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communication:nova1_radio_system [2006/09/25 18:52] – rocketboycommunication:nova1_radio_system [2008/07/19 23:33] (current) – external edit 127.0.0.1
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-====== The NOVA1 Radio Data Downlink ======+====== The NOVA1 Radio Data Downlink (by Steve Randall) ======
  
 The radio system used on NOVA1 was intended to be a test of what could be achieved using off-the-shelf  modules.  The system is essentially a standard 1200 baud packet radio TNC connected to a 10mW 434MHz licence exempt transmitter module - a small circuit is used to interface the two.  The antenna used was a coax dipole, which was directly connected to the transmitter output. The radio system used on NOVA1 was intended to be a test of what could be achieved using off-the-shelf  modules.  The system is essentially a standard 1200 baud packet radio TNC connected to a 10mW 434MHz licence exempt transmitter module - a small circuit is used to interface the two.  The antenna used was a coax dipole, which was directly connected to the transmitter output.
 +
    
 {{:communication:schem.gif|:communication:schem.gif}} {{:communication:schem.gif|:communication:schem.gif}}
 +
 ** Figure 1 - NOVA1 radio system schematic ** ** Figure 1 - NOVA1 radio system schematic **
  
 The whole system was built in a package that was about 70mm x 96mm x 30mm which contained the TNC, transmitter, interface circuitry and a lithium battery sufficient for about 20hours of continuos operation.   All in weight (including battery and antenna) was 135g.  The whole system was built in a package that was about 70mm x 96mm x 30mm which contained the TNC, transmitter, interface circuitry and a lithium battery sufficient for about 20hours of continuos operation.   All in weight (including battery and antenna) was 135g. 
  
- +{{:communication:pack.jpg|:communication:pack.jpg}} 
  
 ** Figure 2 – NOVA1 Data Down-link Radio package ** ** Figure 2 – NOVA1 Data Down-link Radio package **
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 The TNC provides a radio modem capability – converting the data coming from the host computer interface into a format suitable for transmission over a radio channel.  It takes data packets presented at the serial interface into the synchronous format used for transmission. Data is sent using a 1200 baud modem chip – which provides the signal shaping necessary to pass the data efficiently over the radio channel. The TNC provides a radio modem capability – converting the data coming from the host computer interface into a format suitable for transmission over a radio channel.  It takes data packets presented at the serial interface into the synchronous format used for transmission. Data is sent using a 1200 baud modem chip – which provides the signal shaping necessary to pass the data efficiently over the radio channel.
  
-The TNC used is the TNX-X from Coastal Chipworks (see http://www.tnc-x.com/) - which is available as a kit or ready built.  The TNC-X weighs 45g and measures 63 x 96mm.    +The TNC used is the TNX-X from Coastal Chipworks (see http://www.tnc-x.com/) - which is available as a kit or ready built.  The TNC-X weighs 45g and measures 63 x 96mm.  
-Transmitter+ 
 +===== Transmitter =====
  
 The UK radio-licensing regime is such that only a few legal ways to transmit data from a balloon to the ground currently exist.  Unlike the US the UK Ham Radio licence specifically excludes airborne operation and many of the licence exempt frequencies are barred form airborne use.  Narrow-band 10mW licence exempt modules in the 434.04 – 434.79 MHz frequency range seem about the only viable option for High Altitude ballooning at present The UK radio-licensing regime is such that only a few legal ways to transmit data from a balloon to the ground currently exist.  Unlike the US the UK Ham Radio licence specifically excludes airborne operation and many of the licence exempt frequencies are barred form airborne use.  Narrow-band 10mW licence exempt modules in the 434.04 – 434.79 MHz frequency range seem about the only viable option for High Altitude ballooning at present
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 A LM324 quad op-amp was used to interface the TNC-X to the NTX-2. One of the four op amps are used to amplify the audio output form the TNC-X to the level required by the NTX-2 – the circuit also adds DC bias to fully use the  NTX-2 +/-3KHz FM deviation. The other op-amp in the circuit is used as an inverter and level shifter needed to drive the NTX-2 enable input at 3V. A LM324 quad op-amp was used to interface the TNC-X to the NTX-2. One of the four op amps are used to amplify the audio output form the TNC-X to the level required by the NTX-2 – the circuit also adds DC bias to fully use the  NTX-2 +/-3KHz FM deviation. The other op-amp in the circuit is used as an inverter and level shifter needed to drive the NTX-2 enable input at 3V.
 +
 +{{:communication:cct.gif|:communication:cct.gif}}
  
    
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 Ground-station Antenna – 7 element 434MHz “ZL”  yagi (11.5dbd).  A Narrow Band FM  receiver was used – feeding another TNC-X which was then used to feed a PC running a terminal emulation program. Ground-station Antenna – 7 element 434MHz “ZL”  yagi (11.5dbd).  A Narrow Band FM  receiver was used – feeding another TNC-X which was then used to feed a PC running a terminal emulation program.
  
-Accurate pointing of the antenna proved to be critical especially when the balloon was at distance.  In a subsequent flight the receive antenna was mounted on a camera tripod – which made the job of holding and pointing the antenna more pleasant.+Accurate pointing of the antenna proved to be critical - especially when the balloon was at distance.  In a subsequent flight the receive antenna was mounted on a camera tripod – which made the job of holding and pointing the antenna more pleasant.
  
 +{{:communication:tripod.jpg|:communication:tripod.jpg}}
  
 ** Figure 4 - Antenna on tripod mount ** ** Figure 4 - Antenna on tripod mount **
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 ===== Improvements ===== ===== Improvements =====
  
-**Tune up signal** – A signal to allow manual peaking of the antenna direction. +  * **Tune up signal** – A signal to allow manual peaking of the antenna direction.
- +
-A **longer receive antenna** could be used – a antenna double the length of the existing antenna would not be unwieldy or present too much of a problem to align – this should provide an additional 3db of gain (40% in terms of distance)+
  
-The addition of a **low noise pre amplifier** at the antenna output might improve the overall signal to noise ratio (depending upon the receiver)+  *A **longer receive antenna** could be used – a antenna double the length of the existing antenna would not be unwieldy or present too much of a problem to align – this should provide an additional 3db of gain (40% in terms of distance)
  
-Slightly **wider transmit deviation** could be used and still remain within the narrow-band channel – this would improve the signal to noise ratio. +  *The addition of a **low noise pre amplifier** at the antenna output might improve the overall signal to noise ratio (depending upon the receiver)
  
 +  *Slightly **wider transmit deviation** could be used and still remain within the narrow-band channel – this would improve the signal to noise ratio. 
  
  
 +A combination of these improvements might at best double the overall communication distance to about 60Km.
communication/nova1_radio_system.1159210328.txt.gz · Last modified: 2008/07/19 23:30 (external edit)
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