Re: SSTC As a transmitter.

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

Original poster: "Gary Peterson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <glpeterson-at-tfcbooks-dot-com>

> 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..

It may turn out to be a waste of time, but I'm going to assume that Tesla
knew what he was talking about for the most part.  As the publisher of the
book NIKOLA TESLA ON HIS WORK WITH ALTERNATING CURRENTS AND THEIR
APPLICATION TO WIRELESS TELEGRAPHY, TELEPHONY AND TRANSMISSION OF POWER,
which, BTW, I have just gotten through indexing, I'm pretty steeped in the
subject and feel compelled to look further into the nuts & bolts of it.
According to Tesla the object is to suppress the creation of electromagnetic
radiation as much as possible.  It would be nice to have a lower frequency
allocation, say in the area of 73 kHz, to make this a little easier but I
guess beggars can't be choosers.

> 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

Right, it's never good to cite any authority.  The proof is in the pudding
so they say.  A vast majority of the LF work that I'm aware of has been
radio stuff--loading coils, long wire antennas and such.  I'm interested in
seeing the results of real-world propagation studies that involve the use of
slow-wave helical resonators and elevated capacitances.

> 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.

Actually, I live on the edge of close to nowhere and do run partially off
battery power (12 volt photo-voltaic).  It's pretty RF quite here.  I'd like
to hear your estimation of Lyle's tunable preamp circuit at
http://www-dot-computerpro-dot-com/~lyle/preamp/preamp.htm in terms it's
selectivity.

>  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.

Yes, an amplified loop antenna might make a good secondary circuit to use in
conjunction with the grounded receiving coil / elevated cap combo.  A tuning
cap might not be necessary. . . .

> 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.

Tesla liked to use proportionately tall helical resonators when an
application required sharpness of tuning.  This would also help get the
isotropic cap up into the air without having to use an excessively long
vertical conductor, which would be a source of that undesirable
electromagnetic radiation.

> 10 ppm should be easy to achieve with relatively
> inexpensive oscillators (especially if you ovenize it),

I'd like one of those slightly more expensive units with an accuracy of 1
ppm!

> 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)

The lowfers use a technique called coherent CW which I think uses WWV to
synchronize transmitters and receivers.

Regards,
Gary

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, July 23, 2002 4:21 PM
Subject: Re: SSTC As a transmitter.


>
> 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
>
>
>