How about a Fractal antenna for improved bandwidth. Never seen one used below a few hundred megahertz but what the hey.
The tree is a natural example of a Fractal design, the way its branches head off at multiple directions and angles. In fact, a 10-foot tree might be the best possible example of a fractal configuration that could be the 3-D model for a Fractal part 15 antenna.
Perhaps a metal erector set would supply the parts that could be assembled in a Fractal array, insulated from the earth at the base.
Such a tree might serve the double use of being the annual Christmas tree, although festooning it with lights and decorations might detune it.
A 3-meter Fractal tree outdoors would attract the occasional bird.
Another indoor idea would be to build a clothes-tree with Fractal off-shoots, and a sign - "Not For Coats".
At first I planned to use 1640 as the designated indoor antenna test frequency, but now I'm looking at 1710kHz, because of how clear it is.
The lower power levels allowed for 1710kHz may fall right in with an indoor antenna, which will be attenuated by passing through walls and at the outside location where an official field strength reading would be taken will most probably fall safely within 15.223, quoted here:
Operation in the band 1.705 - 10MHz
(a) The field strength of any emissions within this band shall not exceed 100 microvolts/meter at a distance of 30 meters.
30 meters is around 100 feet and that's way off the property.
Does this seem reasonable?
Carl - You might want consider the rest of 15.223, as you find that appropriate:
However, if the bandwidth of the emission is less than 10% of the center frequency, the field strength shall not exceed 15 microvolts/meter or (the bandwidth of the device in kHz) divided by (the center frequency of the device in MHz) microvolts/meter at a distance of 30 meters, whichever is the higher level. For the purposes of this section, bandwidth is determined at the points 6 dB down from the modulated carrier. The emission limits in this paragraph are based on measurement instrumentation employing an average detector. The provisions in §15.35(b) for limiting peak emissions apply.
Yes, considering all of 15.223 is certainly appropriate.
If you will, please explain the portion you cited in light of the known character of a standard AM broadcast signal.
Thank you.
It might be this part: However, if the bandwidth of the emission is less than 10% of the center frequency, the field strength shall not exceed 15 microvolts/meter or (the bandwidth of the device in kHz) divided by (the center frequency of the device in MHz) microvolts/meter at a distance of 30 meters, whichever is the higher level.
For consideration... the r-f bandwidth of a standard analog AM broadcast signal these days is less than 20 kHz, given the definition in FCC §15.223, and the current NRSC standard.
An r-f bandwidth of 20 kHz plugged in to the above quote yields 20/1.71 = 11.7 microvolts/meter as the result.
But also an r-f bandwidth of 20 kHz is less than 1.2% of a 1710 kHz center (carrier) frequency.
So by FCC §15.223, an unlicensed system operating with those parameters is FCC-compliant (if such is desired) as long as the maximum field measured 30 meters from its radiator does not exceed 15 microvolts/meter.
An unfortunate reality in this scenario is that a 1710 kHz field intensity of 15 microvolts/meter is well below the ambient r-f noise level in virtually all locations outside a screen room, let alone the interference-free r-f field intensity needed for useful reception by most consumer-grade AM broadcast receivers for that carrier frequency.
Added later: Even shorter path distances might not provide useful fields.
This is getting a bit technical, no doubt, but that is the requirement given in Part 15.
Rich, would it then be your advice that, although we are only planning to test antennas indoors in this particular discussion, we should stay away from 1710kHz as a test frequency?
I recall from previously having a number of different indoor antennas that some signal does escape, and for most people it would only be a guess as to how much power that actually is out at 30-meters.
Yep, its pretty much pointless to be doing indoor antenna research and using 1710 as the testing frequency with those lower limits than that of 530 to 1705.
I would select a frequency for testing that is mid-range between 1250khz and 1700khz. There is bound to be one in there somewhere that will be close to what most 219'ers are using to do the antenna research.
What..no takes on my hexagon antenna suggestion?
You should try it. I have. Nope, ain't gonna tell! :p
RFB
Hi, Carl -
That's up to you, of course.
You wrote your guess that you will meet Part 15 when using an unlicensed AM transmit system indoors, and if so, then no problem.
But the FCC will doesn't guess, they measure 🙂
None of this matters to me personally except as an educational project, and is offered only as a "heads up."
I seriously doubt any FCC field agents are cruising around neighborhoods at random measuring for someone tinkering with indoor antennas to make sure they are standing straight and feet together and eyes front with chest out and shoulders in and gut tucked.
Good lord, so what if his 1710 signal is above the limits. HE IS TESTING, NOT CONTINUOUSLY BROADCASTING!!
I do believe there is a provision in the rules for periodic tests at far greater power levels and field strengths.
Oh and one more thing, your right, the FCC does not guess, and yes they do measure, but they do not know what to measure or what to go looking for unless someone happens to say...complain enough to convince them that so so may not have their shirt tucked in and their gut is hanging out. :/
Just a heads up.
