We've just installed an ERI A-3 Lightning Spur kit at the top of our 500 foot tower. It has been recommended that we move our 6 bay antenna three feet down from the top of the tower as a safety precaution from lightning, even with the A-3 Lightning spur kit. I hate to lose any antenna height. Your thoughts?
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Antenna Height Question
- Thread starter shreveville
- Start date
Agree with jboyd. Incidentally (IIRC), ERI wants you to have at least 5' of clear tower above & below a 1/2 wave antenna and 10' above & below a full wave spaced antenna. So if you have the antenna even with the tower top, you 'might' get better performance by dropping it down.
3' or even 5' isn't going to make a hill of beans difference in your signal. Which would you rather have? The extra 3' or 5' and the "feeling" that the signal is going farther with a smoked transmitter because of a direct lightning hit OR be down 5' and not have to replace a very expensive transmitter.
You decide...
You decide...
WNTIRadio - good point. That's why I wanted to get your input. 
Shouldn't there be CP for changing HAAT? How strict is the FCC on such matters?
TomT said:
I think it's + or - 2 meters for primary services and 1 meter for translators and LPFM. No need for a 301 or 314 if you're within those parameters. In any event, 3 or 6 feet will make no difference to most stations. If yours is a typical installation, you will loose no coverage.
1/4 wave shorted stubs are also nice to have on your antennas. I used to put them on all of the stations I did.
They'd come a lot closer to giving a licensed station hell for being a few feet higher or lower than what their supposed to be, or the coodinates off a bit than some pirate. Can you say "deep pockets" that hold a license and therefore are a target for a fine that's collectable? Yup! Welcome to today's FCC. It's all about the bread, not about what's right or wrong. Keep that paper tiger feed up boys. Tech specs be damned, the paperwork and nit-picking details MUST be in order or it's an opportunity for the EB. I'd hate to see today's EB personel try to repair a toaster these days. They'd either shock themselves or burn the damn place down. How has things got this bad? Yeah... Congress which is full of lawyers have pretty much demanded the FCC become a money maker. It was all downhill from there.
N
necrat123
Guest
73.1690(c)(1) states:
Replacement of an omnidirectional antenna with one of the same or
different number of antenna bays, provided that the height of the
antenna radiation center is not more than 2 meters (6.58 feet) above or 4 meters (13.124 feet)
below the authorized values.
They still want to see you file paperwork for the change, but this would be a simple license modification to do so.
Replacement of an omnidirectional antenna with one of the same or
different number of antenna bays, provided that the height of the
antenna radiation center is not more than 2 meters (6.58 feet) above or 4 meters (13.124 feet)
below the authorized values.
They still want to see you file paperwork for the change, but this would be a simple license modification to do so.
A 6 bay is 60 feet, then add the tuning stub. COR is the middle. Is this HAAT or HAMSL? Typical values of License are based on contour protection in some cases. This isn't replacing the antenna.
At the station in Evansville in the ERI homeworld the antenna is next to the thing.
Look at the liability of moving a 6 bay antenna. And add replacing the flange because the line is too far up the tower.
At the station in Evansville in the ERI homeworld the antenna is next to the thing.
Look at the liability of moving a 6 bay antenna. And add replacing the flange because the line is too far up the tower.
I am not sure how long all tuning stubs are. I found one a few weeks ago that is 10 feet long. I am reworking an 8 bay. The entire length is 60 feet with the stub, not without. It uses 1 5/8 inch rigid. An old ERI.
A call to ERI would find out quickly for you. If memory serves, the matching sections were normally about 6 feet long. An 'old ERI', is this a G-5 (rototiller style) or a G4 (Ring with vertical ends style)? The G5s were normally built as 50 ohm bays, with the array transformed to 50 ohms total by the use of the tuning section, which has steatite slugs on the inner, the spacing and width being determined by several factors including frequency and number of bays. The G4s had varying bay impedances depending on the number of bays in the array, the impedance being controlled by the balun inners on each bay which varied in dimensions. In other words, as Elemer said, be vewwwy vewwwy careful playing around with the G4s.
In any case, the price of having someone tune the array in place to 50 j0 is worth it.
In any case, the price of having someone tune the array in place to 50 j0 is worth it.
Many years ago, we took down an ancient 10-bay G4 and cut it down to 6 bays for use as an emergency antenna after a tower collapse. The 10-bay was too big to fit on the available tower. As I recall (and memory is pretty fuzzy about it), each bay was about 300 Ohms, so six bays had a nearly 50 Ohm impedance. ERI sent us a new matching section which had steatite slugs in it so that we could field adjust it. That antenna worked quite well.
The input Z of each ERI FM sidemount element as used in FML, FMH etc arrays and their CEC equivalents is based on the number of bays in each section.
For end-fed arrays of n elements (8 max), each element has an input Z of n x 50 ohms. When they are paralleled into the vertical 50-ohm spine this results in a nominal 50 ohm input impedance at the input flange for the array, just below the bottom bay.
The input Z of each element of a center-fed array is set to a value that results in a 50 ohm Z at the input to the tee feeding the upper and lower sections of the array.
A 6-ft matching section at the input connector is supplied by ERI, and used to fine match the complete array to a 50 ohm transmission line, so as to compensate for the detuning effects of the mounting environment.
For end-fed arrays of n elements (8 max), each element has an input Z of n x 50 ohms. When they are paralleled into the vertical 50-ohm spine this results in a nominal 50 ohm input impedance at the input flange for the array, just below the bottom bay.
The input Z of each element of a center-fed array is set to a value that results in a 50 ohm Z at the input to the tee feeding the upper and lower sections of the array.
A 6-ft matching section at the input connector is supplied by ERI, and used to fine match the complete array to a 50 ohm transmission line, so as to compensate for the detuning effects of the mounting environment.
I have been using a ham radio MFJ device for checking all my broadcast antennas. Most of the antennas I use are the low power OMB. Tuned from the factory means nothing as they never are. Tuning on the tower is the best. This doesn't work with the ERI obviously.
This antenna is end fed 8 bay with the vertical stubs.
This antenna is end fed 8 bay with the vertical stubs.
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