Tag: k4swl

A Little More UnUn fun

This past week I wound a few more toroids using a 77 mix. The toroids are 0.5″ in diameter and wound with 22 awg insulated magnet wire. I wound one with a single core and one with a dual core. My goal was to try to get a little better low band performance. I get a kick out making a few contacts on 60-80-160 meters. The finished UnUns are 9:1.

We’ve been going through a heat wave this week with a heat advisory every day. I got up early and tried a couple different antennas. Using antenna wire from my Frankentenna, I built an end fed with a 65′ antenna and a 65′ counterpoise. I also tried the 65″ antenna with a 17′ counterpoise. The set up looked like this.

For this antenna, the best combination was a 65′ antenna wire, a 17′ counterpoise and the single core 77 mix 9:1 UnUn. I got the following readings from my Rig Expert Prostick with 6′ of RG316. As a control I also tested my Sparkplug transformer.
Band SWR (17′)—–SWR (65′)——Sparkplug 65′
160 – 2.4 ———— 4.2 ————– 5.6
80 – 5.4 ———— 1.1 ————–8.3
60 – 1.7 ———— 2.3 ————– 12
40 – 2.9 ———— 3.5 ————– 1.7
30 – 6.9 ———– 4.5 ————– 16
20 – 3.8 ———– 4.0 ————— 1.5
17 – 5.2 ———– 5.7 ————— 9.7
15 – 4.1 ———– 4.3 ————— 1.1
12 – 6.2 ———– 6.9 ————— 10
10 – 4.5 ———– 4.6 ————— 2.6
6 – 5.9 ———– 5.8 —————-14
Fiddling with the counterpoise length could make things a little better, but overall the SWR’s are low enough to match with a good tuner. I realize that running a short feed line would affect the Sparkplug so in another test I added a counterpoise and it did bring down the SWR on some bands. However, to me the winner is still the single core 77 mix 9:1 UnUn.

Another antenna that I like is a random wire antenna I call the K4SWL antenna https://kk4z.com/2022/06/05/k4swl-antenna-plus/. I call it that because it was Tom K4SWL who I got the basic design form. It’s a 29.5′ antenna with a 17′ counterpoise. I built an UnUn based upon a QRP Guys design but wanted to try to get a little better performance on the lower bands. In this case I used a two core 77 mix 9:1 UnUn and got the following results.
Band – SWR
160 —- 2.0
80 —- 1.7
60 —- 1.5
40 —- 1.5
30 — 1.5
20 — 1.4
17 — 1.3
15 —- 1.3
12 —– 1.2
10 —– 1.2
6 —— 1.2
Realize that this is a small antenna and will not be as efficient as a full half wave dipole (on 160 meters, that is 270′). However, it would be fun to see if you can make a contact on 160 or 80 meters in a park with a small antenna. So get out there and play radio! 73 Scott

POTA/SOTA Antennas and More

My amateur radio club, West Georgia Amateur Radio Society (WGARS) decided to participate in Winter Field Day. We are going to operate from Talladega National Forest in Alabama. It doesn’t take much to get me out in the woods with a radio. As a club, we will be operating QRP and I will be doing CW.

Since joining POTA, I have been more inclined to build things. I had forgotten how much fun this can be. So today, I thought I would build a couple of antennas for the outing. My first antenna will be a replacement for my speaker wire non-resonant vertical. The idea came from Thomas K4SWL using speaker wire. It was an okay antenna but it was bulky and heavier (12 oz.) than I wanted it to be.

A British company, SOTA-Beams sells some remarkably thin antenna wire. It is insulated and approximately 24 AWG. The best part is they sell a 100 meters for $10.37 and their shipping rates are reasonable. You can find it here: https://www.sotabeams.co.uk/antenna-wire-lightweight-100m/.

A non-resonant antenna is an antenna that is not resonant on any of the frequencies you plan to use. In non- resonant antennas only forward waves exist. A non-resonant antenna radiates as well as a resonant one. Here is what I started out with.

The end insulator and the wire winders were 3D printed by my son. The battery is for scale. The antenna length is approximately 28-29 feet and the counterpoise is approximately 17 feet. Putting it together was straight forward with the end result looking like this. It weighs 3 oz.

I have discovered that I like working the low bands while on a POTA activation. It takes a little more doing as the antennas get more complex and heavier. My Frankentenna can reach 160 meters but it is a pretty heavy antenna. Again, taking a clue from K4SWL, I acquired a piece of military surplus radio gear. I found an antenna winder for a dipole that is fed with 30 feet of twinlead. I got excited! A doublet is one of my favorite wire antennas as the vertical element can also radiate giving you some DX capability. It will also tune a broader range of frequencies than a dipole. Here is what I started out with.

Note that it is made by the Hughes Aircraft company. I cut the wire at 67 feet per side which should give me an approximately 132 foot dipole. I should be good to go down into the CW portion of 80 meters. While it won’t be efficient, I am thinking I can get an impedance match on 160 meters with my Elecraft T-1 or AH-705 tuner. A half wave dipole for 160 meters is about 270 feet and would be too unwieldy for the field. Getting things hooked up was straightforward.

Everything wraps on the winder. I added a balanced to BNC adapter and two 25 foot lengths of reflective cord I picked up at Tractor Supply. It all weighs 1 lb 3 oz and it all fits in a gallon size freezer bag.

There will be somewhere in the neighborhood of 5 operators at our site, so I don’t know if I will have the room to get the big antenna up. I hope so.

In case you couldn’t tell, I am a big fan of Ziplock Freezer bags in the quart and gallon sizes. They are tough, waterproof and cheap. I buy them in bulk at Sam’s Club. When one wears out, I pull a new one from the box.

Low band POTA activations can be a challenge, but not impossible. My activation at Ft Mountain State Park in GA. proved that. I am one step closer to being ready for Winter Field Day. Should be a lot of fun. It’s supposed to be cold (cold for us southerners) Night time in the mid 20’s and daytime south of 50 degrees. I’ve lived in cold climates; but, what will get me is my hands. I get pretty fumble-fingered on the paddles when my hands get cold. Thank goodnes for propane heaters. We will be operating under the callsign W4D and hopefully be turning in a log to POTA as well. Hope to hear you out there.