All posts by robbie

End Fed HalfWave 40-10m

After being asked to activate a particular park on the air, I was told that an end fed half wave antenna would work well for portable operations. So with that information I began researching how to build an EFHW for 40-10m. I’ve build single band dipoles for these frequencies, but I wasn’t sure about how to go about this.

The main part of this antenna is a 49:1 balun. It is a transformer that has a 7:1 turns ratio, and isn’t too tough to make. So follow me as I lead you on a photo journey of how I built my 40-10m EFHW.

I cut about 136 feet of wire for the antenna. This can be shortened later when it comes time to trim and tune the final product.

Antenna wire wrapped around a spool for easy transport.

Winding the toroid was the next challenge. It wasn’t as difficult as I thought it would be. I followed Steve Ellington from Youtube. Two wraps with twisted wire and then 14 wraps with the long length wire. I used a drill and a vice to wind the two lengths of wire together. Watch Steve wind his transformer. He explains it much better than I can. Solder it into the junction box as shown in the image with a 100pF 15kV cap from tip to ground on the SO-239.

K1TA created this image to show how to wind the toroid. I used 1 core for barefoot ops.
The transformer soldered into the box.

Testing this with my RigExpert AA-170 was a joyous occasion. I was quickly able to loop the end of the wire about 12 inches and zip tie the end together so I could string it up with paracord. 40m, 20m, and 15m were 1.7:1 SWR. 10m was 2.2:1 in the CW portion and 2:1 or below for the voice portion. I consider that a win!

PARTS LIST:
1 4” X 4” X 2” PVC Junction Box (LOWE’S)
1 500 Ft. roll 14 AWG Solid (LOWE’S)
A few feet of 15 AWG Magnet wire Remington p/n 15SNSP.125 (DIGI-KEY 2328-15SNSP.125-ND)
1 Ferrite Toroids / Ferrite Rings 43 Toroid 12.7mm 61mm
p/n 5943003801 (Digi-Key 1934-1592-ND)
1 100pF +/-10% Capacitor 15kVDC p/n HVCC153Y6P101MEAX (DIGI-KEY BC5419-ND)
1 SO239 chassis mount female connector (Amazon sells these)
Various stainless steel nuts, bolts & eye hook

POTA Activation – Doerun Pitcherplant Bog Blog

Eddie, KO4NLL, and I were asked if we would activate the Doerun Pitcherplant Bog in Doerun, Georgia as a Parks on the Air activation. This is a blog on the steps that we took (and the best order of them) to make this happen. The park identifier is K-7882.

3-10-2021 @ 9:16am: Contacted the DNR to ask permission to transmit from the park. I was initially told that it probably won’t be allowed, but my information was passed to someone who might be better to answer that request.

3-11-2021 @ 9:55am: Contacted the DNR to follow up. I gave them a few scenarios for operation to widen the chances of being approved for operating. I said if mounting an external antenna was not allowed I could operate solely from my vehicle in the parking lot. It would only be from sun up to sun down coinciding with the park rules. She said she would speak with the supervisor.

3-11-2021 @ 10:00am: DNR returned call and said that we cannot venture into the woods to operate, but that we could operate from our vehicle using a vehicle mounted antenna.

Amateur Radio Go Box

Eddie, KO4NLL, and I decided to build an Amateur Radio Go Box or Bug Out Box. We wanted it to have a decent portable power supply and a small VHF/UHF radio and a small rollup antenna that could fit in the box when not being used.

We’ve seen the Hammo Cans, but we didn’t feel like we needed all of the extra gauges and plugs. We wanted enough room for extra storage for cables. There will be a SO-239 connector and an Anderson Powerpole connector for either a second device or for charging using a charger designed for LIFEPO4 batteries.

Parts List:

From randl.com:

TYT TH-8600 Dual band radio
10AWG zip cord
1 foot Jetstream Jumper

From amazon.com:

SO-239 bulkhead
Anderson Powerpoles
Miady LFP16AH LIFEPO4 battery

From eBay:

2 Meter Slim Jim J pole VHF UHF Antenna 24ft lead-in DX King

Purchased locally:

50cal ammo can – dimensions roughly 11″x4.5″x6.25″
Nuts, wing nuts, washers, and screws 6-32 and 8-32
1/2″ angle aluminum for battery support
Spade connectors for battery
Sew type velcro
Automatic battery charger

3D printed:

Powerpole Chassis Mount Bracket

Images:


Eddie's finished go box
Eddie’s finished go box

 

The finished inside of the Go Box
The finished inside of the Go Box
Inside diagram of the Go Box
Inside diagram of the Go Box
The outside view of the Go Box
The outside view of the Go Box

Ground Plane Antenna from Coat Hangers

One of my antenna projects was to make an antenna for 2 meters from coat hangers. It’s not a unique project; You can search the web for coat hanger antennas and find plenty. I just wanted to share it because I like how it looks. This is about the easiest antenna I’ve ever built.

