Stealth QRP Transmitter in Berlin

March 7, 2023 Julian OH8STN Antenna Testing, Asynchronous Messaging, Data comms, Digital Communications, Digital QRP, Education, Emergency Communications, Grid Down Communications, Ham Radio, Preparedness, Survival & Preparedness, Tutorials, WinLink, Xiegu x6100 13

Operating a stealth QRP transmitter in a Berlin hotel room was an interesting ham radio experiment. Far away from home or even in a foreign country, think for a moment how one could unwittingly find themselves in the middle of a grid down scenario. How do we let our family know the situation? How do we do it with minimal comms gear, or without standing out?

Before we jump in to this blog, its important to talk a bit about why we should try these type of ops. Very often, there are those who say “That won’t work!”. The opinion is not backed up by their own testing, rather these people have little or no imagination. “My Elmer told me” this or that! This is another phrase often muttered from the mouths of people who for whatever reason, can’t be bothered to try it themselves.

This test in Berlin was done firstly, because I was there. Secondly, it was done to see if it was possible! The more field experience we gain operating in abnormal conditions, the better suited we are to operate in less-than-ideal conditions. Driving to a park, setting up 50 lbs of gear, and calling it “portable” may be fun, but it doesn’t really teach us anything! Taking a pocket-sized radio, tablet, and some wire, operating from a crazy place is much more of a learning experience. So stick your favorite finger up at all the conformists, and roll your own way!

Radio

For my stealth station, I used a Xiegu x6100. The x6100 has some interesting features, giving this experiment a favorable chance of success. It is not a “perfect radio” by any means. It is capable, and solves some of the typical problems we have with portable or remote data operations. Although Wifi and Bluetooth don’t work as one might expect on the x6100, the tuner is great, the filters are great, and noise reduction is better than expected. With a good firmware release, this radio could become as iconic as its older brother the G90. Lets take a look at some of my favorite features.

Xiegu x6100
  • Compact design
  • Internal battery
  • Internal antenna tuner
  • Internal audio interface
  • Spectral display
  • Filters, DSP, and noise reduction
  • 160-6M coverage

Antenna

The antenna chosen was an End Fed Random Wire from Packtenna. Inefficient yes, but an effective tool for the job. The wire would be slid out the window at night, slinking its way down the wall. Of course this meant coverage was directional. It also meant losses created by the antenna’s proximity to the building. Thankfully HF is very forgiving in this regard.

The wire length was about 19 meters or 62 feet. I didn’t think about it at the time, but now wonder how close to the ground the end of the wire was. We expect losses with a configuration like this. However, we also need to avoid adding any additional unnecessary problems, to the antenna configuration.

Previous attempts

Magloop

Previously tried a magnetic loop From within a hotel room in Helsinki. That attempt was to a known station I’d worked, on an earlier trip. Something about the glass in that hotel made getting signals in or out difficult. Although that attempt was a no-go, it would have worked from the Courtyard or a balcony for certain. With that experrience, I decided not to try a magloop this time.

Vertical antenna VHF

Also tested VHF 2M with VaraFM back in January from the same Helsinki hotel. This is a standard configuration for my hotel visits around Europe. For example, I published a video earlier this year of a 6m Winlink connection, from a Helsinki hotel room in the middle of the city.

Although technically nothing wrong with this configuration when tested in Berlin, there were 2 factors contributing to its ultimate failure.

  • The distance to the gateway
  • Not having LOS

When we are talking about VHF, UHF or SHF comms, LOS (line-of-site) is required to make a successful connection. There certainly are exceptions but as a rule, LOS wins the race. This is the reason mesh networks require a much higher node density, than connections over HF. In a MESH, the signal either needs LOS, or to get bounced from node to node, or it needs lots of gain in combination with with one of the others. My VHF attempt in Berlin, had none of these possibilities, s it failed.

Current attempt

This time a “short” end fed random wire was chosen. The goal was to make a ground wave connection on either 40, 60, or 80 meters, to send and receive Winlink messages. It definately wasn’t without its challenges!

The first challenge was the noise on 80, 60 & 40 meters. It was generated by the hotel itself. The noise was easy enough to clean up, using the filters and noise reduction in the X6100.

