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

[DK7FC <73dk7fc@googlemail.com>]

Hi Laurence,

These diodes are ZD15 Z-diodes, just to prevent eventual transients damaiging the board. They may catch some energy from nearby lightnig strikes. All this is very unlikely here, in March anyway...

73, Stefan

PS: Next step will be to run the 7667 on a 12V supply. This should allow me to directly drive my PA which i'm normally using for MF WSPR.


Am 23.03.2015 17:35, schrieb Laurence KL7 L:

Nice Stefan - are the two back to back diodes just before the LPF to catch noise spikes back towards the 7667 or another purpose?
 
Laurence KL7 L

Snowless Alaska
 

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From: 73dk7fc@googlemail.com
Date: Mon, 23 Mar 2015 16:11:08 +0100
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: TXing WSPR on 630m on a Raspberry Pi, Stefan in QRPPPP...

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.