Re: SSTC As a transmitter.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>



Tesla list wrote:
> 
> Original poster: "Gary Peterson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <glpeterson-at-tfcbooks-dot-com>
> 
> Yes, I would have to upgrade to General as well.  I hope the shared
> allocation is given the go ahead.  As for legality, I'd like to know for
> sure.  I suppose it would be okay as long as the transmitter produced
> undamped waves and it had proper bandwidth characteristics.  From the FCC's
> Notice of Proposed Rule Making
> <http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-02-136A1.txt>,
> 
> "We propose to require that amateur stations in the 135.7-137.8 kHz band
> meet the technical limits suggested by Canada in the WRC-03 preparatory
> process, noted above.  As provided in the Canadian proposal, we believe that
> sharing of this spectrum would be facilitated if the amateur station is
> limited to an EIRP of 1 W and the transmission bandwidth is limited to 100
> Hz. Because of possible difficulty in measuring the EIRP of the amateur
> station in this frequency range, as noted by ComEd, we additionally propose
> to limit amateur output power in this band to 100 W PEP. "


Given the hideously poor radiating efficiency of antennas at this low a
frequency, 100W PEP to the antenna is going to be a lot less than 1 Watt
EIRP.   I'd certainly push for the EIRP limit..

> 
> Assuming it's legal, and if Tesla is to be believed, our signals would
> propagate by conduction rather than electromagnetic radiation so a really
> good ground connection would be very important.  According to Tesla 136 kHz
> would be a little high for optimum performance--35 kHz and below would
> apparently work better.  (At 500 kHz EM radiation would have begun to
> predominate.)  A very stable square-wave generator would also be a must.
> The proposed band is only 2100 Hz wide so resonator tuning could be handled
> by varying the height of the elevated capacitance by just a few feet.

Recall that MUCH has been learned about propagation since Tesla's day.  I
wouldn't take Tesla's statements for gospel.  I'd go look at the actual
measured data at 100 kHz (for Loran C) and for numerous NDBs and other
beacons in the 200-400 kHz band
> 
> As for the receiver, Tesla said,
> 
>  ". . . That circuit, and that, and that one must be attuned; this is an
<snip out a goodly portion>
> 
> A good receiver might consist of a well grounded helical resonator with an
> elevated isotropic capacitance--what Tesla called the antenna circuit--with
> an e-field probe in the near vicinity of the vertical conductor  linking the
> coil and isotropic cap.  Lyle Koehler, KØLR has posted a suitable e-field
> probe circuit at  http://www-dot-computerpro-dot-com/~lyle/preamp/preamp.htm.  Any
> standard  communications receiver that tunes the band might do the job, even
> without a preamp.  For initial tuning very close in, a sensitive AC
> voltmeter would work.  A grounded voltmeter with an elevated conductor would
> also be a good instrument for transmitter peaking.

E field probes at low frequencies are a royal pain in the you know where,
unless you happen to live out in the middle of nowhere and run entirely off
battery power. It's very difficult to make them narrow band, so your preamp
has to have huge dynamic range (much more than a typical receiver!) to not
saturate on all the interfering sources. I'd suggest a magnetic probe,
which can be made into a reasonably high Q tuned circuit with a parallel
capacitor, both for receiving and for tuning.

Given 2100 Hz BW out of 130kHz, a Q of more than 50 is probably not
worthwhile, unless you're going to send at very low rates (1 bit/second),
in which case the max practical Q is going to be determined more by your
frequency stability.  10 ppm should be easy to achieve with relatively
inexpensive oscillators (especially if you ovenize it), and you could
always use GPS to discipline a VCXO standard at 5 or 10 MHz.  GPS would
also give you very accurate timing on both ends of the link, which would be
helpful in synchronizing your bit times (use the 1pps from the GPS as a bit
clock, for instance)


Jim, W6RMK

> 
> Gary, KB0DEB