Wifibroadcast is an interesting DIY approach for HD video transmission via the wifi bands. Introduced by befinitiv it has become the backbone of several projects like EZ-WiFiBroadcast, Open.HD and DroneBridge.
A key element are wifi cards, and there is already really much info about which types and brands can be used in the web (here, here, also searching for Kali Linux yields many interesting pages, e.g. here). However, for the 5 GHz band the described/recommended selection of cards is quite small, and quite expensive. I here collect information on the cards which I use.
They are based on the Realtek RTL8812AU chip. This chip can support two antennas, and the crucial thing here is that it does not just do diversity in the common sense of switching to the antenna with the best reception, but in fact does MIMO (see here, or here). There is also a variant of the chip which does 4 antennas, the RTL8814AU. It could be an interesting choice for the ground station.
One may wonder if it would be better to use two single-antenna wifi cards and the basic diversity switchover implemented in e.g. OpenHD or DroneBridge or use one dual-antenna MIMO wifi card. I came to the conclusion that the latter is better, because of MIMO (of course, only if the card indeed provides two equal wifi antenna channels).
1. Alfa AWUS036ACH
2. Alfa AWUS036AC
Alfa AWUS036ACH
Comments
- quite expensive
- The card has a USB 3.0 Micro-B connector (see here). It comes with a pretty thick and heavy USB cable, which is pretty much useless for us. However, the ordinary USB 2.0 micro plug also fits into the USB 3.0 Micro-B connector, and thus any such cable can in principle be used too. I found however that a really good cable needs to be used, since otherwise the card won’t get enough power and won’t work properly. My mobile charging cable works fine. I also bought two so-called charging cables with data transfer, and only one of them did work but the other not. That is, one really needs a good USB cable here. For permanent installation it is recommended anyhow to use soldered wires for the USB connections.
- The card has very sophisticated GHz electronics on it. This is probably a good thing, i.e., may indicate high-quality GHz stages.
- The shielding case is unfortunately not populated. One may thus have to pay a bit more attention to shielding.
- From the data sheet of the used 5 GHz power amplifiers one should expect high power of 400 mW (26 dBm). Sources in the web list them as 500 mW cards. But note that the 26 dBm are nominally per antenna (!).
Pictures
Data Sheets
Alfa AWUS036AC
Comments
- not as expensive as other cards
- The shielding case is unfortunately not populated. One may thus have to pay a bit more attention to shielding.
- From the data sheet of the used 5 GHz power amplifiers one should expect moderate power of 63 mW (18 dBm), which is however nominally per antenna (!).
Pictures
Data Sheets