3D Printing Hacks HF Portable

The GAWANT Antenna

After my QRP/Portable QSO with a Japanese station, I was contacted by Hiroshi JL1KLK who asked if he could mention my post in his blog. I obviously consented. In his post Hiroshi shows the similarities between his QRP operations and mine: we both have glasses, we both wear caps, we both are middle aged, we both operate near the water, we both operated standing. There was, however, a difference that stood out: I use an MLA, while he uses a vertical antenna called GAWANT.

Since I always desired a portable vertical I decided to look into it and eventually build my own. But what is the GAWANT? After some research, I found that it is design somewhat popular in Japan.
Technically, it is an half-wave vertical end-fed in a FT817-friendly package. After asking, Hiroshi very kindly provided me all the details with this wonderful document:

Click for more info

In it, I discovered that the original designer, Ariga JF1QHZ, named it after his native Shinagawa-shuku neighborhood.
I already had everything I needed to build it, except of course for the 2 meter long telescopic rod and the case. The former was acquired at for $8.50 and the latter was designed and 3D printed by myself. You can check it out at Thingiverse, if you wish.

The GAWANT is ofter used directly on the front BNC of the FT817. I find this impractical because the rod will come uncomfortably close to the operator’s head, and also because the leverage force expressed on the connector appears to be too much. I prefer attaching it to the rear SO239 connector, by means of a right-angle PL259 to BNC connector. I am not excluding the idea of redesigning the case in order to address this particular usability aspect.

The first test of the antenna was in my backyard (these days it might be better to stay home…) and the results were encouraging: in just a few minutes during the WPX CW contest I made 3 contacts: Texas, Europe and Africa. Not too bad!

Here are some more pictures:

Will I switch from using Magnetic Loops to Vertical end feds during my operable operations? Probably not, still the GAWANT is a very nice – super portable – HF antenna that I now have available. Given the cost of making it (I estimate less than $20) I think everyone should build one!

Many thanks to Hiroshi-san for providing all the information, and to Ariga-san for the design!

HAB Hacks

K1FM Pico Balloon – Part Two

Great progress with the Pico Balloon project!

The latest release (version 1.3) is 4 layers and weights around 3 grams when printed on a 1.6mm PCB (can further be reduced in the future). It also have some interesting new features: allows self-calibration, can measure its own power supply and has an onboard temperature sensor. Here it is:

Version 1.3 is definitely airworthy and can be used for an actual launch. Schematics and board layout are now available on GitHub:

On the software side, I might use OrionWspr by Michael Babineau which now supports my board. As an alternative, a simpler version I am developing could also be deployed.

The part I am still wondering about is power. Contrary to my initial understanding, it is, after all, possible to avoid using batteries (or super-capacitors) and power the balloon by solar panels only. That would require somewhat larger panels (probably around 6 or 7 grams) that could generate enough current for the board to run under direct sunlight.
An alternative option is to use lighter panel s (1.5 grams or even less) that feed a power charger which in turn charges a 1.5 Farad (5 grams) super-capacitor. Finally, there is the possibility of using lighter panels which directly drive a capacitor without using any chargers. This raw method seems to be preferred by other balloonists but I still don’t have a solution for it.

We’ll see what happens on my next post.


K1FM WSPR Transmitter (aka: el cheapo Antenna Testing)

I recently built a couple of identical WSPR transmitters to be used in direct comparisons between magnetic loops and other antennas, or even between various kinds of magnetic loops. They are now available on Github.

The transmitters are based upon the Si5351 clock generator and their RF section was inspired by the excellent Zachtec’s products. An onboard GPS receiver is used to automatically provide timing and location. In the absence of a GPS fix a button can be used to start transmitting. The same button can also be used to cycle between 5 predefined WSPR frequencies. There are no onboard filters therefore external filters must be used in order to maintain compliance with FCC rules.
SMA connectors provide connectivity for both the HF and the GPS antennas.

The firmware is based upon existing libraries and was created around version 1.0 of the board. Version 1.1 introduces an important extra feature: auto-calibration.

I also built another magnetic loop, identical to the one I already have. Together, they will serve as a testbed for my comparison tests.

HAB Hacks

K1FM Pico Balloon – Part One

The Pico Balloon concept is simple: you build a transmitter small enough to be carried around by one or two common party balloons. As the transmitter floats around the globe it transmits its current position and altitude so you can follow its path in realtime. If you do it right, the balloon will circumnavigate the globe… repeatedly. Great stuff! I had to do it.

After realizing that it was relatively easy to construct a WSPR beacon based on Arduino and a clock generator, a few months back I decided to try building one.

The first attempt was on a breadboard with an Arduino Pro Mini, a uBlox breakout board and the Etherkit s5351a breakout board. After writing a few hacky lines of code (WSPR libraries are already available) WSPR worked! All I needed was making everything small enough to be carried by a party balloon.

I decided I was not going to use the standard Arduino Pro Mini. Rather, I was going to load the Arduino boot loader on a ATM328P myself and have everything else (GPS + Clock Generator) on a the same board.
This unit also worked and, technically, was already small enough to be carried around by a couple of large balloons.

But how was I going to power it? Was a small LiPo battery suitable? After checking the specs I realized that even the smallest ones were too heavy. On top of that, batteries don’t take extremely low temperatures well so it definitely had to be solar power.

In the next revision, which I called 1.1, is where I faced the first serious obstacle. Until that point I was able to successfully load the Arduino boot loader without too much trouble using an ancient Arduino Uno as the ISP programmer. For reasons I still can’t understand, that wasn’t the case anymore with revision 1.1. Fortunately, when I was close to giving up, I remembered that back in the days I had purchased a proper ISP board and tried with that: Bingo! Problem solved.
As you can see, on version 1.1 all necessary programming connections have been moved to a section of the PCB which is supposed to be cut out before launch (the wires soldered on the side were part of my desperate attempts to troubleshoot the ISP malfunction…).

At this point I had a transmitter that – together with the solar panels – weighted less than 10 grams! I really believed it was just about time to buy the balloons when I faced the second problem: I had grossly overestimated how much power solar cells can deliver. Yes, tensions can be pretty high but currents… well, currents are tiny: there is absolutely no way the beacon can be carried around by small balloons while being directly powered from solar panels as I originally envisioned. I needed something light that charged a capacitor and then – only then – I could start transmitting.

By searching things like “Tiny Solar Power Charger” I ended up on Jared’s (N7SMI) page. I was stunned: his pico balloon concept and hardware was identical to mine except that he completed it years in advance and, unlike mine, his actually worked and flew already many times.
Jared had already solved the power issue with a 1.5F super capacitor charged by an SPV1040 controller and two 0.5V solar cells. Brilliant!
Not only that. In order to save power, he provisioned his transmitter to selectively switch off the GPS and/or the clock generator. He also has a temperature sensor and – surprise surprise – a CW beacon too!
Clearly, I now have enough material for version 1.2.

On part two I will publish my current schematics, PCBs and source code.

Hacks SDR

HDSDR OSX version 2.76 released

Once again, with Mario’s permission, I bundled the latest revision of HDSDR to be run on OSX. I also created a new rtl_sdr launcher that should be more stable, easier to use and that incorporates the bleeding edge version of librtlsdr.
I tested this on Yosemite, El Capitan and Sierra. My CPU is a quad i7.

Here is a quick vhf/hf demo that I run using my v3 dongle in direct sampling mode:

In order to download it, please refer to this page.

Latest Release: March 2nd 2017