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TIS on a water tank
- Thread starter xmtrland
- Start date
I'm pretty sure your installation wouldn't be any different than one on any other metal support structure (tower). I would still perform all the usual lightning ground protection for the antenna and install a good RF ground. Nothing special...
W
WCWalker
Guest
I think the maximum height that a TIS is permitted is just a hair under 50 feet.
A
Aljr
Guest
I was talking to an engineer buddy about a similar situation just the other day.(Large 30ft. city garage in a metal building.) I can't recall what his grounding solution was,but I'll be heading over to his place this weekend and I'll ask.
The guy is one of these characters that has forgotten more about RF design than most of us will learn in a lifetime. I've got to take notes to keep with him.
The guy is one of these characters that has forgotten more about RF design than most of us will learn in a lifetime. I've got to take notes to keep with him.
Well, I did some homework for you and found this link. The article includes reference to the FCC sections regarding TIS. It also states that the maximum antenna height is 15 meters.
www.radioedu.com/RG Articles/JAN-2004.pdf
Regarding your question about grounding, follow the local electrical code. Here #8 bare copper wire going to a 10 foot stake in the ground is a minimum requirement. No harm in using bigger (lower #) wire. In any case, the grounding should comply with the National Electrical Code (NEC).
Hope this helps.
Neil
www.radioedu.com/RG Articles/JAN-2004.pdf
Regarding your question about grounding, follow the local electrical code. Here #8 bare copper wire going to a 10 foot stake in the ground is a minimum requirement. No harm in using bigger (lower #) wire. In any case, the grounding should comply with the National Electrical Code (NEC).
Hope this helps.
Neil
I installed the first TIS for this community on a 35-foot phone pole. Five feet of the pole went into the ground leaving 30 feet in air. The TIS antenna was another 15 feet, but two feet of it are used for mounting the antenna to the pole, making the total antenna above the pole 13 feet. For a total above ground height of 43 feet above ground level. I’m hoping to get away with the same type of installation with about the same height minus the pole installation and ground radials.
Would the metal water tank provide a good enough ground plane or should I install about 30 to 40 radials 50 feet long like we did for the first one.
Would the metal water tank provide a good enough ground plane or should I install about 30 to 40 radials 50 feet long like we did for the first one.
xmtrland said:
You described installing the transmitter at ground level and using a short vertical radiator above the water tower so that the top of the short vertical is not higher than the 15 meter height allowed for TIS radiators. If you drive the base of the short vertical through a loading coil there, using a transmitter at earth level, and attach the braid of your coax transmission line to the water tower near the base of the short vertical, then the entire structure (water tower + short vertical) will radiate. In effect it will be an off-center-fed dipole.
Whether or not you can or should install buried ground radials depends on how well this composite antenna radiates. TIS rules limit transmitter power to 10 watts, and the (accurately measured) groundwave field strength at 1.5 km to 2 millivolts/meter. If the efficiency of the antenna system is high, then the transmitter power would have to be reduced so that the field strength limit was met. OTOH, if you can't reach the field strength limit with 10 watts of transmitter power you can't increase the power above 10 watts.
Probably the water tower structure itself is connected to the physical earth, but that wouldn't supply a good r-f ground. A good r-f ground for a vertical monopole requires radial wires extending in all directions from the base of the radiating structure, so that the displacement currents produced by radiation from the antenna can be collected and returned to the tx/antenna system with minimum loss. That loss is in series with the antenna current, and can have a large affect on radiation efficiency.
But a quick look with NEC for the configuration described shows fairly good radiator gain on 1650 kHz. Even if the r-f ground resistance was 100 ohms, it may take just a few watts for this system to produce the maximum legal field for TIS stations.
There is no clear answer here, but hopefully this information will be useful.
//
Speaking of TIS here's a little item from the CGC newsletter:
"The FCC has made "non-substantive" changes to a number of its rules. One change affects Travelers' Information Stations where Rule 90.242(a)(3) is being changed to read, "Travelers' Information Stations will be authorized on a primary basis on 530 kHz and on a secondary basis to stations authorized on a primary basis in the band 535-1705 kHz."
C5
"The FCC has made "non-substantive" changes to a number of its rules. One change affects Travelers' Information Stations where Rule 90.242(a)(3) is being changed to read, "Travelers' Information Stations will be authorized on a primary basis on 530 kHz and on a secondary basis to stations authorized on a primary basis in the band 535-1705 kHz."
C5
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