In trying to decide which approach to take, I’ve done some lowband antenna modeling of inverted Ls and shunt fed towers. I have also asked for advice on the best 160m/80m antenna approach on the towertalk/topband forums. 

My plea for help on the towertalk and topband forums was met with with many great responses. Some guys went to great lengths to review the situation and provide input.

Quite a number of hams suggested that I shunt feed the tower. While that does seem to be an attractive approach for a number of reasons, there are some drawbacks in my scenario:

• The Cushcraft XM-240 40 meter yagi at the top of my stack is susceptible to overheating when the tower is shunt fed. 
• Exposing the SteppIR 4 element controller to voltages when the tower is shunt fed is also a concern. However, many have reported that there could be an advantage to using a SteppIR on a shunt fed tower in that some tuning may be accomplished with this approach.

At the moment, I think the approach I’ll take is two inverted Ls: one for 160m and one for 80m. This pair of inverted Ls will be driven with a variable capacitor of some sort.  There are downsides to this approach… extra wires in the yard, probably will be tricky to tune, and some interaction causing a distorted pattern on 80m.

Still many things to be worked out on this… housing and control of the capacitor, band switching, installation of standoff arms, etc.  I’ll post more as this develops- but feel free to comment if you have ideas on lowband antennas with a self supporting tower.

Overall the SteppIR has been a fun antenna to use on the air. One of the unexpected surprises with the SteppIR was bi-directional / 180 degree feature. Imagine a contester in the Midwest who wants to CQ during a contest. One choice might be to use the bi-direction mode and hit both the east and west coasts (much like a dipole). Perhaps you’ve got that beam focused on 90 degrees when you hear a rare one off the back… You could rotate the antenna by 180 degrees or you could simply hit the 180 degree mode button on the SteppIR control box. Fast – and in ham radio contesting, speed matters.

I’ve had a couple of ice storms here that had me a bit nervous. However, the SteppIR fiberglass elements came back to life without issue.

Again, you should consider the pros and cons before purchasing any ham radio antenna. For me though, the SteppIR 4 element yagi has been a good fit.

Once again, we ran out of daylight… so I didn’t get a chance to take a picture of the XM240 and SteppIR combination fully installed. At long last, we’re seeing the light at the end of the tunnel.

If things go well tonight installing the lightning protection gear, wiring and testing everything, I might be able to make a few QSOs in this weekend’s CQWW SSB contest.

Building, installing and adjusting these ham radio antennas has been a bit of a challenge – but the best part is ahead… using them!

I was curious as to what the MFJ-259 would report for this antenna. Again, it found 7.180 MHz as the SWR minimum, but this time the minimum SWR was about 2:1. Ouch. I took the day off on Tuesday to get some more work done and ponder this puzzle. Why were the Icom and MFJ-259 reporting such different results?

With my troubleshooting hat on, I tried the following:

• Test the XM240 with my Icom 706 MKIIG (installed in my car – this required driving my car to the back yard)…. Results were the same as with the IC-746: a minimum of 1:1 SWR at roughly 7.180 MHz.
• Test the MFJ-259 into a 50 ohm dummy load. Results: 1:1
• Test the car’s High Sierra mobile screwdriver-type antenna. Results: a minimum SWR on the 40 meter band of about 2:1.

Hypothesis: MFJ 259 has been giving faulty readings. More testing required. So, Bill (KØKT) offered to loan me his MFJ-259B with filter. Next:

• Test the XM240 with Bill’s (KØKT) MFJ-259. Results: same as with my MFJ-259, a minimum SWR of about 2:1. Inserted Bill’s MFJ analyzer filter. Same results.

New hypothesis: MFJ 259 analyzers are getting swamped with RF from a nearby source… even more than their optional analyzer filter can handle.

• Finally, tested Bill’s MFJ-259 with my High Sierra. Again, same results, high SWR.

Conclusion… there’s something in my neighborhood that doesn’t agree with antenna analyzers. I may take my MFJ259 with me to work tomorrow and see if there’s a different result far away from my home QTH.