I used five coat hangers, ring terminals, and a butt splice. The hardware used were 3mm screws and nuts.

I started with a 22 inch vertical piece and 22 inch radials then I trimmed them down to the finest SWR that I could be happy with. I was quite surprised.

After a little trimming I had about a 20.5″ vertical and 21″ radials. If you build this antenna, make sure that you start long so that you can trim it to the best SWR.

The radials were soldered to the ring terminals using a propane torch. I scraped the coating off the hangers so that the bare metal would be exposed. I’m sure that the solder doesn’t actually stick to the steel hanger, but it’s close enough.

The vertical was crimped to the SO-239 connector and then I poured solder into the connection so that it would fuse to the center pin. This was because solder would not directly fuse with the coat hanger. If I had used acid core solder that might have been easier to tin the tip of the hanger. Your mileage may vary.

The next step is the figure out how to raise this antenna. I’m thinking of using 1 inch PVC to run the cable through and then mount it to the top of 1 inch EMT using a coupling. I haven’t quite worked this out yet, but I plan on figuring that out later. For the time being I raised the antenna using my painter’s pole and a piece of PVC driven into the ground. Eddie and I tested it out at 5 watts, and he can hit almost any repeater within a 30 mile radius.

Let me know if you’ve built a Sputnik antenna (as I call them).

The ground plane antenna calculator can be found by clicking this sentence.

 

Baofeng Battery Eliminator

3D print and a $3 buck converter!
While I was printing 18650 battery cases for my Baofeng and my Yaesu HTs, I was wondering what would happen if I built a regulated linear power for my Baofeng so I could run it from 12 volts. (You can buy a battery eliminator for about $14, but you’ll still have to cut the cigarette lighter adapter off to use with some other connector.) Back to the DIY…I did some rough math in my head and decided that a linear supply would be a waste of energy in heat that I didn’t want. PLA melts at a low temperature AND I was wanting to use the radio in a battery powered ARDF fox box so power consumption conservation is paramount! I decided I’d look at building a switching DC-DC buck converter which is about 100% more efficient compared to a linear supply (about 90% efficient overall).

After looking at the easy schematic, I quickly realized I could probably get one cheaper than the sum of the parts and shipping. Off to eBay I went. I was not disappointed. You can either buy them in bulk from China for about $5 or you can buy one from a guy in Georgia for $2.75. I’ve included the edited screen shot from eBay. Shipping is fast, and I am very pleased. I’ve bought two from the seller because I reversed the leads on the first one and burned it up. Hint: WATCH YOUR POLARITY! These are not forgiving.

The first step was to print the modified battery case. I used Tinfoil_Haberdashery’s original Baofeng 18650 case, but I used Tinkercad to cut out the middle so the buck converter could fit in it, and I added a hole in the back for the wires. (Here’s my STL file.)

All I had to do then was connect the wires! I chose to use a barrel connector on the back because of the power splitter I’m using in the fox box. I’m usually a fan of Anderson Powerpole connectors, but this time around I chose something different. The input and output polarities are clearly labeled on the circuit board. You need almost no electronics knowledge to make this work! Just watch your polarities.

Finally, you hook it up to a 12v supply and turn the little potentiometer until the voltage is where you want it. I chose 7.4 volts which is the nominal Li-ion battery voltage.

 

 

Yaesu FT-60R 18650 Battery Compartment 3D Print

18650 Battery Box for my Yaesu FT-60

I printed someone else’s 18650 battery box for my Baofeng the other day, and it worked so well that I wanted the same thing for my Yaesu FT-60. I searched the web for a while, and I couldn’t find where anyone had actually printed a battery box for it. I found where they hacked up $25 AA battery boxes for the radio; I don’t want to hack that up. 🙂 For the cost of some Altoid tin steel and a little PLA plastic I was able to make a sweet battery box for my Yaesu FT-60R.

Check out Thingiverse for my post and the STL files.

Raspberry Pi Controlled Amateur Radio Fox Transmitter

My friend KT created a cool looking vinyl fox for the outside of my fox box. The rubber ducky connects to an SMA bulkhead. The screws hold the Raspberry Pi and the interface box inside.

The radio is hanging on a 3D printed bracket, the Raspi is in an enclosure that I found on Thingiverse, and below the Pi is a 3D printed controller box.

