wiki/ LinkBudget

Link budget for LV2

What's our situation?

Here are our requirements for signal strength at the receiver front end, and what the current systems provide.

AM ATV (if we were to use it)

We want -53 dBm
We need at a minumum -63
We have -62
We just pass

FM ATV

We want -63 dBm
We need at a minumum -73
We have -62
We win

WiFi

We want -73 dBm
We need at a minumum -94
We have -70
We win

What signal levels are needed for ATV?

Using FM ATV, P5 occurs at > 50 uV (-73 dBm) Using AM ATV, P5 occurs at > 150 uV (-63 dBm) At 5 uV (-93 dBm), AM and FM are at the same level of "snowyness." It is best to exceed the needed signal requirement by 10 dB to allow sufficient fade margin.

For FM ATV, we need -63 dBm to give P5 picture with 10 dB of fade margin.

For AM ATV would need -53 dBm for P5 and 10 dB fade margin.

What signal levels are needed for WiFi?

This SINAD can be obtained with -83 dBm at the WiFi card. A SINAD allowing the lower limit of 1Mbps on the WiFi circuit is acheivable with -94 dBm signal at the WiFi card. It is best to exceed the needed signal requirement by 10 dB to allow sufficient fade margin.

For WiFi we need -73 dBm at the receiver to give 11 Mbps and the desired fade margin.

Whats available?

The path loss due to free space can be found using an equation from Andrew ® Catalog #33; p8;

Lfs (dB) = 96.9 + 20log10 D + 20log10 f
D is in miles; f is in GHz;

Also the path loss can be calculated using an equation found in the ARRL Antenna Book; P17-6;

Lfs = 20 Log10 4(pi)d / lambda(free space)
where d and lambda are in the same units

The freespace loss equation from the Andrew catalog will be used for this calculation. The worst case path is the distance of our spacecraft at apogee, which is 10 miles or 52,800 feet.

At the ATV frequency, 1.277 GHz. Lfs = 96.6 + 20log10(10) + 20log10(1.277) = 118.72 dB (loss)

At 2.422 GHz Lfs = 96.6 20log10(10) + 20 log10(2.422) = 124.28 dB (loss)


The budget

Add up all the gains and losses from rocket to the ground...

ATV

WiFi


Other stuff

http://www.ydi.com/products/amp2440-amplifier.php


Things to add


Definitions

SINAD From Wikipedia: http://en.wikipedia.org/wiki/SINAD From Aeroflex, a manufacturer of SINAD analyzers: http://www.aeroflex.com/products/signalsources/signalgens/articles/sinad.pdf

BER From Wikipedia: http://en.wikipedia.org/wiki/Bit_error_ratio From HF Electronics article: http://www.highfrequencyelectronics.com/Archives/Jan03/HFE0103_Tutorial.pdf


References

ARRL Handbook
Antenna Engineering Handbook
SMAD III
Tom O'Hara W6ORG; Signal strength needed for ATV