You can add an external antenna to the device with the IPX jack on the main unit.
You can convert it to a standard wifi antenna with an IPX to RP-SMA adapter. You can get these on Amazon - ipx to rp-sma or eBay - ipx to rp-sma or various other places.
Otherwise you can use an IPX antenna, I used this one which I had laying around and afixed the antenna to the bottom of the unit. You can get IPX antennas also from again Amazon - IPX antenna or eBay - IPX antenna or various other places.
I used speedtest-cli to do these calculations. You will need to install python with opkg if you want to use it.
This reply to a thread about the external antenna about better throughput without a resistor. I ran my experiments several ways.
My antenna is kind of crappy, so you may get faster results with a better one.
./speedtest-cli --server 1344
Retrieving speedtest.net configuration...
Testing from Verizon Fios (108.48.93.143)...
Retrieving speedtest.net server list...
Retrieving information for the selected server...
Hosted by InfoRelay Online Systems (Reston, VA) [7.06 km]: 31.376 ms
Testing download speed................................................................................
Download: 20.10 Mbit/s
Testing upload speed................................................................................................
Upload: 27.77 Mbit/s
./speedtest-cli --server 1344
Retrieving speedtest.net configuration...
Testing from Verizon Fios (108.48.93.143)...
Retrieving speedtest.net server list...
Retrieving information for the selected server...
Hosted by InfoRelay Online Systems (Reston, VA) [7.06 km]: 24.007 ms
Testing download speed................................................................................
Download: 19.54 Mbit/s
Testing upload speed................................................................................................
Upload: 19.03 Mbit/s
./speedtest-cli --server 1344
Retrieving speedtest.net configuration...
Testing from Verizon Fios (108.48.93.143)...
Retrieving speedtest.net server list...
Retrieving information for the selected server...
Hosted by InfoRelay Online Systems (Reston, VA) [7.06 km]: 23.796 ms
Testing download speed................................................................................
Download: 6.03 Mbit/s
Testing upload speed................................................................................................
Upload: 9.14 Mbit/s
./speedtest-cli --server 1344
Retrieving speedtest.net configuration...
Testing from Verizon Fios (108.48.93.143)...
Retrieving speedtest.net server list...
Retrieving information for the selected server...
Hosted by InfoRelay Online Systems (Reston, VA) [7.06 km]: 28.346 ms
Testing download speed................................................................................
Download: 1.94 Mbit/s
Testing upload speed................................................................................................
Upload: 3.42 Mbit/s