OH1MAC

After I got bitten by the SDR bug back in 2012, I updated and upgraded my SDR equipment every year. Normally, this meant that I bought and built new SDR receivers, computers, antennas, etc., and upgraded my SDR system from a single laptop computer, one RTL-SDR dongle, and one wire antenna to five Raspberry Pi’s, two NUC PCs, a 6TB external drive, 12 SDR devices, and 15 antennas ranging from long wires to active loops, a 10-meter long vertical whip, and a MiniWhip active ‘can’. Not to mention all other ADS-B, AIS, RTL_433, and so on.

In late 2020, I started my training to become a licensed HAM, a Radio Amateur, and got my license in January 2021. It was time to be reborn and rethink everything I had done before.

As I’ve mentioned before in this blog, my system is located some 250 km away from where I live. I don’t have space for all the antennas in my city flat, nor am I able to install anything bigger than a car whip on my balcony. The SDR equipment I built at my remote site was already working great, and as I later found out, operating HAM radio remotely is not that hard either. The Icom IC-7300 series HAM transmitter is more than a capable device for remote operation, so I could build a fully remote-operated HAM station!

The Shack

Perhaps the most annoying thing about modern HAM radios is that they are noisy, I mean really noisy! The power supply needs to be able to power the IC-7300 with a whopping 25A, about 350 Watts of power – this creates a lot of heat that needs to be pushed out from the PSU. Also, the IC-7300 has a large fan that is not silent either. Additionally, the radio makes noise when transmitting, with relays clicking like a maniac, especially during the tuning phase.

It was clear that I needed to move my system to another place. I had built my SDR-based system next to bedrooms, in an upstairs vestibule on a small shelf high up on the wall next to the ceiling. This place is really not suitable for heavy, noisy devices that are on 24/7 and have bright lights, a big screen, and so on.

The first, initial idea was to move the equipment out of the house, to the balcony into some kind of cabinet. This would keep everything well isolated from the elements of nature and also help with the cabling, as 15 antennas require a lot of cable!

Then, the idea was to build a real shack outside, next to the actual antenna mast, and remove everything from the house. This would also help with the EMI that was present in the house.

The next iteration was to actually get a playhouse and install all the radio stuff there, into some cabinet, and disguise them as some kind of furniture. This was agreed to be the final solution.

So, what was actually done and how?

First came the playhouse. Luckily for us, a family we know was trying to get rid of a playhouse at the same time, perfect! The cabin was awesome, with only some minor adjustments necessary to make room for the “fireplace”.

As it was clear that everything needed to be well-grounded, we decided to mount the cabin using steel poles. These steel poles would go down 1.6 meters into the soil, making them perfect grounding points for the system. We also decided to have a small patio and garden for my nephews and nieces to play with.

The second phase involved power, internet, and grounding. There were a few absolute rules that needed to be followed when it came to the safety of the system, users, and especially kids playing in the playhouse while radios are in use and powered on. No mains sockets or other high-voltage devices can be touched, nor can any part that may become hot be touchable by “small hands”. In the design, this was taken very seriously, and everything was planned and built so that the cabin is as safe as it would be in normal use as a pure playhouse.

The mains come to the cabin via a special 550VA isolator transformer, RF-filtered and isolated from the house mains. This prevents any EMI from traveling from the house via the power line and also isolates the cabin from the main power grid grounding. At the cabin side, everything is grounded via the cabin poles with a sturdy copper line.

The internet connection is provided both via an ethernet cable and a WiFi connection. The ethernet cable has galvanic isolators at both ends of the cable to prevent any DC current from traveling via it from the house to the cabin or vice versa due to potential differences between the house and the cabin. This also helps to prevent any RF interference from causing any harm to the installed ethernet network while the Icom is transmitting.

The power and network cables are installed inside underground tubing, and the grounding copper wire is directly on the ground, connecting all four poles of the cabin and the antenna mast to the same common ground with all the antennas, radios, and all other low-voltage devices used in the cabin (lights, security cameras, and so on).

All the playhouse electric outlets are 12V DC, for lights, toys, and decorations, and are installed so high that the smallest children cannot reach them.

