Optimizing Link Budget for 1.1km Transmission with 875MHz Carrier Frequency

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The discussion focuses on optimizing the link budget for a signal transmission over 1.1 km using an 875 MHz FM carrier frequency. The maximum allowed power is 1W, with low-loss omnidirectional antennas having a maximum attenuation of 0.1 dB. Participants analyze the received power equation, incorporating factors such as free space path loss (FSPL) and antenna losses. Calculations indicate that the FSPL results in a loss of approximately 92.1 dB, leading to a received power of -62.3 dBm after accounting for antenna attenuation. Clarification is suggested regarding whether the 0.1 dB loss applies to each antenna or the system as a whole.
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Homework Statement


A signal needs to be transmitted over 1.1km, with 12Hkz bandwidth on FM carrier.
Carrier freq=875MHz.
Allowed up to 1W carrier power transmitted and received thru omnidirectional antennas.
antennas low loss, max attenuation = 0.1dB


Homework Equations



Received Power (dBm) = Transmitted Power (dBm) + Gains (dB) − Losses (dB)

The Attempt at a Solution



I'm beat
 
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Mickydawg25 said:

Homework Statement


A signal needs to be transmitted over 1.1km, with 12Hkz bandwidth on FM carrier.
Carrier freq=875MHz.
Allowed up to 1W carrier power transmitted and received thru omnidirectional antennas.
antennas low loss, max attenuation = 0.1dB


Homework Equations



Received Power (dBm) = Transmitted Power (dBm) + Gains (dB) − Losses (dB)

The Attempt at a Solution



I'm beat

Well, at least you listed a Relevant Equation. That's good.

Now, what can you fill into that equation? What are the losses for example?
 
are the losses the free space path losses?
((4*3.14*1100*875000000)/300000000)^2

is the gain the attenuation ie G -0.1dB?

Power=1watt=30dB?
 
Mickydawg25 said:
are the losses the free space path losses?
((4*3.14*1100*875000000)/300000000)^2

is the gain the attenuation ie G -0.1dB?

Power=1watt=30dB?

What is "875000000)/300000000"?

The gain would be any antenna gain, but you are told the radiation is isotropic, so there is no gain.

It looks like you are trying to calculate the loss by using the surface area of a sphere of 1100m radius, which is correct. The 0.1dB would be an additional antenna loss to add in.

1Watt is 1000 times 1mW, so yes, that would be 10*log(1W/1mW) = 30dBm.


EDIT -- BTW, the question does not make it clear if it is 0.1dB max loss per antenna or for the two antennas as a system. You should see if you can clarify that (it oly changes your answer by 0.1dB, but it would be good to get it right the first time).
 
f=875000000
c=300000000

using ((4*pi*d*f)/c)^2=FSPL
((4*3.14*1100*875000000)/300000000)^2=FSPL

10log(FSPL)= losses in dB = 92.1dB

assuming 0.1dB attenuation per each antenna

Received Power (dBm) = Transmitted Power (dBm) + Gains (dB) − Losses (dB)
Pr=30dbm + 0 - 92.1dB - 0.2dB

Pr=-62.3dBm?
 
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