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

To: [email protected]
Subject: Re: LF: TXing WSPR on 630m on a Raspberry Pi, Stefan in QRPPPP...
From: DK7FC <[email protected]>
Date: Mon, 23 Mar 2015 17:48:13 +0100
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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
 

From: [email protected]
Date: Mon, 23 Mar 2015 16:11:08 +0100
To: [email protected]
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.
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