Re: LF: TXing WSPR on 630m on a Raspberry Pi, Stefan in QRP...

[IK1WVQ Mauro <ik1wvq@stmb.it>]

Hi Stefan,
years ago I tried a "push_pull" (or, better,
"bridge") configuration with a mosfet driver (I do not remember
the code) with one section inverting, and the other not.. the power
output was over 1W in 10MHz, with 12V supply .. 
I placed a toroid transformer with the primary winding  connected to
the two outputs (via a 100nF to avoid short circuit if raspy stop to
oscillate) ... 

.. little PA grow .. HI!

73 de Mauro IK1WVQ



At 23:17 26/03/2015, DK7FC wrote:
> Hi MF, 
>
> I'm now running the 7667 at 13.8V supply voltage. The MOSFET driver is
> easily keyed by the Raspi, directly with its rectangular output. I
> measured 0.5 W TX power at 50 Ohm. This is what i'm running
> tonite on 630m.
> Not a real PA, just the Raspi and this IC in a DIL-8 case.
> Fascinating!...
>
> 73, Stefan
>
>
> Am 23.03.2015 16:11, schrieb DK7FC: 
> > Hi MF, 
> >
> > I've added a simple ICL7667CPA MOSFET-driver to the GPIO of the
> > Raspberry. It's power supply is 5V coming from the GPIO itselfe. This
> > leads to a 5V rectangular signal with lower output impedance. I've
> > coupled the output matching circuit so that the output power is now 50 mW
> > / 17 dBm, i.e. 7 dB more power then in my previous test.
> > Iamge: 
> >
> > https://dl.dropboxusercontent.com/u/19882028/MF/17dBm%20RPI%20WSPR.jpg
> >
> > The beacon is running now on 475.685 kHz. 
> >
> > 73, Stefan/DK7FC
> >
> >
> > Am 18.03.2015 21:45, schrieb DK7FC: 
> > > Hi MF, 
> > >
> > > Today i've got i 3rd Raspberry Pi. I quickly installed the WSPR softaware
> > > and since a few minutes i am transmitting WSPR-2 on 630m, my usual
> > > frequency 475.685 kHz. 
> > >
> > > I'm directly using the GPIO output pin, without an amp stage behind! The
> > > rectangular 3.3V output voltage is passing a cap and an isolation
> > > transformer (FT50-77) as well as a simple pi-filter, because it is a
> > > Raspberry pi! ;-)
> > >
> > > See:
> > >
> > > https://dl.dropboxusercontent.com/u/19882028/MF/Raspberry%20Pi%20B%2B%20WSPR%20TX.jpg
> > >
> > > I measured an output power of about 10 mW at 50 Ohm. It is now connected
> > > to my MF antenna and transmits in a 100% duty cycle. I still have to
> > > learn how to reduce it but this will not take long.
> > >
> > > With 10 mW TX power i managed decodes by 3 stations now.
> > >
> > > 3 spots:
> > > Timestamp Call MHz SNR Drift Grid Pwr Reporter RGrid km az 
> > >  2015-03-18 20:32   DK7FC   0.475684  
> > > -21   0   JN49ik   0.01  
> > > DH5RAE   JN68qv   345   98  
> > >  2015-03-18 20:12   DK7FC   0.475685  
> > > -24   0   JN49ik   0.01  
> > > F1AFJ   JN06ht   667   247  
> > >  2015-03-18 20:06   DK7FC   0.475683  
> > > -27   0   JN49ik   0.01  
> > > DL1DBC   JO41bi   217   349  
> > >
> > >
> > > Does someone have good ears to get a decode from me? :-) It is a
> > > challenge! :-)
> > >
> > > 73, Stefan/DK7FC
> > >
> > > PS: The signal is so weak that my RX antenna frontend is not overloaded,
> > > so at that power level i can transmit and receive to the same time
> > > :-)
> > > PPS: A small amp stage will follow soon, i intend to use an BS170 running
> > > at 5 V.