Setting new precedent for outdoor Part 15, From Keith Hamilton

[Flying-Dutchman]

The current Administration and the FCC are very pro low power
radio. But, they have their hands tied by congress. They have
been told that they must do more extensive studies before they
can open a new filing window. This may mean many years delay
in getting new service to the public. There have been very few
chances for US citizens to start new stations in the last 15 years.

So, I think they might smile upon the idea to modify part 15 AM.
I think we have the best chance if we propose type certified transmitters and request the ground lead restriction be relaxed. After all, there are safety issues involved.

Under the current part 15, some people can say they bought a type certified transmitter and attached it to an existing surface and the FCC says, case closed. There is a loophole that allows guys who
do not possess a lot of engineering expertise to get some extra range.

But Rich, the FCC feels that engineers like you and me have expertise
and it is we who must abide by field strength when using part 15.
The spirit of the part 15 rule was really for the average Joe to play
with radio. And, guys who possess a field strength meter are expected
to use it and shouldn't use the alternative rule 15.219.

 

[rfry]

Under the current part 15, some people can say they bought a type certified transmitter and attached it to an existing surface and the FCC says, case closed.

Not always, it appears. For example, below is a link to an NOUO for a Part 15 AM whose "ground" consisted of an existing water tower. Common belief is that the transmitter involved was certified for Part 15 AM.

http://www.fcc.gov/eb/FieldNotices/2003/DOC-297435A1.html

There is a loophole that allows guys who do not possess a lot of engineering expertise to get some extra range.

Is that fair to the experts who also want to get some extra range ???

And, guys who possess a field strength meter are expected to use it and shouldn't use the alternative rule 15.219.

Just to note that the r-f noise level in the AM broadcast band is higher than the field intensities allowed under 15.209, except in a screened room. So an operator with a calibrated field intensity meter could not use it to prove compliance with 15.209.

When the FCC cites a Part 15 AM operator in reference to 15.209 it is for a field intensity that greatly exceeds the limit under 15.209.

RF

 

[Flying-Dutchman]

Under the current part 15, some people can say they bought a type certified transmitter and attached it to an existing surface and the FCC says, case closed.

Not always, it appears. For example, below is a link to an NOUO for a Part 15 AM whose "ground" consisted of an existing water tower. Common belief is that the transmitter involved was certified for Part 15 AM.

http://www.fcc.gov/eb/FieldNotices/2003/DOC-297435A1.html

This one is a gray area. In the test he removed the ground lead.
So, how was this water tank radiating? Was it inductive coupling
from a power supply or audio lead? He did mount the device on
an existing surface. There are reasons why this could qualify
for 15.219.

There is a loophole that allows guys who do not possess a lot of engineering expertise to get some extra range.

Is that fair to the experts who also want to get some extra range ???

The FCC could go this way. But, they never have before. To get cited
like this, one would need to be bragging about his expertise and be very rude to the inspector. It wouldn't be very bright to brag about great range and showing off that expensive field strength meter.

And, guys who possess a field strength meter are expected to use it and shouldn't use the alternative rule 15.219.

Just to note that the r-f noise level in the AM broadcast band is higher than the field intensities allowed under 15.209, except in a screened room. So an operator with a calibrated field intensity meter could not use it to prove compliance with 15.209.

When the FCC cites a Part 15 AM operator in reference to 15.209 it is for a field intensity that greatly exceeds the limit under 15.209.

RF

The rules need to be modified and made more uniform so that we
can have more low power broadcasting. Broadcasting is beginning to
turn it's back on our generation. Low power AM might save the AM
band for some time.

And finally, it's not that hard to work with the FCC. If there are rules you don't like, you have the right to petition to change them. You
will win some. You will lose some. But, sometimes you win just because you tried. There are many at the FCC in favor of low power radio.

 

[wkbam1690]

But Rich, the FCC feels that engineers like you and me have expertise
and it is we who must abide by field strength when using part 15.
The spirit of the part 15 rule was really for the average Joe to play
with radio. And, guys who possess a field strength meter are expected
to use it and shouldn't use the alternative rule 15.219.

I believe there is a legal principle called equal protection under the law, where all laws must be applied equally, regardless of an individual's circumstances...

