TH6 on the Rotatable Side Mount

Tri-band yagis are increasingly unwelcome at my station. They're narrow bandwidth, modest performers and can be inefficient. In another time and in another station they are ideal choices: one antenna does so much. With my gradual transition to mono-band yagis they will come down and stay down. The Hy-Gain Explorer 14 has been down for a couple of years and I sold it this fall. The TH7 at 150' has been taken down and it is unlikely to go back up.

This leaves the TH6 as my only tri-bander. For the past few years it has been fixed at ~75' (23 m) on the 150' tower, pointing south to the Caribbean, Central and South America. Previously it had been on top of the 150' tower.

Having it fixed is less than ideal since I would also like it to cover more of North America. NA contacts are needed for points in many contests, and my bigger antennas are usually pointed elsewhere.

I have written previously about different methods of side mounting yagis on towers for partial compass coverage. This year I decided to do it for the TH6. A rotation of ~130° allows compass range from 150° (Brazil) to 275° (VE7 and VK). For my purposes that's perfect.

It amuses me that the antenna and its rotator were manufactured not long after I was licensed almost 50 years ago. I acquired them secondhand in 1985 when I had the house and the means to put up a tower after moving Ottawa as a young man several years earlier. At right is a scanned photo.

Both went into storage when the tower came down and I was out of amateur radio for many years. The rotator, a CDE Ham-M, was refurbished and used when I returned to the hobby and put up a tower and tri-bander in 2014. In 2016 it went back into storage.

I took the opportunity to make repairs while the TH6 was on the ground between being removed from the old side mount and raised to its replacement. It isn't the first time I've dealt with rusty hardware on this antenna, or the second. This time I made a permanent repair to a wire bond that could not be done on the tower.

This is a very old version of the TH6. It predates the switch to stainless hardware in the 1980s. The remains of the filed off rusty screws from the hairpin are at upper right. A badly damaged wire lug was replaced by another and stainless screws installed. 

The boom clamp had to be flipped 180° due to the orientation of the rotatable side mount mast.. It is easily done by removing the two bolts that pierce the boom sections, rotating the clamp and reinstalling the bolts. 

I removed the element and boom end caps since they prevent water drainage. We found water sloshing around in one element and the boom. After an SWR test the antenna was ready to go.

Service of the vintage Ham-M Series 5 rotator went quickly. The only known problems were corrosion on the wire terminals and a jumpy direction indicator. Contact cleaner and steel wool corrected the first problem. The second required opening the rotator. Contact cleaner and a light touch with fine grain sandpaper restored smooth operation. Be careful not to abrade the wire on the potentiometer! Nothing else was amiss so I closed it up, taking care to align the pot, ring gear and bell housing, and not lose any ball bearings from their plastic retainers.

With the rotator, mast and mast bushing installed on the new side mount the TH6 was trammed up (picture in the previous article). At first, all seemed well electrically and mechanically. Although the spacing between the elements on either side of the mast mount is wide enough to clear the tower when rotated, my calculation missed a critical parameter. A manual spin of the yagi on the mount showed where I'd gone wrong.

The driven element didn't quite clear the tower. A few more inches of room would have been enough. I failed to account for the lateral offset of the rotator from the tower. That increases the distance to the far tower leg to eke out 10° more rotation, but increases the required spacing of the element to clear the tower.

With the help of the an ever-helpful accomplice (VE3KAE) we once again lowered the antenna. Some innovation would be required because the boom clamp does double duty as a mast clamp splice for the two boom sections.

I was lucky to find a spare Hy-Gain boom clamp in my junk box. I have other suitable clamp material but with this part it was quicker and easier to mate the Hy-Gain mast clamp at another position on the boom. With better calculations in hand I attached it to the boom 16" (40 cm) from the antenna centre. This is better than going for the minimum since it better centres the antenna for side mount rotation by maximizing the distance to both adjacent elements. The latter reduces tower interactions and varying pattern and SWR when it is rotated. The larger offset also allows the large resin plate over the Balun Designs balun to clear the tower.

The large offset imbalances the antenna. I compensated by offsetting the tram and lifting it with heavy steel hardware as a counterweight on the short side. I placed them within reach from the tower so that I could remove it after the lift. The truss cables had to be redone (they were rusty anyway) to fit the new location of the mast.

