According to the documentation the internal antenna in the RAK7200 has an S11 of greater than -7dB at 868MHz. In general I won’t use antennas with S11’s above -10dB, but ideally I try and find ones with S11 of -30dB.
Does anyone know of a good antenna replacement for the RAK7200 that performs better? I’m looking at the Molex antenna (https://www.molex.com/molex/products/part-detail/antennas/1052620002) but I am afraid it’s too big to fit inside the RAK7200.
I opened up the RAK7200 tracker and I see the antenna that is used by mine is different from the one in the documentation here: https://doc.rakwireless.com/datasheet/rakproducts/antenna-specifications---rak7200
Measuring the antenna in mine it report an S11 of -14dB, which is much better than the documentation states. -14dB is a usable value.
I however see that the LoRa antenna is mounted right above the GPS patch antenna. These two will definitely interfere with this layout.
I’ll try moving the LoRa antenna to the other corner above the battery connector.
In the original state the RAK7200 reached a gateway 4.4km away while laying on my desk indoors (SF12). That’s a good result, so the RAK7200 with its original antenna and original antenna configuration performs well.
I will still need to do a test while driving around to see how that performs.
I’ve found the SF10 or less is required to combat any Doppler issues. With fair use policies and country duty cycle requirements, you may find you won’t be able to transmit many location reports of “real-time” tracking.
@nmcc Your comment is off-topic, but I still want to respond on it.
I believe you are mistaken. The doppler effect will only have an affect on LoRa if you are moving faster than 450km/h. What you are seeing with slow data rates when you are moving is the variation in path fading, causing the FEC to break down.
I’ve been using LoRa trackers for a very long time (look up TTN Mapper). I have found that using the fastest possible data rate when you are mobile works the best. In other words SF7/DR5 in Europe.
Yes I know what the duty cycle limitations are, and LoRaWAN libraries all implement it to prevent breaking the rules. Setting the transmit interval faster will make the device transmit as fast as possible while still staying within the regulations. Depending on the size of the payload this can be as low as every 10 seconds when using SF7. Even if it goes up to once per 60 seconds, it is still good enough for “live” tracking.
Mine was mounted just above the battery. I moved it also to the same spot as you reported, above the batt connector.
