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.
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.
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
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.
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.
TYT TH-8600 Dual band radio 10AWG zip cord 1 foot Jetstream Jumper
SO-239 bulkhead Anderson Powerpoles Miady LFP16AH LIFEPO4 battery
2 Meter Slim Jim J pole VHF UHF Antenna 24ft lead-in DX King
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
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).