XM240 adjustments…

Knowing that we would need to lower, quickly work on and then raise the XM240 before we lost daylight, I sent a plea for help out to the SCARC group and a few buddies. My usual team of helpers (Dave, my father-in-law Duane, and my neighbor Chris) were there, but I was also joined by Arnold (AG3V), Jerry (KØCQ), and Bill (KØKT) from SCARC. We had another perfect Iowa autumn evening (low wind, clear skies and mild temps) and we were organized enough to get the antenna down, make the adjustments and get it up again in very good time.

I’d talked to Cushcraft about the problem. The only thing I was able to come up with was a plan for checking things once the antenna was on the ground:

• Check for DC continuity across the coils
• Check for continuity to the driven element from the balun
• Check measurements (lengths)
• If necessary, replace the balun

The SWR curve looks much better now…

An organized plan, some detective work (to discover this antenna analyzer oddity in my neighborhood) and some great helpers allowed me to get past this strange problem with minimal pain.

Thanks to all involved!

…-.-

This meant that Duane and I had to do some final preparations on the XM240 prior to the installation. We had an hour or so before Dave would get to my QTH and install his gear (ropes, pulleys, mast climbing steps, etc.).

My neighbor (Chris) and a buddy from my church who’s getting into the tower climbing business (Jeff) also came by to help.

My final checklist prior to installing the Cushcraft XM240 included:

• Adjusting the truss system (3 ft above the boom)
• Tightening the bolts/nuts
• Final measurements for the driven element and reflector (just below the mid point of the 40 meter ham band)
• Grounding the reflector to the boom
• Bug-proofing the boom

The last two items were not “per the Cushcraft instructions” but were XM240 tips that I’ve picked up through the internet. Some users have reported a clicking noise on 40 meters due to static build-up and arcing from the reflector to the boom. They’ve cured this by grounding the reflector (reportedly without any performance impact). Additionally, this should help with top loading when shunt feeding the tower on 80 meters or 160. The problem was how are folks grounding that element.

We came up with a battlefield solution… ground the U-bolt to the element by inserting a wire between the element and U-Bolt (in the bushing)… best explained through this photo:

If you look closely you can see a small aluminum wire that’s been bent up and wedged between the U-bolt and the element (in the bushing gap). That should keep the element grounded (via the u-bolt) to the boom).

What’s this about bug-proofing the XM240 boom? Well, from what I’ve gathered, the issue is that Cushcraft supplies plastic caps for the ends of the boom. I’ve read where hams have taken down their XM240s to find a lot of water in the boom – essentially stored in there, trapped by these caps. Not wanting to just leave the ends fully exposed to bugs, birds and anything else, I went to the ham radio antenna building aisle of my local grocery store to find “antenna boom bug filters” – which I then trimmed to size. These should let the water pass through and keep the critters out.

Once Dave was ready, we got the antenna in position and began the lift. We used a pulley at the top of the mast, a pulley at the bottom of the tower and two tag lines. Having the extra helpers really made things go well. Due to a sticky pulley, it took a bit longer than we had hoped (so some of the pics get a bit dark).

By the end of the day the XM240 was proudly mounted ~12 ft above the ANwireless HD-70. Best comment of the day was from my XYL… “It doesn’t look so big up there.”

Here’s a few photos of the SteppIR construction process…

The SteppIR 4 element is a 81 lb beam that ships in two cartons (three including the controller cable). I opened the boxes for inventory and to run through initial setup in the garage.

Here you can see some Noalox (aluminum anti-oxidant compound) between two sections of the SteppIR boom. I’m not planning to take this thing apart any time soon, but just in case, Noalox should help allow for the antenna boom sections to come apart. I also used a generous amount when building the XM240 40 meter yagi.

Here is the wiring connection for the SteppIR controller. With the 4 element SteppIR, a 16 conductor controller cable is required. Some may argue that this added complexity and potential for failure makes the SteppIR a poor choice. After all, there is a potential for connector or cable failure on the antenna controller, potential for failure in the SteppIR motors themselves, etc.

