some laser cutting.....

some RC plane stuff, some other stuff.

Helical STL Scratchpad

A place to store/share construction data. Helical loaded magnetic loop, or “STL” (small transmitting loop) antenna designed by Rich K8NDS 

The blue (magenta) circle dimension is 39″ diameter. The circle is the mean center-line of the 2″ tubing around the octagon. The 40.44″ dimension is the PVC elbow centerline. to centerline distance.
Using PVC supplies from Lowes hardware store- the 45deg bend has 0.5″ insertion allowance on each end, and pipe end-to-end gap is about 2″ fully seated. That gives me a pipe length of 12.7″.  I’ll see how close that estimate is and report back.

.magant octogon1


Later that day…..

I made the frame, all glued up and dry. It came out within half and inch of the drawing, and plus/minus half inch symmetrical. I’ll make up the difference when wrapping the copper.



Tomorrow I’ll bring it inside and wrap the copper. I started gluing the PVC in the basement, but had to move to the freezing  garage as the solvent fumes were building up quick in the house.



Here’s some pics of the connector end of the gamma match. Brass tubing soldered to the N connector, heatshrink covered,  and clearance hole in the copper. Copper is .028″ thick.

loopfeed1 loopfeed2 loopfeed3



Soldering the connector base copper(.028″) to the copper wrap (.010″)  Not the prettiest, but it’s the contact area underneath that counts.


loopfeed 4




March 6 2015:

The vacuum variable cap arrived from Russia. Here’s the start of the cap mounting plate. I hijacked a kitchen cutting board and cut it to 16″ by 5.5″.  Lowes hardware supplied everything else.  Plastic electrical conduit clamps to mount the board on the pvc antenna, and steel 2″ pipe hangers to hold the cap. (part# 302045) I don’t know how they measure 2 inches, but it’s a near perfect fit on the 60mm vvc cap ends.  The copper foil ribbon will be folded and wrapped between the cap and clamp. No extra soldered connections.


vvc4 vvc5 vvc6




March 7 2015


The motor drive has reached a stall because I can’t find a suitable shaft coupler that adapts 12mm to .250″.

In the mean time I couldn’t wait to try this out. I started to manually tune the cap for highest signal level at 14.250 MHz, then I played with the gamma match for the lowest SWR, and back to cap adjust- – – -back and forth. At ground level I got 1.4:1 and heard stations a couple S units below my dipole.  Can’t wait to get this thing outside and motorized!!.

magloop2 magloop3



March 9, 2015


Still motor-less. I spent the first sunny above freezing afternoon trying to tune the Gamma Match feed. I tuned the cap to best swr at 14.2 mhz. Like others said, the match is different on the ground vs 6 feet high. Many times up and down on the tripod, tune and test…..  the best I could get is 2.3:1 at any 20 meter frequency. But the great news is it’s easily one S unit above my 20 meter wire dipole. Once I get things locked down below 2:1 I think it will just get better.


March 21

Finally locked down and soldered the Gamma match. I can get 1.5:1 or better SWR from 40 to 15 meters. I bought a RigExpert AA170 S11 analyzer and that really helped the process. Below are some screen captures from the Rig Expert AntScope app.

loopdata1 loopdata2 loopdata3 loopdata4



March 27: The Mini-6

I wanted to try a mini loop for portable and marine 6 meters.  Here are a couple of 1st version prototypes. I first made a solid core loop, just shooting in the dark for size, feed, and cap value. Ended up with a 10″ diameter of #6 wire, and a Johanson 22pF cap. It’s a low voltage cap for receive only, but I did get 2 watts into it to test SWR and pattern without it popping.

I then wound a helical loop on 3/8″ PEX tubing using copper tape of .500 by 1.5 mil dimension.  Still 10″ diameter, but now with 50 inches of copper tape (25 per side).

Both of these loops are tune from 40 to 90 MHz easily with the 22pf cap. The usable bandwidth of the helical wound loop is about 40% better being about 100KHz wide at under 2:1 swr !

