Hi Frank
You might be thinking a bit too linearly. I have a feeling that modeling
becomes MORE important the LESS you have to spend.
Your 1/2 wave example might be the perfect launching point. It's a good
estimate, but from an engineering standpoint, it is also sometimes the 800-
pound flyswatter. Sure it gets the job done, but perhaps there's a more elegant
solution.
Let's say you're putting up a 40m yagi pointed at Japan. Let's say that you
could invest in, say, 60 feet of tower as a brute-force estimate.
But let's say that HFTA tells you that due to terrain, not only could you save
the cost of 30 feet of tower, that entire 60-foot height is actually
detrimental to your goal. Would you find that information to be valuable?
Or maybe you want just an all-round general-purpose tribander. Let's say HFTA
tells you 60 feet for 20, 45 feet for 15 and 40 feet for 10. Let's also say it
shows a nice, sweet-spot compromise at 50 feet for all three bands. Is that
information valuable to someone with a limited budget?
There are guys who were expecting HFTA to confirm their brute-force estimates
of, say, 100 feet, but instead were told to go with 20 feet, due to terrain.
HFTA isn't perfect, no modeling is, but it gets you closer to hand-grenade
range than any estimates someone might derive from just reading.
The beautiful thing about ham radio is you can play however you like. Tinkerers
might find the journey more satisfying than the destination. And I guess
modelers are tinkerers too, just in a virtual domain.
73, Kelly
Ve4xt
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On Mar 2, 2012, at 5:50 PM, Frank <frankkamp@att.net> wrote:
> Pete Smith N4ZR wrote:
>
>> Frank, all that any good current book on antenna design will do is refer
>> you back to the same propagation realities that are used by HFTA and
>> other modeling software. HFTA produces nomograms that show what the
>> best takeoff angle will be for a particular target area, as share of 100
>> percent. Those are then matched with the antenna patterns generated
>> over real ground profiles, and a figure of merit is produced that tells
>> you, on *average*, how well a given antenna system at your QTH will
>> perform relative to the target area. Of course, conditions will vary
>> from day to day, or year to year, that is exactly what you want to
>> know. It doesn't absolve you from the need to design and build a good
>> antenna, but even the best antenna will be (on average) inferior if
>> placed at the wrong height.
>>
>> 73, Pete N4ZR
>>
>>
> Thanks for the explanation, Pete.
>
> I guess I did not fully understand what HFTA was all about.
>
> Now that I do, I am not convinced it is entirely useful, at least not to
> me since I don't have the resources to raise or lower my antennas at
> will. I just raise them up to 1/4 wavelength at the lowest frequency
> of interest and hope for the best.
>
> So far that has worked for me.
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