DELARANEWS

Tech

The DX Commander Antenna

Callim, M0MCX the “DX Commander”

My Vertical Antenna & Common Mode Choke Build –

Part 2

Vertical Antenna: In last month’s newsletter, I wrote about assembling my DX Commander vertical antenna for Field Day at the ARC. It was something I threw together in the middle of the night, and managed to get operational on just a couple of bands for Field Day Sunday. It was held together with bits of electrical tape, and I only got it to tune on 20m out of sheer luck. It seemed to work well, but needed a lot more work to finish the build. I set my sights on the Ohio QSO Party in August. I wanted to finish the build and make it field-ready, so it would just pop-up and be ready to go. This would mean finishing all the various band elements, tune each band, and replace all the temporary bits of electrical tape with proper heat shrink and fastening clips. I wanted it to be easy to assemble, disassemble, and store – making it my go-to antenna for portable operations. For those not familiar with the DX Commander, it is described by the inventor as a Fan Dipole turned vertical. Think of a typical multi-band Fan Dipole antenna. Its feed point is in the middle, and there are elements extending ¼ wavelength left and ¼ wavelength right of the feed point. Turn it vertical, and bring the feed point down to ground level. Those elements that were extending right of the feed point are now reaching up in the air. Those that were to the left of the feed point are now spread out as ground radials. And just like the Fan Dipole, It uses ‘spreaders’ to keep the radiating elements separated. The antenna is built around a telescopic graphite mast that extends 10m tall (that’s 33 feet or approx. ¼ wavelength for the 40m band), with plastic discs at key points acting as spreaders to keep the radials in position. Each time you deploy the antenna, you need to attach the elements for the bands you want to operate. It supports up to 6 elements at once. When you first build the antenna, you cut bulk wire to the required lengths for each element, including: 10m, 12m, 17m, 20m, 30m, 40m (which also supports 15m as a ¾ wavelength), and 80m. The instructions say 30m and 80m are mutually exclusive – pick one or the other as you assemble the antenna. To make assembly quick and easy, I printed labels for the posts on the radiating base, the holes on each spreader, and the end of each radiating wire element. I just didn’t like the paper labels on the wire, and wanted to use something more durable. I decided to use numbered bracelet beads instead (see Figure 1). I used heat shrink tubing to hold them in place (see Figure 2). This makes it easy to attach the elements correctly (see Figure 3). Figure 1 Figure 2 Figure 3 To hold each element in place, the kit comes with a number of short elastic cords and clips. To prevent the fiberglass mast from collapsing due to tension or moisture, several hose clamps are provided (with plastic tubing to protect the finish on the mast). Assembly would normally require placing each of these components on the pole one-by-one in the correct order. But I found that I could loosen the hose clamps, and leave everything in-place on the collapsed pole (see Figure 4). That includes all the cords and clips as well. I purchased a dedicated nut driver for the hose clamps, and keep it in the go-bag. To assemble, I just start extending each fiberglass element (smallest to largest), twist into place, and tighten the hose clamps at each join. I then run the wire elements up the pole where the clips are waiting to receive them. Figure 4 Tuning was the last step. As with any Fan Dipole, the adjustment of one element tends to have an effect on the others. So there is a lot of trial and error. Adding the 80m element has the most significant impact to other bands, so it was critical that I include that during my tuning effort. If you choose to attach it, the 80m element is strung up as an inverted L. You need a high support (tree or line of some type) to hold up the far end. That makes raising and lowering the mast more effort, and you have to do that several times during initial tuning. I tend to cut elements long (you know, ‘just in case’), so I needed to shorten each one a bit. Using a RigExpert AA-600 analyzer, I measured SWR across all the bands used in the Ohio QSO Party (see Figure 5). I was surprised to find 80m under 3:1 across the entire band. That means I can do both phone and digital modes down the road, which I really want. 40m, 20m, and 15m (the money bands) all came in below 2:1. As expected, 10m doesn’t want to be under 3:1 across the entire band. I may be able to get closer with more adjustment. But I stopped tinkering when all the target frequencies for OH SQL Party were around 1.5 or lower. Figure 5 Overall, I’m very happy with the result. Yes, it does take more time to raise the antenna when you are dealing with the 80m inverted L. And yes, there are a lot of bits and pieces to deal with. But having all bands 80-10 available in one go-bag is really nice to have. And having a vertical does give you an option for low take-off angle and more potential for DX contacts. As for the Ohio QSO Party, we ran into more issues with multi-station interference at the ARC. We were also limited to one station/mode per band at a time. As such, I didn’t get to put the DX Commander to a full test. I’ll leave that for a nice fall day, when I get the urge to go play radio at a park or open field. Super-Choke Here is a quick update on the Common Mode Choke I built in last month’s newsletter. If you recall, I had created a form to make the choke, and managed to get 8 passes of LMR-400 (equivalent) coax through 2 sets of 3 toroids (see Figure 6). I stopped the build when I struggled with soldering on the PL connectors. The solder kept balling up on the iron’s tip, and wouldn’t flow into the connector. Figure 6 The Messi and Paoloni Evolution PL259 connectors I’m using are not typical (https://messi.it/en/catalogue/rf-coax-connectors/uhf-pl259-male/10mm/solder.htm). The tip is soldered inside the body of the connector, not at the actual tip. The hole is very tiny, and the solder I was trying to use was oversized for the job. The same is true for the female SO-239 connector. So, I purchased some solder flux and small diameter solder. My soldering skills are still terrible, but I did manage to get the job done. I went with male and female connectors on the choke, so I wouldn’t need to use a barrel connector to insert it between a radio and the feed line. Has it made a difference? Well, no – not yet. I used it at the Ohio QSO Party, but the issue there wasn’t caused by common mode current on my feedline. I have a lot of QRM at home, but haven’t seen any improvement with this choke alone. I still need to place chokes on the power and computer connections to the radio, add a common mode choke out at the antenna feed point, and ground the coax at entry of my house. Then I need to add chokes to all the problem devices throughout the house. In other words, I wouldn’t expect one piece of the puzzle to solve everything. I have a lot of work ahead of me. If you want to read more on Common Mode Chokes, here is the guide I followed from Chuck Counselman W1HIS. http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf - Mike W8MDC
DELARANews

