Line Isolator

One of my favorite portable antennas is a 30-ft wire fed through a 9:1 unun.  This type of antenna generally the uses coax feeder as a counterpoise, since the 9:1 unun configuration provides no line isolation.  Most of the time, this has worked well for me with no issues with stray RF getting back into the equipment.

On a couple of occasions, my Elecraft T1 auto tuner began to act up, refusing to load up on one or more bands. (Running through the T1’s diagnostic mode always seems to restore operation to normal.)  I’ve also had one of my keyers behave erratically once or twice.  Since this has only happened when using the 9:1 unun, my suspicion is that common-mode RF currents on the coax shield are the culprit.

My proposed solution for this is to use a line isolator between the tuner and the coax feeder.  (Note:  Using a line isolator at the antenna end of the coax would defeat the purpose in using the coax as a counterpoise.)  A quick survey of my junk box stash of parts showed I had everything I need to build a line isolator from scratch.

Parts List

  • RG-174/U coax (approximately 24 inches)
  • FT-140-43 ferrite core
  • (2) BNC-F chassis mount connectors
  • Hammond Manufacturing 1591MSBK Enclosure (2.2 x 3.3 x 0.8 inches)

Construction

This is a very simple project.  You can build one in well under an hour.

  • The RG-174 coax is wound on the FT-140-43 core for a total of 10 turns.  Take note of how the 5th turn goes across the core.  This makes installation in the case a little easier.  I used a couple of small nylon tie-wraps to hold the windings in place.
  • Drill the holes for each of the BNC connectors and wired up the choke, as shown.  I used a 5/64-inch drill bit and had to use a reamer to get the holes to the right size for the BNC connectors I used.
  • Solder the coax to the BNC connectors.
  • To mechanically secure the core, I used a piece of two-sided foam mounting tape to mount the choke to the bottom of the case.  As an additional precaution, I put a piece of packing foam on top of the choke before attaching the lid.  This foam provides a slight downward pressure on the choke to prevent it from shaking loose in the case during handling.
line_isolator_core
Core winding
isolator_core_installed
Core installed in case

Testing

I don’t have access to the equipment necessary to do any type of exhaustive testing of the line isolator.  In lieu of that, I hooked it up to a 50-ohm dummy load and checked the SWR.  It was basically flat from 160M through 6M.  While that tells me nothing about how effective it is in reducing common-mode currents, I at least know I didn’t make any serious screw-ups in building it.

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Completed line isolator

In Operation

Well, this part will have to wait until I have a chance to get out for some portable operating.  I want to make sure that the line isolator doesn’t affect the T1’s ability to tune my antenna.  Since the initial problems were very intermittent, only time will tell if I solved those problems or not.  I’ll be sure to update this post with any new insights I gain.

Update 5/16/2017:

Since this article seems to get a lot of traffic, I figured it was time for a long-overdue update.  Not long after this post was published, I tested this 1:1 unun in line with the coax to my 30-foot wire and 9:1 unun.  As I suspected it might, it affected the tuning of the antenna.  One or two bands wouldn’t load up properly.  This made sense to me, since this antenna configuration relies on the shield of the coax for the counterpoise.  So, there’s some RF on the coax shield by design.  This device obviously is blocking some RF, as it should.  I haven’t pursued it further and I still have done any measurements to determine its effectiveness.  With a change of connectors on the output side, it could definitely be useful as a 1:1 balun, I suppose.

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Tilt Stand for the YouKits HB-1B

This is another one of those projects that took longer to write up than to build.

The top facing controls on “trail-friendly” radios like the YouKits HB-1B and others are very convenient when you’re sitting on the ground out in the middle of nowhere. When operating “picnic-table-portable,” however, the display can sometimes be a little hard to read. For those situations, I came up with a little tilt stand using some stuff I had on hand.

tiltstand-1
Magnet applied to the corner brace.

The tilt stand I came up with has a grand total of two parts. First is a steel inside corner brace. You can find these at any hardware store. The one I used is 3/4-inch on each side and 1.5 inches long. You can use whatever size gives you the amount of tilt you’re looking for. The other item is a small but powerful magnet. The one I used is about the size of a nickel. I secured it to the corner brace using some Goop adhesive. To use the tilt stand, just use the magnet to put it on the bottom of the HB-1B, as shown in the pictures.

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Tilt stand attached to the radio

This tilt stand works best when you have rubber feet on the bottom of the radio, as I have on mine. In fact, I added those the first time I used the radio, to keep it from sliding around on my desk.

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Tilt stand in use

This little gizmo will a permanent part of my HB-1B portable station for those “picnic-table-portable” operations.

73, Craig WB3GCK

Clipboard Keyer

I purchased a set of Palm Mini paddles for portable operating a while back. I love the magnet base, which attaches nicely to the side of my little YouKits HB-1B transceiver. However, in some situations — like sitting on the ground or operating from inside my truck — that isn’t always the most convenient arrangement for me. Here’s a little hack I came up with to solve that problem.

