Cellular Option for the Coastal Marine WiFi System


There are times when either there are no WiFi hotspots available or else the required security information isn’t available.  In such situations being able to switch to a cellular connection can be valuable if internet connectivity is required.

The Pepwave Surf-On-The-Go (SOTG) is a ‘relatively’ low cost 3G/4G WiFi router that, in addition to providing a WAN (Wide Area Network) connection to the WiFi radio (Ubiquiti Bullet) for connecting to distant hotspots, also supports connection to a cellular network via a USB cellular modem.  The EasyBullet app developed by Coastal Marine WiFi makes it very easy to switch from WiFi to cellular and back again.  When the CMW system includes the Pepwave SOTG router with a cellular modem attached, the ‘SelectHotspot’ page includes a button ‘Switch to Cellular’.  When this is pressed, the app tells the SOTG router to switch from ‘wired’ mode (i.e. the wired ethernet connection to the WiFi radio) to Cellular mode.  The connection to the cellular network then provides internet access to the SOTG, and therefore any devices connected to the SOTG.  When the SOTG is in cellular mode, the app displays the cellular page, which indicates the carrier connected to.  That page has a button ‘Switch to WiFi’.  When that button is pressed, the app tells the SOTG to switch back to wired mode, so it now ‘talks’ to the WiFi radio, allowing you to scan for and select a WiFi hotspot connection.

The USB modem requires insertion of a full sized SIM card for which a suitable data plan has been purchased.  (A SIM card adapter can be used if your SIM card is the micro or nano size.) Use of an unlocked USB modem allows for different SIM cards to be used depending on location e.g. one can acquire a SIM card for different countries as needed.  If the cellular system is to be used in a single country, or if the data plan supports roaming in different countries, there will be no need for an unlocked USB modem, but the modem does need to be compatible with the selected carrier.  Because an unlocked modem can work with any carriers’ SIM card it offers more flexibility, however, this is only true for cellular carriers that use GSM technology. Carriers such as Verizon, Sprint and US Cellular use CDMA technology which means that a USB modem specific for that carrier is needed.

Unlike the Ubiquiti Bullet, which has a direct connection to the WiFi antenna, and therefore incurs no coax cable loss, the USB modem is typically some distance away from the cellular antenna.  This is particularly true if there’s a need to change SIM cards.  We strongly recommend the use of low loss coax cable to connect the antenna to the USB modem (or maybe a cellular amplifier – see below).  LMR400 coax cable has much less signal loss than the RG58 typically suggested.  See http://www.timesmicrowave.com/calculator/ where you can determine the signal loss for different cable types (don’t forget to specify an appropriate cellular frequency).  For example, all US carriers use 1900 MHz for 4G/LTE networks.  At that frequency, 25 ft. of LMR400-Ultraflex cable has a loss of just 33%, whereas RG58 cable has an estimated loss of 71%. 

Generally losses are measured in decibels (dB).  The terms dBm indicate an absolute level of power, and dBi is specifically used for the gain of an (isotropic) antenna.  10 dB is indicates a gain of 10, and 20 dB is a gain of 100.  So an amplifier with a gain of 15 dB (a gain of 31.6) coupled to a 6 dBi antenna (a gain of 3.98) results in an overall decibel of 21 dB (a gain of 126).  It is easier to add/subtract power measured in dB than it is to multiply several gain values to get the final result!  So the loss for that 25ft LMR400-UltraFlex cable is -1.76 dB (negative because it is a loss) and for the RG58, the loss is – 5.4dB.

The recommended components are as follows:

a)      The Pepwave SOTG WiFi 3G/4G router.  Since the power draw of the router is a maximum of 5 watts ( less than 1/2 amp at 12vdc) the SOTG router can be powered by our dual PoE injector.  We will configure the SOTG router to the name (SSID) and password you select when ordering a system, as well as appropriate settings for cellular support.


b)      21” Wilson cellular antenna with a signal gain that varies from 3.1 dBi to 6.1 dBi for the majority of 4G/LTE frequencies used by USA and Canadian carriers.  See https://www.wilsonamplifiers.com/frequencies-by-provider for details.


c)       A Wilson Direct Connect 4G amplifier.  Although quite expensive, this amplifier provides 15 dB of gain i.e. enhances signal strength by a factor of about 32.  Together with an average antenna gain of 4.2 dB, the overall signal strength will be enhanced by a factor of about 100.  The amplifier can be ordered either with a DC-DC converter requiring a voltage supply between 12vdc and 24v dc, or with an AC adapter.


d)      An unlocked USB Modem.  We have tested the Sierra Wireless 313U and 330U and both work well.  The 313U and 330U differ in that the 330U supports the 2600 MHz band which is not in widespread use.   The 340U, which is identical to the 313U except that it has an LCD display has reliability issues with the SOTG router, and so we cannot recommend it.
NOTE: For Verizon, Sprint and US Cellular carriers, a dedicated USB modem from the respsective carrier would be needed; Verizon, Sprint and US Cellular do not use 'standard' (GSM) SIM cards. Examples of suitable USB modems would be the U620L from Verizon, or the U600 from Sprint. Ideally the USB modem would have ports for connecting an external antenna. Please check with your carrier for more details.

In addition there are cables required to connect the Direct Connect amplifier to the USB modem, and a USB extension cable to allow the USB modem to be located some distance from the SOTG router if required. 

When planning a system with the cellular option, the following decisions have to be made:

1.       The location of the cellular antenna.  The base requires a standard 1”-14 antenna mount. If the mount has a hole in the center the coax cable can be passed through that to connect to the antenna, but the antenna is supplied with a small extension that allows the cable to pass to the outside.


2.       The location of the USB modem.  This will be affected by whether there’s a need to replace the SIM card or not, and also whether the Direct Connect amp is to be included.  Ideally the location of the USB modem will be as close as possible to the antenna so that the coax cable length will be minimized.


3.       Whether the Wilson Direct Connect amp is to be included or not.  If it is, it has to be located close to the USB modem (the connecting cables are very short).  The amplifier is supplied either with a DC-DC converter having leads over 10ft long (so 12v or 24v dc power needs to be available within 10ft of the amplifier location) or with an AC Adapter (has a 6ft cable).


4.       The location of the SOTG WiFi router.


Once these locations are known

-          the length of the coax cable connecting the antenna to either the Direct Connect amp or the cable connecting to the USB Modem, and

-          the length of the USB cable connecting the USB Modem to the SOTG

can be determined. If the USB modem is more than 9 ft. away from the SOTG, an active USB cable will be needed (it will boost the signal levels).

Please note that at the current time we are not able to provide the additional items listed below, however, we can provide advice regarding these items should that be required.

The following are suppliers of the various items required in addition to the Pepwave SOTG supplied by us:

From 3GStore.com

Wilson 21” Marine Antenna  (http://3gstore.com/product/3146_21_inch_marine_antenna.html )

Wilson Signal 4G Direct Connect amplifier with DC-DC converter (optional but highly recommended)
(DC Version: http://3gstore.com/product/6663_460219-wilson-signal_4g_direct_connect.html)
(AC version: https://3gstore.com/product/6524_wilson-signal_4g_direct_connect.html)

Sierra Wireless Adapter Cable (FME/Male on one end, and a specific connector for the USB modem on the other)  The standard connector (http://3gstore.com/product/3332_usbconnect-momentum-adapter-cable.html) is somewhat problematic since the casing of the USB modem inteferes with the end of the cable. We suggest instead the OEM version SMK TS-9 available from https://antennagear.net/smk-ts-9-oem/

FME/Female to SMA/Male Adapter (http://3gstore.com/product/4005_fme-female-sma-male.html)

Note1:  The antenna has a SMA/Male connector and the Direct Connect amplifier has SMA/Female connectors, so the coax cable has SMA/Female on one end (to connect to the antenna) and SMA/Male on the other end to connect to the amplifier. 

Note 2: The FME/Female to SMA/Male adapter is used to connect the Sierra Wireless adapter cable to the amplifier.  If you decide not to purchase the amplifier, then instead of the FME/Female to SMA/Male adapter, you would need the FME/Female to SMA/Female adapter (http://3gstore.com/product/3989_fme-female-sma-female.html)

From Air802.com

Appropriate length of LMR400Flex equivalent coax.  The website http://www.air802.com/CA400FLEX-White-Antenna-Cables-LMR-400-UF-Ultraflex-Identical/  is for white cable, the website http://www.air802.com/CA400FLEX-Black-Antenna-Cables-LMR-400_UF-Ultraflex-Identical/ is for black cable.  In both cases select SMA Jack/Female-straight for connector A, and SMA Plug/Male-Straight for Connector B, then select the length you require.

From eBay.com

eBay is the least expensive source for unlocked Sierra Wireless USB modems (mostly branded for AT&T) but if unlocked, they will support SIM cards from any carrier. 


If needed, the active USB cable can be purchased from a number of places e.g. Amazon, Startech, etc.