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## <a name="Link budget for LV2"></a> Link budget for LV2

### <a name="What&#39;s our situation?"></a> 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)

<table border=1 cellpadding=0 cellspacing=0>
  <tr>
    <td> We want </td>
    <td> -53 dBm </td>
  </tr>
  <tr>
    <td> We need at a minumum </td>
    <td> -63 </td>
  </tr>
  <tr>
    <td> We have </td>
    <td> -62 </td>
  </tr>
  <tr>
    <td> We </td>
    <th bgcolor="#99CCCC"><strong> just pass </strong></th>
  </tr>
</table>

FM ATV

<table border=1 cellpadding=0 cellspacing=0>
  <tr>
    <td> We want </td>
    <td> -63 dBm </td>
  </tr>
  <tr>
    <td> We need at a minumum </td>
    <td> -73 </td>
  </tr>
  <tr>
    <td> We have </td>
    <td> -62 </td>
  </tr>
  <tr>
    <td> We </td>
    <th bgcolor="#99CCCC"><strong> win </strong></th>
  </tr>
</table>

[[WiFi]]

<table border=1 cellpadding=0 cellspacing=0>
  <tr>
    <td> We want </td>
    <td> -73 dBm </td>
  </tr>
  <tr>
    <td> We need at a minumum </td>
    <td> -94 </td>
  </tr>
  <tr>
    <td> We have </td>
    <td> -70 </td>
  </tr>
  <tr>
    <td> We </td>
    <th bgcolor="#99CCCC"><strong> win </strong></th>
  </tr>
</table>

----

### <a name="What signal levels are needed fo"></a> What signal levels are needed for ATV?

- P5 signal from the ATV circuit

Using FM ATV, P5 occurs at &gt; 50 uV (-73 dBm) Using AM ATV, P5 occurs at &gt; 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.

### <a name="What signal levels are needed fo"></a> What signal levels are needed for [[WiFi]]?

- A SINAD that allows 11 Mbps on the [[WiFi]] circuit

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.**

### <a name="Whats available?"></a> Whats available?

- Antenna and amplifier gains

- Path losses

The **path loss due to free space** can be found using an equation from [Andrew](http://www.andrew.com) ® Catalog #33; p8;

_Lfs (dB) = 96.9 + 20log10 D + 20log10 f_<br />D is in miles; f is in GHz;

Also the path loss can be calculated using an equation found in the [ARRL](http://www.arrl.org) Antenna Book; P17-6;

_Lfs = 20 Log10 4(pi)d / lambda(free space)_<br /> 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)**

----

### <a name="The budget"></a> The budget

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

ATV

- [[CommLinkBudgetLV2ATV21Jan2004]]

- [[CommLinkBudgetLV2ATV26Jan2004]]

- New [[CommLinkBudgetLV2ATV30Jan2004]]

[[WiFi]]

- [[CommLinkBudgetLV2WiFi21Jan2004]]

- [[CommLinkBudgetLV2WiFi26Jan2004]]

- New [[CommLinkBudgetLV2WiFi30Jan2004]]

----

### <a name="Other stuff"></a> Other stuff

- The FM ATV exciter puts out 50 mW (+17 dBm) this needs to be attenuated by 7dB for it to match the required +10 dBm signal input of the M67715 power amplifier. This is done with a Pi attenuator added to the input of the power amplifier board. The R values are 130/47/130 ohms.

- Also see System Operating Margin [(SOM)](http://www.ydi.com/calculation/index.php) described by <cite>® Young Design, Inc.</cite>. Their calculator is very useful. Actually the calculators have been moved to the Terabeam Wireless site: [Calculators](http://www.terabeam.com/support/calculations/index.php)

- The P number system is a metric for picture quality. P5 is best "closed circuit quality", and P1 is barely descernable. See ARRL Handbook. Tom O'Hara W6ORG provided the signal strength information needed for various P levels.

- The units of dBm at the transmitter is the only place where reference to milliwatts is applied. All other dB values are unitless ratios, thereby the final result is in dBm.

- _dBd = +2.15 dBi_<br />
- _dBm = 1mW @ 50ohm @ 1GHz_ (absolute reference level)

- Reciever preamp [KU2000LSF](http://www.db6nt.com/preamplifier.html) from Kuhne Electronic, GMBH. Typical gains of their Ga As components are 35 dB or better, with noise factors around 1.0 or less.

- Receiver preamp for 1.2 GHz, part number _DEM 23 LNA_ from [DEMI](http://www.downeastmicrowave.com) had 15 dB gain with 0.7 NF.

- Install a hybrid "brick" linear power amplifier such as Mitshubishi [M68719](http://www.mitsubishichips.com/data/datasheets/hf-optic/1_2ghz.html) New link -&gt; <http://www.g8ajn.tv/images/M68719.pdf> between the transmitter and antenna on the spacecraft. This puts out +42 dBm at 1dB compression (16W), consuming about 5 amps at 13.8 VDC supply (69 W). Thats an efficiency of 23%! Mitshubishi M67715 <http://www.qsl.net/n9zia/atv/67715.pdf> puts out 3 watts, using 1.5 amps of 12 VDC

- If a receiver with 6kHz bandwidth performs well at -87 dBm, a receiver of 6MHz bandwidth (1000 times more spectrum to fill with energy) will need (10 log10 (1000) = 30 dB) -87 + 30 = -57dBm signal to perform similarly.

- Other preamp products for signals below 1GHz can be found at [Advanced Receiver Research](http://www.advancedreceiver.com/index1.html).

- Information on the 2.4GHz amplifiers:

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

----

### <a name="Things to add"></a> Things to add

- Noise Factor, Noise Figure, Signal strength, SNR, SINAD, channel capacity?

- [[WiFi]] bandwidth related to signal strength?

- Helix gain and half power beamwidth? Helix bandwidth?

----

### <a name="Definitions"></a> Definitions

<cite>SINAD</cite> 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>

<cite>BER</cite> From Wikipedia: [http://en.wikipedia.org/wiki/Bit\_error\_ratio](http://en.wikipedia.org/wiki/Bit_error_ratio) From HF Electronics article: [http://www.highfrequencyelectronics.com/Archives/Jan03/HFE0103\_Tutorial.pdf](http://www.highfrequencyelectronics.com/Archives/Jan03/HFE0103_Tutorial.pdf)

----

### <a name="References"></a> References

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