 

[Flying-Dutchman]

But Rich, the FCC feels that engineers like you and me have expertise
and it is we who must abide by field strength when using part 15.
The spirit of the part 15 rule was really for the average Joe to play
with radio. And, guys who possess a field strength meter are expected
to use it and shouldn't use the alternative rule 15.219.

I believe there is a legal principle called equal protection under the law, where all laws must be applied equally, regardless of an individual's circumstances...

Maybe, broadcasting should be a right. But, currently it falls under
the category of privilege. A drivers license is also a privilege. Under
a privilege you do not have the same expectation as you would with a right.

The FCC can always find a violation at any and every radio station.
So, it's best to be friendly when they drop by. I've known inspectors
who let the operator fix problems in front of their face and even lent a
hand. Some of them have quite a sense of humor.

 

[Ermi Roos]

The Canadian version of Section 15.219 rules (Industry Canada RSS-210, Section A2.2) has an alternative field strength limit (when the 100 mW and/or 3 meter rule is not met) that is more reasonable than the one given in 15.209. It is 250 uV/m at 30 m. This is only about a tenth of the field strength that can be easily achieved by a 15.219 station mounted at ground level, but it is at least greater than the field strength of the usual background noise in the AM BCB. The Canadian rules (like the US rules) do not say that you have to use the alternative field strength limit if you own a field strength meter.

Don't be fooled by an inspector's pleasant demeanor. It is a survival technique. He is unarmed, and he doesn't know what kind of person he is confronting.

 

[pianoplayer88key]

And, guys who possess a field strength meter are expected to use it and shouldn't use the alternative rule 15.219.

Just to note that the r-f noise level in the AM broadcast band is higher than the field intensities allowed under 15.209, except in a screened room. So an operator with a calibrated field intensity meter could not use it to prove compliance with 15.209.

When the FCC cites a Part 15 AM operator in reference to 15.209 it is for a field intensity that greatly exceeds the limit under 15.209.

RF

So what would be average noise levels in the AM band? I would think it's well below 100 microvolts/meter, due to the fact that I have logged stations around noon well outside radio-locator's predicted 0.15mV/m contour. For example, from near La Mesa / El Cajon, CA, I can usually hear 950 KIXW Apple Valley, CA, every day. I have also heard 700 KALL North Salt Lake City, UT, and 1530 KFBK Sacramento, CA, a few times around noon (KFBK usually only in winter though). I am about 33% farther than KIXW's 0.15mV/m estimated contour, and about twice as far for KALL and maybe farther for KFBK. I also know of someone on here (rbrucecarter5 - haven't heard from him in a long time though) who has received 50kW stations from Chicago in Texas in the daytime using a few foot diameter loop antenna. I can hear KIXW barefoot on my PL-380, and KALL was heard with the Select-A-Tenna by carefully nulling a local 77kW station on 690. KFBK was also heard with the SAT, but was strong enough that the signal could be faintly detected without it.

 

[Ermi Roos]

Most of the backround noise in the AM BCB is man-made, such as from automotive ignitions. It is lower in rural areas, and highest in built-up downtown areas. In my area, which has single-family residences within the borders of a big city, the background noise is in the vicinity of about 150 uV/m.

I made a small loop antenna with known antenna current to generate a field strength of about 15 uV/m at 30 m. The modulation was 100 % with a 1 kHz tone. I was just barely able to detect the presence of some sort of signal at 30 m using a car radio. The signal would not have been able to transmit any intelligence.

 

[wkbam1690]

The rules need to be modified and made more uniform so that we
can have more low power broadcasting. Broadcasting is beginning to
turn it's back on our generation. Low power AM might save the AM
band for some time.

And finally, it's not that hard to work with the FCC. If there are rules you don't like, you have the right to petition to change them. You
will win some. You will lose some. But, sometimes you win just because you tried. There are many at the FCC in favor of low power radio.

I'm afraid if there are any modifications made to Part 15 it will only result in more restrictive requirements...it wouldn't surprise me if they eliminated the 100 mw provision and left only the field intensity requirements.