Lately I have been reading about Amateur Radio fox hunting, and I wanted to make my very own fox. I saw some cool transmitters that are very small, and I have seen transmitters in ammo cans, and I really like the look of the ones in the ammo cans. I also set out to spend as little money as possible, so buying a small transmitter (around $100), was out of the question. I needed to use as much as I had at home.

The first thing to do was to acquire an ammo can from the Army Navy Surplus Store. This set me back $10 cash. I had some at home, but I didn’t want to empty them. Now, it’s time to get to the fun part.

Schematic and wiring diagram.

Some people used Arduino microcontrollers to do the PTT and audio. I have an Arduino, but I really didn’t want to be limited to the audio created by software; I wanted to be able to use actual audio files right out of the box. This was what drove me to use a Raspberry Pi. Someone else used a Model B Pi as a transmitter. I didn’t want to go that route, but it looks really cool, and it was really small! I have more of the first rev B models than I do Arduinos anyways, and I’m always wondering what I could do with them since they pale in comparison to their newer model 3! The trade off is power consumption. The model B Raspi uses about 400mA. Using a newer model would improve this, but I’m using what I have in abundance.

The Raspberry Pi with connections on top of my Engineering Notebook.

The biggest part of this project is the Python program that I wrote. I am using an audio file from a text-to-morse audio converting website to create .wav files. Using the Raspi gives me the flexibility to play any type of audio file, and I can also access the GPIO port to control the radio or read switches. (For later revisions of the project…I’m thinking switches for different messages or a battery monitor to alert users the system is running low!)

Without going into step-by-step instructions on how I built it, the pictures should show a good representation of how this ammo can fox came to fruition. As of this writing I do not have the power supply in the box yet. Santa Claus is supposed to bring me that. I’m opting for a 12v/5v “security camera” power supply. The 5v will power the Pi, and the rest will run off the 12v side.

The Dummy Load

I built a 2.5 watt dummy load from ten 1/4 watt 510 ohm resistors soldered in parallel.  The case to hold the dummy load was 3D printed and has vents to allow heat to escape. While it’s just a theory, I am hoping that having the radio transmit into the dummy load might make it harder to find. I won’t be able to test this out in the field until I have the portable power supply. Carrying around the deep cycle marine battery isn’t any fun, and certainly expands the level of suspicion of a box with an antenna on it.

The Circuit

I had to look at a diagram for how the PTT and mic for the FT-60 worked. The system I devised might work for other radios if the jack is adapted for the other radios. I have a Baofeng that I would like to use, but the 3.5mm jack is wired differently AND I do not have a way to power it externally, yet. A battery eliminator is about $3 on eBay. A work around would be to use your radio’s VOX setting. In this case, you could EASILY omit this circuit altogether and just run an audio cable to a Baofeng (cheap).

I wired the circuit for my FT-60 on a “surface mount style” board. I used a Dremel tool to etch a few pads. I’m really liking how fast I can throw together a working prototype using this method. I used a 2-pin header to connect the interface to the Raspberry Pi GPIO using jumper wires.  (Hint: The schematic/wiring diagram is near the beginning of this long article.)

The 3D Printed Objects

The next thing I wanted to do was 3D print the other parts that I needed to mount the radio controlling circuit, the Raspberry Pi, and the radio into the ammo can. I haven’t had my 3D printer long, but I figured out how to use Tinkercad to create custom parts and learned how to download pre-designed stuff from Thingiverse. Piece of cake!

I printed four parts for the fox box: the dummy load housing, the Raspberry Pi case, the radio clip mount, and the interface box. It’s amazing what you can accomplish with a 3D printer. Having custom parts has never been so easy. All you have to do is design it or find it and print it. Boom!

A Raspi case modified and posted to Thingiverse by RichRap. The one I printed is black.

The Power Supply

The supply I chose for this project isn’t a gel cell like most use. I had a choice to make; I could use the 12v gel cell and make a 5v linear regulator or I could just buy a supply that had both power supplies already built. This one is by TalentCell on Amazon and sells for about $34. It is marketed towards LED strip lighting and CCTV cameras. It should fit perfectly in the fox box based on the dimensions. At 12V 6Ah, it should be able to power the fox long enough for simple hunts. Later on it might be cool to add a power connector to the outside of the fox so it can be charged without opening the ammo can. I probably have the parts for this is the garage. I’m leaving room for improvement.

The Working Prototype

I want to share the working prototype as a conclusion. This was my test program to see how things would work before actually putting the parts in an ammo can. I was using a big screen TV as my monitor so I could type the program. Proof of concept! Are you planning on making a fox box? Share your stuff in the comments below.

Files/Downloads

foxhunt.py file shared from my Drive