Mr Blare posts:
After all, at 10 or 20 feet from the transmitter it will be recievable. I kind of like the idea of being unreceivable by the public.
If a 10-ft to 20-ft coverage radius from a legal, unlicensed AM transmit system is adequate or maybe preferable to you, then what was the reason for your posts about installing extended ground wires from your "Wintenna" setup, so that your AM transmissions could be heard about 500 feet away, up a hill?
There seems to be no demand for intelligent programming.
That is a judgment call. But probably an AM "broadcaster" with a useful coverage radius of 10, 20, or even 5,280 feet would not include many potential listeners with such demands.
Rich asks the probing question: "If a 10-ft to 20-ft coverage radius from a legal, unlicensed AM transmit system is adequate or maybe preferable to you, then what was the reason for your posts about installing extended ground wires from your "Wintenna" setup, so that your AM transmissions could be heard about 500 feet away, up a hill?"
Psychology of the human animal is strewn with inconsistencies, and then we spin.
In my particular arena, having a garden variety part 15.219 (AM) setup presents the alure of tweaking for maximum range within the measure of the rule with the assumption that no one in the surrounding public will take any notice whatsoever.
15.239 (FM) at first seemed ridiculous but then taught me the game of finding use for a small signal, which has gone well.
While on one hand we have launched an initiative to improve 15.239 so the footprint better matches that achievable under 15.219, the reverse situation holds true as is...
15.223 (AM 1710) collapses the AM range so that it neatly matches 15.239 (FM). The FCC anticipated the human drive for symmetry.
Fun facts Carl. I've got my buddy working on experimenting on inside antennas for AM so I can get the most range and have a nice size antenna I can have in the house for AM. I just got done doing some low power FM tests and I'm going to try upstairs now too to see what I get. But I'll post that in a different thread lol.
In Post # 11 Robert kc8gpd states: "and again carl, carrier current can be used in any band under part 15 where it is technically feasible and governed by field strength, there is no regulatory restrictions limiting carrier current to 15.221. carrier current if i recall is feasible up to about 3 MHz."
In the back of the mind I realized Robert was right, after all the old intercoms and baby monitors used carrier current to communicate outside of the usual medium wave band, but the section of the FCC rules that allows it is very hard to spot. That's why I scanned the rules at 1:30 in the midnight hours.
It's hidden in Subpart B: Unintentional Radiators - 15.209 - Radiated Emission Limits (e) Carrier current systems used as unintentional radiators that operate in the frequency range of 9 kHz to 30 MHz shall comply with the radiation emission limits for intentional radiators provided in 15.209.
Looking at 15.209 - Radiated Emission Limits; General Requirements. (a) frequency 1.705 to 30.0 MHz emissions shall not exceed 30 microvolts/meter at 30 meters.
That comes out to twice what Rich calculated in Post # 12.
Mr Blare wrote: "... Looking at 15.209 - Radiated Emission Limits; General Requirements. (a) frequency 1.705 to 30.0 MHz emissions shall not exceed 30 microvolts/meter at 30 meters. That comes out to twice what Rich calculated in Post # 12."
CLIP FROM FCC §15.209:
§ 15.209 Radiated emission limits; general requirements.
(a) >> Except as provided elsewhere in this subpart, << the emissions from an intentional radiator shall not exceed the field strength levels specified in the following table:
Freq (MHz) Field (µV/m) Distance (meters)
0.009-0.490 2400/F(kHz) 300
0.490-1.705 24000/F(kHz) 30
1.705-30.0 30 30 ...
Here is a quote from a subpart that provides an exception to §15.209(a):
CLIP FROM FCC PART 15.223:
(a) The field strength of any emission within the band 1.705-10.0 MHz shall not exceed 100 microvolts/meter at a distance of 30 meters. 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.
Please note that:
1) §15.209 covers the spectrum 1.705 to 30 MHz. §15.223 covers the spectrum 1.705 to 10 MHz.
2) §15.209 does not refer to the bandwidth of the radiated signal. §15.223 does.
3) The spectrum bandwidth of a modulated AM broadcast signal is much less than 10% of the center frequency in the 1.705 to 10 MHz band, therefore the following applies from §15.223: 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.
4) I didn't calculate anything requiring more than simple math skills that can be done in one's head. I just read, understood, and repeated the field limit for an unlicensed AM transmitter on 1.710 MHz as defined in FCC rules. That limit is 15 µV/m at a distance of 30 meters.
The rules seem to say two different things in two different sections, simple math included.