The way I look at the SteppIR 4 element yagi antennas is that this antenna is actually a mono-band 4 element antenna for each band that I’m going to use. It’s a 4 element yagi on 10 meters, a 4 element yagi on 12 meters, a 4 element yagi on 15 meters, a 4 element yagi on 17 meters and a 4 element yagi on 20 meters.

There are other ways to get four element monoband antennas… many separate monobanders or a few multiband antennas (Optibeam, Force 12, etc.) – but the trade off is mechanical complexity with many elements in the air.

Here is the completed SteppIR. After installing the elements, I plugged in the control box and ran the tests. Thankfully, I had installed the control cable properly and all tests passed.

Overall, the assembly of the SteppIR was not too bad. It took longer than I had thought it would and there were times where the documentation could have been more clear. Here’s a hint for installing your own 4 element SteppIR… they continually update the documentation and the latest version is much better than the version you may have.

Today I finished the trusses for the antennas and then went onto the trenching. My neighbor, Chris, asked when I wanted to put the trench in at about 3 pm. We rented a trencher and had it basically done by 4:30pm.

We then returned the trencher and finished up with hand shoveling around the septic lateral lines (we were very careful around those lines). Finally, we started putting together the PVC until we’d lost daylight and were too sore to go any further.

The XM240 is a two element yagi with a 22 ft (6.7 m) boom and 43.5 ft (13.3 m) elements. The antenna weighs 55 lbs (25 kg)… for me, it’s a serious ham radio antenna.

This is how the finished antenna should look. You can just barely see the “capacity hats”.

A pair of capacity hats and loading coils are found in each element to electrically lengthen the element which keeps the size a bit more manageable for for typical ham radio operators who cannot install a full size yagi (with a bit of performance cost).

I do have a few minor complaints about the construction of the Cushcraft XM240:

• Some tolerances don’t quite match up. For example, there were times when I could not get the lengths exactly as documented – like when I needed to have a certain length between two pieces but the insulation around the loading coils prevented the length from being achieved.
• The hose-clamps that hold the element sections together don’t completely do the trick. I thought I had a clamp tightened all the way, then bumped the element tip and the length changed. I’ve seen that others add a bolt to lock (or pin) the antenna element sections together – I’ll do that as well.
• There was a couple of times where I had to get the drill out – either to slightly widen a hole for a bolt or to clean out a bolt hole that had black insulation in the way.

That said, it wasn’t that bad. The documentation was relatively good and I was able to single-handedly build the antenna without bloodshed. Some sections are reinforced quite well and look to be very sturdy.

I also used some NoAlOx between the element joints to help prevent corrosion and to make it a bit easier for the day when I need to disassemble this antenna.

Just for fun, I ran a piece of RG213 coax to the antenna and turned on 40m on my IC-746 – while the XM240 was still sitting on sawhorses. Sure enough, there was some activity on 40 meters. That’s a good sign. I’m hoping that this thing plays well when it’s at ~82 ft and about 10 ft above the 4 element SteppIR.

Now I need to select antennas for the other HF bands: 30m, 80m, 160m. Primary interests are contesting and DXing (all modes). I have a used AlphaDelta sloper antenna for 80 & 160 meters ($15). However, I’m thinking that a better choice would be to look into shunt loading the tower for the low bands. Another possibility would be an shortened inverted V. I don’t really have any trees or other support structures to use in the area – so I’m a bit limited with wire antennas for low bands. Something else to cause me to scratch my head.

Someone had asked what the Butternut looked like after the storm had passed. I finally uploaded the pics showing where the antenna had failed mechanically:

Here is a wire that broke:

Finally, here’s a picture of some corrosion around a capacitor. Can’t blame the ice storm for that:

I think that with some work, the Butternut could be brought back to life, but its best days are behind it. Oh well, I’ll get to it after the tower.