This the coldest time of year in most of the northern hemisphere. It occurs about 1 month after the winter solstice when incoming solar isolation equals outgoing radiation. From now until mid-summer the former will be greater than the latter so the temperature will gradually rise.
While it's nice to know that we're over the "hump" we still have to survive the weather that comes our way. In particular, our stations have to survive. The topic seems timely with a major winter storm about to hit the US and probably us as well. It's -30° C on Saturday morning as I type these words.
Cold temperatures are not by themselves an impediment to tower work. I've lived in colder climates and I've done tower work at temperatures as low as -15° C. There is little margin for error on high towers since you must plan for the time it takes to get down before your extremities go numb. That can be disastrous. On shorter towers it is easy enough to climb down for a warm up.
Despite the need for speed, never stint on the use of fall arrest equipment. It'll slow you down and you'll get even colder, but you'll live to tell the tale. When I was young I didn't appreciate the risks I was taking. Now I know better. So should you. It is all too easy to hit a patch of ice on a tower strut or lose your grip due to thick gloves or partly numb fingers.
A far greater serious risk than temperature is wind chill. I've lived in climates where there were regular warnings about exposed flesh at risk of freezing in as little as 30 seconds. I know many others that have lived and worked in colder climates, including the high Arctic. When I first moved to eastern Ontario long ago I used to joke, when asked why I moved here, that it was for the mild winters.
No matter your cold tolerance or your enthusiasm, it is prudent to build stations that can survive the cold. Better to stay warm in your cozy shack and operate to your heart's content than to find yourself trudging through the snow and biting wind to chip the ice off electrical enclosures to make repairs. You'll find yourself shouting words unsuited to polite company
I want to minimize the risk during the peak of contest and DXpedition season. We do tower and antenna work in the winter only when conditions are favourable. Many repair jobs should be left until spring for reasons of safety, no matter how important the malfunctioning item to your operating goals.
What can go wrong in the deep cold?
- Moisture and ice inside cables and connectors, both RF and control
- Grease that turns semi-solid
- Electrical components that fail or radically change value
- Water inside enclosures that turns to ice and shatters PCBs and other fragile components
- Hard plastics become brittle and will shatter, and the pliable ones become rigid
- Cable jackets crack and accumulate water and ice
- Tension on guys and cables increases
- Chunks of ice can fall from higher up onto fragile antennas and unprotected heads
Of course we all have our environmental challenges, even those living in warm climates. These include: hurricanes, salt, wildlife, intense UV exposure and more. This is not a contest over which group of hams suffers the most. The annual threat of frigid temperatures is simply what I have to deal with.
I will not delve into extreme detail on the matter of protecting our stations from winter's assaults. A few examples can prove helpful to ensure we make the right decisions. When everything seems fine in July it is difficult to imagine what that box of electronics will experience in January. A few careful choices will get us most of the way there.
In an earlier article I mentioned that the TH6 had failed. I opened the re-housed Balun Designs balun and found the ferrite and coax winding fully submerged. The PVC enclosure had a seemingly small crack and water got inside. That may have been due to the cold but could just as easily have been caused by a material defect. There is no indication of UV deterioration. Thermal cycling in our climate can be insidious.
I removed the water as best I could but that didn't help. There were no weep holes. Although that day was above freezing it is likely that the water had frozen and thawed, perhaps more than once. My time was limited so I couldn't positively confirm that the stress of the freeze-thaw cycle was responsible. Repairing or bypassing the balun could not be done quickly (winter days are short) so I left it for another time. I'll have to get by without the antenna.
There is a wide variety of electrical tape on the market. The cheapest does poorly in cold weather. It may seal effectively but it cannot be worked. Better tape is required to be usable in the cold. The above picture is an extract from 3M's spec sheet for Scotch 33+ tape. This is the minimum quality tape to use for effective sealing and cold weather use; I have better when needed. Note the temperature data.
Keep in mind that electrical tape that cannot be applied in cold weather can still work well after having been applied in warmer weather. In the cold it can't be worked so you can only remove it with a knife. The best tapes can often be removed and even reused in freezing weather.
Even the best products have a low temperature cutoff below which you can't work with it. In very cold weather I keep tape rolls in a pocket or under my parka rather than a tool pouch so that it stays warm and pliable until needed. It will cool quickly when attached to cold metal such as coax connectors so don't dawdle.
