Avionics/communications - Video sub system
We went over the interconnection details of the video subsystem. Here is a drawing of the connections. Note that some of the shielded cable connections don't have their shields connected on both sides to avoid ground loops. The ATV transmitter has an SMA female RF connector. Frank needs to know the physical pin header connector details on the ATV transmitter. We thought it possible to just use the mating connector end that was removed from the packaging if we have a problem finding the proper connector.
Frank will make actual measurements of the curent draw of each component. Below is our conservative estimate so we can specify a DC-DC switching converter, which is on the critical path.
- Camera (12.0 VDC, est 300 mA)
- Overlay (12.0 VDC, est 100 mA)
- Digitai video recorder (use internal LiIon battery)
- ATV transmitter (12 VDC, 500 mA)
To estimate the ATV current draw, it was assumed the transmitter was 20% efficient, and puts out 1 watt of RF power. Usually the total power is only seen when a completely black raster image is being sent (true for FM modulation?) so this value is important to actually measure.
The WiFi amplifier also needs 12 VDC. Assume it puts out 3 watts also at 20% efficiency. So this conservative estimate gives is a 1.25 A load for the WiFi PA.
Here are some possible DC-DC converter solutions;
Requirements; Input: 10-20 VDC Output: 12.0 VDC @ 2.2A
945-1275-ND In: 9-36V Out: 12.0V / 2.5A http://www.recom-international.com/pdf/Powerline-DC-DC/RP30_FW.pdf 33 Avail - $83.28 for 1
945-1281-ND In: 9-36V Out: 12.0V / 3.33A http://www.recom-international.com/pdf/Powerline-DC-DC/RP40-S_DGW.pdf 7 Avail - $102.32 for 1
Will need to fabricate a carrier board. There is a positive logic ON-OFF control.
Avionics/communications - Helix antennas
We found two COTS sources of 2.4 GHz helical antennas, and one COTS source of 5.8 GHz antennas.
2.4 GHz Helix antennas
Bart (and others) want to replace the BBQ grill antennas used for the 802.11b signal path between the launch tower and launch central. These old BBQ grill antennas have become problematic at the feed because of excessive handling over the years, and they have a very narrow (about 10 degree) half power beam width which makes aiming them critical requiring tower climbing. The choice to go to a circular polarization on the ground was made to help with alignment simplicity, and to reduce suspected reflection impairements. We verified the tower height needed to maintain 60% fresnel zode clearance between the 0.25 mile signal path to be around 13 feet. This is consistant with what we thought and experienced.
We also need a 2.4 GHz CP antenna to receive the ATV video on the ground using the TM3K.
WP Wireless Stub feed axial mode helix (Appears to be a Virginia Tech design) http://www.wp-wireless.com WPANT CP B R0 A0130 2 WP B 12-14 dBi / 40-45 deg HPBW $150.00 1-707-996-5201 Dan Paulson
Luxul Axial mode helix http://www.tessco.com/products/displayProductInfo.do?sku=356035&eventGroup=4&eventPage=1 Tessco SKU 356035 13 dBi / 32 deg HPBW $124.95 http://www.tessco.com
5.8 GHz Helix antennas
- This is to transmit/receive the 802.11a/n signal on the ground using the TM3K.
WP Wireless Stub feed axial mode helix (Appears to be a Virginia Tech design) http://www.wp-wireless.com WPANT CP J R0 B0130 2 WP B 12-14 dBi / 40 deg HPBW $150.00 1-707-996-5201 Dan Paulson