Eddy,
#2 ... If the steel structure was fully enclosed all of the induced
currents would remain on the INSIDE of the structure only and never
escape the box. Look up "Faraday shield" if you don't believe me. If
the steel structure was not fully enclosed you would, depending upon the
size and shape of it, suffer severe pattern distortion as the currents
and re-radiated fields bounce all over the place before they escape the
structure. And if the steel structure had resistive losses, much of the
energy would be dissipated as heat before the energy escaped it. I
don't see why anyone would view any of that as desirable.
#4 ... As I and others have tried to point out to you, "ground" is not
automatically a heatsink for RF. Currents passing through lossy ground
will indeed be dissipated as heat, but merely connecting a metal
structure to ground does not necessarily mean that significant currents
will flow through ground. If you can't grasp that you don't understand
the wave nature of RF.
By the way, I never mentioned anything about a lossy VFO cover and I
don't have the slightest clue what you are talking about. But I will
say this ... from a practical standpoint there is no way a lossy box can
be made that shields as well as a fully conductive one. The lossy box
would have to be physically very thick. I know you won't understand
that, but it it helps any try to think of the difference between a
reflective heat shield and an insulating one. Physically the analogy is
greatly flawed, but the concept is the same.
Lastly, I never said that trees weren't nature's gift to hams. I relied
on trees for years to support various wire antennas, and many of the
folks on this reflector have done the same with fine results. Running a
vertical antenna up the trunk of a tree is not the best of use one, but
frankly I'm getting really tired of trying to explain to you why.
Dave AB7E
On 12/28/2011 6:27 AM, Eddy Swynar wrote:
> On 2011-12-27, at 8:29 PM, David Gilbert wrote:
>
> #2 Just because steel has lower loss than a wet tree doesn't mean that it
> would be smart to built an antenna inside of a steel structure when it would
> be better all the way around to put it in the clear. Why would you ever do
> that?
>
> ---I guess you'd do it because, using the logic of "wood" vs. "steel" that's
> been utilized here so far that says there are absorptive losses in wood /
> trees, whereas RF would simply reflect off of metal---correct? So why not do
> it...? The signal would simply "...reflect its way" out of the steel
> enclosure with minimal loss, if I understand things so far...in a wood
> enclosure, it would be absorbed& lost.
>
> #4 Actually, at least a few people have already answered your questions.
> Conductive but mostly lossy structures absorb RF ... conductive but mostly
> non-lossy structures deflect or block RF.
>
> ---If the structure is conductive and non-lossy, would it not then simply and
> efficiently re-direct all that RF directly to ground, creating an even
> GREATER loss in our far-distant signal? Think of your OT VFO enclosure:
> shielded, bypassed, and GROUNDED. Taking the logic of this a step further, if
> a well-grounded low resistance cover over a VFO was ineffective because it'd
> merely "deflect" RF, then why not simply place a small wooden apple basket
> over top of it...? Surely the lossiness of the wood would "absorb" any RF
> fields emanating from the VFO itself, right...?! And a grounded cover would
> thus be rendered a moot point!
>
> Nobody is "having it both ways" ... you just don't grasp the difference.
>
> ---No Dave, I guess I do not grasp the difference...and I'm glad of it! If I
> were to accept such an "ism" as the gospel truth, I would never have gotten
> my station on the air 40 years ago...and I would have razed each& every tree
> in the immediate field of the tower that I have here now, too. Trees were the
> gifts of nature that allowed me to get on the air years before I could even
> dream of ever getting a free-standing steel tower...and I think that any
> prevailing "...tribal knowledge" that alleges they are bad to the hobby is
> anathema to sustained growth in our ranks, too...think "stealth", think
> inexpensive aerial supports.
>
> It's your turn to think about it....
>
> ---There. I've thought about it! And I remain unconvinced... :>)
>
> ~73~ de Eddy VE3CUI - VE3XZ
>
>
>
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