Talk:Friis transmission equation

In the dB version, shouldn't that be 10*log10(etc) rather than 20*log10(etc)? It's power, not amplitude. — Preceding unsigned comment added by 129.55.200.20 (talk) 14:04, 29 August 2016 (UTC)

Is friss free space equation same as space-wave field of a horizontal dipole in plane perpendicular to axis of dipole?

There seems to be an equation missing in here.

The standard form shows that the lamba/(4 pi R) term is squared. When this square term is put in front of the log, it becomes a times two, which gives us the 20 log instead of 10 log. This is the same reason why voltage gain is 20 log - the square. TheUnnamedNewbie (talk) 14:33, 21 July 2017 (UTC)

antenna gain unit

"To use the equation as written, the antenna gain may not be in units of decibels,"

I suggest saying which antenna gain unit shall be used, instead of naming one of possibly several units that are not applicable. Darsie42 (talk) 15:45, 18 September 2011 (UTC)

Fixed. crcwiki (talk) 20:18, 25 August 2017 (UTC)

This issue is now OBE since Friis never implied the use of numerical gain preferring antenna aperture as the expression of antenna gain per his original article.crcwiki (talk) 18:46, 10 October 2017 (UTC)

friis equation publish date

According to the paper "A Note on a Simple Tansmission Formula" the Friis formular was published 1946 not 1945 as stated in the article http://dsc.ufcg.edu.br/~maspohn/adhoc-grad/papers/Friis%20transmission%20equation/01697062.pdf. It may aswell be developed in 1945 but I did not find a source for that --Patrickf4v (talk) 16:31, 15 December 2014 (UTC)

Fixed. crcwiki (talk) 20:18, 25 August 2017 (UTC)

Wholesale edits made

There were some glaring issues with the finer points of the article. I have tweaked it quite a bit citing references where applicable. crcwiki (talk) 20:18, 25 August 2017 (UTC)

Big thanks to the anonymous editors who corrected my misspelling of Friis. Guess I will be making that mistake for the rest of my life.

Power received greater than power transmitted?

What am I missing here? It looks like the equation as written doesn't preclude the received power being greater than the transmitted power.

${\frac {P_{r}}{P_{t}}}=\left({\frac {A_{r}A_{t}}{d^{2}\lambda ^{2}}}\right)$

Quick test, so what if A_r is 10 square centimeter, A_t is 10 square centimeter, d is one meter (100 cm), lambda is 1 cm

(10*10)/(100^2*0.01^2)= 100.

That can't be right; what am I doing wrong? Skepticalgiraffe (talk) 21:33, 9 May 2023 (UTC)

@Skepticalgiraffe: Hello. You did nothing wrong. A ratio in the form $P_{r}/P_{t}$ is referred to as an "unnamed power gain" and it can be greater than one. Detailed examples of the phenomenon that you are mentioning are provided in a recent article. See Section III and figures 3, 6 and 8 of this reference. FreddyOfMaule (talk) 11:28, 3 January 2024 (UTC)

Thanks for the citation. I'm still not sure what I'm reading. Can you give a top-level summary of how the receiver can receive more power than the amount transmitted? Skepticalgiraffe (talk) 13:47, 19 January 2024 (UTC)

@Skepticalgiraffe: In the original Friis transmission formula, $P_{r}$ is the power available at the antenna port. This power available at the port of the receiving antenna, also referred to as "available power" at this port, is the greatest average power that can be drawn from this port by an arbitrary linear time-invariant (LTI) and passive load (see the Section I of ). It is well known that such an LTI passive load has an impedance equal to the complex conjugate ${\overline {Z_{A}}}$ of the impedance $Z_{A}$ presented by the receiving antenna. Thus, $P_{r}$ is not the power delivered to the actual load of the receiving antenna, but the power that would be delivered by the receiving antenna if the impedance of this load was ${\overline {Z_{A}}}$. As you see, $P_{r}$ and $P_{t}$ correspond to different circuits. This is why power conservation does not prevent $P_{r}$ from being larger than $P_{t}$. FreddyOfMaule (talk) 09:31, 26 January 2024 (UTC)

References