Field testing in receive mode will be nex week out in the cornfields. I’ll compare it to a tripod mounted Buddypole dipole setup with the help of another portable operator.

My next goal is to get some 3/4″ plastic tube,and 5 mil copper to wind a new one, and search out and find either a 1KV standard variable or a small VVC and run it remotely. I only plan to run 25 watts when this is done.


Keep experimenting and 73


loop 6meter 1 loop 6meter 2 loop 6meter 3 loop 6meter 4

Winter Project: Dynaflite Decathlon

My winter build is underway.  A few weeks in and I have it mostly framed up. 88 inch wingspan, 30cc motor and probably 13 to 15 pounds. Cutting and shaping all the wood is pure Zen relaxation.


front layout 1 firewall3

all bones 1 fuse bones 2 shavings1 shear web glue 1 tail group 1 tail group weight 2

Antenna Projects

This is a new antenna I invented. At the lower frequencies it acts like a fat monopole, and at higher frequencies it’s a tapered slot antenna. it shows a very nice SWR below 2:1 from 150MHz to 10GHz. Of course I didn’t invent either type, but I’m  positive I’m the first to combine them into one antenna.

egg1 egg2 eggswr


Below are pics of a 12DBi helical. I made the helix support from laser cut lexan. The first 1/4 turn feed transition was the critical part in tuning.


100_1564 100_1563

Below are more variations of the tapered slot / fat mono.  The one in large blue foam is an extended low frequency model. With the larger ground plane and copper tape “top-hat” it’s now usable to 70MHz.

xlegg1 dualbandegg1 elipse with supports[1]


For my Ham Radio HF station I made my 4:1  balun for my Off-Center-Fed antenna. The core is a 140-77 ferrite, wound with teflon wire. Plots shown with 200 Ohms on output.  So far good for a couple hundred watts.

balun_open_sm balun_imp balun_swr mast2

Power supply puzzles for the Taranis

I was thinking about installing a 3S lipo in my Taranis.  The optimistic thought was besides longer run time, maybe there could possibly be a teeny tiny increase in output power resulting from a sloppy regulator that allowed more voltage to the RF board.
BAAAAAAA!!! Wrong answer Hans!
On the bench with a lab-grade 10A variable power supply showed different.   I ran this test 3 different times with different bandwidth settings, and different antenna orientations, and it’s repeatable and constant.  The RF circuit seems to be more efficient when the radio DC power is at a lower voltage.  Running at 12VDC shows almost 0.5 dB decrease in RF output power as opposed to 7.2VDC.   Maybe it means nothing, maybe it’s just my radio… what’s half a db between friends, I found later that at 12volts, there is about twice as much ripple and noise (.06v)  on the rf board voltage compared to 9volt input. One of the universal truths in radio design…Poor power supply=poor RF.



The next issue is notable.  You see 3 different color traces in the plot below. The Orange trace shows a baseline output plot from the Taranis with no audio playing.  The Yellow is a plot while audio wave files like – low rates, high rates,  gear up, ect were playing constantly at full volume.  The Aqua trace is the RF output while music is played at full volume. There seems to be about a 1.5dB decrease in power while loud audio is playing.    Again, I aint sayin’ nuthin…  Just thinking about power supply current shortcomings. I’m going to re-do this test after I record some constant-tone wave files.



Lastly below, for edumatainment purposes, and not just for X9D owners, I did a plot of antenna polarity coupling to show the  importance of never pointing your antennas at each other.  Think of the co-pol as both antennas pointing straight up, then laying ONE down 45 degrees sideways, then 90 degrees sideways, then finally pointing each antenna end-to-end.  You’re losing 13dB  by doing that.  That means your 100 mW signal is now 5 mW, and you STILL have to calculate the distance path loss to that faaarrr away model.  It’s brown short time.

taranis polarity


FrSky X6R innards

frsky x6r a frsky x6r b

I was working at the bench and heard a crunch under my bigass workboot. I accidently stepped on a receiver that must have fallen off the bench and cracked the cover off. Oh well good opportunity to check out the innards.  Looks like it survived just fine.

