| |
G0FTD > VHFUHF 09.02.06 02:52l 70 Lines 2342 Bytes #999 (0) @ WW
BID : 273430G0FTD
Read: GUEST
Subj: Selective propagation model
Path: ON0AR<ON0AR<HS1LMV<I0TVL<ED1ZAC<GB7YKS<GB7SYP<GB7ESX<GB7NNA
Sent: 060209/0025z 79148@GB7NNA.#31.GBR.EU $:273430G0FTD [Witham, Esx]NNA V3.1
Right then I'm gonna try another way of portraying my thoughts (rightly or
wrongly) to get a better understand of what's happening and what I'm trying
to describe.
Here's my basic model below.
_
. . /|
. . . /
. /.
. ./. .
. ./ .
. / .
. ³ .
. ³ .
³
³
³
³
³
³
³
³
³
x
Point x is the antenna and we are looking DOWN on the antenna (birds eye
view) and the dotted area is another famous "lump" of air mass where it's
refractive index has gone up.
Although it has refractive properties I've shown a refracted wavefront as
as a simple reflected wavefront in the diagram.
From point x we see a line which is a wavefront at 470Mhz, there is also
one at 500MHz but since we are looking down on both signals along their path
we can of course only see one line.
As both frequncies head into our lump of tropo they should be refracted
in angular terms by the same amount bar a very tiny amount due to the
tiny difference in wavelngth.
If it had been a 10GHZ vs 433Mhz comparison then the assumption would of
course be invalid due to the large difference in wavelength.
Right then, based up the above as my undertanding of the propagation model,
why does the 470Mhz signal and the 500Mhz signal appear to be being
selectively enhanced or attenuated ?
Even the movment of a tx mast would surely not matter as the point source
is the same for both signals.
OK - so what am I missing ?
I think it was Bryan who passed comment about the refracted wave being
out of phase with my directly received wave, yes I can see that would
would then the signal levels BUT surely ALL the mulitplex of channel
within the group should all be similary effected at the same time ?
That's NOT what I observe, it's still this bit that I'm failing to
understand ;-)
- Andy -
Read previous mail | Read next mail
| |
