When you start thinking about the possible range you can/do get from one particular type of antenna as compared to another type of antenna, there are a few things that you should keep in mind. Here are a few of those thingys, certainly not all by any means, and not even close to enough of those 'thingys' to even calculate more than just 'sort of right' cuz they ain't absolutely wrong. (If you really want a nightmare list of things to consider, take a look at the design characteristics for any of the NEC based antenna modeling programs.)
First, you are dealing with propagation, shape of the radiation pattern, the electrical characteristics of the various levels of the ionosphere AND the various states that ionosphere assumes under different conditions in solar 'flux', some trigonometry so you can figure reflection/refraction angles, spherical trigonometry cuz none of this 'stuff' happens on a flat plane, and to top it all off cuz the one signal you are analyzing is never the only one 'there' so can be affected by another signal (intermod) - how two signal interact and the results.
Let me know when you get your head around all that so we can continue...
[Do I already have my head around all that stuff? Of course, naturally! ... And if you believe that, there's no hope for you at all. All those things really are considerations for antenna comparisons. The only part that isn't 'true' is that I understand it all, I certainly don't. I've been exposed to it! But I've been exposed to a skunk too! I don't plan on ever being exposed to either one again if I can help it.]
Just some 'common' stuff.
How much is reflected from the ionosphere is frequency related. Lower frequencies tend to get 'bent' and reflected back more often than higher frequencies are. Those 'lower' frequencies tend to sort of be divided from those 'higher' frequencies somewhere around 30 - 60 Mhz. (Why 6 meters seems sort of 'odd' in relation to either low/high frequencies.) Those lower freqs that are reflected are not totally reflected, only partially. No idea what that % is, not sure I even want to know. If you think of a signal as being razor sharp when first transmitted, when it get's reflected the first time, it's about as razor sharp as a baseball bat after wards. The second, third, whatever reflection makes it even more 'fuzzy', creates a huge number of multiple reflections because of that 'fuzziness', and therefore 'weaken' each of those reflections.
Under conditions where everything is controlled (yeah, right!), the results of a comparison are 'close enough' for an 'average'/valid comparison. Under conditions where you can't control all that stuff, the comaprison might still be ~sort~ of valid. And that's really okay for the average person. But the 'catch' is that it's only valid for the exact conditions under which the comparison was made. Take it all to a different location and all bets are off. OH BOY, we get to do it again! Why what you may find as a totally worthless antenna in your location may be the absolute bestest performer in another location.
Sort of gives a 'ball-park' estimate a whole new meaning, huh? Also why a salt-shaker is a nice thing to have around sometimes. Am I saying all antenna comparisons are trash? No, I'm not! Just keep that salt handy...
- 'Doc
