some laser cutting.....

some RC plane stuff, some other stuff.

Thanks

Thanks for all the comments and questions. I’m happy some people are reading this!!.  You can email me  tom@thelasercutter.com  This site/blog is done in WordPress and hosted by Godaddy.

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 top mounted balun for my Off-Center-Fed Windam antenna. The core is a 240-77 ferrite, wound with teflon wire. Should be good to 1000 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.

07.212.0

 

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.
8888

 

 

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 bhttp://www.st.com/web/catalog/mmc/FM141/SC1169/SS1031/LN1565/PF164476

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 speaker hum… one of many solutions.

Just to set this straight…  This is the greatest radio since Marconi asked “Can you hear me now?” Since the beautiful Hedy Lamarr said “Jam THIS!”  This is an RC transmitter that has every switch and function user assignable, almost unlimited mixes, and plays music while some sexy fembot announces receiver signal strength, lipo voltage,  and GPS coordinates  !!! The audio hum was hardly there. I had to hold the radio within 12″ to hear it. It didn’t even bug me, but everyone was talking about it.  It’s like you live somewhere for years and one day your wife points out the stain on the ceiling…  Jeeez thanks!  Well I had the tools and figured what the hell.  I have the “B” model, and it already had the “Scott’s Special Speaker Mod”

I didn’t fall off the turnip truck yesterday…..  That happened weeks ago, and as a paid RF noise chaser I had some clues. The hum changed on how you held the radio. It also changed with antenna position.  When I opened the radio, the hum was VERY variable according to which wires and ribbons were moved. That led me to believe there is/was a lot of RFI noise inductive coupled into the whole wire harness.  Usually I find that the noise is from DC/DC switching converters.  Next in line is the processor clock. That’s what I found on the Taranis.  The inter-board ribbons were pretty hot with EMI from 160MHz to 600MHz. The CPU clock frequency RFI has sub-harmonics like a big ugly comb generator response. These harmonics get into the DC bias lines, and pollute all the op-amps and audio amp chips.  Even though they’re in the micro volt level, they get amplified up with the audio signals you want.

Since I don’t have a schematic,  I didn’t want to do a lot of probing and testing to find where to install filter caps and inline induction. That would cost millions of dollars and government forms would have to be filled out.  A simple, quick way of reducing the transfer of RFI between system boards seemed like an easy try.  Noise is born on the processor mainboard, and I want to strangle it on it’s way to other boards.

For some fun I display a sample from the “big box o’ ferrites”  EMI arsenal. Rings, clamp-ons, beads,  plates, tape. Actually the plates are an idea I had in mind to epoxy on the bottom of the boards, and/or to fit and position between the boards when the case is closed. The smallest beads could work, but I’d have to disassemble the ribbon connectors to get them on. I decided on the ferrite tape.  I fount the hottest ribbons and gave them a few wraps of ferrite.  The probe is so sensitive that I could isolate the two noisiest wires from the ribbon and just wrap those. The ferrite tape seemed to absorb a good amount of RFI, and the noise reduction from one end to the other was about 15dB  The audio hum was so reduced that I had to hold the radio at my ear to even acknowledge it.

Please click on the pics for the full view. I show the EMI response before and after, some pics of how I wrapped the ferrite tape around the ribbon cable, and a pic of my DIY near-field EMI probe. The description and diagram of the probe and be found here.  http://www.compliance-club.com/archive/old_archive/010327.html

 

 

noise1noise2noise3noise4noise5noise6noise7

After a couple days of test, I finalized and improved . The tighter the ferrite tape is against the wires- the better. I re-wrapped them and tied it up with waxed lacing string.

Even though the tape mfg claims surface resistivity in the MegOhm range I also put a square of foam over the board so it wouldn’t rub against it when the case is closed.

I found out this also reduced the headphone hum.

noise8

 Here’s the ferrite tape fitting. The upper ribbon cable gets two pieces of 2″ long tape wrapped around all wires.  The lower ribbon in the pic-  separate the last two wires from the ribbon, and wrap them with a piece of tape lengthwise. 

Here are some links to ferrite tape manufacturers / distributors.

http://www.digikey.com/product-highlights/us/en/3m-emi-rfi-absorbers/2210

http://intermark-usa.com/wp-content/uploads/products/pdf/FFSX-Ferrite-Sheet-X-series-061112rev1.pdf

http://www.murata.com/products/catalog/pdf/o63e.pdf

http://www.emitape.co.kr/02_wa/sub1.html

 

This EMI / noise mitigation was fueled by beer and rushed to press. Next time I do a mod I’ll have the video camera and whiteboard set up :P :)

IF you’re not a Taranis owner, check it out here- http://www.alofthobbies.com/frsky-taranis-x8r-combo.html

Take Care,

Tom

Imax Charger, and ….

I overloaded a circuit and popped a breaker, nothing that I hadn’t done dozens of times,  but this time it took out my imax lipo charger.  Well, half took it out. The display went  strobe-like and was unreadable and I wondered if it was the display itself, or the ARM processor.  I had a smaller display I kept for my Arduino projects and gave it a shot before tossing the the charger in the trash.  Success.. Now just to mod the case to hold the smalled LCD screen.

imax b8-a

 

And for all the complainers, haters, nincompoops, pissypants….

beating a dead antenna

 

 

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.

candyappletaranis1

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.


 

 

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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.