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

To: [email protected], [email protected]
Subject: Re: LF: TXing WSPR on 630m on a Raspberry Pi, Stefan in QRP...
From: IK1WVQ Mauro <[email protected]>
Date: Fri, 27 Mar 2015 11:32:00 +0100
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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.

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! ;-)


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.
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