2020-02-16 I've been wondering how this antenna would change if the radials were on the ground. So today I dropped them to the ground, making no other changes and compared the signals reported on the Reverse Beacon Network.
When I sent CQ with the radials elevated as they have been for all my development work and all previous QSOs I was heard by twelve stations. When I dropped them to the ground (actually to the snow!), not a single station heard me. But when I returned them to their elevated position I immediately got reports again, comparable with the previous ones.
I also noticed that the SWR was considerably higher with the radials on the ground. I'm guessing that had I tuned it up with ground radials the SWR would have been fine with them. Whether it would have radiated as well as with the elevated ones, I don't know. I may experiment with my Wolf River Coils antenna sometime which is very similar in design but easier to change the "taps" on the coil by simply moving the sliding collar.
As noted above in the log of contacts I was able to have two good 30 meter QSOs with it this morning, with the elevated radials. I still have not managed any QSOs on either 60 meters and only one on 80 meters. 20, 30 and 40 seem productive. I'll keep trying on 60 meters.
2020-02-15 OK, I think I have conquered this thing. I've been struggling with it the past few days as I'd think I had the taps in the right place only to think otherwise the next time I put it up. Much to my embarrassment the problem was that I mixed up the top and bottom elements with the ones for my QRPGuys Tri-band vertical. Turns out a few inches makes a difference! So today I sort of started over by selecting the top element (11' 3" long) and then adjusted the bottom element (48") until the antenna resonated right where I wanted it on 20 meters, which bypasses the coil entirely. Then I worked my way down the taps from there. Most of them were where they needed to be but a couple needed changing. I also added a tap for the lower part of 75 meters. It would take at least three taps to cover the whole 75/80 meter band. But I'm mostly interested in the CW portion. and the tuner in both my G90 and x5105 can compensate for the off-frequency SWR. The charts below show what the antenna looks like now. I wrote the lengths of the top (11'3") and bottom(48") elements on the inside of the ends of the coil form so I can do it right next time! I think I'm done!
Here are the inductance measurements of the taps measured from the top 20 meter tap down: 20mtrs: .41uh; 30mtrs: 5.67uh; 40mtrs: 14.34uh; 60mtrs: 31.80uh; 80mtrs: 75.75uh. I'm sure my measuring instrument is not that accurate but it's what I have so there are the numbers.
2020-02-14 Did a bit more tweaking of the taps on the coil today. It now resonates at 3.507, 5.28, 6.94, 10.22 and 14.07. SWR is usable on all bands except the middle to higher end of 75 meters. I marked another tap location to cover that but didn't add it. 40 is still a bit low. Need to move that tap one more turn up the coil. But you get tired of fiddling with it after a while! :-) As the log shows above, it works.
2020-02-12 In spite of the fact that it was 19 degrees outside this morning, I swapped out the QRPGuys antenna for this one. The fiberglass Wonderpole was not happy to collapse until I warmed up the slip joints with my hands, which are now in need of being warmed up! But I got it up. To start testing I clipped the pigtail to the end of the 75th turn and came inside to check it out. Amazing! It resonates at 3.8 mhz!
As expected the bandwidth is very narrow. I recall my screwdriver mobile antenna being like that on 80 meters as well. My G90 tuner can bring the SWR down but I'm guessing its efficiency is not great even at its resonant frequency. It would be nice if its resonant frequency were a bit lower frequency as I'm most likely to use it in the CW portion. I may add a few turns to see if I can get it down to about 3.55mhz or so.
Well, couldn't wait so took the antenna down and added ten more turns, all I could get on the form! 85 total turns, 75uh. Put it back up and checked it again. Right on! Resonates at 3.54mhz, right where I wanted it. Done! Maybe. I keep thinking of things to look into or try. NO, I'm not going after 160 meters! Sorry. :-)
I declare it ready for the big leagues!
2020-02-11 tonight I added more turns to my loading coil bringing the total number to 75. It measures 62uh total inductance. Now tomorrow, if I can survive the cold that's predicted, I'll replace my QRPGuys 3 band vertical with this and see if it will resonate on 80 meters. Will be interesting to see how it performs if I am successful.
I asked recently on Facebook about people's experiences or thoughts on elevated vs. ground radials. As will all things antenna, the feedback was mixed. The general opinion seemed to be that in the field, whatever advantage their might be to elevated, tuned radials was offset by the somewhat more complicated use of them. So most just go with ground radials. I experimented a bit yesterday with my WRC TIA using three 16'. 23' and 33' radials rather than the supplied three 33' ones. Not sure I could tell any difference... All were on the ground.
2020-02-07 Like I said, a DIY antenna is never "finished!" To prove the point I did a bit more work on it today. I added a 60 meter tap and replaced the banana plug on the bottom element, putting red shrink tubing on it to make clear it is the hot wire! Then I strung it up again, being a bit more careful with the radials, which by the way are elevated. I draped them over shrubs and tied them to twigs to keep them a couple feet off the ground. Then, I had a QSO with F6HKA in France on 20 meters CW! Above is my total log of contacts with this antenna to date. SWR is almost flat on all bands except the top end of 40 which rises to near 3:1. Center frequency could probably be moved up a little but I favor the bottom end of the band so am happy with it.
The coil form is 1-1/2 inch diameter and about 7 inches long as shown. It could be trimmed by a couple inches but I left it long just in case I want to try to add 80 meters later. The coil itself is tight wound with the #24 speaker wire and is 3 inches long overall. The taps are as follows:
The finished product, including 25 feet or RG-174 coax, weighs just ten ounces and after putting it up several times now, it took me just shy of ten minutes to set up, a few minutes ago on my Wonderpole, which was already standing supporting my 4020 trap inverted vee.