The third phase involved antenna cabling. Currently, there are fifteen different antennas connected to the system. Some of them require lightning protection, while others do not. Some are used for GHz bands, and some for VLF. All the antenna cables are protected at least with a ferrite ring against RF interference, and most of the antennas also have gas tube lightning protectors. The transmit antenna uses a thick 10mm EcoFlex coaxial cable.

The fourth phase involved the Radio-Cabin. All the radios (SDRs) and the transmitting rig (Icom IC-7300), PSUs, and computers are installed inside a standard metallic U-rack. The rack has been grounded to the same grounding as the cabin poles, all the antennas, and the antenna mast. There are also tens of meters of copper wire buried underground, along with 5 meters of copper tubing in several locations around the premises. All this is to ensure that the grounding is perfect for both EMI & RF protection, as well as for lightning protection and prevention of static electricity build-up with the antennas.

The Radio-Cabin also has a remote-controlled security camera installed inside, mainly used for maintenance and checking LEDs and other lights on the computers. The Icom has its own high-resolution camera pointing directly at its screen so that I can see a real-time stream of the actual display of the Icom in case the remote controlling software has some problems displaying data.

At the bottom of the Radio-Cabin, there is a cheap 15” monitor screen. As there are lots of computers and sometimes one needs to see what’s happening in the console, I installed a screen at the bottom of the Radio-Cabin. When not in console use, it can play an HD “Fireplace” movie for the kids playing in the playhouse. It even has small speakers so one can hear the crackling noise of the fire. This is a remotely controlled screen, so it is not on 24/7, not only to save the life of the screen but also because this kind of screen is a huge source of RF interference.

Temperature and humidity control. As there are several devices creating a lot of warm air, I installed remote and thermostat-controlled fans at the bottom of the Radio-Cabin and also at the roof of it. Three Ruuvi-Tag sensors measure the temperature and humidity inside the Radio-Cabin, and in case of too warm, too cold, or too humid values inside the cabin, the fans are started. Floor fans circulate the air inside the Radio-Cabin to level the temperature, and if that is not enough, the roof fans are started and will push hot air out from the Radio-Cabin. Fresh cold air is sucked in via a floor vent (filtered). There is also a humidity collector bucket (that blue one) that keeps the overall humidity in control. It uses a special chemical compound that ‘melts’ slowly from solid to liquid by absorbing humidity from the air. It has a small fan installed at the top of it to speed up the air circulation (which can be remotely controlled on or off).

Based on my experiences, the internal temperature of the Radio-Cabin is above 0°C when the external temperature is not below -15°C. If the external temperature is lower than -15°C, good external insulation is needed – so during winter time, the Radio-Cabin has its own ‘overalls’. With this, the internal temperature always stays above 0°C, even when it’s -25°C or colder outside.

The system has worked without any problems with external temperatures ranging from -28°C to +43°C.

Radio-cabin winter clothing 🙂

The final step is security. As the playhouse has quite expensive equipment installed and only some plexiglass windows and thin wooden walls protecting them, it was important to have some security installed. The cabin itself has several RuuviTag sensors measuring all the movement of the cabin. The sensors are so sensitive that if someone walks near the cabin, the sensors can measure it.

The tremors that opening the door of the playhouse or someone trying to open the Radio-Cabin by force causes, triggers an audible alarm played by one of the computers installed in the Radio-Cabin. Also, an email alert is sent to my email address. There is also another security camera that records any movement with audio, so if someone tries to steal something, he/she will be recorded with HD resolution and sound.

The camera is also equipped with a two-way intercom, so I can speak to whoever is at that moment next to it. The camera and its internet connection are also battery-powered, so even if the main power is down, there is power in these security features for several hours.

Final Words

This has been an extremely interesting and fun project. Not only with the SDR & HAM radio stuff, but also building such a playhouse, power systems, security, and all the other things needed for such a system. I am sure that, as it happened with my SDRs, this playhouse project will continue to grow year after year – I’ll try to keep you posted about the latest modifications with it.

73’s! de OH1MAC a.k.a Mac

Hop in – would you like to have some tea or coffee? 🙂