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Figure 1. Washers attached to clipboard
clipboard-2
Figure 2. Paddles attached to clipboard

I purchased an inexpensive 6-inch by 9-inch, acrylic clipboard at my local office supply store. I used some GOOP adhesive to attach two steel washers to the clipboard, as shown in Figure 1. I made sure that the washers lined up with the magnets on the base of the paddles. Figure 2 shows the paddles attached to the clipboard. Figure 3 shows the clipboard in use during a recent outing. For transport, the little clipboard fits in the small plastic container I use for the HB-1B and accessories.

clipboard-3
Figure 3. Clipboard & paddles in use

For less than $2.00, this little accessory makes portable operating a bit more convenient.

73, Craig WB3GCK

Jackite Pole Hacks

I’m a big fan of the Jackite fiberglass poles for portable antenna supports. I have two of them have have seen a lot of use over the years. Here are a couple of quick and simple hacks that improve (in my opinion) on an already great product.

Keeping the Cap From Falling Off

While the overall quality of Jackite’s products is excellent, there is one thing that I find annoying — the caps have a tendency to fall off when transporting the pole. To overcome this, I attached a velcro strap to the cap (Figure 1). The Velcro is something I had on hand in my junkbox. It’s about 8 inches long by 1 inch wide. I used a #4 machine screw with some flat washers, a lock washer and a nut (Figure 2). I used an awl and a small phillips screw driver to make the hole in the cap. I then attached two Velcro strips (the fuzzy part) on either side of the pole (Figure 3). When transporting the pole, just secure the Velcro straps (Figure 4) and you’re good-to-go.

Figure 1
Figure 1
Figure 2
Figure 2
Figure 3
Figure 3
Figure 4
Figure 4

Easy Extension

This quick mod might seem kinda pointless to some users. In fact, I hesitated about writing it up. Anyway, you be the judge:

Figure 5
Figure 5

In cases when I need to bungee or strap the pole to a fixed support, I would first need to extend the top-most section first. This is because the top section sits down inside the other sections when collapsed. What I did was attach a key ring (aka split ring) to the eyelet on the top section (Figure 5). The ring I used is approximately 7/8-inch in diameter. So, I can strap the collapsed pole to a support, remove the cap, reach in and use the ring to pull the top section out (Figure 6).

Figure 6
Figure 6

Again, you might not see the value in this one, but I find it helpful.

73, Craig WB3GCK

Guy Ring for a 31-ft Jackite Pole

Here’s a neat idea I “borrowed” from my QRP buddy, Ed Breneiser WA3WSJ. When I need my Jackite pole to be self-supporting and I don’t have to carry stuff very far, I usually opt for my Jackite ground mount stake. It’s quick and effective but too heavy to carry on a hike. Not to mention the need for a hammer (or large rock) to drive it into the ground. So, in situations where the ground mount is impractical, I use a set of guy lines to hold the pole up. Here’s a simple way that Ed came up with for securing the guy lines to a 31-foot Jackite pole.

It’s pretty simple to build one of these…

Pick up a 2-inch, Schedule 40, PVC end-cap at your local hardware store. You’ll also need some nylon line. I used some 1/8-inch braided nylon rope from my local Walmart store.

  • Drill a 1.75-inch hole in the top, using a hole saw attached to your drill. When slid over the Jackite pole, the guy ring should rest on top of the bottom (largest) section of the pole.
  • Drill three evenly spaced holes around the outside of the end cap. Use a drill size just large enough to accept the size of line you are using.
  • Drill a second hole about 0.5 inch to the left of each of the three original holes. So, you should wind up with 3 pairs of holes around the end cap.
  • Cut three pieces of line. I made each of mine about 9 feet long.
    Thread the line through the end cap holes, as shown in the pictures, and secure the end with a knot.
  • For the other end of each line, I tied a taut line hitch. This allows you to adjust the tension on each guy line.
PVC end-cap drilled out
PVC end-cap drilled out

My completed guying kit consists of the guy ring with the lines attached and four small plastic tent stakes. Everything fits nicely in a zip-lock bag. (I sometimes throw a lightweight, plastic mallet/stake puller in my backpack to drive in the stakes.) To use it, I drive in one of the tent stakes where the pole will go and three equally spaced tent stakes around it. Put these three tent stakes about 5 or 6 feet away from the center stake. Take the bottom cap off of your pole and place the pole over the center tent stake. The center tent stake should prevent the bottom of the pole from kicking out. Attach the guy lines to the three outer tent stakes and adjust the taut line hitches for the proper tension. That’s all there is to it.

Attaching the guy lines
Attaching the guy lines
Completed guy ring
Completed guy ring

I also built one of these for my 28-foot Jackite pole. For this pole, I used a 1.5-inch end cap. I used a 1.5-inch hole saw to make the large hole. The hole was a bit too small, so I did some filing on it to get the proper fit. The final hole size is approximately 1.6 inches. Again, the guy ring should rest on top of the bottom section. Everything else is the same as for the 31-foot pole.

Thanks again to WA3WSJ for sharing this idea with me.

73, Craig WB3GCK

Yet Another QRP Blog…

Craig WB3GCKYep.  That’s right.  After maintaining my static website for many years, I decided to start a blog.  While my existing website gets a fair amount of traffic, it’s just too cumbersome to add new content.  So, most of my new content will be posted to this blog.

The old website will stay on the air but will see fewer and fewer updates (not that I have been making many new updates to begin with).  A few items from the old website will probably find their way over here.

So, I hope you find something that interests you here.

73/72, Craig WB3GCK