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Setting new precedent for outdoor Part 15, From Keith Hamilton

D

druidhillsradio

The Ken Cartwright (Filter) situation

We are setting precedent with all outdoor part 15 it seems, though I really haven’t been saying much about it, and I have not gotten any “official” word from the DC OET yet, (and may never) but, the agent there in Washing state seemed to find the ground AM1000FIL filter “very” effective, he spent the entire day testing it. The agent himself mention how “precedent setting” the event was. He is reporting everything back to the DC OET

I want to be clear there are two filters we offer, the AM1000FER filter, this is just a bulk inductance ferrite filter and offers really no lighting protection. There are instructions for building this on our website. Then we offer the new AM1000FIL fast transient response filter which offers excellent filtering AND good lightning protection. The filter that has been tested by the FCC was the AM1000FIL. , though in testing here at our shop the AM1000FER provided equal filtering performance.

I think the interesting thing is that I am seeing several other agents (not Washington) asking people in their area to install one of these filters, just this week, (after the test took place) so I wonder if an internal memo went out saying that the filter is a good thing and acceptable in doing the job, but who is to say for sure, they don’t report to me  I find out what they are doing usually by what is happening.

I can also tell you that the agent went away asking that KENC to place one of these filters on his other transmitter, saying he was out of compliance on that unit until he did so.

So I think the filter is a good thing , and will hopefully solve the problem , and conflict of people disconnecting their ground on outdoor antennas, because of fears of being found out of compliance, as we all know is very unsafe. The new AM1000FIL we provide isolates the antenna system to the 15.219 3 meter limit, while provide good lighting protection, not as good as a direct connection, but almost there.

The other interesting thing I cannot verify is there “seems” to be some sort of “3 foot allowance” to a “ground of the agents determination” before they will even ask for a filter, the filter is just asked for in the case of a long wire or ground they feel is adding significant radiation. If you have a less then 3 foot connection to an acceptable ground, apparently there is something in the new FCC manual that says that will pass or be acceptable. Again I cannot verify that so far.
 
Re: Setting new precedent for outdoor Part 15

druidhillsradio said:
The Ken Cartwright (Filter) situation We are setting precedent with all outdoor part 15 it seems, ...
Click to expand...

Observations:

If one or more filters truly isolate the ground/power/audio conductors of an elevated "Part 15 AM" setup so that the system functionally meets 15.219(b), then the transmitter may as well be installed at earth level, as probably it would have greater coverage from there when using a reasonably low-resistance r-f ground.

And if it was, then filters wouldn't be needed, and it would have better lightning protection than when elevated, using filters.

This is demonstrated by the information at http://i62.photobucket.com/albums/h85/rfry-100/150_microvolt_per_meterRadius_Part_.gif

It will be interesting to learn what the FCC really thinks/did about KENC this week, and the evaluation techniques leading to their action, when accurate, verifiable information is available about that.

Suggest that, for credibility, it comes as a direct output from the FCC, and is not provided by third parties -- especially by those using hearsay statements, and other unverified comments about the FCC action that "seem" to be true to the persons posting them.

RF
 
Maybe the lesson here is, "don't confront the inspector." Ken Cartwright reports on his website, www.kencradio.com , that he has had to shut down two of his three transmitters because of ground lead issues. Ken thinks that the problem the inspector has with him is personal, and maybe it is (at least partially). Ken complained about the inspector and the FCC to Senator Wyden, and it is also rumored that Ken is suing the FCC.

As for the ground lead filter, which the inspector tested at Ken's site, Ken reports that it hasn't yet been approved by the OET. In my opinion, this is because it isn't in the best interests of the OET to approve this filter. Since Part 15 hobbyists don't have approved FSMs, it would be up to FCC inspectors to demonstrate that the the field strength reading with the filter, and with the ground lead disconnected, are about the same. This would place a big additional burden on the inspectors. The whole point of Section 15.219 was to permit hobbyists to demonstrate compliance with the rules without needing expensive and sophisticated test equipment. The ground lead filter would bring a calibrated FSM into 15.219.
 
Ermi Roos said:
Maybe the lesson here is, "don't confront the inspector." Ken Cartwright reports on his website, www.kencradio.com , that he has had to shut down two of his three transmitters because of ground lead issues. Ken thinks that the problem the inspector has with him is personal, and maybe it is (at least partially). Ken complained about the inspector and the FCC to Senator Wyden, and it is also rumored that Ken is suing the FCC.

