AmateurRadio.com

The weather was too nice to sit inside. In the low 70′s with a very slight breeze so after church and a short nap I headed out to try my hand at giving out points in the QRP ARCI Homebrew Sprint. My startup was delayed by curious folks in the lakeside park wondering what in the world I was doing and how I got that string and wire so high up in the nice tall pine trees!

Next to the Lake in the Sun

I checked 40m first with an inverted L end fed half wave and my trusty Stuner (KI6S Stu’s kit) and decided to change to 20m after not hearing much activity. 20m was decent and there were a few of the big gun qrp contest regulars shooting it out. N4BP, K4BAI, K0ZK and a few other were running stations while the little guys like me were mostly doing Search and Pounce. Hey it is fun even if you cannot run a frequency, right?

Sun went down about 1745 local and the mosquitos were quick to find the hole in my hat and attack. This time I remembered the repellant and after a few bites I took time to spray my hat and hair and the backs of my hands. The temperature dropped fast and my hands got a bit stiff pounding out the morse code on my J-47 straight key. 50 degrees is cold for a Florida evening. The darkness also brought out the raccoon family and it was fun to shine my flashlight on them and watch them stand on their hind legs and stare into the night wondering what the funny guy was doing in the dark.

Sun is almost outta sight

40m came to life after sunset and I finished with a respectable 20 contacts for about 3 hours of operation and was able to give some Christmas contacts to the needy fellow contesters who were chasing another certificate. What a great way to spend the afternoon… by the lake in the sun and outdoors playing radio.

I learned a few lessons — the hard way — while building this New Carolina Windom. At risk of making myself look like an idiot I’ll share some of them with you here so that you can learn from my mistakes.

You might wonder how a guy who has been a ham for 33 years could be so ignorant about some of these things, but understand that up until this project I had never even put up an outdoor antenna on my own. My dad was the one who did all this when I was a kid. When I became a homeowner, all my antennas were indoor, stealthy antennas located in my attic — a whole different ballgame. That doesn’t work in my current house, so for the first time I’ve had to build up an outdoor antenna-system.

Anyhow, here they are (in no particular order):

