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Re: Basic Antenna Question - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


nsolanki
 Post subject: Re: Basic Antenna Question
Posted: Wed Aug 01, 2012 8:59 pm 
 
Lieutenant

Joined: Wed Aug 01, 2012 8:54 pm
Posts: 3
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


 
   
 
biff44
 Post subject: Re: Basic Antenna Question
Posted: Thu Aug 09, 2012 5:11 pm 
 
Colonel

Joined: Wed Apr 08, 2009 11:07 am
Posts: 34
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.

_________________
Rich
Maguffin Microwave Consulting
www.MaguffinMicrowave.com


 
   
 
nsolanki
 Post subject: Re: Basic Antenna Question
Posted: Mon Aug 13, 2012 3:29 pm 
 
Lieutenant

Joined: Wed Aug 01, 2012 8:54 pm
Posts: 3
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


 
   
 
biff44
 Post subject: Re: Basic Antenna Question
Posted: Mon Aug 13, 2012 4:38 pm 
 
Colonel

Joined: Wed Apr 08, 2009 11:07 am
Posts: 34
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.

_________________
Rich
Maguffin Microwave Consulting
www.MaguffinMicrowave.com


 
   
 
nsolanki
 Post subject: Re: Basic Antenna Question
Posted: Mon Aug 13, 2012 7:23 pm 
 
Lieutenant

Joined: Wed Aug 01, 2012 8:54 pm
Posts: 3
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




Posted  11/12/2012

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