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

To: "RSGB LF Group" <[email protected]>
Subject: LF: Re: TXing WSPR on 630m on a Raspberry Pi, Stefan in QRP...
From: Guyé André <[email protected]>
Date: Fri, 27 Mar 2015 11:26:17 +0100
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Hello Stefan.
Ok about your interesting test with 0.5 TX Power. Sorry, I cannot copy you on day time, due to high carrier QRM just on your transmitting QRG. On the way now, the G3WCB signal is good around 0 dB S/N, at about the same distance as you.
I am now transmitting 2 or 3 times to see the difference in ON7YD and OR7T reports.
You know that I am always transmitting QRP on MF. Maximum power is 3 Watts output TX. Now I have exactly the same power as your : 0.5 Watt. On night this winter I was mostly using below 0.1 Watt.
My large winter antenna (Inv L) is dismounted and I am using a single 25 meters vertical tube without top hat capacitance. The effeciency is around – 20 dB, so the PAR (apparent radiated power) is 5 milliwatt.
If you want to have real QRPP test, you can test WSPR at 500 micro watt PAR, and still have lucky reports up to 1500 km.
Best 73. Andy F6CNI – JN19QB
Sent: Friday, March 27, 2015 10:29 AM
Subject: RE: LF: TXing WSPR on 630m on a Raspberry Pi, Stefan in QRP...

Hi Stefan,


solid signal here, best decode was at -8dB!


73, Rik ON7YD - OR7T


Van: [email protected] [[email protected]] namens DK7FC [[email protected]]
Verzonden: donderdag 26 maart 2015 23:17
Aan: [email protected]
Onderwerp: Re: LF: TXing WSPR on 630m on a Raspberry Pi, Stefan in QRP...

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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