The next challenge was finding the appropriate band for the connection. This was almost a no-brainer, as It would be a groundwave connection during the night, to a station 20-25 clicks out. Without a doubt, either 60 meters or 80 meters would bring success.

Another challenge was extremely low power. The power started off at 3 watts, then reduced to 1 watt during the connection. There was no other reason for doing this, than to see if it would work. It did, and it was an increabile learning experience.

Microsoft Surface Go 2

About a year ago, I published a video about ham radio with the Microsoft Surface. The Microsoft Surface was the single largest contributor to a positive data mode experience. Although unsure about the decision at the time, the Surface ultimately replaced the raspberry pi as my primary field computer. The results were so outstanding, I simply won’t look back. The number of hours spent configuring and supporting the raspberry pi, made it unsustainable as a primary field computer.

At the time of writing this post, there have been no hardware or software failures on the Surface or any of the software packages used for my communications. Zero failures, zero hours spent supporting the device! Other than basic maintenance and occasional updates, the Microsoft Surface has been a magnificent addition to the station. In fact so much so, I just oredered a second one.

Now we arrive at the Stealth station in Berlin video. As always, these blog posts augment the videos, helping to fill in the blanks. The video shows you a first person perspective of what can’t be conceptualized in a blog.
I do hope you enjoy it.

Gear used:

73
Julian oh8stn
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12 Comments

  2. Great blog, great videos. Keep up the good work Julian. In a world of problems, we need people providing solutions.

  3. Doing is usually the best way of learning — keep mucking it up until you figure out how it works. On what floor was your room (I’m guessing 3rd or higher)? Back in the day, we were trained to look for just what you deployed but most people don’t look up so you were probably safe (I’m also assuming that good tradecraft had you reel in the antenna when you were finished so it wasn’t flapping in the breeze all night inviting the BND to have a look). The key part of your Berlin TX, for me, was the reduction in power to 1w. The next step would be to see how low you can go in an urban environment and still make contact. Well done! 73 Garu

    • Thanks!
      5th floor in Germany, 6th in “American”. YES Indeed. Made the connections, then reeled in the antenna wire. It actually “felt” kind of sneaky! Getting those messages out, under the cover of darkness…
      The 705 has much better tx power adjustment resolution than the x6100. I’ll try next time using the 705.
      73
      Julian oh8stn

  4. Thanks for another great post! I too have done a QRP setup from a few hotel rooms. Last year I was in Dublin Ireland and deployed a random wire out the window of my hotel room, connected to my IC-705. I was able to hit a number of stations all over Europe using FT8 and 10 watts. Amazing. I’ve also had good luck using a magnetic loop antenna mounted on a tripod. I like the mag loop as it’s directional (assuming it’s mounted vertically), so you can play around to see what direction provides the best signal (and/or to null out noise sources to a degree). I’m definitely going to need a Surface Go 2 for digital modes. That’s an amazing amount of power for such a lightweight machine!
    73,
    Mark K0EHR

  5. Great blog and photo’s Julian.
    I hope the Berlin hotel don’t see the blog or video! Haha
    Did you deploy your antenna with a Ninja outfit and balaclava? Haha… now that would be an awesome photo! 🙂
    Thoroughly enjoying all you do and learning alot for when I get the X6100 too.
    Take care and make sure your get a believable story ready if you get interrupted during HOTA.🥷 73

    • Thanks for the wonderful comment. I did have my balaclava, but didn’t need it. At 1 point there was a drunken pedestrian walking by, who probably thought I was about to jump out the window 🤣

  6. Great blog and photo’s Julian.
    I hope the Berlin hotel don’t see the blog or video! Haha
    Did you deploy your antenna with a Ninja outfit and balaclava? Haha… now that would be an awesome photo! 🙂
    Thoroughly enjoying all you do and learning alot for when I get the X6100 too.
    Take care and make sure your get a believable story ready if you get interrupted during HOTA.🥷 73

  7. Great video, as always!

    I never considered windows a problem, but now that you mentioned it, we have triple-glazing with the inner four surfaces coated to reflect sunlight, mainly to keep the heat out during summer. That coating is usually made of thin layers of metal, which are bound to interfere with RF signals.

    73,

    András

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