I have spent a good hour or so (i actually lost track) has been spent on that second link posted above and there is a ton of good useful information there.
What if i just broke all the rules (no not the part 15 rules) and turned two AM transmitters into beacons of sorts? A talking house would be easy, it already has a digital recorder built into it, while it isn't anything close to BPSK or any other automatic keying circuit, it doesn't involve moving parts or programming from a pc or chip.
Why not record some morse code with say -... -... .-. / .---- -.... ..--- ----- / -... . .- -.-. --- -. / . .- ... - . .-. -. / -.- -.-- / ..- ... .- / --- .-. / -... -... .-. / .---- --... ..--- / -... . .- -.-. --- -. / . .- ... - . .-. -. / -.- -.-- / ..- ... .-
Which for the CW (morse) impaired translates to:
BBR 1620 Beacon Eastern Ky USA or BBR 172 Beacon Eastern Ky USA
The talking house can be the 1620 beacon, the sstran , provided i get it to transmit on 170-172 khz could perhaps employ some type of keying circuit like BPSK or one of the various flavors of auto-keyers.
Just some wild ideas i've had in the past hour or so, kind of bored and at the same time, if i am going to do anything at all, i'd better get it done before i am unable to wield a soldering iron. Even finger dexterity is not what it used to be and i am only 49!
Not complaining or looking for sympathy, that ain't me but the truth is some tasks are becoming more difficult for me due to essential tremors.
The neurologist said "they may not get any worse" gee doc, that does leave some doubt there doesn't?
From Neil in Reply 13: Just out of curiosity as to what could be involved with a loading coil for this project, I used Rich's number for 5228 uH and ran it through a design program. ... This is rather big but it is doable.
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I was curious as to the equivalent series (r-f) resistance of such a loading coil needed to resonate a 3" OD, 49.2-ft, base-driven vertical monopole at 170 kHz. The graphic first below shows it to be about 16.7 Ω.
Below is a re-calculation of the spreadsheet to show the operating parameters for 16.7 Ω loading coil resistance, 750 mW r-f power at the coil input, and probably a more typical value of resistance in the r-f ground connection.
Thanks for the spreadsheets and the calculations Rich, it always helps to have a few numbers to get an idea of what we're dealing with. That's some narrow RF bandwidth if you want to transmit AM, with Q=70, but it makes sense with 3 degree high antenna.
Those coils do get big fast as you go lower in frequency, hitting millihenries, which might be a reason not a lot has been done with longwave broadcasting in North America, a little harder to build receivers and get access to the land needed for the antennas.
I was wondering if anyone has thought of trying the AMT 5000 on longwave, with the class E circuit, that might be something different to try.
I see that there are already some larger inductors in series with the output, selected by jumpers, what looks like a 200 uH and 1 mH that can be switched in, I'm assuming for the lower portions of the AM band. If you need 5 millihenries, then you'd need to add something or use an external coil, like the hams are using on that site, variometers with teflon Litz wire.
As an aside, bless simple web page design like that, the info you need and can take the time to read and absorb, not like the Vegas-style trash sites being put out by commercial interests.
Continuing, is there any reason you have to use such a big coil, especially at the lower power that rock97seven is proposing? Yes there may be some high voltages, but what about finding a few pie-wound RF chokes from tube gear, like the used-to-be-common 2.5 mH kind, then add a capacitor at the output, or two of those chokes in series, or make up the inductance with an adjustable coil?
Yes, the coil resistance would be higher, but when you're trying to experiment without buying big spools of magnet or Litz wire, it might be good to start with something simple, and as long as the inductance is right it should work fine.
Tesla people resonate their coils with long PVC tubes wrapped by wire, and that might be another thing to look at, as most Tesla coils are run on longwaves.
Another idea would be to find out what kind of transmitters Antique Radio folk are using to transmit audio to their receivers that have longwave bands on them.
... Continuing, is there any reason you have to use such a big coil, especially at the lower power that rock97seven is proposing? ...
Yes, if the goal is to resonate an electrically short vertical monopole -- which maximizes its radiated fields.
Resonance* of such an antenna system is independent of the applied r-f power at its feedpoint.
* resonance = a load impedance having zero inductive/capacitive reactance at the operating frequency
I meant big as in physical dimensions, just as a builder might elect to use the molded inductors inside of popular budget transmitters like the Spitfire, or bypass the small inductors and put a larger size loading coil external to the transmitter, having the same inductance.
For example, in the lab I have molded inductors the size of half watt resistors and 1 millihenry or 1000 microhenry, color code brown, black, red, silver, and those could be used in series to get 5000 microhenries, and I don't think they could overheat at 100 mw, and they could be used to resonate the 50 foot antenna, all for under a dollar.
These are desired to give high Q which translates to low losses. The larger coils also have reduced winding turn to turn capacitance. The coil I illustrated in Post #13 was specified to have a length/diameter = 1.5 which is recommended for high Q.
Neil