[hfsig] TAPR 20M WSPR Board/Raspberry Pi 3

[Bruce Raymond]

Hi Merv,

I don't really know the ins and outs of the 20m WSPR transmitter (I 
created the 30m unit and I believe that the software is similar). The 
WSPR subband is only 200 Hz wide, so if you're not in the subband nobody 
will decode your signal. From the WSPR webpage 
(http://wsprnet.org/drupal/node/218):

  * Band    Dial freq (MHz)       Tx freq (MHz)
  * 20m 14.095600          14.097000 - 14.097200


The tricky part here is that WSPR is using audio frequency shift keying 
(AFSK) (I think I have this correct - could be wrong) with an offset of 
1500 Hz. What this means is that your 20m transmitter would be set to 
14.0956 MHz, but with the 1500 Hz audio offset you would actually 
transmit at 14.0971 MHz (14.09560 + 0.0015) which is smack in the middle 
of the subband (14.0970 - 14.0972).


I see from the manual that you use something similar to the following 
command to start up WSPR -
*

sudo ./wspr -r -o -s VK6BMT OF87 20 20m

*
The software should take care of setting the frequency automatically. 
The '20m' callout will do that.

I hope this helps. If not, please write back.

73 Bruce Raymond/ND8I






Merv Thomas wrote on 1/7/2019 8:24 PM:
> Hi,
>
> I just acquired the 20M board and set it up to transmit into my 
> Magnetic Loop (tuned accurately to the WSPR transmit frequency of 
> 14.097100).
>
> I have run this unit for many hours without anyone receiving my 
> signals.  Measured output on my power meter shows 90 mW and on my 
> spectrum analyzer the signal looks very clean and shows with around 
> 100mW output.
>
> Measured frequency of transmissions are up to 200Hz different to what 
> is being shown on the WSPR data screen in my Win10 PC - could this be 
> the reason no one decodes my transmissions?
>
> If I use my Yaesu FT-450 throttled down to as low as I can get it 
> (150mW) into my loop antenna I get numerous received reports so it 
> seems the loop antenna is not the problem. Using WSPR Ver 2.0_r174.
>
> I'm new to the forum so hope I do not breach any of the rules!!
>
> 73,
>
> Merv  VK6BMT
>
>
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