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#31612 11/28/03 07:46 AM
Joined: Dec 2000
Posts: 4,291
Member
I'm not very knowledgeable about radio antennas, but I know some of you are. Here goes:
We're building a new BMW dealership right next to the KNX-AM (as in major powerful)radio antenna.
The antenna currently has conductors just under the surface of the ground, in a radial array, 1 every 1-1/2 degrees (240 in all).

Our specs include an underground ring of bare 2/0 around the building, with exothermic welds to the rebar every 4', and about 30 ground rods. It will involve about 2700' of conductor, and maybe 400 cadwelds. This is then to be connected to the underground array of the antenna.

I've been told that the portion of the antenna that we see is only 1/2 the antenna, and that since we're building on top of the old underground array, we've got to replace what we're disturbing.

Anybody have ideas? I don't...S

#31613 11/28/03 09:52 AM
Joined: May 2001
Posts: 717
G
Member
Major powerful indeed, 50k is one monster station. Hey, take pics of what you find, first, it documents your progress, and second, WE wanna see it, ya got lots of antenna buffs here.

The radial system SHOULD be a tuned system, though with 50 k, who cares if your slightly out. I can't imagine anyone wanting to de-tune part of his system.

With your close proximity to the antenna, you NEED to attach to the station ground, but I would not allow you to attach to my radials.

If the radials were properly installed copper, they should be fine forever, and what you are doing should have no detrimental effect on them.

Frankly, it sound to me like someone knows these radials are defective and wants you to fix it.

This antenna is grounded, the guy wires will be grounded, if you attach anywhere on this system, you would be covered.

Still, with a 50k antenna over the dealership, you're gonna have a lot of RFI "ghosts" to deal with, if not some downright interesting problems.

Short answer, I don't feel you should be attaching to the radials, and you should not injure them to the point that you have to replace them if you do. I would discuss this with the station engineer if they insist on your continuing. BTW, the FCC database should list the station licensee and the engineer, I didn't look it up, but may get back to it.

Ya know, it IS the day after Thanksgiving, and I AM out of coffee here, SOME things DO take precedence. [Linked Image]

#31614 11/28/03 10:30 AM
Joined: May 2001
Posts: 160
C
Member
I agree with George in the sense that I would not connect the BMW bldg ground to the radio station ground radials.The grounding system for the station also called a counter poise, is considered electrically the "other half" of the antenna and like George said is part of the antenna tuning.This is an issue to consider carefully because of the power levels(50Kw).
Chris

#31615 11/28/03 10:50 AM
Joined: Apr 2001
Posts: 507
G
Member
A very interesting situation. Certainly not one you run across everyday.

I don't know that much about radio antennas, so I can't even guess what the proper action would be. If I were in your shoes, I would ask for specific instructions from the project electrical engineer and follow them to the letter. It's really his responsibility to make sure this is done right.......yours is to follow his directions.

GJ

#31616 11/28/03 12:41 PM
Joined: Aug 2002
Posts: 1,081
T
Member
CBS Inc - KNX Am Radio, General Offices, KCBS TV Channel 2
6121 West Sunset Boulevard
Los Angeles, CA 90028
323-460-3000

Quote

KNX CA LOS ANGELES USA
Unlimited

Licensee: INFINITY BROADCASTING OPERATIONS, INC.

1070 kHz Licensed
Domestic Station Class: A Region 2 Station Class (corresponds to W. Hemisphere): A
Coordination Status: Canada: - Mexico: - Region 2: -
File No: BL-- Facility ID No.: 9616
CDBS Application ID No.: 306961

33° 51' 35.00" N Latitude Power: 50.0 kilowatts (kW) Unlimited
118° 20' 56.00" W Longitude (NAD 27)

ND1 - Non-directional Antenna: Same constants day and night

RMS Standard: 0.00 mV/m at 1 kilometer
RMS Theoretical: 400.73 mV/m at 1 kilometer

1 tower CDBS Ant. System ID: 6777

Tower information: Tower No. Field Ratio Phase (deg) Spacing (deg) Orientation(degrees) Electrical Height (deg) Twr Ref. -No Top Loaded or Sectionalized Tower(s)- Antenna Structure Registration Number (#0) A B C D
1 1.000 0.00 0.00 0.00 193.50 0 0 0.00 0.00 0.00 0.00