• Drilling holes in masts: Use a titanium bit. It’s worth the money! I used lesser bits at first, to my frustration. Titanium bits cut through aluminum like a hot knife through soft butter, and they make short work of steel, too. If you’re drilling anywhere but in a workshop, make sure you put down newspaper or something to catch the metal shavings; metal shavings do not contribute to a “barefoot lawn!” Also, build a good jig if you’re drilling all the way through the mast. The jig I built did a good job of holding the mast in place but next time I’ll improve it with a guide that ensures top-dead-center and (in lieu of a drill-press) perfectly perpendicular drilling.
• Cutting & handling antenna wire: Be generous when cutting the legs of your antenna. I thought I was generous, but when it came time to make my final adjustment (after SWR testing) I could have used just a few more inches than the extra 15″ I had allowed myself on the long leg of my New Carolina Windom. And when handling 14 AWG copperweld, watch out for kinks! As hard as I tried, I came mighty close more than once to putting a bad kink in that unwieldy stuff.
• Erecting masts: Use a level to make sure the mast is vertical. I know, DUH! I did use a level when I put the tripods up, but when it came time to put the masts in I had forgotten to bring it up on the roof with me. It was just too tempting to pop them in without checking to see that they were perfectly vertical. I found out the hard way that a mast can be tilted quite a bit and still look perfect when peering up its length!
• Working safely on the roof: Use a safety-line. The first time I went up on my roof I was surprised at how much steeper it was than the one I used to scramble around as a kid. Frankly I was scared stiff up there, especially with this bum leg of mine. I’ve heard there are safety harnesses out there, but I couldn’t find one. So what I did was to throw a safety-line over the roof and tie it off to something stout. That at least gave me some added security on the side of the roof opposite the attach-point. Just make sure your rope is strong and your knots are good!
• Soldering wire on the roof: Buy or borrow a butane soldering iron. I found out the hard way that even a 100 watt soldering gun is useless at the end of a long extension cord. It worked fine for soldering lugs onto the end of my 14 AWG copperweld, but not for soldering the same wire twisted onto itself. And a regular propane torch is definitely not the right tool for the job (I know, I tried!). Also, you might want a drop-cloth up there. By the time I was done with the job using a propane torch (you should have seen it — it was pretty comical), I had more than one solder-drip on the shingles.
• Waterproofing coaxial connectors: Use coax-seal or self-amalgamating tape. As I mentioned in my earlier post on this subject, I at first just used electrical tape to wrap my coaxial connectors. After being persuaded by several kind hams who posted comments on that post, I ordered some coax-seal. It’s a good thing I did; I am grateful to those hams for their good advice. When the shipment arrived, I went up on the roof to discover one of my nice pretty tape-jobs already coming apart at the seams after less than two weeks! By the way I found out that five feet of 1/2″ coax-seal is good for only three connections, at least the way I wrapped them.
• Using pulleys: Use big enough rope. The first time I hoisted my antenna the rope was too small; it quickly jumped off the pulley and got jammed between the pulley and the housing. Fortunately I got it free. I swapped out the thin rope for something much stouter, and now it will never get stuck. (By the way, I’ve read one ham’s advice not to use pulleys at all but ceramic egg-insulators instead; there’s nothing for the rope to get stuck on and they’re durable enough that he’s been using one as a pulley for 20 years.)
• Allowing for radials: Build in an attach-point for radials at the base of your RF choke if you’re building a New Carolina Windom. Only after my antenna was complete did I read about the benefits of adding radials to this antenna. There is no good way that I can think of for me to connect radials directly to the coaxial connection. Next time I build an RF choke I’ll provide some lugs (or a plate or something) on one end for this purpose.
• Testing SWR: Make sure you hoist your antenna all the way up before testing its performance. I tried testing my antenna before climbing up on the roof — my son held the mast upright and I tied the legs of the antenna off as high as I could to nearby trees, but the SWR was just too high on 40 meters due to the proximity of the antenna to the ground.
• Throwing lines: If you have trouble throwing a line, try a heavier weight at the end. I now know that throwing lines is an art. At various points in this project I experimented with a sling-shot, potato-gun, and throwing by hand. Each of these techniques has its place. At one point the best way for us to get a line where we wanted it to go was by simply whirling a weight and letting it fly — but only after we figured out that we needed a good heavy weight at the end. At first I used just a few ounces of metal, but it kept getting hung up in the branches we were penetrating. Once we switched to a pop bottle full of water, it worked on the first try.
• Pounding ground rods: Put your connectors on the ground rod before pounding it all the way in, if they’re the kind of connectors you have to slip on over the top of the ground rod. By the time I was done pounding in my 8-foot ground rod, the top was so flattened out I couldn’t get the one-piece connector over the top. (An angle-grinder solved the problem; I cut off the top and slipped the connector on.)

No doubt some of these lessons I’ve only partially learned (and maybe some of them I haven’t learned well at all). If you have any better suggestions, or if you have some of your own hard-won lessons you’d like to add, fire away. If we can learn from each other here, maybe we won’t have to learn quite as many lessons the hard way!

Here is a spreadsheet I designed in Microsoft Excel for calculating the first cut and the final cut (after testing) of a 1/2 wave dipole, whether center-fed, classic off-center-fed, Windom, or New Carolina Windom. If you use it for a plain ol’ center-fed dipole, just ignore the references to “long leg” and “short leg” — the numbers will still be right. Anyhow, you’re welcome to use it, pass it around, whatever:

DipoleWorksheet.xls (Microsoft Excel)

I’d enjoy hearing from any of you who end up using this spreadsheet to build an antenna!

If you find any bugs in this spreadsheet, please let me know. Note that it is protected for your convenience, but you can unprotect it anytime you like to see the formulas in each cell (there is no password).

What is the best way to hang an off-center-fed dipole or windom antenna as an inverted-V? Should you hang the feedpoint at the apex, or hang the center of the antenna at the apex?

From an electrical standpoint the best way is to hang the center at the apex. That is where the current is at a maximum on the lowest resonant frequency. But that leaves all the weight of your balun, coax, and (in the case of a New Carolina Windom) RF choke unsupported by anything but the antenna-wire itself. So from a mechanical standpoint the best way is to hang the feedpoint at the apex, with all that weight hanging straight down from the hanger. Either way it’s a trade-off.

