wiki/ news/ 2008-04-09 - Ad Hoc comm team meeting on communication system frequencies

Maria, Glenn, Frank, Josh, Sarah, Jamey and Andrew talked comm stuff tonight.

We decided to try and nail down our frequencies so that we can begin designing new patch antennas. And that, of course, got us to ask: what frequencies are we using?

Clearly, the GPS L1 frequency of 1.575 GHz is not going to change :) But what about our ATV and telemetry systems?

ATV Frequency

LV1 used 440 MHz for ATV, since having an inverted-V antennas sticking out of the nose cone wasn't a problem. LV2 used 1.2 GHz with patch antennas because of the potential speed of the rocket. 1.2 GHz required a "hacked" exciter (the part that ups the NTSC signal to 1.2 GHz) and a power amplifier. Note that it's hard to get those exciters these days.

Andrew had the dubious thought that we could employ a suite of 4x 2.4 GHz colro security cameras for our ATV system. They're cheap, they have built in transmitters that probably don't require hacking, and they're small [1]. The problem is, their four channels are at 2.414, 2.432, 2.450, and 2.468 GHz, which means we can technically only use the first two channels since the S band only extends up to 2.450 GHz [2]. But heck, two channels isn't bad, and it's a pretty packaged deal, and the cameras come with their own "exciters", and we can definitely find 2.4 GHz amplifiers to boost their signal... so Andrew still doesn't hate it. The question is, how bad do these cameras suck? 380 lines isn't bad, but what's the modulation on these cameras? AM? FM? Glenn? Andrew has one, so we can play around with it if we want.

Telemetry frequencies

If we move the ATV to the S band (2.4 GHz), then what do we do with the telemetry link? We move to the 5.x GHz c band, and use 802.11a, of course! But do USB to 802.11a sticks exist? Apparently the answer is "yes", so the real questions are 1) can we build a 5 GHz antenna, and get a 5 GHz amplifier? And do any of the 802.11a channels correspond to any of the ham band channels?

Telemetry Hardware

So, what's the next telemetry hardware going to be? Well, the new FC is architected for USB communications, so we currently imagine it to be some kind of USB to 802.11x adapter. We've put off the search for a while, because we thought we needed specialized hardware here, but we learned tonight that many of the USB sticks are pretty close to software-defined radios (SDRs). IN fact, many wifi chipsets have the Linux kernel doing even as far down as the Mac (network) layer [4], which is very cool because we want to strip out all the junk that 802.11 ad hoc mode comes with. In particular, according to Jim Binkley's February 2004 talk, we want to strip out SSID broadcast, the 100 Hz beacon, and all RTS/CTS acknowledgments from ad hoc mode. We could actually possibly do all this if we used the softmac bits, which is exciting.


TO DO

  1. Maria, add your notes here. Also, the chipsets we found?
  2. Glenn: cross-reference the 802.11a channels [3] with the AR bands [2]. Also xref with space bands, for fun [also 2?].
  3. Glenn: small 5.x GHz amplifiers?
  4. Josh: could you please put together a list of supported chipsets that support the linux softmac layer and look sane? Maybe some USB keys that look sane (from a software point of view, too?
  5. Sarah: Ask your coworker about what we can/can't control in the 802.11 world?

Additional Meeting Notes (from Maria)

is there an amateur band in the c band (5.8 (?) GHz) that we can use?

is there an 802.11a to usb adapter that's within the C band?

if so, can we realistically use this?

can we get 5.8 GHz Amateur amplifiers?

the one thing that doesn't change is gps which is L band (confirm)

http://us.zyxel.com/web/product_family_detail.php?PC1indexflag=20040520161256&CategoryGroupNo=PDCA2007080 http://linuxwireless.org/en/users/Drivers/zd1211rw#SupportedDevices http://zydas.rapla.net/ References: