1.6.3. Mobile hotspot

Many people have built or purchased a pi-star hotspot and connected to their home WiFi network. Some have popped them in their cars and connected to their mobile phones using mobile hotspot. These all can work very well, however for me I want to be independant of my mobile. This is for several reasons

  • Power drain on the phone is high, so I would need to keep the phone connected to power for long duration usage

  • Phone needs to remain in close proximity of the hotspot.

Ultimately I want a self contained unit which has a battery and mobile connection. There are two ways to handle the internet connection.

  1. WiFi connection to a MiFi device

  2. USB GSM Dongle

Using a MiFi device does offer an advantage in that other devices such as laptops could also use the same internet connection, however in my case I’m only interested in providing internet to the DMR hotspot. A possible downside is getting the devices to communicate with each other. They also both require power which might reduce the run time specially as they are both using RF to run the WiFi connections.

For the DMR hotspot I picked the “Jstvro duplex” as I wanted a small footprint but also duplex. The price of this unit seems to have rocketed up to over £100, when I bought mine it was £50. Any of the simplex versions also work if the price doesn’t drop back down.

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1.6.3.1. Parts List

  • Jstvro MMDVM Duplex hotspot

  • Huawei E3372 USB GSM modem

  • OTG (On The Go) USB cable

  • Micro USB power cable

  • USB Battery pack

1.6.3.2. Building

Set up the pi-star hotspot as documented elsewhere, there is no additional settings or installs required to support the 4G USB module. When it’s plugged in the pi-star will see it as ethernet device (eth1) and will start sending traffic over it. By default the pi will report having an IP address of 192.168.8.100, and the USB module will be addressable as 192.168.8.1.

If the pi-star is setup to for “(AP) Access Point” mode, then connecting a laptop to the Pi-Star’s WiFi will allow access to the pi-star for further configuration. It is also possible to allow routing to the wider internet as well.

1.6.3.3. Bandwidth Usage

For each DMR network used the hotspot will use around 18Mb per hour just to remain connected. For example If connected to Pheonix and Brandmeister the hotspot will use 36Mb (18*2). As you make/receive calls this usage will of course increase.

1.6.3.4. Mobile Phone service

The GSM modem is unlocked and can take any SIM card. The hard part here is finding the right mobile phone provider and tariff to sign up to. Depending on how much usage you are expecting to have will highly determine the right service for you.

At the moment I’m using the hotspot infrequently and so would rather not pay a regular monthly cost for the service which might not be used much for a few months and then other months be used very heavily.

If I an running frequently then a monthly tariff is likely the most cost effective, for example “smarty” are offering 4Gb per month for £6.

For this device I’ve chosen to use 1pmobile which offers a flat fee of 1p per MB. The advantage here is that the data expires after a long time. For £30 you get 3Gb of data to use over a year. You can top up at anytime and as you top up, depending on how much determines how long it lasts before expiring. DMR traffic is very low when not sending audio so this should offer several months of usage.