I think it makes sense to hang the feedpoint at the apex if the angle of your V is reasonably broad. The mechanical benefit outweighs the electrical cost in this case. As you can see in this diagram, you really don’t give up much height at the center of the antenna. My own 40m New Carolina Windom, with the longest leg at 74^o from vertical, sacrifices only 2.3′ at the center of the antenna. Even if it were cut for 80m the sacrifice would only be 4.5′. A 160m version (I know of one fellow who plans to build one!) would give up almost 9 feet, though. You might want to hang the center at the apex in that case, unless it’s already so high that 9 feet doesn’t matter much. You can always figure out a way to support the feedpoint in some way if you need to.

This changes if you mount your V with a narrow angle. Dropping the longest leg to 45^o from vertical would cost me 6′ on my 40m New Carolina Windom! In that case it would probably make more sense to hang the center at the apex.

The way to calculate this is shown in the figure above. Notice how I labeled the sides of that triangle with “H” and “A?” Now why did I do that? Glad you asked! The “H” stands for “hypotenuse” and the “A” stands for “adjacent” — adjacent to the angle of 74^o in this triangle (your own angle may be different, of course). Just remember this sentence: “Oscar And Ole Have Huge Appetites.” (Up here in Minnesota we all love that name Ole, don’t ya know!) That will help you remember the way to calculate the sine, cosine, tangent, arcsine, arccosine, and arctangent of any angle. “O” stand for opposite (the length of the side opposite the angle you’re dealing with), “A” stands for adjacent, and “H” stands for hypotenuse:

Oscar And Ole Have Huge Appetites!

So to figure out the height of the apex above the center of my antenna, I figure:

A/H = cosine(74^o)
A = cosine(74^o)*H
A = 0.276*8.5′ = 2.3′

There you go! Of course, you’ll have to know the angle to figure this out. To see an example of that calculation, check out my previous post.

Of the three support-points for my wire antenna, one of them has caused me some concern. The end of the longest span of my New Carolina Windom is attached to a rigid, unguyed 12 foot steel mast by a very short length of rope — not nearly long enough to stretch and absorb the shock that a wind-whipped wire might induce in a good storm. Furthermore, this 12 foot mast is set in a small 3′ tripod without any reinforcement below the roof. Obviously this isn’t good enough for a heavy load, but I’m hoping it will suffice to support one end of a 42′ wire. As a precaution, I’ve built a shock-absorber into the system:

This is a spring that I bought at the local hardware store. I didn’t do any calculations to select the thing. I just went through the drawers and handled all the likely-looking springs they had. This one felt about right when I pulled on it. I tied it into the 3/32″ braided dacron/nylon rope with a loop long enough to match the length of the spring when fully extended. The electrical tape is to prevent chafing for as long as it stays on.

The spring is strong enough that on a calm day it doesn’t stretch at all, but it still has plenty of give if the wire gets to whipping around. Will it help this antenna-system weather the storms we get out here in western Minnesota? Time will tell!

For a great tutorial on waterproofing coaxial connectors, check out this post by Paul, AE5JU, over at K9ZW’s blog. I didn’t use Scotch 130C Coax Seal like he does since by the time I discovered its existence I was out of time to acquire it for this project. Next time!

[Update: After the helpful comments I received on this from VE3WDM and others at amateurradio.com, I’ve ordered some coax seal and plan to finish the job as soon as it arrives. What I’ve done here is better than nothing — certainly good enough until I can get the good stuff — but it doesn’t afford long-term protection.]

[Update: When I went to put on the coax seal, I discovered my nice pretty electrical tape already coming apart after less than two weeks! Use coax seal! Another thing I’ve learned about is “Magic Tape,” the self-amalgamating silicone tape you can easily find even at stores like Target and Walgreens. Some hams have told me it works great to put over the coax seal.]

What I did do was wrap the connectors with teflon plumber’s tape, then covered it with black 3M electrical tape. The teflon tape is intended simply to keep adhesive from gumming up the connector. I put several layers of electrical tape down and made sure to wrap the last layer up, i.e. toward the sky, so that the turns are stacked like shingles on a house with their seams pointed downward. Here’s a slideshow:

Click to view slideshow.