FrSky Receiver size, and X9D Pot repair.

A comparison of assorted receiver sizes. I thought the Hitec was small, but damn….rcvr compare angle rcvr compare top1 x6r coin


A combination of bad soldering joints, and my opening the case too much and disturbing wires resulted in failure of the aileron  pot wires.  The pics show overwicking of solder on the red wire (indicated by the kink), which made it very inflexible. Upon opening  the dust cover, I also found the brown wire detached.  Last pic shows the repair.

broken pot wire 1 broken pot wire 3 broken pot wire 4

Taranis RF

I wanted to get some baseline measurements before I replaced my antenna for a removable one.
It’s just comparative reference plots, so don’t expect absolute values with quotable numbers. I will return to this for more measurements, but have to get back to balsa building while I wait for my DigiKey order 

In comparing the Taranis to Hitec, which I always thought well of in regard to their RF link, I’m happy to see the Taranis has at least or better peak power, but it’s TWICE the bandwidth as Hitec. This could be good or bad depending on your application.

First pic is the quick and dirty setup with each transmitter antenna exactly12″ from the analyzer antenna. I also swapped transmitters around and saw no measurable difference. Plots are labeled.

You can see how the LR12 mode gets better range. I haven’t measured the timing yet (as I only wanted an RF reference) but explained simply,
If I’m yelling at you from very far away, you can understand me better if I talk slower. LR12 is less data at same power.

xmit test plot 1 xmit test plot 2 xmit test plot 3 xmit test plot 4 xmtr test set 1

Added a plot showing the difference between Americas and Europe RF settings.  I can’t see any.  I truly don’t know if the specs or regulations are different.

xmit plot eu vs am


FrSky Taranis

Laser +  Boredom + Urge to “pimp-out” a new radio =  ________

plate2 plate4 tar4


I just painted a new Taranis shell with Candy Apple Metallic Red, laser engraved walnut trim, and copper mesh speaker grill.


candyappletaranis3taranisred2 taranisred4 taranisred5



Here is a video I did showing the extremely tight coax connection between the RF board and the antenna. Way too tight IMO, and in need of a re-work. New parts from Digi-Key on the way.



(no title)

balsastack1 bee1A new load of wood arrived and time to start cutting out pieces.  I got a few plans printed out at the local UPS store for a very reasonable $0.50 per square foot.  Not much lasercutting  to do on the Lazy Bee as it’s mostly sticks.


CNC Router

Rollerskate bearings riding on iron pipe, driven by screws and toothed gumbands.

I’m not really sure why I built this router.  At the time I had no immediate need for it.  I think  it was my dad’s fault. He was a master engineer/hacker/builder/pennypincher. After he died I inherited quite a few boxes of his tools, parts, uncompleted projects, junk, and memories, and it was when I kept trying to thin out these boxes, that I kept running across a few assorted little stepper motors.

At the time I was cutting out guitar bodies on the bandsaw, and knew other people who were using CNC routers to cut out Telecaster bodies and though that was pretty cool.  I knew nothing about CNC, but started hanging out on the CNC Zone Forum learning about this stuff.  After a while I invested $60 in a stepper control board, and decided if I could get down the process of drawing a simple circle in a CAD app, turning the circle into a list of coordinates, and then watch the motors move to those numbers, I’d start building the router.  I thought it would be smarter than building the machine first then finding I was too dimwitted to get anything to move-lol. So in the past year I’ve only cut one guitar with it, but I have cut plenty of airplane parts, do-dads, geegaws, and thingamajigs with it.
Here’s some pics od it in progress and a video cutting stiffer spindle mounts.

Including PC and software, the whole thing probably cost me around $700 and a couple months to build. The router plans are at .  The controller is a $60 Toshiba tb6560 from ebay.  The major costs were 1/2″ Acme dual thread  and the Acme zero-lash nuts from and the stepper motors from .

router2 router5 router8