The AM Forum

I don't know if we should be concerned about this or not.  I know that new cell tower construction is really the target here and they have been voluntarily coordinating for awhile, but unintended consequences of this rulemaking could be an effect on amateur antennas and other structures.

http://forums.qrz.com/showthread.php?t=192653

73,  Jack, W9GT

Hi Jack,

Hopefully, it appears that unless someone is within the pattern forming area of a commercial broadcash stations's antenna array, there is no problem and the old rules would still apply.

I would think that if someone were at least two miles away, there would be no interaction requiring detuning a ham tower.  But it all depends on what direction we are in the pattern and where the lobes and nulls lie. 

Worst case, detuning a tower for the BC band is a minor operation. (Unless they require THEIR apes to do it for big $$)   :o

Tom, K1JJ

Hi Tom,

Yes, well it looks like it is dependent upon the freq of the AM station and the distance in wavelengths from the antenna(s), not just the mileage.  I'm about a mile or so from a 4-tower directional 3KW religious station on 1090 KHz.  It is most likely a low-budget operation...so I wonder if there is any need to be concerned about it.  The point is....I was here first!!  My tower was in place long before that station went on the air....now do I have to coordinate every time I hang an antenna on my tower or effectively make it higher?  My tower is 80 ft high + mast and antennas that make it about 90+ feet tall overall.  I'm not in the near field and there is a lot of other ground clutter, but depending on where they measure the field strength for the proof of performance for the directional pattern, they would probably "see" my tower.

I was contemplating putting folded unipole skirt wires on my tower anyway and tuning it for 160M, however, I'm wondering if that would also make it invisible to the broadcast station's pattern?  Would you tune the tower at their freq or away from their freq to make it invisible to their pattern?

73,  Jack, W9GT

Jack,

Yes, 550 khz and 1600 khz are a long percentage apart and would affect the wavelengths and distance markedly - good point.

From my own ham experience de-tuning my towers so they don't affect the 160M vertical array, I tuned them so they are not resonant anywhere near 160M.  This was done with a vertical wire attached somewhere near the top of the tower and pulled out a few feet - and run to the ground and L/C tuned for the desired freq. (Away from the freq NOT to be affected)  There's stuff on the web for procedures to do this.

Yes, if you tune your tower for resonance on 1900 khz, chances are you will be away from the 1090 BC band - including beam capacitance loading and non-resonance effects.   


Bottom line: I would just keep doing what you're doing and let them continue to make their periodical field pattern tests. Chances are they will never contact you cuz your tower has no effect on their pattern.  Even though 1 mile is close, the chances of all the factors lining up to cause a problem are small, in my opinion.  Even if it does, it's easy to cure.

Maybe some of the BC pros here will add their opinions too.

T

Yes, I think you are correct Tom.  I'm not going looking for problems.  Anyway, it seems that this ruling would apply to commercial licensees who include the characteristics of their antenna systems in their license applications and are granted operating authority based on those submissions.  Ham's stations are not licensed in that way.  We only need to abide by over-riding concerns, such as FAA rules/restrictions which require special considerations when near airfields or when antenna structures exceed 200 ft. in height.

73, Jack, W9GT

The wording of the FCC release seems to refer to new tower construction or alteration of an existing tower.  It appears that if a new AMBC station is built near an existing tower, the burden of bringing that tower into compliance would fall on the AM station owner.  But if a new tower goes up in the vicinity of an existing AM station, the burden would fall on the owner of the new tower.

I wouldn't worry about it until someone notified me  that there was a problem.  This rule  has been around for a  long time, but I have never seen anything pertaining to it in Part 97.

Yes, I have been aware of voluntary coordination efforts with cell towers that have gone on for some time.  I'm not concerned about it from the standpoint that my tower was here first anyway, however, I am always changing stuff on the tower which could definitely change its resonance characteristics, like adding and removing antennas, putting more stuff on top, etc.  Don't want to be in a situation of having to coordinate stuff like that!

73,  Jack, W9GT

This is related to how AM stations measure thier patterns. The rules were changed so that computer modeling can be used to check the performance of an array instead of performing proof of performances or partial proof of performance field strength measurements.. The rules as far as towers within the specified radius' don't change, just how they measure what effect those change are. If anything, the dope in the QRZ article may want to keep his mouth shut. These rules were already in place, and would bring alot of unwanted attention to amateurs. Let sleeping dogs lie.

Yeh Jack, I wouldn't spend any time worrying about this.  You are too far from the BC station to cause a problem.  Your antennas aren't the correct length to re-radiate any energy at their operating frequency and, IMHO, the BC owners would have to establish that you are effecting their pattern.  Besides they are going to computer modeling, instead of field measurements  (Method of Moments - based on measured current and phase in their array) and unless your system effects their current and phase measurements, they will never know you are there.  Keep on cranking out the RF --- who listens to that "talk radio" broadcast AM crap anyway. Real AM is on the ham bands... 73 Jeff  ;)

Besides Jack, it is a religious broadcaster.  They won't bother with the FCC and will just send a lightning bolt your way instead  ;)

Rodger WQ9E

This rule has been around forever.  It is an extremely remote possibility you will ever be affected.  If your tower existed before the station, they adjusted for it when they did construction and proof of performance.  Frankly this is not something I would ever worry about.  Only worry if a BC engineer shows at your door complaining.

If your tower was there first, ask him what he is going to do to fix it, if you are the new one, tell him you will work with him.