 

[pianoplayer88key]

Aren't there separate part 15 rules for unintentional and incidental radiators vs. intentional radiators?
I think the intentional radiator rules should be relaxed across the board.
However... I really think the FCC dropped the ball with the unintentional radiator rules. For one thing, they aren't nearly restrictive enough, and also I suspect that the FCC is lax on enforcement. As for what the rules should be... I'm not going to specifically specify field strengths, as I'm not sure what they would work out to. However, I will say that the limit should be at least 120dB below the lowest naturally-occuring noise (atmospheric, galactic, etc), as measured at the edge of the device from which the unintentional radiation emanates, with any insulating cover removed. For example, extending a longwire beverage antenna into a large, typically "noisy" factory tool should not get any detectable signal, even if you use a few Hz wide receiver bandwidth with a BFO to try to coax out the weakest signal possible. Also, no noise at all should be picked up from high-voltage cross-country power lines, even if your antenna is directly touching them.

And another question (although this may be a bit off-topic for this board (and would probably be better in DX & Reception or someplace like that)).... So how would the LW, AM, SW, FM, TV radio broadcast landscape change if the separation rules were made more strict? For example, let's assume that you're using a radio that has the best sensitivity possible (with a longwire or high antenna, for example), along with the worst selectivity possible (preferably something that would make a crystal set without any tuning on the antenna seem like a few tens of Hz wide QRSS CW (or is there another mode that's capable of being detected even with a weaker signal?) DSP filter by comparison). Under NO circumstances should you EVER be able to detect two signals at the same time, including the most efficient possible basic signals (whether that would be few-Hz QRSS CW or something else, I'm not sure). That INCLUDES adjacent-channel interference, intermods, harmonics, and co-channel interference from groundwave, normal skywave, e-skip, tropo ducting, etc. Assuming that whatever signals had been on the air are "grandfathered" in and all others that wouldn't meet those new no-interference requirements, what would be left on the air?

 

[Ermi Roos]

There has been some criticism of the use of simulation programs to evaluate the performance of antenna types. It has been said that field tests should be used instead of simulation. It is no wonder that simulation is used so much these days. Thanks to the availability of computers and software, it is now the easiest part of the antenna design process. Previously, simulation was nearly impossible to do because of the incredible mathematical difficulties associated with antenna analysis.

The object of antenna design is to construct functioning antennas. The process begins with a concept, which is then simulated using NEC (usually), or sometimes wipl-d, if sufficient funding is available to buy the software. Then the antenna is constructed and tested. The value of the simulation step is that many unworkable ideas can be rejected quickly prior to construction. For hobbyists, the equipment (FSM) is simply not available for proper testing. About the best the hobbyists can do after the concept phase is simulate using NEC, and then construct. After construction, the testing would consist of trying to determine the range, which is very inexact measurement.

The hobbyist has to rely heavily on simulation when designing antennas, because there is not a lot of field testing that he can do.

 

[rfry]

... About the best the hobbyists can do after the concept phase is simulate using NEC, and then construct. After construction, the testing would consist of trying to determine the range, which is very inexact measurement.

Measuring the groundwave field intensity of medium-wave signals has some margin of error, mostly related to the specifications of the measuring instrument. However experience in the AM broadcast industry shows that such measurements should not always be considered as very inexact.

In the case of the first NOUO issued by the FCC to KENC, it is surprising how closely the field calculated by NEC can agree with the field measured by the FCC for that installation -- when using reasonable values for the NEC input parameters.

Here is a paste from that NOUO (http://www.fcc.gov/eb/FieldNotices/2003/DOC-294572A1.html ):

The field strength of the signal on frequency 1620 kHz was
measured at 4000 microvolts per meter (uV/m ) at 137 meters, which
exceeded the maximum permitted level of 14.8 uV/m (24,000/1620) at
30 meters established in Section 15.209(a) of the Rules (See 47 C.F.R.
S:15.209(a)).

In addition, Section 15.219(b) of the Rules states "the total length of
the transmission line, antenna, and ground lead (if used) shall not exceed
approximately 3 meters." During the inspection on October 20, 2009, the
agent observed that the vertical whip antenna used by the station was
approximately 3 meters long, however, the referenced antenna's ground lead
was attached to an unshielded radiating metal tower in which the height of
the tower measured at approximately 40 feet long (12.2 meters). This
antenna installation violated Section 15.219(b) of the Rules. See 47
C.F.R. 15.219(b).

Below is a paste from the output of a "Demo" (free) NEC program. The input parameters were set for the KENC 40-foot tower and 3-meter whip. Transmitter output power and resistive losses were set to values within the range of "typical" for such an installation.