RFB
RFB wrote: I do believe there is a provision in the rules for periodic tests at far greater power levels and field strengths.
This is an interesting belief, and very useful to those subject to FCC Rules -- if you can provide legal documentation to prove its accuracy.
Hopefully you can, and will do so. And if not, probably you should retract this post of your belief.
Otherwise your post could lead others into the risk of FCC citations, would you not agree?
My remarks right now about the status of 1710 kHz is not editorial commentary in protest of existing rules. It's more of a passing observation on this space flight known as life.
1710, empty and unused on all modern AM radio receivers, reminds me of our public parks. Parks are "public space" and 1710 is on the "public airwaves.
But there's no parking in the park after 10 PM, there's a park curfew; sleeping or camping overnight is an arrestable offense. The public is not allowed in the park during arbitrary hours.
1710 is not in use. It could come in handy for a small time part 15 broadcaster. But it's closed, albeit abandoned.
Some rules make the gentry class seem a little too tightly sphinctered, but the species in general isn't all that successful anyway, so I think I'll use 1640 for indoor testing.
My belief is this. It does not matter what I believe, does it.
However the belief that you wish to throw out here is that if anyone so much as steps 1 nanoflea volt or watt beyond the width of a hair past that black and white writing on the wall, they had better just turn themselves in and declare themselves as the biggest baddest rule violators ever to dabble with radio.
I believe however, that if you go look at the entire Part 15 section containing the various bands, you will see provisions in some of them that allow for periodic transmissions with much greater field strengths.
No one said anything that there was a specific provision for the MW band. I simply said that there are provisions in Part 15. You can find them I am sure of that..as I am sure and believe that you are aware of those provisions as well.
So I guess even researching indoor antennas has to be so scrutinized down to the nth decimal place within our own homes now.
All the while one of your licensed goody good doers who currently has 4 STL violations spanning 16 years along with 2 other outstanding NAL's for two other cities and has no CAP at ANY of the stations, just got a get out of jail free card (3 of them) from the FCC, 3 brand new STL licenses which 3 of those 4 STL violations ARE THE SAME STL.
Don't play no game I can't win, you will be the only player.
Do you want to see my papers too?
You know what, why don't you go call these licensed to violate law abiding station owners and point out some rules to them.
Since I can still add to this post much later, I will. Forgive me for the harsh stance tonight. I have stood for playing by the rules all my life. Devoted a lot of resources into having the right tools and knowledge to see me through. I was raised to be respectful, even to those whom I disagree with or even do not like. It is that which gives me reason to apologize to Rich for being harsh. Though the system isn't perfect, it certainly is not so crippled as to let by such huge violations and reward that with new licenses on STL's that are currently tagged with NAL's, amongst 2 other past and still outstanding NAL's and there is a lot more I guarantee everyone.
It is so frustrating, seeing something that you have wanted all your life, be in someone else's hands where said someone doesn't give a flip about FCC rules or licenses or real radio broadcasting so much to ruin and seriously affect an entire market for the other stations and here I am, with my little Part 15 stations applying REAL broadcast industry standards and procedures to their operations and technical specifications to 209, 221 and 239. I invested a lot of $$$$ on proper test gear to ensure they operate within the rules, and to add to it, reading someone quote to me and other Part 15 operators about functionally compliant and etc etc.
Does anyone else understand the level of "close to home" impact this is having here, not just with the radio scene here in Casper, but also directly impacting me, and other people who were unfortunate to get a dose of the owner's care and love for radio. Hint, he is NO broadcaster.
Anyway, back to indoor antenna research. Carl, I have to ask you, would you really give some serious consideration to working with the hexagon pattern? I think you might find something very interesting about it and resonating it with RF.
RFB
I have been completely involved
with family/home stuff, as you know.
HOWEVER, I am still looking from
"the outside -in" to what is going
on here.
I can't really contribute to discussions at
the moment. I miss that.
Also, I can see that you guys are
having some "spirited discussions"
regarding THIS subject. I haven't
really paid too much attention to
what's been going on here - until
this morning on this thread.
I can see that I miss the "spirited
discussions," too.
Very Best Wishes,
Bruce, Monitoring From West Hartford, CT
The legal questions about part 15 ground have become controversial, but the actual importance of RF ground for good performance is vital knowledge that can be under-appreciated.
I am the poster child for being clueless about RF ground, having for years thought that the antenna alone was the key to success.
The discussions on this website have slowly penetrated my "knows-it-allness" and made me finally wake up to how important RF ground is.
This indoor antenna project will very much address RF ground, and from a separate point of view, the legalities of various ground schemes.
WOOPS! I just responded to a comment made by RFB on the tail end of page 1, and here we are are page 3.
As far as the hexaganol antenna is concerned, where is the feed point?