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Scope of the term "Amateur"
On 6/29/2016 12:19 PM, Jeff Liebermann wrote:
On Wed, 29 Jun 2016 11:29:12 -0400, rickman wrote: Mostly yet. That should be "yes". In a hurry today (like all other days). However, some bands do not require a license and operate under FCC Part 15: http://www.lwca.org https://en.wikipedia.org/wiki/LowFER http://www.arrl.org/lf-low-frequency https://hackaday.io/project/6882-lowfer-transmitter-for-your-arduino etc... Very interesting. I see a difference between the ARRL article and the Hackaday page. ARRL says the power limit on the US 1750 meter "free band" is 1 W into the "transmitter's final stage" while the Hackaday page says the limit is 1 W into the "feedline" and antenna system. This might help: http://www.lwca.org/sitepage/part15/index-what.htm http://lwca.org/library/reference/ Note that it's a bit out of date. Adjust the links for 2016. You want part 15.217 (Operation in the band 160-190 kHz.) http://www.ka7oei.com/ct_lowfer_archive.html I see that kind of stuff quite a bit in the FCC rules-n-regs. They sometimes fail to specify WHERE the transmit power is to be measured. Is it at the input to the xmitter, output of the xmitter or at the end of a lossy feed line. What does one do if the system is not 50 ohms? I don't have an answer and since the FCC never will admit to making a mistake, it's unlikely to be fixed. Should you ask for clarification, you'll probably get an answer from the FCC which you don't want to hear. Been there, many times. My best advice is do your best with what you have, don't try to play FCC attorney, and muddle onward into the unknown. Thanks for the links. I found 15.217 and it says, 15.217 Operation in the band 160–190 kHz. (a) The total input power to the final radio frequency stage (exclusive of fila- ment or heater power) shall not exceed one watt. Since they specifically exclude the filament power I supposed that 1 watt limit is on the power from the supply rather than the "input" power to the grid/base/gate of the active element. So in reality the 1 watt limit at the input to the final stage will produce less than 1 watt at the output of the final stage. With the frequency being so low, a class D output could potentially provide nearly the full watt to the feedline I expect. Some amount of filtering would be needed to prevent the carrier from making it out the antenna, but using sigma-delta techniques should help to minimize that. With such low power and simple output stage, it could be placed at the antenna which would allow the full 15 meters to be antenna. -- Rick C |
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Scope of the term "Amateur"
On Wed, 29 Jun 2016 12:53:28 -0400, rickman wrote:
I'm back from the dentist drilling holes in my teeth and bank account. Thanks for the links. I found 15.217 and it says, 15.217 Operation in the band 160–190 kHz. (a) The total input power to the final radio frequency stage (exclusive of fila- ment or heater power) shall not exceed one watt. Yep, that's it. Since they specifically exclude the filament power I supposed that 1 watt limit is on the power from the supply rather than the "input" power to the grid/base/gate of the active element. So in reality the 1 watt limit at the input to the final stage will produce less than 1 watt at the output of the final stage. With the frequency being so low, a class D output could potentially provide nearly the full watt to the feedline I expect. Some amount of filtering would be needed to prevent the carrier from making it out the antenna, but using sigma-delta techniques should help to minimize that. Yep, except why bother with an amplifier? You could just modulate a 200Khz switching power supply and get similar results. Lots of other options available, but few of them involve a traditional amplifier multiplier chain. With such low power and simple output stage, it could be placed at the antenna which would allow the full 15 meters to be antenna. Any way you look at it, it's going to be flea power buried under tons of atmospheric noise. Everything you do up to about 300 meters range is near field. http://www.part15.us/forum/part15-forums/general-discussion/part-15-am-communications-near-field http://www.part15.us/forum/part15-forums/general-discussion/longwave-broadcast-dx-171-khz -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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