Unfortunately, ANTENNA is not defined for Part 15.219 other than the total length which is to include antenna lead wire and ground wire.
That being said, you're not going to find anything in the rules that says you can or can not use a helical wound antenna or any other antenna for that matter. But, if the Inspector decides the coil of wire is the antenna, he can say the antenna exceeds the 3 meter rule. After all, the rule says "length" not vertical height.
I’m sure we all could come up with some exotic antenna designs that physically fit within a 3 meter space but fail the 3 meter rule.
Top Hats and counterpoise are a good example. Neither radiates when properly designed. But, both alter the efficiency of the antenna by greatly improving its performance. And yet, it’s been stated you have to include the radius length of the Top Hat and counterpoise are cause for concern. Again, that is a “prevailing opinion” because neither is addressed in Part 15.219.
Perhaps nothing is in the NOUO's about helical wound antennas because none has been involved in the listed actions. Not to advocate breaking rules but you can use anything you want, until you're caught.
RFB, ask your FCC contact to post his opinion in this thread. It would be great to know what HE thinks about this since the rules don’t spell it out and his decision makes or breaks the call.
And after all is said and done, you can be 100% legal and still be shut down.
Top Hats and counterpoise are a good example. Neither radiates when properly designed. But, both alter the efficiency of the antenna by greatly improving its performance. And yet, it’s been stated you have to include the radius length of the Top Hat and counterpoise are cause for concern. Again, that is a “prevailing opinion” because neither is addressed in Part 15.219.
Stated by whom? An actual legal representative of the FCC rules? FCC field engineers are not attorneys or even qualified to legally interpret those unclear rules to begin with. Also there is no rule with a limit in creating an antenna that has very high efficiency when it adheres to the 3 meter length limits either.
Perhaps nothing is in the NOUO's about helical wound antennas because none has been involved in the listed actions.
Perhaps the reason why none have been involved in the listed actions is because those particular installations were interpreted to be compliant by either the field engineer right off, or by legal representatives interpreting the letter of the law in a court hearing over such an installation using a top hat or a coil antenna or buried counterpoise?
Sometimes its best to not just "go where the prevailing wind blows". It can be a good safety net for sure..no argument there. But as to the taking of the prevailing opinion to be bottom line interpretation on the letter of the law, we all should change jobs and become lawyers at that point.
A note to all including the editor:
As to my contact at the FCC, I should have left that reference to him out of this and I apologize to all here for that, I was merely trying to explain my setup which is built based on the conversations I have had with him over the years. It was not meant to create a pressure suit for him to put on and represent the FCC in the legal sense.
He is an FCC engineer, not an FCC attorney qualified to "bottom line interpret" the rules for us..and he most likely would refuse an invitation anyway because of those legal concerns. His supervisor would probably agree with that assertion too.
Anyway we are getting off topic with all of this about my contact. My apologies again to all and the editor. I respectfully will state now that I will not ask my friend to participate here to interpret the rules for us nor bring him up again in any further postings by me.
Back to topic:
In the meantime until the rules are clarified, we can at the very least experiment with those things such as top hats and coiled whips keeping within the 3 meter length limit. I cant find for some reason the rule where it says "thou shalt not experiment with ye top hat or thy wound coil" 😉
Then again..I am no FCC attorney. 😀
Personally I think the rules got twisted up and miss mashed with confusion on purpose. From what I understand, a lot of the wording and proposals to the revised rules were left out...now THAT is something that we all should investigate and discuss....why they are so unclear and at times controversial to themselves.
A good example is the frequency ranges in the Part 15 209/219/221 for the MW band. The rules state "525-1705". VERY IRONIC! What AM broadcast band receiver these days which comprise 99 percent digital tuners can tune to 525 or 1705??? I see them capable of tuning as low as 520 and as high as 1710. But not a single one tunes 525 or 1705. And the standard channel spacing allotment is in 10Khz steps for the US. You cannot tune 525 or 1705 with a 10Khz channel spacing allotment and expect to tune the proper channels of 530, 540, 550...1000, 1010, 1020, 1030....1600, 1610, 1620.....1690, 1700, 1710!!!!
One would think that the rules would be correct in that aspect to properly fit in the channel assignment allocations...right?
It is stuff like this that plague the rules that are a core of confusion, such as the no specifying of the use of a top hat or buried ground radial system or coiled whip, and the frequencies of 525 and 1705 to boot.
I say lets ban together and petition the FCC to clarify these rules and to include the questions regarding top hats, coiled whips and buried ground radial systems. From my understanding...if there are enough people pitching complaint or concern about a rule/s, they pay attention and address the issue.