As for the ground lead filter, which the inspector tested at Ken's site, Ken reports that it hasn't yet been approved by the OET. In my opinion, this is because it isn't in the best interests of the OET to approve this filter. Since Part 15 hobbyists don't have approved FSMs, it would be up to FCC inspectors to demonstrate that the the field strength reading with the filter, and with the ground lead disconnected, are about the same. This would place a big additional burden on the inspectors. The whole point of Section 15.219 was to permit hobbyists to demonstrate compliance with the rules without needing expensive and sophisticated test equipment. The ground lead filter would bring a calibrated FSM into 15.219.
Click to expand...

Your comment about Section 15.219 is exactly right. The very intent of this rule was to simplify the inspection process when called for. Field strength is not supposed to apply to transmitters that have been Type Accepted under this rule.
 
Section 15.219 does not explicitly specify a maximum field strength, but there is an absolute maximum physically possible field strength that is inferred. With 100% efficiency of the transmitter and antenna system, the maximum possible radiated power with 100 mW of input power applied to the final transmitter stage is 100 mW. 100 mW of radiated power from an electrically-short vertical monopole over ground produces a field stength of 100,000 uV/m at 30 meters. Of course, the actual field strength with 100 mW of input power applied to the final stage will be a lot less than this because any transmitter and antenna system will have considerable losses, and the effieciency will be a lot less than 100%.
 
Interestingly enough, TIS is another sort of "100 mW" system. The field strength limit of TIS is 2 mV/m at 1.5 km (a little less than a mile), which corresponds to 100 mW of radiated power for a ground plane with high conductivity. If the ground system does not have high conductivity, then higher radiated power is needed to get 2 mV/m at 1.5 km because of ground wave attenuation. Part 15 has 100 mW of input power to the final stage, and the radiated power is a lot less than 100 mW because of low transmitter and antenna efficiency.

I have seen several posts expressing astonishment that the FCC would be concerned with only 100 mW of power. TIS is a licensed AM service, and it can have as little as 100 mW of radiated power. There is a TIS station four miles from my home, and it can be heard clearly, although it is a little noisy. At six miles, it can still be heard, but the audio is not intelligible.
 
That TIS stations are allowed 10 watts is a popular misconception. The field strength limit is 2 mV/m at 1.5 km. There is an additional limit that the output power of the transmitter cannot be more than 10 watts, but the field strength limit of 2 mV/m at 1.5 km still has to be met. TIS stations are allowed to operate down to 530 kHz, and the 10 watt transmitter output power limit becomes significant at the lower frequencies, and if very short antennas are used. See Section 90.242 of the Rules.
 
Looking at some old posts on this website, I saw a post from a few years back that suggested using TIS for "community radio." It happens that the TIS station in my area is actually one such station. It has nothing to do with information for travelers, but broadcasts public notices relating to town business. Music is not allowed on TIS, but this station broadcasts some music. The music sounds terrible because of the narrow audio bandwidth required for TIS stations.

TIS licenses are isued only to government entities, and so the content would be controlled by the local government that was issued the license. Part 15 AM has a maximum input power of 100 mW, but TIS has a maximum radiated power of 100 mW (or somewhat more). TIS definitely has the advantage. It might be okay to approach the local administration about starting a TIS community radio station, but remember that everything related to the station will be very likely controlled by the office staff at the town hall.
 
Ermi Roos said:
Music is not allowed on TIS, but this station broadcasts some music. The music sounds terrible because of the narrow audio bandwidth required for TIS stations
Click to expand...

True, but probably that was the intention of the FCC when allowing TIS stations.

The TIS stations I've listened to when driving on the Interstate highways are more objectionable for their hum/clicks/pops and their poor low frequency audio response than for their lack of the higher audio frequencies.

FCC Part 90.242 has this requirement for TIS stations:

Each transmitter in a Travelers Information Station shall be equipped
with an audio low-pass filter. Such filter shall be installed between the
modulation limiter and the modulated stage. At audio frequencies between 3
kHz and 20 kHz this filter shall have an attenuation greater than the
attenuation at 1 kHz by at least:

60 log[10](f/3) decibels.

where “f” is the audio frequency in kHz.

That equation permits flat audio frequency response to 3 kHz, and a minimum of 7.5 dB reduction at 4 kHz -- which bandwidth doesn't sound all that bad for speech if the program audio fed to the transmitter has a good signal-noise ratio, low distortion, and reasonably flat response below 3 kHz.

Below to illustrate that is a link to a short MP3 file clip of the audio from a standard AM broadcast station. It was recorded in 16-bit, 22,050 Hz mono. The receiver bandwidth was set to 6 kHz at the start of the recording, and then adjusted downward at 2-3 second intervals through 4, 3, 2 and 1 kHz bandwidths. When the announcer is talking about regulating banking the receiver bandwidth was 3 kHz.