Tech

The DX Commander Antenna

Callim, M0MCX the “DX Commander”

My Vertical Antenna & Common

Mode Choke Build – Part 2

Vertical Antenna: In last month’s newsletter, I wrote about assembling my DX Commander vertical antenna for Field Day at the ARC. It was something I threw together in the middle of the night, and managed to get operational on just a couple of bands for Field Day Sunday. It was held together with bits of electrical tape, and I only got it to tune on 20m out of sheer luck. It seemed to work well, but needed a lot more work to finish the build. I set my sights on the Ohio QSO Party in August. I wanted to finish the build and make it field-ready, so it would just pop-up and be ready to go. This would mean finishing all the various band elements, tune each band, and replace all the temporary bits of electrical tape with proper heat shrink and fastening clips. I wanted it to be easy to assemble, disassemble, and store – making it my go-to antenna for portable operations. For those not familiar with the DX Commander, it is described by the inventor as a Fan Dipole turned vertical. Think of a typical multi-band Fan Dipole antenna. Its feed point is in the middle, and there are elements extending ¼ wavelength left and ¼ wavelength right of the feed point. Turn it vertical, and bring the feed point down to ground level. Those elements that were extending right of the feed point are now reaching up in the air. Those that were to the left of the feed point are now spread out as ground radials. And just like the Fan Dipole, It uses ‘spreaders’ to keep the radiating elements separated. The antenna is built around a telescopic graphite mast that extends 10m tall (that’s 33 feet or approx. ¼ wavelength for the 40m band), with plastic discs at key points acting as spreaders to keep the radials in position. Each time you deploy the antenna, you need to attach the elements for the bands you want to operate. It supports up to 6 elements at once. When you first build the antenna, you cut bulk wire to the required lengths for each element, including: 10m, 12m, 17m, 20m, 30m, 40m (which also supports 15m as a ¾ wavelength), and 80m. The instructions say 30m and 80m are mutually exclusive – pick one or the other as you assemble the antenna. To make assembly quick and easy, I printed labels for the posts on the radiating base, the holes on each spreader, and the end of each radiating wire element. I just didn’t like the paper labels on the wire, and wanted to use something more durable. I decided to use numbered bracelet beads instead (see Figure 1). I used heat shrink tubing to hold them in place (see Figure 2). This makes it easy to attach the elements correctly (see Figure 3). Figure 1 Figure 2 Figure 3 To hold each element in place, the kit comes with a number of short elastic cords and clips. To prevent the fiberglass mast from collapsing due to tension or moisture, several hose clamps are provided (with plastic tubing to protect the finish on the mast). Assembly would normally require placing each of these components on the pole one-by-one in the correct order. But I found that I could loosen the hose clamps, and leave everything in-place on the collapsed pole (see Figure 4). That includes all the cords and clips as well. I purchased a dedicated nut driver for the hose clamps, and keep it in the go- bag. To assemble, I just start extending each fiberglass element (smallest to largest), twist into place, and tighten the hose clamps at each join. I then run the wire elements up the pole where the clips are waiting to receive them. Figure 4 Tuning was the last step. As with any Fan Dipole, the adjustment of one