RFB
The rules state "525-1705". VERY IRONIC! What AM broadcast band receiver these days which comprise 99 percent digital tuners can tune to 525 or 1705???
These "off channel" frequencies are not intended to be the carrier frequencies for modulated signals, rather they establish the band limits beyond which no radiation is permitted (excepting out of band emissions suppressed according to the rules). For example, an AM station operating on 530 kHz with a max audio frequency of 5 kHz would have the lower sideband extending to 525 kHz. This is clearly demonstrated in the rules for amateur radio frequency allocations.
Also note that there are no "channel" assignments for part 15 devices, only operating band limits.
Neil
Some of my favorite threads tend to be those about antennas, because I believe, with almost a religious faith, that new discoveries in antenna design have yet to be discovered.
So now, we're not talking specifically about antennas anymore, but about the innate human ability to explore, even when it seems everything has already been discovered.
If the very long wavelengths of audio, which are several miles long at the low frequencies, can be reproduced from ever smaller loudspeakers and even smaller microphones, it would seem to me that there must be corresponding ways to handle radio wavelengths with increasingly smaller devices.
This thread is not about a "smaller" antenna, because 3-meters is already small, but it is about making the 3-meter limit more efficient, which amounts to the same thing.
"If the very long wavelengths of audio, which are several miles long at the low frequencies"
No, audio, i.e., sound travels at about 1100 ft/sec. The lowest note on a bass guitar is 50Hz.
Thus: 1100/50=22 ft.
These "off channel" frequencies are not intended to be the carrier frequencies for modulated signals
Yes establishing the upper and lower limits. However given the 10Khz spacing, and the added fact that most transmissions are not going to be limiting themselves to a mere 5Khz bandwidth, 525 and 1705 do not simply fit or make any sense. Also some TX's out there do tune past 525 and 1705...making those upper and lower limits mute.
Also note that there are no "channel" assignments for part 15 devices, only operating band limits.
Obviously considering Part 15 is NOT a licensed or any sort of official radio service! You cannot have an official channel assigned by the FCC in an un-official, unlicensed radio authorization as Part 15!
However, no matter the case...the fact IS that the channel spacing standard IS 10Khz no matter how you slice it which way to Sunday, be it for Part 15 or Part 73.
Point is the rules are confusing and have been so since their last revision. I think the important thing to be looking at here is the reality of a confusing set of rules that contradict themselves through and through. I do not think I would get any argument from anyone over that fact except from the very few who throw in more confetti than what is already making a mess to begin with!
Be nice for once to have it told like it is, for what it is and says what it means and means what it says.
RFB
No, audio, i.e., sound travels at about 1100 ft/sec. The lowest note on a bass guitar is 50Hz.
Thus: 1100/50=22 ft.
Ah, but you didn't account for the cycles per second (Hz) in the denominator
1100 ft/50 cycles/sec = 22 ft/cycle/second, or 22 ft/Hz which doesn't seem to result in a usable value (the only "foot Hertz" I know of comes after a long walk - sorry, couldn't resist!)
Wavelength (inches) = K/F(MHz) where K=11811
Wavelength (inches) = 11811/.00005 MHz
Wavelength (inches) = 236220000
63360 inches/mile
236220000 inches/63360 inches/mile
The inches cancel
Wavelength = 3,728 miles
Wait a minute - that can't be right - anyway, the math is pretty
And back to Carl's point, speakers and microphones do what they do because they efficiently vibrate at, or sympathetically vibrate with, the appropriate wavelength - but the power involved is many orders of magnitude greater than the tiny amount of work our tiny transmitters offer. Even in the case of microphones, vocal cords move lots of air over long distances (work) and provide far more power than our transmitters - which might be why we sometimes feel we could yell farther than our transmitters transmit - far more power 🙂
I did not answer the first question in this thread earlier because I did understand it at first. As I looked at the post more carefully, It seems like Pilot assumes that a short CB antenna with a loading coil has the same "electrical" length as a full-lenth CB whip. This assumption is not correct. The loading coil only increases the electrical length of the short whip by the few inches of the length of the loading coil itself. The function of the loading coil on the short CB whip is to tune the whip to resonance at CB frequencies. It does not significantly increase the electrical length of the whip.
So, there is no legal problem with using the short CB antenna with the loading coil as the top portion of a 3 m Part 15 AM antenna. There is no performance advantage either, so there is no particular reason for doing it. The CB loading coil merely reduces the inductance needed for the AM loading coil at the base of the 3 m antenna by a small amount.
Cycles are dimensionless units. Don't include cycles in your wavelength calculation results. Hz is in cycles/s; so Hz would have the dimension 1/s.
(1100 ft/s)/50 cycles/s = 22 feet [(1/s)/(1/s)] = 22 feet