1.2 Antenna
There are different antennas on the market. Cheap ones as well as expensive ones. Some perform very decently while other models are not working at all. We like to build our own antennas which should be:
- Cheap to build
- Easy to build
- Small so installation is not an issue
- Long range
- ADS-B -> PCB Antenna
- AIS -> Diamond X-30
- Radiosondes -> Diamond X-30
The groundplane is very cheap to make and is a decent performer when build to spec.
- Cheap (roughly 5€ without cable)
- Easy to build
- Good reception
- Looks homemade
- Fragile when transported, not so much when installed
- You may need a VNA to tune it to the optimal performance
- N socket
- 40cm copper wire (1.5mm² or better 2.5mm²)
- 4 M3 bolts and nuts (you may want to add washers)
- SMA -> N RG58 cable to connect it to your bandpass filter and rtl_sdr (length depends on your setup, the shorter the better, we usualy use 1m)
- Soldering iron + solder
- Wrench for the M3 nuts or pliers
- Wirecutter
- Screwdriver for the M3 screws
We use a NanoVNA to check our Antennas.
As you can see the SWR@1090mhz is 1.13:1
Cut 4 about 8cm long copper pieces and create a loop on each end which is big enough for a M3 screw.
Solder the loops end for more stability.
Cut one 8cm long copper piece
and solder it into the antenna jacks middle pin.
Screw the four pieces withe the loops to the antenna at an 45° angle
and bend them down 45°.
The 5 pieces of copper are a little bit to long for 1090MHZ by design so you can tune it perfectly by shortening them with the help of a nanoVNA
Connect the antenna and install it in an upright position with clear line of sight.
This antenna is a readily available PCB you find online from China. We build an enclosure to make it waterproof and add mounting brackets.
- No soldering required
- Already tuned to frequency
- Very robust (good for traveling or harsh conditions)
- Looks quite professional
- Excellent performance
- A bit more expensive than the ground plane (roughly 20€ without cable)
- If you do not want to drill a big hole for the SMA connector in the bottom you need to crimp your own sma cable after passing it trough the endcap
- PCB Antenna (search for ADS-B 1090MHz ANT V1.0)
- 30cm of 25mm diameter plastic tube (cable installation tube works great and is cheap)
- 13.8cm of 16mm diameter plastic tube (cable installation tube works great and is cheap)
- 2 plastic endcaps for 25mm diameter (chair leg caps work great)
- 2 1/2" or 22mm conduit clamps with m8 mounting thread
- 2 conduit clamps according to your mounting pole
- 2 3cm long m8 threaded rods (you can use threaded rod cut to length or m8 screws from which you cut off the head)
- sma to sma cable as long as you need, the shorter the better (we use rg58 and crimp our connectors after feeding the cable trough the endcap)
- Screwdriver for tightening down the clamps (often a size 2 pozidriv)
- Hacksaw with metal cutting blade
We use a NanoVNA to check our Antennas.
As you can see the SWR@1090mhz is 1.33:1
- Cut your 25mm diameter tube to 30cm
- Cut your 16mm diameter tube to 13,8cm
- Drill a hole in the center of one endcap, choose your drillbit size big enough to feed your sma cable through
- Feed cable through endcap and put cap on tube (can use some glue but not needed)
- Pull the cable through the 25mm diameter tube and the 16mm tube
- Screw the sma connector to the antenna
- The smaller tube will sit inside the bigger tube to prevent the pcb antenna from sliding down
- Pull everything carefully into the tube until the pcb sticks out about 1-2mm
- Put the other endcap on top. No hole and no glue here, so you can access the antenna later on for repairs
- Mount the 22mm conduit clamp on the lower end of the tube 2mm from the endcap with the cablefeed
- Mount the second 22mm clamp a bit higher on the tube in the same direction (stay in the area where there is no pcb to avoid interference with the antenna. 5cm clamp to clamp distance is fine)
- Connect each of the other two conduit clamps with a threaded m8 rod with the clamps on the antenna
- Mount the thing on your mounting pole
You can build a groundplane antenna for radiosondes like the ADS-B one just with longer copper pieces. Exact measurements TODO
The Diamond X-30 is our choice as a dualband antenna for AIS and Radiosonde reception - it just works.
The Diamond X-50 can be used like the X30 for AIS, radiosondes and much more it is a bit longer, a bit more costly and has a bit more gain. We do use it and are quite happy with the results. If you should splurge on this one or save some bucks and buy an X-30 - only you can decide. Either way you won't be disappointed.
You may find used marineband antennas for cheap prices online. They obviously work great for AIS and are a no-brainer for that purpose. You may also receive radiosondes with them, but that's not guaranteed. Check for the SWR with a VNA.