To reduce the need for expensive long runs of cable I've reduced the 8-conductors for Hy-Gain rotators to 5. Two of those conductors (#4 and #8) are eliminated by placing the motor phasing capacitor (it's a "run" capacitor, not a "start" capacitor) on the tower near the rotator.
Many electrolytic capacitors are specified to operate down to -40° C. If suitably protected they are safe and reliable for outdoor use. The capacitor at right was an inexpensive product purchased online. I don't know whether the specs are to be trusted for these nameless Asian imports, but it has been reliable down to -20° C, so far.
A different brand of motor capacitor that was used on an earlier side mount rotator is still fine after several years of service. It can't be seen in the pictures of the linked article but it's just to the right of the terminal strip underneath the wide angle bracket. The twin of the one pictured is on the tower with the side mount bracket for the rotatable 15 meter yagi. The rotator turns well in the current spate of very cold weather.
Motor capacitors, run or start, are intended for industrial and critical applications. They are usually located inside the motor, not on the outside as I am doing. The temperature inside a metal motor will not be much different from one that isn't enclosed, but it must be protected from snow, ice and sunlight. I wrap mine in UV-resistant plastic and mount them under the bracket that supports the rotator.
Relays are devices that do not always perform well or quickly in the cold. Above is an extract from the spec sheet for an Omron G2RL DPDT relay. I have many of them in my station. Note the temperature rating. I always check that line before placing an order. Some are rated to only -30° or even -20° C. That's insufficient where I live.
I have had relays stick or freeze in the cold. Several G5V relays from the same manufacturer occasionally need to be cycled on and off a few times in cold weather before they will operate normally. Sealed relays keep out moisture that can imperil relay performance and lifetime.
Any discussion about temperature has to include grease. Grease is most commonly used in our stations inside rotators and bearings. For the 6201 bearings above, it is generally better to use a double-sealing bearing like that on the right. However, check the catalogue to ensure that it is rated for the expected temperature range. Sealed bearings have a lower RPM rating at low temperatures due to the grease. In most high speed applications that is acceptable since its temperature will quickly rise.
I used a variety of lithium wheel bearing greases for years on rotators with little trouble except at the very coldest temperatures. Synthetic greases have a wider temperature range and remain stable at high temperatures. The latter is important even in our climate since the inside of a rotator exposed to July sunlight can get very hot indeed. The grease should not thin so much that it oozes out.
The greases on the right were used on one of my prop pitch motor gearboxes. They work well in the cold but there are better products available. This is not a product review or recommendation! Specialty automotive shops can be a good source for the range of products we need in our stations. Shop online if you must but read the specifications carefully.
One last example is that of metal expansion and contraction. It is easy to think of steel and other metals as temperature stable. They are when compared to many other materials. Yet seasonal temperature cycling will have an impact.
Fasteners can loosen due to thermal cycling. The bolt and nut can have different coefficients of expansion (CoE) or the preload (initial torque setting) may be set less than expected due to friction when tightened. As the fastener cycles between temperature extremes the clamping force can be periodically reduced and they can turn (loosen).
This is more common for large size hardware used to fasten together tower sections, bushings and rotator housings. But it can occur on electrical connections, whether ground wires or terminal blocks for control cables.
It can be difficult to diagnose after the fact since you can't be certain whether the preload was properly set, the screw never tightened properly or the copper wires being secured yield under excess force. I've had cases where I suspect thermal cycling as the cause.
Tower guys are also subject to thermal cycling. In our climate the preload on a guy can change by up to 10% between annual temperature extremes. For the CoE of the 5/16" EHS guys on my big towers the preload is specified as 1100 lb, or 10% of breaking strength. If you set it in January it may be 1000 lb in July.
That isn't necessarily dire since the 10% value is not a rigid directive. However, as hams we typically don't use very accurate tension gauges. The Loos gauge I use is designed for the multi-strand cable common on sailboats. The correction is inexact and must be calculated. For this reason it is better to set the tension so that it is no less than 1100 lb in mid-summer. Higher tension in the deep cold of winter is safer than a low tension in summer.
Throw another log on the fire and keep warm. Spring will come again.
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