Miscellaneous stuff that can help
An interesting article about ESD protection (thanks MAX) http://www.eetindia.co.in/ARTICLES/2004DEC/A/2004DEC03_RFD_AN02.PDF?SOURCES=DOWNLOAD
The NXP RF design guide http://www.nxp.com/acrobat_download2/other/discretes/nxp_rf_manual_12th_edition.pdf
Four graphics that show transponder reception power over distance
A table that shows design parameters of certain device congurations:
| The minimum input level that can be detected at the antenna input (dBm) due to thermal noise.
|vor AD8313 bei MIN
|The power level at the logamp input when a minimum input level is present. The logamp can detect signals between -65 and 0 dBm. Anything that is lower than -65 dBm cannot be detected.
|Ant. bei PO1dB
|The power level at the antenna input when the last LNA amplifier reaches its 1 dB compression output level. This means that the output/input function becomes non-linear. Usually a bit above this level PO1dB the amplifier would go into saturation (at level POsat) and an increase in input level would not provide an increase in output level. With the type of modulation used by Mode-S there is less danger that this means an immediate loss of signal detection. A low value can hint to reception problems when closer to the aircrafts transponder antenna.
|Ant. bei POSAT
|The power level at the antenna input when the last LNA amplifier reaches its saturation level. Not all LNA devices have a published POSAT. In this case PO1dB is used for calculation. With the type of modulation used by Mode-S there is less danger that this means an immediate loss of signal detection. A low value can hint to reception problems when closer to the aircrafts transponder antenna.
|vor SAW bei POSAT (*PO1dB)
|The power level at the input of the last SAW in the chain when the preceeding LNA is operated at its POsat or PO1dB value. SAW devices have a maximum input power level limit which can be e.g. 0 dBm or 10 dBm. It is not known what type of signal is exactly associated to this limit (continous, intermittent). Some devices have no published maximum input level.
|The range of antenna input level that can processed by the device. A lower value does not necessarily mean that the device will show less performance,
|The minimum sensitivity of the receiver at the antenna input. This is higher than the limit due to thermal noise if the LNA chain amplficiation is not sufficient to exceed the logamp intercept value
Log-Amp Output for various LNA combinations:
Quick reference table for LNAs and Filters
BGM1014 supply = 5V*/21 mA (17 - 25)
BGA2748 supply = 3V**/5,7 mA (4,5 - 8)
BGA2715 supply = 5V*/4,3 mA (3,5 - 5,5)
* 4,5 - 5,5V
** max 4V
Estimation of DF20, 21 replies:
These are the 3 registers that are queried in LTMA.
Afaik others are neither queried nor used.
Here is what works quite well:
(Bytecount of message starts at 1)
First check the bit rules, then calculate the values, then discard if not in range.
I would assume data quality when checks are passed is better than
95%. Sometimes heading shows 000 or 001. I dontknow how many responses
are discarded though. Most newer aircraft show all parameters.
Remember data are not squittered, but need interrogation, which is
site dependant. It certainly is less than one query per antenna
(MCP altitude, QNH setting, AP Mode)
Byte 2 and 04 =1
Byte 4 and 20 =1
Byte 5 and 01 =0
Byte 6 and FE =0
Byte 7 and 18 =0
Then calculate MCP altitude and check for < 471 or discard
Then calculate QNH and check between 960 and 1070 or discard
Byte 2 and 10 = 1
Byte 3 and 01 = 1
Byte 5 and 20 = 1
Byte 6 and 04 =1
Then calculate rollangle, gs, ttrack, turnrate and tas.
Compare GS, Ttrack with data derived from squitter. Discard if not reasonable in range.
Discard if TAS less than lets say 555 (unless you have a supersonic one in front of you)
(Heading, IAS, Mach)
Byte 2 and 08 = 1
Byte 3 and 01 = 1
Byte 5 and 05 = 0
Check values are in a reasonable range.