However, there are no plans afoot to operate in carrier current mode on 1710 kHz because my single carrier current system is committed to operation in the center of the medium wave band and it's only possible to run a second carrier current transmitter on a single electric line using two different frequencies with the use of a custom made combiner, which are commercially unavailable.
Because my one and only use of 1710 will be according to 15.233, Rich's head-derived field strength limit of 15uS/m @ 30 meters applies without argument.
The official KDX AMT5000 Transmitter from sstran.com operates at 1670 kHz, which is close enough to 1710 kHz to conduct experiments as if actually transmitting on 1710 kHz.
The first experiment is almost ready to go, operation with 35 mW to the final RF amplifier without changing the antenna or tuning.
We will walk a radio out to 100-feet and observe the received signal level. If we hear the signal, it is still too strong; if the signal is buried in background garble, it may be ready for 1710.
Park your attention here for more reports.
Plans to operate a verty very low power transmitter on 1710 kHz are not forgotten.
"First Trial," described in the preceding post, is yet to be done using an AMT5000 as described.
This morning I recall owning a Ramsey AM25 and have decided to dedicate that transmitter to "Project 1710," employing the refinements charted by Neil Radio8Z as linked here:
http://www.part15.us/blogs/radio8z/modifications-increase-efficiency-ramsey-am-25-transmitter
It is also decided that, after trying the 100-foot test mentioned previously I will ultimately lower the power of the AM25 until the 1710 signal is already riding on the noise floor at close range (10 to 20 feet) from the transmitter.
The deadline for doing this is still December 2015.
As planned, today the power setting for the AMT5000 was turned fully counter-clockwise for an input to the final of 35 mW, followed by a walkdown to the street 100' away.
The program at 1670 kHz was still coming in very well, it had not faded into the noise, at about 1 PM CDT.
What did we learn?
The input to the final will need to be a lot lower or the antenna detuned to lower the field into the background noise as required for operating on 1710.
The input to the final will need to be a lot lower or the antenna detuned to lower the field into the background noise as required for operating on 1710.
-----------------
Happy experimenting, Carl.
Just to note that lowering the true, radiated field of any "AM broadcast" setup using a 1710 kHz carrier to the 15 µV/m limit at 30 meters permitted by FCC Part 15 is not dependent on the noise level at that receiving/measuring location (assuming that those two fields were measured with acceptable accuracy).
The background r-f noise level easily might exceed 100 µV/m at 1710 kHz, for many/most real-world locations outside a screen room.
At first I took these words to mean - (The background r-f noise level easily might exceed 100 µV/m at 1710 kHz, for many/most real-world receive locations) - that I'd be held responsible for the 100 uV/m level produced by the ambient noise, but upon further reflection I realize that you mean that the TARGET field level from the 1710 signal (15 uV/m at 30m) could still be too high even when submerged in the noise floor.
Sinking confidence as it seems that even a proper field strength meter couldn't separate the one from the other.
All right, I'll sink the signal into the noise at HALF the distance, at 15 meters.
At least I'll be closer to the proper level and maybe even a little under.
I see triumph ahead.
Once un-piled from its storage box the AM25 transmitter will be upgraded based on the studious work of Neil Radio8Z who explored ways to improve the Ramsey kit.
http://www.part15.us/blogs/radio8z/modifications-increase-efficiency-ramsey-am-25-transmitter
Something I'd hope to add is an RF power control, able to take the carrier down to nothing and back up to full. This is will be the desired means to conform with 15.233, the special rule for 1710 kHz.
... I realize that you mean that the TARGET field level from the 1710 signal (15 uV/m at 30m) could still be too high even when submerged in the noise floor. ...
Kindly note -- the groundwave field intensity of an AM signal itself, 30 meters away from its transmit antenna system when using a 1710 kHz or any other carrier frequency is not related to the ambient r-f noise level at the location where such an AM signal is received/measured.
Those two fields will combine at each receive location -- and normally cannot be distinguished from each other, accurately.
Adjusting a "Part 15 AM" setup operating on a carrier frequency of 1710 kHz so that its field at 30 meters is "submerged in the noise floor" is not necessarily proof that such a system actually complies with Part 15 (should that be the goal of its operator).
A signal so weak it cannot be distinquished from random noise... can't be sorted from noise at 30 meters... a rule that cannot be obeyed... what a country!
SDR or Software Defined Radio's plug into the usb port of a laptop or pc and allow reception of nearly all of the radio spectrum using software to show and play weak signals over computer speakers. You can also record what the SDR hears.
With filters provided by the software, it is possible to pull in weak signals using an SDR, which means your small signal has a small chance of being received by a dx'er across the street or a mile away.
Stranger things have happened.