Hi John,

  I went to the M.I.T. library and made copies of Alexanderson's
original papers and did some other research beyond that. The
Alexanderson alternators were good up to about 20kHz, they achieved
higher frequencies by feeding the output of the alternator into a
saturated reactor which generated harmonics, they then filtered out
the harmonic that they wanted and fed it to the antenna. Not sure but
the antennas were of such high Q that additional filtering might not
have been necessary. They would indeed fly apart if they tried to
generate a 100kHz fundamental directly from the alternator!

About 15 years ago, I led a group trying to make high-speed energy
storage flywheels, they rotated about 45,000 rpm. Initial attempts to
use mechanical bearings mounted in  a springy steel housing were a
failure, magnetic bearings (with a dsp based controller) were
absolutely necessary to get through the various mechanical resonances.

I made a trip to see British Nuclear Fuels in the U.K.,  they did make
a technically  successful high speed energy storage flywheel, but it
flopped commercially since it was too expensive to make for the
intended markets.

A group of Aero engineers at M.I.T. tried to make microturbines with
dime sized rotors etched out of silicon or silicon carbide, they hope
was to have a small power generation source that would operate from a
gaseous fuel and replace batteries. The M.I.T. turbines would spin at
over 100,000 rpm and generate A.C. (R.F.) at 3 to  4 MHz!  I met with
Alan Epstein  and his group at M.I.T. back in the early 2000's  he
detailed some of the problems they were having. I believe the project
was ultimately abandoned.



73 Warren

On Wed, Dec 21, 2016 at 10:41 AM, John Rabson <[email protected]> wrote:
> Alexanderson generators were built for frequencies up to 100 kHz and did not 
> display a tendency to fly apart. For background information on the 17.2 kHz 
> installation see CREGJ 96.
>
> John F5VLF
>
>> On 21 Dec 2016, at 13:54, Martin Evans <[email protected]> wrote:
>>
>>
>> Ah yes- of course Andy.
>>
>> Better stand well back when I try it then!
>>
>> Martin  GW3UCJ.
>>
>>
>>
>>
>>> 8000 * 60  = 480000 RPM
>>>
>>> 'jnt
>>>
>>>
>>> On 21 December 2016 at 12:42, Martin Evans <[email protected]> 
>>> wrote:
>>>
>>> Forgive me for asking what may be quite obvious to many - but does this 
>>> mean that if I spun a magnet at 8000rpm then I would generate a 8kHz radio 
>>> signal, identical in every way to an 8kHz signal generated in a more 
>>> conventional manner?
>>>
>>> If so, it sounds a lot easier than winding all that wire.....until the 
>>> magnet flew apart anyway!
>>>
>>> Martin  GW3UCJ  Swansea.
>>>
>>>>
>>>> ever heard of a "A MEchanical Based Antenna" ?
>>>>
>>>> Me neither until today ;-)
>>>>
>>>> 73, Rik  ON7YD - OR7T
>>>>
>>>>
>>>
>>>
>>
>
> [email protected]
>
> Researching history of RABSON, BLACKSHAW, GAUNTLETT, VERLANDER and ROBSONNE
>
>
>
>
>



-- 
73 Warren K2ORS
                WD2XGJ
                WD2XSH/23
                WE2XEB/2
                WE2XGR/1