Computers for EMCOMM

Computers are indispensable in EMCOMM. The times when you accepted a message by voice radio with paper and pen from the fire brigade and then passed on to the police are long gone: Digital radio systems and closed cell phone networks tore down the communication barriers in the world of official disaster relief. Digital technology has also expanded our possibilities enormously. Computer technology also has its problems, from electricity needs to cable salad.

Available Computer Worlds
Reducing Power Requirements
Operating Computers Headless
Notes on Remote Control
Avoiding Ground Loops
Radio Interference?

Available Computer Worlds

Currently four operating systems for private users are available:

The majority of the relevant programs are available for Windows. Basically, some Windows programs can also be used on other operating systems. However, this requires special knowledge and, because of the special perephery such as radio devices, quite a bit of handicraft work. This is critical for EMCOMM, because complex solutions are usually less stable, often require more resources and increase the power requirements.
You can also work with Linux on the largely the same hardware. With this operating system you can also use hardware that Microsoft has declared obsolete. Many Windows 10 computers cannot be officially operated with Windows 11 and do not get a free Win11 update. Especially open source programs are relatively easily ported between Linux and Windows. The driver supply can be difficult.
There is also amateur radio software for the Apple world. As far as I know, this world is quite small. I have no experience here and therefore hold out.
Linux runs not only on normal PC hardware, but also on small computers such as the Raspberry PI. This technical basis has its special advantages such as small form factor, low electricity requirements of the ARM processor and a variety of connection options. However, there are reasons that speak against this technology: OH8STN switched to Windows tablets [1], similar to KM4ACK [2]. If you want to operate a WSPR bake or such, you are well served with a Raspi [3].

The Raspberry Pi had the unique selling point of the lowest energy consumption for a long time. Some Apple hardware has enormous times in battery operation.

However, there is now also PC compatible hardware with very limited power needs. A nice example are the N100 and N150 CPUs from Intel, which are made with 10 nm line widths. The permissible power consumption (TDP, Termal Design Power) of the N100 is 6 W. The N150 has, depending on the cooling system, up to 25 W of TDP. Intel is known for relatively power hungry CPUs, but I have no experience with recent AMD CPUs.

A Raspberry Pi 5 with comparable SSD might have a marginally lower power consumption than a N100 system. Exact power consumption for a specific task is difficult to estimate fo both technologies.

In contrast to its predecessors of the Celeron and Atom series, a N100 system offers enough performance for most ham radio applications under Windows 11, also for digital signal processing. Even with two of the 4 cores of the N100 switched off, I can run VarAC and SDRplay for my SDR with 2 MHz of bandwidth in parallel without any problems.

Reducing Power Requirements

An energy -efficient processor is only one component. A lot of power can also be wasted by multiple voltage conversions and energy-hungry monitors. Most smaller computers are either operated from a 19 V source, like most notebooks, or with USB Power Delivery. All of this does not match the 11-15 V that most of our batteries deliver.

So I was looking for small Windows-compatible computers with 12 V power supply. They can hardly be found on the German market. I therefore invested EUR 200 in a China direct import, not wanting to spend more money because of the planned experiments.

My basic consideration was that modern computer technology hardly ever works at 12 V. Common operating voltages are 5 V and 3.3 V. Processors and RAM are often operated with variable voltages in the range 0.9-2 V. I therefore assumed that the 12 V are directly fed ton a switching voltage regulator that can cope which a little higher voltages. So far, this has been true: My N100 computer works without any problems with the 13.9 V, that my solar charge controller maxinally delivers to the LFP battery.

I chose 13.9 V because the cell balancing in a LFP battery only works properly above 13.6 V. Considering the up to 200 mV voltage loss from the charge controller through the necessary fuse to the battery, there is not much meat left. This problem is not as grave as it might appear: In the afternoon solar harvest drops, charge currents drop and the voltage loss, too. Additional contact problems might send the 13.9 V directly to the computer.

With lead batteries, you will usually choose an even higher charge voltages to prevent sulfating. I have my doubts that my computer would tolerate 14.6 V. I have not disassembled the computer so far that I could examine electrolytic cpacitors. But I do not expect them to have more than 15 V of operating voltage. The Chinese can calculate too well for this.

Operating Computers Headless

The most bulky components of a computer system are screen and keyboard. The most common way out is the use of a notebook. Then you have everything in one piece. But: How do you connect the perephery? Either you have cables on the notebook. Or it very quickly gets a composition for WLAN and Bluetooth.

Additionally, many digital modes are mostly used without someone at the station. For example I have VarAC running most of the time, with alarm sounds aktive. When I hear a CQ call I go to the nearest computer and and do the QSO from there. A monitor would be off most of the time and often noth where the operator just needs it.

Therefore I went a different way: The computer is an integral part of the radio installation and is operated without keyboard and mouse. The computer is remotely controlled using standard methods: WLAN and VNC software. Some radio devices include Bluetooth and/or WLAN, but usually with significant restrictions. I therefore control my IC-705 via USB.

