The
controversy seems to come from the interpretation of the rules, and what
applies to who.
One rule, 73.1692, is for
broadcasters, and applies primarily to their directional antenna systems.
The rule is listed under Part 73, Radio Broadcast Services; Subpart H, Rules
applicable to all Broadcast Stations.
The other rule, 22.271, is from the
Telecommunications Commission; Public Mobile Services. This rule would seem
to apply to Cellular and PCS Carriers, and towers constructed for those
Carriers. They are one section Public Mobile Services, and they are not a
Broadcast Station by any stretch of the imagination.
There are really
two major differences in the two rules.
1. One is
the distance that coordination is required. 73.1692 specifies a distance of
3.2 kilometers for directional
broadcast stations, while 22.371 specifies a distance of 3.0
kilometers for directional broadcast stations. For
a non-directional broadcast station, the distance under 73.1692 is
0.80 kilometers, while under 22.371 it is 1.0
kilometers.
2. The second major difference is what is required in respect to
field strength measurements. 73.1692 requires
a Partial Proof of Performance (eight measurements on each of the
monitored radials, with a minimum of four
radials - for a total of at least 32 field strength measurements)
for both pre- and post-construction. 22.371
only specifies that "measurements" need to be taken on both pre-
and post-construction. It should be pointed
that approximately five years ago, 22.371 did specify that a
"Partial Proof of Performance" was required, but
that was changed to just "measurements", which then allow it up
to the discretion of the consulting firm in
conjunction with the radio station as what "measurements" would
be taken.
I believe it is necessary to look at the intent of each of the rules.
73.1692 is a rule that applies to broadcast stations.
The beginning of the rule refers to when the addition of antennas, changes,
and even major repairs that are made on the directional antenna, that a
Partial Proof of Performance is required. There is a reason for this.
Making changes directly on a tower that is part of an directional array can
change the impedance of the tower, and the mutual impedance of the system,
all of which can directly affect the actual shape of the directional antenna
pattern. In this case, the only way to insure that the pattern is working
properly is probably with a Partial Proof of Performance. This rule has
been in effect for many years. Many years ago FM antennas were routinely
added to AM towers, and I am certain this had a bearing on the need for this
rule. The latter part of 73.1692 does refer to when towers are constructed
near a broadcast array, but the distance to when coordination is required is
different from 22.371. I tend to believe this rule applies to when a
broadcast station adds towers that would affect either their own pattern, or
that of another broadcast station. (Example - a new FM station builds a
tower within 3.2 kilometers of an existing AM directional broadcast
station. In this case, the new FM station would be responsible to conduct a
Partial Proof of Performance on the existing AM station). In other words,
the rule applies to Broadcast Station to Broadcast Station (both of which
operate under Part 73), not Broadcast Station to Public Mobile Service. I
maintain this position because the rule refers to "broadcast station or
permittee (permittee being a broadcast entity that holds a construction
permit to build either an AM, FM or TV station)
Now, consider 22.371. When cellular first started, a number of cell towers
were being constructed, affecting AM broadcast station patterns. However,
these facilities did not fall under Part 73 (obviously, they were not radio
or TV stations), therefore, the stations had to file a complaint with the
Commission, or take other legal action. Thus, the need for a rule that would
make Public Mobile facilities responsible not to cause a problem with the AM
broadcast stations. When the rule first started, it also said that Partial
Proof of Performances were required for both pre- and post-construction.
However, they placed a undue burden on the Public Mobile Service because
many of the towers constructed were in the stations pattern minimum, or were
very short, inefficient re-radiators. There was no need to spends tens of
thousands of dollars to take over a hundred field strength measurements when
it was known that the tower would have no effect on the AM station. Thus,
the rule was changed to read that "measurements" should be taken to insure
that there was no effect. Depending on the situation, often Monitor Points
only will suffice as adequate measurements, on a few measurements on a
monitored radial, but rarely will a full Partial Proof of Performance would
be required. I believe it is important to realize that the Commission did
drop the requirement for a Partial Proof, even though many consultants and
broadcast engineers often demand that these be taken. The rule does specify
that the station must be notified, and at this time it can be spelled out
what measurements will be taken for the pre- and post-construction
measurements.
There are a
couple of important points about this rule. One is that the AM station
should be notified prior to construction. This way, any issue regarding
field strength measurements can be resolved prior to the construction of the
tower. I believe a Certified Letter to the stations General Manager or
Chief Engineer is in order. The other important point is that some type of
pre-construction field strength measurements should be taken. If no
pre-construction measurements were taken, you would have no reference point
and post-construction field strength measurements would be meaningless.