2020-02-06 Well, today I think I "finished" this KW4JM vertical multi-band antenna. Of course a DIY antenna is never finished, but I think this one is at a "steady state" for a while. It is almost identical to where it was yesterday with a bit of tweaking of the windings for each band and cutting off the "sewer pipe" coil form. The whole thing weighs just under 6 oz.
Here are the details:
- Coil form is 6-1/2 inches long.
- The coil has 47 turns, of which 23 are currently used as shown in the picture. I didn't implement 60 meters.
- 20 meter tap (screw eye) is at the top, in the first turn.
- 30 meter tap is in the 11th turn, 3uh down from the top.
- 40 meter tap is in the 23rd turn, 14uh from the top
- The radiating element measures 11' 10" long from the top of the coil form.
- The bottom element measures 48" from the alligator clip to the banana plug.
- The three radials measure 33', 23' and 16'
- SWR is essentially 1:1 across the entire 20 meter band, below 1.5:1 across the entire 40 meter band and around 2:1 on the 30 meter band.
The measurements can vary a little without much impact on the antenna. To set it up I suggest cutting the top element slightly until it resonates near the center of the 20 meter band with the very tip of the coil tapped.
Then you can find the tap location for the other bands without messing with the length of either the top or bottom elements. A simple way to fine the tap locations is by carefully pushing a straight pin through the insulation and into the wire, being careful not to damage the wire. I marked my coil with a felt tipped pen every five turns from the top to make it easier to tell where I was with my straight pin.
Once you have the tap locations, I used a scratch awl from my T-Square to carefully push a hole through the winding and make an indentation in the form. Then moved the windings to either side of the resulting dimple and drilled a 5/64 inch hole through the form. Then I moved the winding over that hole and using the awl carefully enlarged hole through the wire. Finally, I was able to screw a 13/16 inch brass Screw Eye through the winding and into the hole in the form, making a solid and stable point to clip the alligator clip.
Since I used the 24 gauge speaker wire, this antenna is not physically robust! It needs to be handled carefully. If I continue to be happy with it I may make another using somewhat larger or stronger wire. Hopefully I can use the wire measurements from this antenna and simply change the number of turns to arrive at the measured inductance at each tap, allowing a little extra for final adjustment. I might also replace the BNC to banana plug adapter also, though that adapter works pretty well and is inexpensive.
2020-02-05 A few days ago I watched a video by KW4JM describing his DIY No-Stick Buddy-Stick Antenna. We had a QSO a couple days earlier when Scott was a SOTA activator on a SUMMIT in the Western Carolina Mountains. His antenna seemed so simple and straight forward and so similar to the Wolf River Coils TIA and Pac 12 antennas I've been playing with that I had to give it a try. So this afternoon I built my version. Mine is essentially a 17 foot, 1/4 wavelength vertical on 20 meters with a center loading coil tapped for the lower frequency bands. The radiator above the coil is 12 feet long, the coil is about six inches long and the bottom section below the coil is about 4 feet long. All combined it is 17 feet long give or take a couple inches. The pictures pretty well describe it.
The schematic shows the overall antenna as KW4JM describes it. I made a small change based on my experience with the Wolf River Coils TIA antenna, and made the bottom section below the coil 4' long instead of 3' as his was. Another small change I made was the coil form. He wound the coil on a six inch piece of 1-1/4 PVC. That seemed heavy to me so I found a plastic plumbing pipe that normally attaches between a sink drain and the water trap below the kitchen sink. It is a bit smaller O.D. but much lighter weight. I wound 47 close-wound turns of 24 Gauge RCA Speaker wire and stopped, because my wire ran out! The entire thing is made using that 24 Gauge speaker wire. I had one of those BNC to banana plug adapters so used it like Scott did. I also cut the three radials 16', 23' and 33', also made of speaker wire. As Scott suggests I used a straight pin to poke through the insulation into the wire at various places to "tune" the loading coil.
It was early evening when we finished dinner, and dark and cold outside. But I couldn't wait. So I strung it up in our stairway. I put a small nail in the door frame of the upstairs bathroom and looped the tip of the radiator around the nail, and then gently stretched the thing down the stairs and taped the bottom wire to the hand rail, letting the Connector dangle a foot or so below the rail. Then I strung the three radials around the house as best I could, connected a 25 foot piece of RG-174 feedline to my NanoVNA and turned it on. With the straight pin in the wire at the very top of the coil, to my surprise it was resonant in 20 meters, 14.070 to be exact with a very low SWR! Playing with the pin in different turns of the coil I discovered that 8 turns from the top resonated in the 30 meter band, 20 turns in 40 meters and 47 turns in the 60 meter band! And the SWR dips were clean and sharp!
Being impatient, and with my wife out of the house helping with AWANA, the children's program at church, I quick got my xiegu x5105 and connected to the coax. With the pin in the 20th turn for 40 meters, I turned on the radio and amazing, there were signals, good ones! Again, unwilling to wait for one of the QSOs to end so I could call one of the stations, I tuned to 7.054 which was clear and called CQ. When I finished my second CQ call WB1GYZ, Bob, in CT answered. He was 589! Talk about being surprised! We had about a five minute QSO, solid all the way. When I told him what I was running, he responded "hi hi!" That's OK, I was laughing too. One QSO doesn't prove much but I'm happy tonight. Thanks, Scott, for the SOTA QSO a few days ago, and this great antenna idea! And thanks, Bob, for the motivating contact tonight!
I still have a little work to do on it before I declare it finished and ready for the cold, cruel world. I need to decide whether to lengthen the coil and try it on 80 meters, then I will cut the "sewer pipe" to length. I also need to add the little brass screw eyes to make the taps permanent. I don't think the stick pin is a good field idea! But I will be using it once the weather warms up a bit here in Wisconsin.