Categories
3D Printing HF Portable

K1FM Magnetic Loop: 2020 edition

I really, really like magnetic loops.

After making a bit of a splash with at the Dayton Hamvention and publishing how to make your own on QST I decided to improve the design a bit more, so here I am with the latest iteration of the K1FM Magnetic Loop.

The new design improves the older one in a few key aspects:

– Entirely 3D printed
– Readily available, made in the USA variable capacitor
– Easy to assemble

Basic geometry and main electrical characteristics remain unchanged:
– 4o to 10 meters
– 125 inches radiator
– 165pF variable capacitor (dual gang series)
– QRP power (it actually can handle a lot more but, as you know, using a magnetic loop in close proximity with more than a few Watt is against FCC guidelines and potentially dangerous. Don’t do that)

Fully 3D printed, capacitor enclosure

The new enclosure requires no rework in order to be mounted. It is now quickly detachable by using the same mount type as the radiator/exciter assembly. This makes the antenna even more portable and, at the same time, opens the possibility of using other support types in place of the selfie-stick (fishing rods, PVC pipes etc.).
The capacitor uses a 3:1 planar reduction that, combined with the a fairly large knob, makes tuning quick and easy. A 3D printed indicator (blue) shows the current shaft position: just by looking at enclosure you can tell where about you are currently tuned and act accordingly when it’s time to tune again.

Exciter loop splitter

Thanks to a new splitter design, the exciter loop is now conveniently made out of a standard LMR240 BNC-male to BNC-male pigtail. The splitter also allows the possibility of using multiple radiator/exciter assemblies in order to, for example, work 6 meters.

Radiator loop mount

I also redesigned the radiator mount to follow the different bending radiuses of the radiator and the exciter loops. Both cables now snap-in with just the right amount of force, therefore zip-ties are no longer needed.

The new loop looks great and works better!
I’ve decided to call it K1FM-Loop. If you want to build your own, here are the instructions to do that

Categories
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 buddypole.com 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!

Categories
HF Portable

Portable QSO with Japan!

Last Sunday I took my Portable setup to the river, as I often do. Propagation was a bit short with Europe totally closed when suddenly – to my disbelief – JH4UYB popped up at S8.
I had heard Japan twice before with the Loop, but never as strong as that.

After beaming about 330 degrees (the same direction I normally use to work W7) I immediately started calling. Incredibly, part of my callsign was picked up right away! The rest of the QSO, however, took more than 3 minutes to complete thanks to the perseverance and the professionalism of Masaki, the Japanese operator.

Categories
HF Portable

QSO from the Pier

Once again in Italy, once again at the beach. The weather was a bit cold but propagation warmed me up good.
Heard a lot of US stations but couldn’t make the pile-up. On the other hand, I had the pleasure of a QSO with OH73ELK.

Categories
HAB

K1FM-3 Launch

During my 2019 xmas holiday I took the occasion to launch again in Italy. Unfortunately I made the mistake of loading too much gas and, as a result, one of the two lift balloons popped shortly after take off.

The silver lining of this short-lived launch is that I think I found my definitive construction style.
The think food foam sheet I used is useful to provide some mechanical resistance to the solar cells and also to keep the transmitting electronics a bit warmer.

I have a feeling that next launch is going to be much, much longer!