Quote RFB:Do not forget about 15.21
Which says:
"Section 15.21 Information to user.
The users manual or instruction manual for an intentional or unintentional radiator shall caution the user that changes or modifications not expressly approved by the party responsible for compliance could void the user's authority to operate the equipment. ...."
And so?
The authority to operate comes from part 15 rules, not the manufacturer. Obviously, a manufactured device or a kit could be non-compliant due to modifications but part 15.21 does not prohibit modification. It only requires an advisement to the user that modifications COULD void authority to operate.
Though this rule applies to the manufacturer, I consider myself to be the "party responsible for compliance" regarding my operation of my devices. You made this point in your post so I wonder the purpose of referencing 15.21.
When I was studying for my ham license and was talking about what ifs and extending the rules to many different situations a lawyer friend and study partner told me "Just read the damn rule. What does it say and what does it not say?" This was good advice.
Neil
RFB, You know that was sarcasim right?
This has been talked about before, but if only there was a meter that would show the exact milliWatt value present at the input to the final. And a dial so it could be exactly put on perfect compliance every day. With some headroom up to, say, 1-Watt, so we would be ready for any future relaxing of the rules.
Neil's comments about reading the rules for what is said and not said is exactly why we tend to preface our remarks with, "I'm not an attorney, but..."
What is good for everybody when it comes to studying "what the rules say, " is that it teaches the super valuable skill of "critical thinking," something no longer taught in schools. It is very smart to analyze every sentence in The Rules and go over them several times while contemplating all the aspects..."What does it say?" "What is left unsaid?" "How does this part relate to certain other parts?" and very important, "Is there perhaps some OTHER way to interpret this? That is, more than one meaning that can be found?"
Criticizing the rules and one's own thoughts is not negative, it is constructive.
"My SSTrans, both of them, show a power level of 96mW to the final stage. Perhaps that value can change with fluctuations in the electric power service, which is known to fluctuate to the degree that electric clocks will drift slow and fast over a period of time."
That's probably true to some extent, but less if you use a regulated and filtered PS. Unless you've really ticked off an FCC field agent, no one is likely to come after you for such things.
All the rules for Part 15 are designed to do is the primary: Part 15 devices are unlicensed and cannot cause interference, and must allow interference from licensed stations.
That's why the restriction rules exist.
Tell ya what ... I'm not going to wake up in a cold sweat worrying if my final is a couple mw over or under, nor if the field strength occasionally steps a few microvolts over or under the limit, nor if my antenna is a 1/2" too long or too short.
If I were an FCC inspector, I would consider Section 15.219(a) (100 mW input power limit to the output stage) to be difficult to enforce. This is something hard to measure in the field. In contrast, 15.219(b) (3 meter rule) is easy to check. A field strength of more 100,000 uV/m at 30 m would be prima facie evidence that 15.219(a) is violated, because exceeding this level is physically impossible for any compliant transmitter, no matter how technically advanced it is. I would consider a field strength of more than about 20,000 uV at 30 m to be suspect of violating 15.219(a), and would want proof of compliance. I have seen an FCC measurement as high as 70,000 uV/m for a supposedly certified transmitter. First of all, I would send the field strength meter back to the shop to be checked out. If this is a real field strength measurement, I have no doubt that 15.219(a) is violated.
I have seen only one NOUO where 15.219(a) compliance was actually checked by the FCC in the field. Whether the transmitter is certified or not, the operator should think about some means that the 100 mW input limit can be proved at his installation, especially if the transmitter and antenna system performs extremely well.
I am still working on reading everything
you guys have said.
Here's how I feel about top hats. A correctly
designed top hat is not supposed to radiate.
So... I don't think it's an antenna. I think it's
a capacitor. So I think top hats don't have to be
counted as the length of the antenna. But that's
just me. Oh, yeah - the whole longwave Part 15
community uses top hats. You can look at the
Lowfers website and it's various links.
I have experimented with gigantic top hats, almost
5 feet in diameter.
However, if a local broadcaster wanted me off the air,
and they go through channels to do that, I would comply.
If they use the argument that my antenna is too long,
I would comply and shut down.
But in my case, I don't think too many commercial
stations would be threatened by a little teeny signal that is
playing 1920s -1950s jazz and blues.
Especially way up at the top of the dial. And I'm off the
air anyway.
Thanks for letting me put my little piece in. I love this
board. And I'm not kidding, either.
Bruce, MICRO1690/1700
There's a message somewhere in this forum from one of us about an FCC agent's advice that buried ground radials would not be considered as antenna length, nor the windings in a loading coil, but that a top hat or above ground radials would be.
While true it doesn't exactly radiate, it does help prevent vertical signal loss to atmosphere, so it gets more out of the signal. Here's an example of a commercial application of a low mid-wave antenna used in NDB applications:
If I get a chance I'll take a shot of our new NDB at FHR (designator for Friday Harbor Airport). IIRC it has 12 50' buried ground radials and a 6-element capacitive hat.
I have thought about sticking a pie-pan on my antenna, but it wouldn't withstand the high winds of winter and early spring storms, at least not without exorbitant reinforcement.
Ken: Thanks for the reference to
the FCC agent's word on top hats.
I must have missed that one.
I think I'm going to listen to your station now.
Thanks again!
