Wednesday, July 11, 2018

The quest for smaller, lighter and economical portable digital

This is all KN4CRD needs to work
portable digital (and a radio of course).
For a while now I'm following posts on facebook, blogs and instagram from OH8STN, MW1CFN and KN4CRD. They all use a Raspberry Pi 3B+ as computer for use with digital modes. I have other things on my mind at the moment but find it very interesting to see it works well. It's a small computer, low cost (approx 40 euro) and it doesn't use much power. You can buy a small HD 7 inch screen to connect to the HDMI port and it does feature USB ports for GPS and CAT control connecting. Most interesting so far is the 3D printed case for the computer from KN4CRD, it includes a complete computer including battery and touch screen pocketsize.

I've been interested a lot in working portable digital. But there are some things to overcome. You need a light and small economical computer with GPS device to sync the time, you need enough electrical power, you need a place to hide for the sun and rain.

A large crack in the touchscreen...
At first I thought the easiest way for a lightweight economical computer is to buy a Windows 10 tablet. It is cheap, it already has GPS although I don't know if it can be used for sync the time, you can install every digimode software for free. It has bluetooth and WiFi to eventually connect to a phone with internet. And it has a built in soundcard. I bought one, and it works well. I thought "this is it". Then I noticed the micro USB connection is very flimsy and so is the 5V charger connector. 5 minutes later a crack appeared into the touch screen, ok it still functioned. But again 5 minutes later the crack became all over the screen and nothing functioned anymore. Then I realized a tablet is not very rugged and certainly not good enough for portable operation for my standards. I like the way KN4CRD has been developing his computer, very small and economical. The use of linux these days should be no problem for at least the use of well known digital communications. Personally I'm thinking about a small 10 inch laptop with SSD drive and dual boot W10/linux. However, the internal battery will only last for 1 or 2 years to function well. Most laptops need 18-20VDC for supply. For that a Raspberry Pi is much more economical, these days you can buy reasonable priced 5V powerbanks which can supply the Raspberry for hours.

Sync the time with GPS device should be no problem these days. I've been experimenting with it before and it worked, however with the bleutooth device I use now the sync software does lock after some time. The one you see on the photo should be better I guess. They cost about €7,75 including shipping via AliExpress.

Electrical power...I guess you better read posts about that on OH8STN Julian's site. Julian is using foldable solar panels to get power from the sun. He developed his own battery with the use of separate Life4PO cells. It's just how far you will go in buying these things. Most important is the weight. I've been using a 7Ah SLAB, it's cheap but is relatively big and heavy. Building a LifeP4PO pack might be not that expensive but a foldable solarpanel is. It's just what you want to invest. I came across a Einhell cc-js12 Li-Ion 12Ah pack with 12v, 5V and...19V output.  The 12Ah is overrated and I guess at 5V, the manual says the battery capacity is 41Wh. The Ft-817 does need 1A average, sometimes more depending modes (2,2A@5W TX carrier) I expect it to hold about 2-3 hours. With the laptop connected hopefully 1 hour. The battery and radio are considered the heaviest weight on your portable pack you really have to take care of them being as light but as rugged as possible.

If solarpanels will be cheaper I'll invest in one. Till then I will manage and hope I don't have to use it in a emergency situation but just for the hobby.

Then another issue, a shelter. Ever tried to read a tablet or laptop screen in the sun? And everyone knows electronics can't stand rain/water. You need a place with shadow, you need a place that is dry. And preferable in winter you need a place that is warm enough to operate your gear. Well, I guess that's the biggest investment you need to do if you want to run portable over the whole year. If you like to know more about it you really should take a look at OH8STN's site.


  1. Great article! One thing is for sure, this kind of portable operating is becoming much easier with time. Battery development is happening at very fast rates now, and the move to digital modes means there is no necessity for high power and big antennas.

    On the time synchronisation question, my Raspberry Pi 3B+ makes its connection to the wider world via my mobile phone's WiFi hotspot function. After many days of testing, I found the Raspberry Pi maintains the kind of time error (0.1-0.2s) that you usually get when using Dimension 4 on a PC. In other words, it is more than accurate enough without any GPS or special time sync. I think the Rasperry Pi must be syncing from the internet frequently by default. Of course, it is different if there is no mobile phone signal!

    1. Hello John, probabely Linux has a built in time sync? Just like apple OS. Windows has this as well but is not working most of the time. I sync my laptop with my iphone wifi connection as well as spotting to PSK reporter and Hamspots. Though in the field a GPS could be a good backup indeed when there is no mobile phone coverage. This article is written as a first post about decreasing the weight of my portable station. 73, Bas


Thanks for your comment. Bedankt voor je reactie. 73, Bas