In our transition from LV2 to LV2.3, we've moved from S to C band for our telemetry because it's Just Better Up Here - we get smaller antennas, and less noise. More importantly, it gets our amateur TV out of the L band and into the now vacant S band, reducing interference with the also L band GPS. In the amateur radio world, running 802.11x in the amateur radio regulations (FCC Part 97) is called High-speed multimedia radio (HSMM).
- Should be USB-based.
- Should support a knon C-band standard, e.g. 802.11a.
- Should have soft MAC or other features which would allow us to customize how the radio behaves.
- Should be small and cheap, with an external antenna connector.
- Should support ad-hoc mode.
- Must be supported in the Linux kernel, or have a communication interface supported by Linux.
We're currently using the Alfa Network 802.11a/b/g/n/ long-range wieless USB adapter model AWUS051NH which seems to work great.
iwlist, the adapter supports the following channels:
**Channel 36 : 5.18 GHz** Channel 40 : 5.2 GHz Channel 44 : 5.22 GHz Channel 48 : 5.24 GHz Channel 52 : 5.26 GHz Channel 56 : 5.28 GHz Channel 60 : 5.3 GHz Channel 64 : 5.32 GHz Channel 149 : 5.745 GHz Channel 153 : 5.765 GHz Channel 157 : 5.785 GHz Channel 161 : 5.805 GHz Channel 165 : 5.825 GHz
The adapter literature claims it supports 5.15GHz to 5.35GHz and 5.725GHz to 5.825GHz. That's good, except the high end ought to be a bit higher, like 5.83 GHz to really run in channel 165. Huh.
If possible, we'd like to aim dead set in the middle of one of those two bands, so we have room to move up or down in order to match whatever our actual cylindrical patch antenna center point ends up being. And of course, we like higher frequencies, so maybe aim for channel 157 (5.785 GHz)? Although the higher band has a ± 40 MHz range while the lower channel has a ± 60 MHz range.
After testing the CPA, we found a sweet spot nearest channel 36.
- Must support (1,3,5) watt output (see the link budget page)
- Must be small enough to fit in the rocket
- Should have decent locking connectors, like SMAs.
- Must have a (3.3,5,12) V power input
We use the the RF LINX Corporation's now obsolete "ANTENNAFIER 4900-5800 CA SERIES" power amplifier. It has:
- 32dBm peak TX amplifier (1.5 W) and a 10 +/- 2.5 dBm RX amplifer with a not-so-great 2.5 dB noise figure.
- It takes 12V +/- 5% @ 250 mA (max)
- It's a very compact and hackable little PA, so it works nicely in one of our RF side chambers in the avionics system.
- Here's the datasheet.