shows low angle
>> paths to be better far more often than higher angle paths. It also shows
>> high angle paths some smaller percentage of the time.
>>
>> The HUGE problem with using the concept of "takeoff angle," and ONLY the
>> takeoff angle to describe and evaluate antenna performance is that by
>> looking at only one curve at a time, it fails to compare one antenna or
>> mounting height to another. Again, my work looking at the effects of
>> antenna height in a "flatland" QTH have all plotted the complete
>> vertical pattern ON THE SAME GRAPH, which clearly shows that for the
>> range of vertical angles where we can use the ionosphere, higher is
>> better! N6BV presents this quite well as a "figure of merit" for the
>> plots of his elevation studies in HFTA, while also showing the complete
>> vertical data.
>>
>> 73, Jim K9YC
>>
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