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Subject: Project 15: Spark transmitter

Ha ha - here's project #15, Stephen (hee hee hee hee hee hee......)



TSB xmitter  

                                          spark-gap
                                                    o  o---+-----o ant
                                                    |      |         
                                                    (      )
                                                    ( L1   ) RFC  
                                                    (      |
                                                    (     ###
                                                    (
           _______________________________________  (
          |                      | /           L2 ) (
          |                     --- C1         ___) (
          |                     ---           |   ) (
          |                    / |____________|___) (_______
          |                      |            |            |
   833    |                833   |            |           ###
        __|__       L3         __|__          |________________o +3000v 700ma
        .....___            ___.....         _|_
       __/^\__  UUUUUUUUUUUU  __/^\__        ___ .1 uf 5kv
       |     |       |        |     |         |
       |     |       >        |     |        ###
       |     |       <Rg      |     |
       |     |.001uf >  .001uf|     | <--- caps rated 1000v
       |     +-)(----+-----)(-+     |
       |     |       |        |     |     
       |     |      ###       |     |
       |     |                |     |
       |  +----------+-----------+  |
       |_ | _|       |        |_ | _|
         UUU         o          UUU      10v 10a ct xformers
       =======      \o S1     =======
       MMMMMMM       |        MMMMMMM
      |       |     (.)mtr   |       |
      o 117v  o      |       o 117v  o
                    >D                           F-24-a 's may be subbed for
                     | carbon mic                 833's if supply's are made
                    ###                           larger.

How it works:

The 2 tubes form a push pull power oscillator which makes alternating
current, but at a radio frequency.
This is done by use of L1 , L3, and the 2 little tubes.

In this case, the actual frequency is not important, sence the objective
is to generate maximum bandwidth...the goal of any 'phone station.
C1 is used to obtain maximum power by resonating L1 to L2's natural freq.

This RF voltage is stepped up by a factor of 30 to 100X by L2 and sent on
to the spark-gap, where the actual RF-to-be-sent is generated.

The RFC keeps the ant ckt at DC ground, yet will not short out the RF...which
is sent from the sparkgap, to the ant.

The ant wants to be one wire, and end fed. No coax required..just hook 'er
up and duck.

The length of the antenna determines the  sending band  it will be on.
The formula to use to get that length is...

      Feet  =  (468/(((F*F) +730 ) -(F*F))) *35.5

F = frequency in Mhz ( rounded off to nearest 100 Khz )

Voice modulation is done by use of a special Carbon Microphone, as used in
the 1920's...which can handle several amps.

Here, rather than sending RF thru the mic as was done back then, only DC
is sent thru.

That way, the operator (or inflictor) won't get an RF burn on his lips if
he speaks too close to the mic.

That modulates the power to the tubes , which varies the intensity of the
spark which then puts quite suitable a signal on the air.
The itellegibility will match the content of some of the QSO's now on the air.


To operate:

1  Place mouth near carbon microphone.
2  Close S1 and adjust C1 for dip in current (mtr) quickly.
3  Make oinking and Mooing noises to indicate your presence to everyone.
4  Open S1 when you get around to it.