Loudoun Amateur Radio Group
Balloon Committee
1200 Baud Telemetry Link
Budget
By Tom Dawson, WB3AKD
Committee Chairman
Metric |
English |
Remarks |
|
| Frequency (MHz) | 145.650 | ||
| Wavelength | 2.058 | 6.749 | |
| Antenna Height (Tx) (meters or feet) | 30487.805 | 100000.000 | Balloon at Burst height |
| Antenna Height (Rx) (meters or feet) | 9.146 | 30.000 | Receive antenna on house |
| Horizon Distance (Max Range Tx to Rx) | 829062.015 | 447.247 | Based on Burst height |
| Desired Path Length (km or miles) | 55611.000 | 30.000 | Rough Slant range requirement |
| Free Space Path Loss (dB) | -110.620 | Attenuation due to inverse square law | |
| Tx Power (dBm) | 10.000 | Transmit Power in db WRT 1mW | |
| Tx Antenna Gain (dBi) | 0.000 | ||
| Rx Antenna Gain (dBi) | 0.000 | Assume worst case no gain antennas | |
| RX Cable Loss (dB) | -4.000 | ||
| Rx Input Power (dBm) | -104.620 | Signal power into receiver | |
| Fade Margin (dB) | 0.000 | Not an issue for high elevations | |
| Rx Noise Figure (dB) | 7.000 | Typical for VHF receivers | |
| Rx BW (Hz) | 30000.000 | Determined by NBFM Filter | |
| Rx BW (dBHz) | 44.771 | 10*log10(Rx BW) | |
| Rx Noise Power (dBm) | -122.229 | -174+Noise Figure + Rx BW(dB) | |
| S/N (dB) | 17.609 | Receive Power(dBm) -Noise power (dBm) | |
| Data Rate (Baud) | 1200.000 | Same as Bits per second in our case | |
| Bits/Symbol | 1.000 | Simple AFSK modulation | |
| Eb (dBm) (Energy/bit: equals sig pwr/rate) | -135.412 | ||
| No (dBm/Hz) (Noise Density:=Pn/BW) | -167.000 | ||
| Eb/No (dB) Determines Bit Error Rate | 31.588 | Eb/No is used to find the Bit Error Rate (BER) of the system. Some complicated probability equations relate Eb/No to BER. Fortunately, there are curves published trhat are close enough for our project. Anything above about 15 dB Eb/No should give us a BER < 10^-6.
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