In the shack I run a network segment with a WLAN access point of the 30-EUR class that makes networking in the shack independent of internet access. This WLAN access point is powered by the emergency power supply in the shack and provides DHCP etc. I would have needed an Ethernet switch anyway. If the computer can do WiFi, you could also make it into a WLAN access point, for example with [4].

This way you can use any computer without a special software installation for remote control of the station: Connect any computer with any operating system to the WLAN and use easily available remote control software.

I use the VNC protocol, which should be available for almost every operating system. For Windows servers there is also the RDP protocol, but I have no experience with it. On my Windows computers I use TightVNC, under Android Avnc.

If you have the right clients with you as installation packages, you can use any computer to operate the station with little effort.

One problem I have not yet dealt with: how to extend audio interfaces by (W)LAN. For my emergency radio operation, it is sufficient to use the speaker in the radio via remote control and CAT. Obviously there are solutions for this.

Notes on Remote Control

There are two occasions where I need connect keyboard, screen and mouse to the computer in the shack: If I want to enter the BIOS or if VNC no longer wants to work. The first case could only be solved otherwise with data center technology, where the servers have a separate Ethernet connection for such work. For the second problem, press the reset button, which usually means a longer press on the switch.

The desktop size is often a problem. It is helpful if you operate the radio computer with a smaller screen size than the computers you use to control the radio computer. Therefore, the Shack computer is set to 1440 x 900 pixels.

From a smartphone you rarely want to control desktop software. But it works well with a tablet computer. What is easy to read on a 24-inch screen is eye powder on a 10-inch screen. Therefore it is helpful if you can enlarge the computer desktop in the VNC client. The program window just used can usually be read and operated well on a 10-inch screen. You have to move the desktop cutout if necessary.

FT8 & Co can still be operated with a screen keyboard. For example at VarAC this becomes very tedious. Then Bluetooth keyboard and mouse at the tablet computer help. But you will experience why wireless keyboards and mice usually bring their own USB dongle: The Bluetooth stack obviously terminates connections relatively quickly if they are not used. Then the connection must first be rebuilt, which takes a few seconds. The first key presses and mouse movements are therefore lost.

Incidentally, Bluetooth keyboards and mice transfer special characters, press the right mouse button or press on the roller wheel from Android to the computer desktop. Only characters that are entered via the Alt-GR key may have to be searched first. Using function keys can also be difficult. In any case, I do VarAC QSos quite relaxed out of the armchair in the living room.

Nothing is as vivid as an example: I am sitting in my armchair reading something. Then I hear the VarAC CQ sound from the shack – noticeable but not too distracting (for YL). When I feel like doing a QSO, I grab my Android tablet and start the VNC app. If the station is strong enough to hear my QRP station, I respond.

Often, the other station sends me an URL during the QSO. With a mouse click, I open the corresponding website in VarAC. It might be difficult to read desktop websites on a tablet. Then I put the web browser (on the shack computer running Windows) in the background. Sometime after the QSO, I go to the home office and start a VNC session for the shack computer. Now I can comfortably view the website.

Avoiding Ground Loops

At the very latest, when the transmitter can output more than 10 W, you should consider ground currents. This is no serious problem between the radio, power amplifier, and Matchbox because the coaxial cables create low-impedance ground connections. However, it would be critical if the ground connection of the radio or computer became too high-impedance. Then, much larger currents could flow through the thin USB cable than the developers could have imagined. Standard audio interfaces also isolate computer and transceiver.

So I routed the USB connection between the shack computer and the transceiver through an USB isolator. These are available for under EUR 20. Devices in this price range can transmit a maximum of 12 Mbps, which should be sufficient for CAT and a sound card. To allow me to use the USB isolator universally for USB2, I spent EUR 40 on a USB isolator that can transfer up to 480 Mbps. It is best to use a device with a USB connection cable, so the USB isolator does not block any of the already scarce USB ports on the minicomputer.

Radio interference?

I regularly hear complaints about radio interference. Some are justified, but most point to problems with the receiver installation. RFI through radiation is usually overestimated – where, for example, is a USB power adapter with any kind of effective shortwave antenna? Experience shows that most interference enters the receiver along some kind of cable. I have already written extensively about this topic in this Web site (sorry, German only). I stick to this, even if OH8STN, for example, claims otherwise [5].

The fact is: My radio installation includes various switching regulators and computers, and I have not had to deal with radio interference. This explicitly includes a cheap 2 kW inverter that is electrically connected to the radio station. With two thin ferrite rings, I managed to make it so quiet that I can work QRP stations on 40m in North America.

References

[1] Off-Grid Ham Radio OH8STN: Goodbye Raspberry Pi
[2] KM4ACK: Why I Quit the Raspberry Pi
[3] WSPR-Bake with Raspberry Pi: http://www.hjberndt.de/dvb/wspr.html
[4] MyPublicWIFI This program turns a Windows computer into an access point.
[5] Off-Grid Ham Radio OH8STN: Victron SmartSolar MPPT Charge Controller
In this video, Julian wrestles with a Victron MPPT charge controller. He puts current chokes to almost all the cables, but not the most important one: the antenna cable. I operate several, even more powerful, devices from this exact series. Every shortwave antenna cable needs to have common mode chokes at both ends!