Hello all. My first post; hope it comes through OK.
Inspired by Peter HB9EBE’s L-match posts, I built one with a few twists. Main features:
- built in plastic Sucrets (throat lozenge) box, hence the “soothing” moniker
. Impedance mismatch might be like a sore throat for your antenna; so this may help! Plastic housing isolates XCVR BNC from any common-mode currents arriving at the antenna BNC.
- size: 95 mm x 63 mm x 30 mm; 95 g
- schematic attached. Block sequence: XCVR → CMC → SWR bridge OR decade-style L match → RF indicator → ANT
- twist: I used a DIP switch block for the decade inductor switches. It seems to work fine at QRP RF. Use stub of bamboo chopstick for easy DIP switching and minimizing hand effects. DIP switches are a good way to shrink /P equipment. Easiest to flip in inductors on DIP switch for maximum receive noise, then switch in the SWR bridge (TUNE) and adjust variable cap until SWR LED goes out. Switch back to OPERATE, tweak cap for max brightness in RF indicator and work the world!
- RF indicator is simple LED direct to 3 t on ferrite core on ANT lead. This shows relative RF antenna current, which we want to maximize through an ATU. Highest ant RF current typically (but not always) corresponds to lowest SWR. Tune for maximum brightness on RF LED.
- I sized L-match inductors to resonate from 3 MHz to >50 MHz. I have used this unit to match impedances for whip/radial and EFRW antennas from 40-10 m. Should work from 80- 6 m.
More photos show insides and /P operation on recent trip to Newfoundland. If anyone wants cobstruction details, please contact me at scott dot schillereff at gmail dot com.
Best 72, Scott VA7SNJ
12 Likes
Hi Scott,
Nice compact setup but pls enlighten me. Why would I need/want to use something so unnecessarily complicated (micro switches and tiny knobs) on a summit?
- Either use an ATU
- or a resonant antenna like an Endfed even for multiple bands.
As simple as possible is the way from my point of view. Enough other things can and will go wrong on a summit activation.
73 Joe
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Hi Joe
Thanks for your comments. You are right; for alpine style summits (e.g., precarious crag, limited space and time, wind, maybe poor weather) simple is good and a resonant antenna with no ATU may be the best option. For those operating in a wider range of portable settings and wishing to easily switch HF bands including WARC bands (like me ), an L- match ATU is useful. Part of my motivation for this build was to see if the DIP switch concept would work and to see if I could fit it into the small Sucrets box. None of the electronic elements used here are new, just repackaged. So far, this little ATU works (no smoke!) and surprisingly is not fiddly to use; just one step smaller than other builds using a series of tiny toggle or slide switches for the decade inductors. Good luck with your activations! 72, Scott VA7SNJ
2 Likes
Very nice setup, Scott! I like the simplicity and robustness of the L-match, which gives you all bands with a piece of wire. It also allows a lot of experimentation, which is part of the fun… And it feels good to build your equipment, if you enjoy building. The DIP switches are certainly a new idea. Of course, an ATU is easier to operate, but somehow it feels odd to pair a T1 or similar with a $100 radio such as the QMX. At least for a casual /p operator like me who does not own a T1 already 
73, Peter
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Hi Peter
Thanks for email. Agree on all points. Yes, fun to build your own gear; very satisfying (when it works! ).
I realize that there is a nomenclature mismatch here which might lead to confusion. I see that both you and Joe earlier referred to an “ATU”. I reckon you are using that acronym to mean “Automatic Tuning Unit” (like a T1). Perhaps that’s a European thing?
Many hams (me included) use “ATU” to mean “Antenna Tuning Unit”. So one could have a manual ATU or an automatic ATU. So in my usage this “Soothing” L-match is a type of manual ATU. Hope this clears the fog a bit 
. I personally prefer manual ATUs, as they are lighter, don’t require a power source, and I like twiddling knobs 
.
Best 73/72, Scott VA7SNJ
3 Likes
This ambiguity could easily be avoided with the abbreviations MATU and AATU - which sounds pretty nice, doesn’t it?
But then there’s still the ambiguity of tuning an antenna - if you get what I mean by that. 
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