| |
G8MNY > TECHNI 24.08.20 16:43l 82 Lines 3397 Bytes #-1528 (0) @ WW
BID : 39331_N1URO
Read: DJ6UX DF7EAV GUEST DL9YCC OE7FMI
Subj: Understanding a Multipath
Path: DB0FHN<OE2XZR<OE5XBL<F1OYP<IZ3LSV<I3XTY<I0OJJ<GB7CIP<N3HYM<OK2PEN<
VE3CGR<N1URO<N2NOV<K5DAT<PE1RRR<GB7CIP
Sent: 200822/0758Z @:GB7CIP.#32.GBR.EURO #:2331 [Caterham Surrey GBR] $:2331_GB
>From g8mny%gb7cip.#32.gbr.euro@n2nov.ampr.org Sat Aug 22 04:03:50 2020
Received: from n2nov.ampr.org by n2nov.ampr.org ([JNOS]) with SMTP
id AA144073 ; Sat, 22 Aug 2020 04:03:50 EDT
Message-Id: <2331_GB7CIP@k5dat.bbs>
>From: g8mny@gb7cip.#32.gbr.euro
X-JNOS-User-Port: Telnet (k5dat @ 44.92.0.84) -> Sending message
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Feb 06)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
If you Rx a RF signal by more than 1 path this is what you get..
Reflection or Tx
tropo refraction. /'
The angle BC is / '
proportional to . . B / '
frequency with .' ' / '
refraction or . / . ' Path A is
defraction. . ³ . ' a direct
. ³ . ' or another
` .³. ' ' tropo path.
path length = B+C ³ 'A
³ '
C³ '
³ ' / 1st nul 150/(B+C-A) MHz \
³ ' Nulls due to path | further nulls repeat at |
³ ' length difference \ 300/(B+C-A) MHz spacing /
³' ³ ³
Rx _ _ _ _ ___ up to +6dB
/' `\ /' `\ /' `\ /' `\ enhancement
The affect of reflection, | | | | | | | | over 1 path
refraction or defraction º º º º
due to the anomaly is the ÄÂÄÄÄÄÄÅÄÄÄÄÄÂÄÁÄÄÄÂÄÄÄÁÄÂÄÄÄÄÄÅÄ Null > -20dB
make the tropo beam 300 400 500 600 700 800 Frequency
heading appear to change
with frequency! Of cause _ _ _ _
as the anomaly moves `\ /' `\ /' `\ /' `\ /' ` Path difference
causing the path lengths | | | | | | | | moved by « a
to change all the null º º º º wavelength
spot frequencies slide up ÄÂÄÁÄÄÄÂÄÄÄÁÄÂÄÄÄÄÄÅÄÄÄÄÄÂÄÁÄÄÄÂÄ
or down as well, changes 300 400 500 600 700 800 Frequency
in dual path amplitude
will cause the null depth _ _ _ _
to change, from not \ /' `\ /' `\ /' `\ /' `\ Unequal signals
detectable to extreme `Ä' `Ä' `Ä' `Ä' no deep nulls
nulling. ÄÂÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄÂÄ
300 400 500 600 700 800 Frequency
LENS EFFECTS
My experience with a group of well scattered users of 23cm GB3HV ATV repeater
at High Wycombe, may put more light on the subject. During a Wx front it became
apparent that large lens of heavy damp air was moving through many viewers Rx
paths....
GB3HV
_..._
/'' ``\
( DENSE AIR )
BASINGSTOKE \.._ _../
0dB """
READING CROYDON
-20dB -3dB
ALTON
+20dB
Signal were lost in some palaces & much enhanced in others by getting on for
ñ 20dB as the Wx front moved west to east. Most sites saw the effect over an
hour or so.
Why don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
Read previous mail | Read next mail
| |
