</chapter>
<chapter>
<title>Specifications</title>
-
<itemizedlist>
<listitem>
- <para>
- Recording altimeter for model rocketry.
- </para>
+ <para>
+ Recording altimeter for model rocketry.
+ </para>
</listitem>
<listitem>
- <para>
- Supports dual deployment (can fire 2 ejection charges).
- </para>
+ <para>
+ Supports dual deployment (can fire 2 ejection charges).
+ </para>
</listitem>
<listitem>
- <para>
- 70cm ham-band transceiver for telemetry downlink.
- </para>
+ <para>
+ 70cm ham-band transceiver for telemetry downlink.
+ </para>
</listitem>
<listitem>
- <para>
- Barometric pressure sensor good to 45k feet MSL.
- </para>
+ <para>
+ Barometric pressure sensor good to 45k feet MSL.
+ </para>
</listitem>
<listitem>
- <para>
- 1-axis high-g accelerometer for motor characterization, capable of
- +/- 50g using default part.
- </para>
+ <para>
+ 1-axis high-g accelerometer for motor characterization, capable of
+ +/- 50g using default part.
+ </para>
</listitem>
<listitem>
- <para>
- On-board, integrated GPS receiver with 5hz update rate capability.
- </para>
+ <para>
+ On-board, integrated GPS receiver with 5hz update rate capability.
+ </para>
</listitem>
<listitem>
- <para>
- On-board 1 megabyte non-volatile memory for flight data storage.
- </para>
+ <para>
+ On-board 1 megabyte non-volatile memory for flight data storage.
+ </para>
</listitem>
<listitem>
- <para>
- USB interface for battery charging, configuration, and data recovery.
- </para>
+ <para>
+ USB interface for battery charging, configuration, and data recovery.
+ </para>
</listitem>
<listitem>
- <para>
- Fully integrated support for LiPo rechargeable batteries.
- </para>
+ <para>
+ Fully integrated support for LiPo rechargeable batteries.
+ </para>
</listitem>
<listitem>
- <para>
- Uses LiPo to fire e-matches, support for optional separate pyro
- battery if needed.
- </para>
+ <para>
+ Uses LiPo to fire e-matches, support for optional separate pyro
+ battery if needed.
+ </para>
</listitem>
<listitem>
- <para>
- 2.75 x 1 inch board designed to fit inside 29mm airframe coupler tube.
- </para>
+ <para>
+ 2.75 x 1 inch board designed to fit inside 29mm airframe coupler tube.
+ </para>
</listitem>
</itemizedlist>
</chapter>
</chapter>
<chapter>
<title>Operation</title>
- <para>
- Placeholder.
- </para>
+ <section>
+ <title>Radio Link </title>
+ <para>
+ The chip our boards are based on incorporates an RF transceiver, but
+ it's not a full duplex system... each end can only be transmitting or
+ receiving at any given moment. So we have to decide how to manage the
+ link...
+ </para>
+ <para>
+ By design, TeleMetrum firmware listens for an RF connection when
+ it's in "idle mode" (turned on while the rocket is horizontal), which
+ allows us to use the RF link to configure the rocket, do things like
+ ejection tests, and extract data after a flight without having to
+ crack open the airframe. However, when the board is in "flight
+ mode" (turned on when the rocket is vertical) the TeleMetrum only
+ transmits and doesn't listen at all. That's because we want to put
+ ultimate priority on event detection and getting telemetry out of
+ the rocket and out over
+ the RF link in case the rocket crashes and we aren't able to extract
+ data later...
+ </para>
+ <para>
+ We don't use a 'normal packet radio' mode because they're just too
+ inefficient. GFSK is just FSK with the baseband pulses passed through a
+ Gaussian filter before they go into the modulator to limit the
+ transmitted bandwidth. When combined with the hardware forward error
+ correction support in the cc1111 chip, this allows us to have a very
+ robust 38.4 kilobit data link with only 10 milliwatts of transmit power,
+ a whip antenna in the rocket, and a hand-held Yagi on the ground. We've
+ had a test flight above 12k AGL with good reception, and my calculations
+ say we should be good to 40k AGL or more with just a 5-element yagi on
+ the ground. I expect to push 30k with a 54mm minimum airframe I'm
+ working on now, so we'll hopefully have further practical confirmation
+ of our link margin in a few months.
+ </para>
+ <para>
+ Placeholder.
+ </para>
+ </section>
</chapter>
<chapter>
<title>Using Altus Metrum Products</title>
<para>
The best hand-held commercial directional antennas we've found for radio
direction finding rockets are from
- <ulink url="http://www.arrowantennas.com/" >
- Arrow Antennas.
- </ulink>
-The 440-3 and 440-5 are both good choices for finding a
-TeleMetrum-equipped rocket when used with a suitable 70cm HT.
+ <ulink url="http://www.arrowantennas.com/" >
+ Arrow Antennas.
+ </ulink>
+ The 440-3 and 440-5 are both good choices for finding a
+ TeleMetrum-equipped rocket when used with a suitable 70cm HT.
</para>
</section>
<section>