The changes in bandwidth can be seen fairly easily using a program like Goldwave with its spectrum analyzer display enabled.

Accessing the MP3 file is a bit of a hassle, but for anyone interested...

http://rapidshare.com/files/384155961/AM_Clips_at_5_Audio_Bandwidths.mp3

RF
 
A new precedent has been set, and it is not a good one for providing good range on Part 15 AM. Ken Cartwright reports on his website, www.kencradio.com, that the FCC has rejected the ground lead filter designed by Hamilton.
 
If the ground lead filter was totally effective, it would make the transmitted signal much weaker than that produced by a ground mounted system since half of the antenna-ground system would then be missing. This would also radically change the transmitter tuning. Without knowing the facts, I am inclined to believe that in this particular case, the audio and power lines to the transmitter circumvented the isolation that was supposed to be provided by the ground lead filter (unless they were fully choked as well).

Until the Commission can be persuaded to update its rules to provide workable options for elevated systems, ground mounting with the best available ground system remains the best option for Part 15 AM operation.
 
Re-reading the post opening this thread conveys quite a different analysis and reporting of this subject than has now developed, where the FCC has concluded that the filter had little affect on the radiation from the long ground conductor that resulted in the original KENC NOUO.

In light of this, what could be the basis for these original statements attributed to Keith Hamilton in the opening post, "...the agent there in Washing state seemed to find the ground AM1000FIL filter 'very' effective, he spent the entire day testing it. The agent himself mention how 'precedent setting' the event was."

RF
 
It is my opinion, that no matter what 'corrective' action was taken at KENC, it would never be good enough. Seems to me that this particular agent and his office have it out for Ken Cartright. The only way to satisfy these thugs, will be to have KENC Off the Air for good. It's really a shame, considering multiple unlicensed operations in big cities continue, with many of the operators actually making money from ad revenue. KENC on the other hand, operating as a non-profit community service, with flea power (filter or no filter) to begin with in a small town, continues to be the target of the feds.

Glad to see they have their priorities straight....
 
edarmsttrong said:
It is my opinion, that no matter what 'corrective' action was taken at KENC, it would never be good enough. Seems to me that this particular agent and his office have it out for Ken Cartright
Click to expand...

The FCC would have no legal basis per 47 CFR Section 15.219 to cite any unlicensed, intentionally radiating transmit system in the AM broadcast band that actually met 47 CFR Part 15.219.

However it appears from the FCC NOUO that KENC did not do so before the filter was installed, and that installing the filter "made no appreciable difference" to that determination.

This whole issues revolves around the total length of the conducting path between the transmitter and the functional r-f ground used by the Part 15 AM system (something buried in the earth, typically).

Some Part 15 AM microbroadcasting proponents define the "ground lead" as stated in 15.219(b) to be limited to a short conductor attached from the transmitter to the top of second conductor, and that a Part 15 AM system meets Part 15.219(b) as long as the sum of the length of that short conductor and the length of whatever conductor is attached to the antenna connector of the transmitter does not exceed 3 meters.

That second conductor is defined by these proponents to be "ground." In the KENC case, the length of that second conductor (the tower) appears to have a length of something like 40 feet, where it connects at its base to one or more buried ground rods -- which ground rods are the functional r-f ground for the system.

What if a single 40-foot conductor was used between the transmitter at the top of the tower and the ground rods? Probably those same proponents of Part 15 AM microcasting then would recognize that such a configuration would not be compliant with 15.219(b).

But physics and field experience show that there is no practical electrical difference in the performance of a Part 15 AM system using a single 40-foot "ground" conductor, or one using two conductors in series whose total length is 40 feet -- where the shorter length is called a "ground lead" and the longer length is called "ground." Calling the longer lead ground doesn't make it function as a ground, as far as r-f energy is concerned.

The accurate definition of a ground lead used at radio frequencies is the conducting path leading from the r-f ground terminal/chassis of an electrical device, and connecting it to a functional r-f ground (ground rods, or similar).

Such long conducting paths (whether comprised of one conductor or more) between the transmitter and a functional r-f ground carry all of the r-f current that the transmitter can produce in that installation.

An r-f current flowing along a conducting path between the ground rods and the transmitter produces radiation. That is the reason that 15.219(b) includes the length of that conducting path in the 3-meter limit. Effectively it is a radiating part of the antenna system, along with the "3-meter whip."

RF
 
In the past, the FCC recognized new and pre-existing construction.
Under this interpretation of the rules, they would not have considered
the water tower as part of the ground. But, they would count a new tower that one built specifically to broadcast.

This is a setback for those who want to do low power community broadcasting.

I don't believe KENC was harming anyone and was providing a service
to a small town.
 
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