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Water Problems

radio8z's picture

It has been over a year since the installation of my outdoor ground mounted AM transmitter and, until today, there have been no problems when it was discovered that the transmitter was off the air...not a weak signal but no signal at all.

The transmitter was brought to the 8Z labs and the problem was obvious when the lid on the enclosure was opened revealing about a quarter of an inch of water in the bottom of this water proof box. The water could have entered where the RF and power/audio lines enter but the duct seal compound at these points was intact. Water could have entered through the power cable which is a simple vinyl covered multi-conductor cable where the water can creep through the cable between the outer jacket and the conductors but there was no evidence of this. The water could have entered if the cover gasket was not seated and, indeed, inspection of this gasket revealed that it had some gaps where it was not smooth. Though not definitely determined, this is the most likely path for the water entry.

The water did not damage anything but it did affect the PLL frequency generator most likely by entering the DIP frequency selector switch. The PLL frequency was 8.9 kHz rather than the usual operating frequency which could have been caused by water in the switch bridging the contacts which were supposed to be open. A few minutes of gentle application of a heat gun fixed the problem.

The next step will be to place a plastic bucket over the enclosure to make it harder for water to enter, or even better still, maybe install a mini sump pump in the box.

Neil

Waterproof??

Neil, this nuisance has been a constant problem at my day job, a major cable MSO/Telecommunications company. We use waterproof strand mounted enclosures to house and protect fiber splices and also passive filters, aka multiplexers, de-multiplexers, aka (again) muxes or d-muxes, or even more commonly just called muxes. There are no active components in these enclosures (thankfully), but still, every winter we experience several outages due to water getting in somehow then when it freezes it puts pressure on the fibers, often causes micro-bends in the fibers, and our customers go down.  It's not like it happens to every one of them all the time, but when you have 150,000 miles of fiber and tens of thousands of these enclosures, it's quite a problem. Waterproof is not always waterproof!

This is why I've been hesitant to mount my xmtr outside but in order to be legal I must do it. The box I will be using is a Multi-Link NID designed only for fiber connections, and is typically wall mounted outside and attached to a building, so it's much more sheltered than when it will be mounted on an antenna mast. I am going to apply a fine beed of silicone along the groove where the door interfaces with the rest of the cabinet  since this model has no sealing grommet, even though it's an outdoor box. All the connections will drop out the bottom through rubber grommetted slots and of course I'll add a drip loop to each cable. What concerns me most is the antenna mount.  The easiest approach will be to drill a hole in the top of the cabinet, bolt the antenna in and seal the hell out of it with silicone, which I may do but I still worry about water in-gressing through it anyway. A1 better solution will be to drop the antenna feed out the bottom and mount the antenna on the side of the enclosure, which I guess I'd have to bore holes and mount the antenna on the side of the cabinet using pipe clamps to hold the antenna securely. Again, more drilling and silicone. Finally, once transmitter is tuned for its final setup I will wrap the transmitter in a heat shrink bag, shrink it tight, for a little more protection, then place inside the enclosure.  I may also use your idea of a plastic bucket over the xmitter for a little more protection, but again, another hole to be drilled for the antenna to pass through the bucket, and more silicone needed!

BTW, about 15 years ago I set up a consumer grade wireless access point in a Tupperware container on my roof, on a 10ft mast on a 5' tri-pod. The plan was to feed one of my daughter's girlfriends, whose mother, father, and brother were blind, and could not afford Internet,and also a kid running a deli across the street. I had seen that deli go out of business 6 times in 5 years so I offered it up to him. A year later he too was out of business but at least he did not have to spend $150/month on a commercial cable modem connection in the meantime.

I actually got about a half-mile radius of coverage with that AP, and the two years it was up, no water damage!

Jim

Jim Henry HBR Radio 1610, serving Honey Brook, PA. and NW Chester County.

Recurring Water Trouble

Jim,

I had forgotten about my original post on this topic.  Last fall I had the water problem again, this time there was damage to the transmitter board.  I still do not know how the water is getting in.

One technique I have seen used is to drill a small drain hole in the bottom of the enclosure but it is my experience that doing so forms a portal for insects.  With two outdoor "weathertite" 120 VAC installations here ants had invaded the work boxes in sufficient numbers to become roasted and trip the GFCI.  A method to prevent this is to use a wick material in the hole but wicks work both directions.

The big boys use positive pressure dry nitrogen but this is beyond my means.

My antenna is mounted on a PVC pipe so it doesn't depend on the box for support.  The antenna/ground connection is via a 6 inch whip coax so installing an inverted bucket is an option but I haven't done so at this time.

Someone suggested using dessicant silca packs but these would require frequent maintenance and are hygroscopic and could make the problem worse if they saturate,

I still suspect that water is wicking through the power/audio cable so maybe all that is needed is to seal the end of this cable and get it out of the weather with a shield.  This is probably the next thing I will try.

Neil

 

 

The Risks of Outdoor Operation

As a radio station moving toward having two or more outdoor antenna sites I am disturbed by seeing these reports of more natural hazard than I already expected.

Until now I have innocently expected that "weatherproof boxes" really are (weather proof). I imagined that lightning, wind, falling trees and larcenous humans were the common dangers.

I have fantasized about installing the things in tents, tool-sheds or dog houses to conceal them and even provide a luxury to the technician  (myself) out there tuning things in sub-zero weather.

Astounding are your reports that large industrial applications of outdoor enclosures are prone to failure. That essentially tells us that you can't fool mother nature; she's a sly devil out to ruin our plans.

My outdoor plans are suspended until further thought.

Carl Blare

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