The tram ride proceeded without drama. Adjusting the boom truss was interesting due to the weight imbalance. I made a judgment call that the rotator is able to handle the imbalance. So far there has been no trouble with high winds.

This time a manual rotation test showed that the yagi cleared the tower nicely at both rotation limits. The antenna is shown at its west limit on the left and at its southeast limit on the right. Soft bumpers will be added to soften contact with the tower. The Ham series rotators have low turning torque and cannot really do any damage to the tower, antenna or itself when the boom strikes the tower. It simply comes to a sudden stop.

At that time the project came to a standstill. I connected the coax to make use of the antenna but the rotator was not yet wired. With all the ongoing work at the top of the tower (10 and 40 meter yagis) the orientation of the TH6 had to be fixed so that ropes and cables for rigging wouldn't snag and damage the lower antennas. 

Rotator wiring was completed in a series of steps done between higher priority tasks. A barrier strip was attached to the underside of the large aluminum angle stock of the side mount. The aluminum was drilled and tapped for stainless screws. A short length of rotator cable runs from the rotator to the barrier strip. 

A weather cover for the barrier strip has yet to be fabricated. Most precipitation is held off by the overhanging angle stock and the barrier strip hardware is tinned. After the picture was taken the cables were dress so that the cut ends pointed down, not up, to keep water from easily getting inside.

Notice that the common pin (#1) is tied to the tower. The 14/3 house wiring cable runs to the ground where the common lead is tied to the tower ground. I could have used 14/2 but the bigger cable was sitting around after my electrician deemed it unsuitable for a house wiring project. I used the extra conductor to increase the number of grounding points.

The motor run capacitor is mounted and wrapped for weather just off the right side of the picture above. It is connected to pins #4 and #8 with purple wire. Many install their Hy-Gain rotators this way to eliminate two conductors. This class of non-polarized electrolytic capacitors for industrial electric motors are typically rated for temperature extremes in the great outdoors. They seem to hold up well in our climate.

I went further with the conductor reduction. The 14/3 cable carries pins #1 (common), #2 (brake solenoid) and #5 & #6 (motor windings, via the limit switches) to the bottom of the tower. Cat5 cable for pins #3 and #7 (direction pot) connects at the tower base to an existing trenched control cable. The other 6 conductors are available for future antenna switching projects.

A 14/2 cable runs (overground for now) back to the Trylon tower carrying pins #2, #5 and #6. Common (pin #1) is carried via the coax shields. At the Trylon all the coax and control cables terminate and are switched to the runs into the house and shack. 

There is an 8-conductor rotator in a trench from the Trylon to the house. The rotator cable has water damage but is usable after scrubbing the wire tails with sandpaper. I will replace it in the coming months. The separate control cables already route the pair used for the pot into the house. I picked them up there with another short Cat5 run to the rotator cable splice point inside the house. 

Common (#1) is again tied to ground at the Trylon ground rod. The complicated wiring ensures minimum loss for the motor and brake solenoid using relatively inexpensive AWG 14 house wire. It is an economical solution compared to purpose made commercial rotator cable. By using the common station and safety ground one heavy conductor is eliminated. The higher resistance AWG 25 Cat5 conductors for the direction pot is easily calibrated out at the rotator controller.

The rotator controller is ancient. It ought to be in a museum instead of on my operating desk. It is a little better on the inside, as is the motor, since I upgraded both long ago. It's as robust and stable as a Ham-III. I repurposed the switch on the left as a brake control since the original design switched the motor and brake in tandem. 

Newer Hy-Gain controllers allow manual brake engagement after the motor coasts to a stop. The best controllers make the procedure automatic. If I get bored this winter I may add a feature or two to the controller to make it more user friendly.

The meter face is north centred but in this application the rotator is south centred. I checked the back of the printed plate and it is bare aluminum rather than a south-centred meter face. I stuck on labels (that don't stick too well) with the true major compass headings and the approximate limit positions.

After CQ WW and before winter strikes hard the cabling will have to be cleaned up. The main run of 14/2 is on the surface and needs to be trenched. The cable splices are so slapdash I am too embarrassed to post pics. Despite its present ugly state I am happy to have this additional rotatable yagi in time for the contest.