EZNEC Demo ver. 5.0

KENC on 40 ft Twr 7/23/2010 6:00:25 AM

--------------- ANTENNA DESCRIPTION ---------------

Frequency = 1.62 MHz
Wire Loss: Zero

--------------- WIRES ---------------

No. End 1 Coord. (m) End 2 Coord. (m) Dia (mm) Segs Insulation
Conn. X Y Z Conn. X Y Z Diel C Thk(mm)
1 GND 0, 0, 0 0, 0, 15.2 15 19 1 0

Total Segments: 19

-------------- SOURCES --------------

No. Specified Pos. Actual Pos. Rel Amplitude Phase Type
Wire # % From E1 % From E1 Seg (V/A) (deg.)
1 1 80.00 81.58 16 1 0 I

-------------- LOADS (R + jX Type) --------------

No. Specified Pos. Actual Pos. R X
Wire # % From E1 % From E1 Seg (ohms) (ohms)
1 1 80.00 81.58 16 10 3451.2
2 1 0.00 2.63 1 50 0

No transmission lines specified

No transformers specified

No L Networks specified

Ground type is Perfect

--------------- NEAR-FIELD PATTERN DATA ---------------

Frequency = 1.62 MHz
Power = 0.03 watts
Max field = 4.17227E-03 V/m RMS
at X,Y,Z = 137, 0, 0 m

Electric (E) Field (V/m RMS)

X (m) Y (m) Z (m) Ex Mag Ey Mag Ez Mag Etot
137 0 0 0 0 .00417227 .00417227

The field of approximately 4,172 uV/m calculated for 137 meters from the transmit antenna by NEC is very close to the 4,000 uV/m measured field that the FCC reported in their NOUO.

Going back to the experience of the consultants who design and prove the performance of the directional broadcast antenna arrays used by many AM stations, the field intensity values measured after installation and commissioning agree within a few percent with the original NEC calculations for the array.

RF

 

[Ermi Roos]

I would attribute the closeness of the measured and calculated field strengths to dumb luck. The FCC field strength measurement is given to only one significant digit.There is a building (Ken's music store) right at the side of the tower, which is not accounted for in the simulation. The antenna is in the commercial area of Stayton, OR, not in an open field. The assumptions made in the analysis are guesses. It is misleading to imply that NEC will give such a close comparison (within a bit more than 4 %) in other situations.

 

[rfry]

Medium-wave signals are not much affected by buildings of the size and construction common in metropolitan areas. If they were, then the daytime signals of licensed AM stations would be greatly affected after crossing major metropolitan areas like Chicago. Their measured fields do not show this.

Below is a link to a graphic showing the path to one of the monitoring points for the directional pattern of WIND in Chicago. The field at that monitoring point must be within the limit shown on the station license. As is seen in the graphic, the path to that monitoring point crosses many structures, including a rather large commercial building.

The nighttime field limit for that monitoring point based on the directional pattern licensed by the FCC is:

Radial Distance From Transmitter Maximum Field Strength
(Deg. T) (km) (mV/m)
154 3.22 36.92

The description given to locate that monitoring point as shown in the station license is:

Direction of 154° true North. Starting from the transmitter proceed south on Colfax Street for a distance of approximately 1.9 miles to the intersection of W. 45th Ave., and Colfax. Turn left onto W. 45th Avenue and proceed East for a distance of approximately 0.5 mile to the intersection of Burr Street and W. 45th Avenue. Turn left onto Burr Street and proceed North on Burr then follow curve East on 44th Ave., to dead end. The point is by the South-East point of House 5312.

Medium-wave fields are not overly difficult to measure with the accuracy needed to prove compliance with a directional pattern licensed by the FCC, even when the array is located in/near a major metro area.

http://i62.photobucket.com/albums/h85/rfry-100/WIND_Mon_Pt.gif

RF

 

[Ermi Roos]

Just the potential error made in the assumptions guessed at in the analysis could have produced a lot more than the 4 (or so) percent difference that was obtained.

 

[rfry]

Just the potential error made in the assumptions guessed at in the analysis could have produced a lot more than the 4 (or so) percent difference that was obtained.

All I wanted to show by my NEC analysis of KENC vs. their first NOUO was that it is possible to produce the field intensity measured by the FCC at the radius distance it was measured -- using NEC input parameters that can be considered reasonable for the Part 15 AM setup reportedly used by KENC.

RF