Bruce, MICRO1690/1700
I have thought about sticking a pie-pan on my antenna, but it wouldn't withstand the high winds of winter and early spring storms, at least not without exorbitant reinforcement.
Have you considered one those small camping bbq grills as a top hat? I have seen them in sizes of about 12 inches and less diameter. They would be a lot stronger than an aluminum pie plate that's for sure.
Yes adding a top had does add to the length measurement. However you overcome that by simply reducing the length of the vertical element in proportion to the diameter of the hat and increase your coil winding count a bit, maybe add another tap point or simple peak of the variable cap across it....if its 12 inches diameter, you reduce the vertical element length by 12 inches...re-tune and your in the green at that point.
RFB
If I were an FCC inspector, I would consider Section 15.219(a) (100 mW input power limit to the output stage) to be difficult to enforce. This is something hard to measure in the field.
No doubt. There is so much induced noises all around us that those measuring devices the FCC field agents use can pick up a reading of a faulty spark plug wire on the neighbor's lawn mower or the welding shop down the road a half mile. Let's hope that during a field strength measurement test that there aren't any nearby lightning storms or some other AM station is splattering the band.
Their job is quite tough enough as it is making sure licensed stations aren't spewing out garbage all over the dial and outside the bands, and I have seen quite a few doing just that and some of them getting away with it.
I know of one site where the transmitter (an FM 25Kw ERP) in Nebraska that is running with NO output filter on that feed line! No the TX does not have it integral in the final PA cavity nor is it up high on the 300 foot tower. A low pass filter for that power level is not hard to miss! Yet this site does not have one! Go figure.
RFB
RFBurns information about the 60Hz power line frequency being better regulated than in the past was interesting to hear, because my last education on that topic was many years ago.
Although the grid maintained 60 cycles within 1 cycle or so across a 1 minute time frame, just calculate how fast a motor driven hand clock will be off within a 12 hour period..much less a 24 hour period!!
Today's generator armatures and step up transformer stations use computerized synchronization to maintain that 60 cycles well within a fraction of drift over that 1 second time frame and are faster to adjust that 60 cycle frequency because those computers are referencing time bases that have a drift factor of barely a fraction of a percent over a 250 thousand year period. (aka atomic clock)
Yes the voltages do sag and rise on the line during varying load conditions, as I explained in our interview about Carrier Current and why it is imperative to have a proper coupling device so that your transmitter constantly sees a 50 ohm load no matter how wildly the line swings in inductance and loading. But even the power company attempts to regulate those voltages quite tightly during the load variances, and their computers keep a track record of the changes over a time frame so a good amount of "look ahead" correction is incorporated.
But even with all that, the line can sag and rise enough to even see it occur on the output meter of a broadcast transmitter, especially if the site is at the tail end of a power grid run, and a few oil well pumps are also tied to that same feed before it. Just ask any engineer down in west Texas and they will verify what I am talking about!
At KPEJ Ch 24, back when I was assistant chief engineer 1993, it ran at 4.5Mw ERP using a Phillips two klystron unit with 30Kv collector voltage and 4kv beam voltage. The power grid feed would fluctuate so much that when the station's transmitter site was installed, they had to install this incredible mains voltage regulator, a huge contraption of large mechanical sliders that made contact with 3 transformer coil windings and the transformers stood 4 feet tall. Although the contacts had your typical brush contacts as found in a motor, this thing had to bounce back and forth so much just to maintain the mains within +/- 50 volts that it ended up wearing down those brush contacts and eating away at the winding coils! A 50 volt swing may not sound like much at 440 vac 3 phase in, but by the time you run that through a step up transformer for 30Kv and then further ran through 3 diode stacks comprising of 150 diodes each, well imagine what kind of swinging takes place then!
It took them 5 years to finally get the power company to run them a separate power mains feed, which even that still fluctuated, but not so much as the previous one, the monster mains voltage regulator was bypassed and removed.
RFB
We need only one more person to chime in on this and then we'll be complete!
The "top hat" has been spoken about with praise by some, and there has been theory put forth. But I am still mystified by what is happening.
Is it the same as sending up a vertical 10-feet high and then a horizontal offshoot of however long at the top? Isn't it simply a horizontal element added to the vertical?
Or is it like an upside down miniature ground plane up above the antenna rather than below it?
Or both? Or neither?
Is it the same as sending up a vertical 10-feet high and then a horizontal offshoot of however long at the top? Isn't it simply a horizontal element added to the vertical?
As the actual name of it implies..."Capacitor Hat"....it adds capacitance to the antenna. It helps to improve the distribution of the RF along the vertical more evenly instead of most of it hanging around the lower section. With the RF more distributed along the vertical length, that increases the footprint of that signal emitting off the element.
Think of it like loosing weight around the waist.
Wouldn't loosing the spare tire around the waist be as simple as putting on a top hat?!
If only things were that simple.
RFB
Like I said in a previous conversation, you have a knack for good descriptions. As a matter of fact the movie actor W.C.Fields wore a top hat which made his waste look thinner.
Getting me two top hats today. One for the stick and one for the bean.
But wait. Capacitance? I know that a capacitor has two "plates" placed hair-close to each other. What is the 2nd plate of an antenna hat? Is it the air? Maybe there should be a second "plate" 1-hair's distance from the 1st "plate," with a wire coupled to the air by a round ball of metal like some Tesla experiment.