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G8MNY > TECH 24.05.23 10:15l 173 Lines 7717 Bytes #999 (0) @ WW
BID : 48199_GB7CIP
Read: GUEST
Subj: Understanding a Multipath
Path: IW8PGT<I3XTY<IZ3LSV<DB0ERF<OK0NAG<OK0NBR<SR1BSZ<EA2RCF<LU9DCE<VA3TOK<
VE3KPG<GB7CIP
Sent: 230524/0810Z @:GB7CIP.#32.GBR.EURO #:48199 [Caterham Surrey GBR]
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
SB TECH @ WW
Mobile Mast Madness
By G8MNY (Updated Aug 07)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Some time ago I watched another TV phone in programme, where RF death beam
hysteria & NIMBY (not in my back yard) ruled OK. This was triggered by another
report that cancer "might" be cause be the radiation from the 47,000 UK masts.
A similar program on WiFi, expressed the same irrational science, e.g. no
substantiated evidence of any harm, so ban it from schools just in case.
1/ The idea that radiation from phone mast kill people is absurd, quite the
opposite is true.
2/ Mobile phones actually save lives. 100s per day as emergency calls for
accidents, heart attacks, robberies, & assaults etc. are made right from the
incident site, with no added delay accessing a land line phone. So the
services are more likely to get there in the crucial life critical "golden
hour" time. Something like this..
100%_
Lives³-...___
Saved³ ~~--..__
³ ~~-.
³ ~-.
³ ~-.____
ÀÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÄ>Incident
1m 2m 4m 8m 15m 30m1h 2h 4h 8h Time
3/ The idea that the radiation Rx from masts is high (compared to the phones)
is wrong. The fact that the RF field from masts is millions of time weaker
at ground level than from a phone by your ear is never mentioned! The maths
of "Square law" is unknown to the media?
³Ý
RF Field³³
Strength³ |
V/M ³ \
³ ~-._
³ ~~--...___
³ ~~~~----...._____
ÃÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄ
0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 Distance
4/ The idea you can put the masts somewhere else is also untrue. You need the
masts in the populated area because the range is so low (about 1kM max in
the clear on 2.7GHz).
Masts further away will cause bigger cells & hence less traffic capacity per
area. Also your handset will have to Tx much higher power (shorter Tx
time/battery life etc.) if the cells are large.
Hill 1 Hill 2
± ± Hill 1 & 2 cells
_³_ _³_ do not want see
/~ ~\ /~ ~\ QRO phone signals
\ ± / from the next hill
\_³_/ that may be on the
Populated same frequency!
Valley
Other than high population areas, masts are generally sited in valleys that
would be otherwise be RF holes, & on hilltops, where phones can then run low
power & stop multi cell hilltop QRM.
5/ From 3 & 4 it is NOT a good idea to have masts further away from schools, in
fact the school could well do with the mast site money to pay for better
education. Lowest radiation is often close up to a masts under the beam!
@20m _ . Ä ~
±= : _ ~
³ ~ Ä- . _
º Main beam ~ Ä- . _
Þ > 100M ~ Ä- . _
Û to ground level ~ Ä- . _
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
6/ The long safety record of other UHF RF radiation, like QRO TV Tx (Mega Watts
ERP), or the extreme QRO of air traffic microwave radar (Giga Watts ERP) is
never considered relevant to mobile mast radiation safety case, why not? Or
for that matter the not insignificant RF leakage of microwave ovens in most
kitchens.
7/ The only real loss of life due to mobile phones, is due to the stupid
drivers holding a mobile up to their ear, driving one handed & not
concentrating on their driving. This is now illegal in most countries, but
these driving laws have had little effect!
8/ About 40% of the population will get cancer (noticable as we live longer)
statistically cancer clusters will occur. E.g. a street may have no cancers
in it & another have 100%, This is normal random distribution, & as masts
are everywhere people are, so they get blamed. If it were true there would
be 47,000 cancer hot spots in the UK! (It used to be witches that were
burned at the stake, now it is masts,)
Unfortunately this NIMBY attitude over masts & RF, has impacted on the Amateur
radio hobby from both the uninformed public as well as planners.
On a different topic...
Note 2/ also shows the opposite view, "that speed humps save lives".
London Ambulance Service has be quoted before now to say that 700 lives are
lost per year on average, directly due to London's speed bumps & traffic
calming measures, by increasing time critical emergency journey times. The same
is true for Fire engines, that also burst their water tanks over these bumps.
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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