[Lowfer] Ultimate LOWFER Transmitter?

[Stewart Nelson]

Hi all,

Some good/bad news about an "array" of lowfer transmitters:

The good news is that performance could be outstanding.  If you have four
synchronous one-watt transmitters, and the antennas are sufficiently
spaced so that their ground and other loss resistances are effectively
independent, the combined far field strength will be four times greater,
the equivalent of one 16-watt Tx!  IMO, 50 to 100 foot spacing is
adequate.

The bad news is that it could be very tough to make legal.  If multiple
devices are "connected by wire or cable", they are considered to be a
"composite system" and in our case would limit the total power input to
one watt.  There are several mentions of this concept in Part 15.
As a start, look at 15.29 (h) and (k).
See http://www.lwca.org/sitepage/part15/index.htm or a complete edition.
You might get around this limitation by coupling the carrier optically,
inductively, or by radio on another frequency.  I don't know whether
the units would be considered to be "connected by wire or cable", if
they were merely connected to the same mains.  If so, the transmitters
might also need to be solar/battery powered.

73,

Stewart KK7KA

> >As for the multiple amplifier concept, I also call your attention to Section
> >15.204, External radio frequency power amplifiers and antenna modifications,
> >paragraph (b):
> >
> >"A transmission system consisting of an intentional radiator, an external
> >radio frequency power amplifier, and an antenna, may be authorized, marketed
> >and used under this part. However, when a transmission system is authorized
> >as a system, IT MUST ALWAYS BE MARKETED AS A COMPLETE SYSTEM AND MUST ALWAYS
> >BE USED IN THE CONFIGURATION IN WHICH IT WAS AUTHORIZED.  An external radio
> >frequency power amplifier shall be marketed ONLY IN THE SYSTEM CONFIGURATION
> >with which the amplifier is authorized and shall not be marketed as a
> >separate product."  (emphasis mine)
> >
> >In other words, if he wants to market it various such versions, he will have
> >to test it in EACH such a configuration, and sell it in exactly the
> >configurations as tested.  Sell a two-output version, get Type Acceptance
> >for a two-output version; sell a four-output version, get Type Acceptance on
> >the four-output version; etc.
> 
> I think you misunderstood although this is good information cogent to an 
> ongoing argument we've been having on another forum, so thanks! :-)
> The system as-is is Certified to be used in the manner I described but each 
> unit has only one output, and each is a standalone unit not just an RF 
> power amp. They can share carrier from a master unit (or not, each can have 
> it's own xtal and can be trimmed to exact freq.) but that master when used 
> as such is also a standalone unit not just an oscillator. These things are 
> whole transmitters in other words, not piece parts of a system.
> I assumed that most Lowfers wouldn't want this option but only mentioned it 
> anyway just-in-case.