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Re: Basic Antenna Question - RF Cafe Forums
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| nsolanki
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Post subject: Re: Basic Antenna Question
Posted: Wed Aug 01, 2012 8:59 pm
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Joined: Wed Aug 01, 2012
8:54 pm
Posts: 3 |
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Hi Everyone,
I am RF student. I have a question
about the antenna receiver and transmitter.
Question: If I am transmitting constant power
with the ideal environment with no loss. Will the
receiver absorb some of the wireless signal strength.
So if i have more number of receiver there is more
rf power loss.
What bugging me is if RF
wave induce current in the receiver then there must
be a signal loss due to law of conservation of energy
right ?
Thank you.
nsolanki
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biff44 |
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Post subject: Re: Basic Antenna Question
Posted: Thu Aug 09, 2012 5:11 pm
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Joined: Wed Apr 08, 2009
11:07 am
Posts: 34 |
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Well, yes an no.
If you have 1 omnidirectional
transmit antenna, and two receive antennas 10 foot
radius away, but not too close to each other, then
the presence or abseince of either of the receive
antennas does not change the receive power to either
of the antennas.
But, each receive antenna
has an "effective aperture", so much of the signal
sent at that aperture will go into the antenna.
So if you place one antenna 10 feet away, and another
antenna 15 feet away on the same azimuth/elevation,
then the first antenna does suck up a lot of the
power at that particular solid angle, and only some
of the power sneaks by to the second farther antenna.
So in that particular case, the power to the 2nd
antenna is reduced somewhat. The first antenna either
absorbs, or reflects the power at that solid angle.
An obvious example would be a dish reflector
antenna as the 1st antenna. Not much is going to
get by the reflector dish to the 2nd antenna if
they are on the same radial.
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nsolanki |
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Post subject: Re: Basic Antenna Question
Posted: Mon Aug 13, 2012 3:29 pm
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Joined: Wed Aug 01, 2012
8:54 pm
Posts: 3 |
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Hi Rich,
Thank you very much for you reply.
This is the exact answer I was looking for. I read
my own question and realize that it was ambiguous
to understand since English is not my first language.
Now your explanation leads to me another question
(I will try my best to communicate properly):
If we have one closed hall with absorbing walls
(so no reflection of signal) and constant Wireless
power for wifi/mobile phones, does the effective
receiving power decreases with increases of number
of receiver? In other words do I have to increase
the transmitting power with increase number of receiver
since each receiver absorb some power? What happens
with the same scenario with non absorbing wall?
nsolanki
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biff44 |
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Post subject: Re: Basic Antenna Question
Posted: Mon Aug 13, 2012 4:38 pm
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Joined: Wed Apr 08, 2009
11:07 am
Posts: 34 |
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Putting 50 receivers in the (big) room will not
change the received power than it there is only
1 receiver in there.
That said, if those
50 receivers are also sometimes transmitting, then
you run the risk that they may step ontop of the
one signal you are trying to receive. You need a
certain signal-to-noise ratio for communications
to make it thru without bit errors, so too much
noise in the room may require more transmit power
for the one signal you are trying to receive.
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nsolanki |
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Post subject: Re: Basic Antenna Question
Posted: Mon Aug 13, 2012 7:23 pm
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Joined: Wed Aug 01, 2012
8:54 pm
Posts: 3 |
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So in essence power absorb by the receiver (if receiver
never transmit back) doesn't really affect the total
signal power.
Thank you Rich.
nsolanki
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Posted 11/12/2012
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