Call Sign: KNX
Facility Id: 9616
Community of License: LOS ANGELES, CA
Service: AM
Fac Type:
Status: LICENSED
Status Date:
Frequency: 1070
Channel:
Digital Status: Hybrid
Lic Expir: 12/01/2005
Licensee: INFINITY BROADCASTING OPERATIONS, INC.
Address: 2000 K ST NW STE 725
Address 2:
City: WASHINGTON
State: DC
Zip Code: 20006
Phone Number: (202) 457-4505


[This message has been edited by ThinkGood (edited 11-28-2003).]

[This message has been edited by Webmaster (edited 12-11-2003).]

#31617 11/28/03 03:10 PM
Joined: Dec 2000
Posts: 4,291
Member
I'm not sure that we are to be attached to the antenna's radials. I've just been told that it will be "connected to the antenna" (by others).

If we can simplify things to something even I can understand:
Is the radial array like the "dish" of the antenna, and the actual tower, sending the signal every direction, reflecting its signal from the radials?
See, I told ya' I don't know Jack, all I can relate to are the petals and the pistil of a flower, or my satellite dish.
KNX has a very knowledgeable (of course)
engineering dept. working as well on this. I can't imagine they'd sacrifice their signal. There's a good deal of new construction going on in the immediate area.

#31618 11/28/03 05:07 PM
Joined: Apr 2002
Posts: 2,527
B
Moderator
Good points have been raised in this thread, and this is certainly not an every-day issue for electricians.

One thing I would suggest is, after the new construction is up and running, that some measurements be made on “your side of the fence”, as to how much of the broadcast signal is being induced into, say, the building telephone/datacomm and paging system and various radio-frequency receivers on your site, that could be periodically tested should it ever become a problem. Some sort of AC-voltage benchmark{s} measured between the building ground ring and a remote electrode dedicated to that measurement may be appropriate.

The effects of intentional connection {or deliberate isolation} of the two grounding-electrode systems are not trivial and one practice versus another to inhibit interference will not be a precisely cut-and-dried task. [At first, It may be a fight with the architect to allow space, but an empty sheet of plywood at the building phone backboard/network cross-connects could prove irreplaceable for locating filtering components.]

No doubt the station engineers are very concerned as a “good neighbor”, but don’t forget that the dealership is the “new kid on the block” and must cope with the long-preexisting AM transmitter.

#31619 11/28/03 11:09 PM
Joined: May 2001
Posts: 717
G
Member
Electure,
Yup, ya got it dude. The radials are there to reflect the signal from the earth into the sky (but not STRAIGHT into the sky please [Linked Image] ). If they don't the earth will absorb a good deal of the signal, negating a lot of your output power.

Take that to heart when you uncover one of the radials....... there's 50k watts on the other side, so be darned careful.

BTW, I've never heard that station, being in VA, but I just sat here and tuned it and am listening to it now. NOW THAT's power!!!!!!!
I do have a bit better antenna than most I expect, but ya gotta admit that coast to coast is pretty impressive, just goes to show what 50k will do.

I expect you're gonna meet the guys from the station (or someone from the construction side will) so let us know how it comes out.

#31620 11/29/03 12:10 AM
Joined: Jul 2002
Posts: 8,432
Likes: 3
Member
George,
That's a very good point about the possibility of RF burns.
Is it possible that you can get RF burns from a tower like this by merely touching the tower and ground at the same time?.
I'm reminded of an incident in Australia, where a Base-Jumper, attempted to climb an AM transmitter tower and was burnt by the RF energy,from the tower?. [Linked Image]
Also, wouldn't the sheer power output from this tower "splatter" across the bands of any radio/TV in close proximity to the tower?.

#31621 12/11/03 08:15 AM
Joined: Dec 2000
Posts: 4,291
Member
Here's a picture of the footings:

[Linked Image]

Every rebar joint is welded. Our guys Cadwelded the copper conductors to short pieces of rebar, and the welders then welded the assemblies to the footings.
The stakes with the caution tape are where the conductors come up, to be connected at a later date...S

[This message has been edited by electure (edited 12-11-2003).]


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