element tends to have an effect on the others. So there is a lot of trial and error. Adding the 80m element has the most significant impact to other bands, so it was critical that I include that during my tuning effort. If you choose to attach it, the 80m element is strung up as an inverted L. You need a high support (tree or line of some type) to hold up the far end. That makes raising and lowering the mast more effort, and you have to do that several times during initial tuning. I tend to cut elements long (you know, ‘just in case’), so I needed to shorten each one a bit. Using a RigExpert AA-600 analyzer, I measured SWR across all the bands used in the Ohio QSO Party (see Figure 5). I was surprised to find 80m under 3:1 across the entire band. That means I can do both phone and digital modes down the road, which I really want. 40m, 20m, and 15m (the money bands) all came in below 2:1. As expected, 10m doesn’t want to be under 3:1 across the entire band. I may be able to get closer with more adjustment. But I stopped tinkering when all the target frequencies for OH SQL Party were around 1.5 or lower. Figure 5 Overall, I’m very happy with the result. Yes, it does take more time to raise the antenna when you are dealing with the 80m inverted L. And yes, there are a lot of bits and pieces to deal with. But having all bands 80-10 available in one go-bag is really nice to have. And having a vertical does give you an option for low take-off angle and more potential for DX contacts. As for the Ohio QSO Party, we ran into more issues with multi-station interference at the ARC. We were also limited to one station/mode per band at a time. As such, I didn’t get to put the DX Commander to a full test. I’ll leave that for a nice fall day, when I get the urge to go play radio at a park or open field. Super-Choke Here is a quick update on the Common Mode Choke I built in last month’s newsletter. If you recall, I had created a form to make the choke, and managed to get 8 passes of LMR-400 (equivalent) coax through 2 sets of 3 toroids (see Figure 6). I stopped the build when I struggled with soldering on the PL connectors. The solder kept balling up on the iron’s tip, and wouldn’t flow into the connector. Figure 6 The Messi and Paoloni Evolution PL259 connectors I’m using are not typical (https://messi.it/en/catalogue/rf-coax- connectors/uhf-pl259-male/10mm/solder.htm). The tip is soldered inside the body of the connector, not at the actual tip. The hole is very tiny, and the solder I was trying to use was oversized for the job. The same is true for the female SO-239 connector. So, I purchased some solder flux and small diameter solder. My soldering skills are still terrible, but I did manage to get the job done. I went with male and female connectors on the choke, so I wouldn’t need to use a barrel connector to insert it between a radio and the feed line. Has it made a difference? Well, no – not yet. I used it at the Ohio QSO Party, but the issue there wasn’t caused by common mode current on my feedline. I have a lot of QRM at home, but haven’t seen any improvement with this choke alone. I still need to place chokes on the power and computer connections to the radio, add a common mode choke out at the antenna feed point, and ground the coax at entry of my house. Then I need to add chokes to all the problem devices throughout the house. In other words, I wouldn’t expect one piece of the puzzle to solve everything. I have a lot of work ahead of me. If you want to read more on Common Mode Chokes, here is the guide I followed from Chuck Counselman W1HIS. http://www.yccc.org/Articles/W1HIS/CommonMode ChokesW1HIS2006Apr06.pdf - Mike W8MDC