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

[Bruce Raymond]

Hi Bryan,

Thanks! I suspect that Merv was trying to make sure that he had 
everything covered and typed in the frequency to the command line rather 
than take the lazy way out and use '20m'. This is the approach I'd take 
to minimize the chance of getting it wrong rather than type in something 
that looks like 0.020 Hz   :-)

At any rate, what's listed on the website is for WSJT-X software running 
on a PC, so I suspect that the 1500 Hz offset (sound cards don't work 
real well at DC) was bundled in to the "dial" frequency to keep things 
simple.

The software on the pi (Wsprry) is adjusting the pi master oscillator 
frequency and doesn't need an offset, so you would enter the  "tx" 
frequency.

The fix is to enter the band (20m) and let the software sort it out.

Merv, I hope this is correct. If not, just ignore it.

73 Bruce/ND8I


Bryan Corkran wrote on 1/7/2019 11:20 PM:
> I replied earlier using the wrong mail !
> So Bruce has beat me to it!
> I may be wrong but how is the internet connection Merv ?
> Can you use it on the pi for other internet stuff ?
> The frequency is adjusted by the pi contacting the ntp server every 
> transmission .
> The -s on the command line does that.
> For me it was  something like this : sudo ./wspr -r -o -s VK3KEZ 
> QF31GQ 20 20m
>
> From the readme:
>
> “Known PPM correction to 19.2MHz RPi nominal crystal frequency.
>  -s --self-calibration Check NTP before every transmission to obtain 
> the PPM error of the crystal (default setting!).”
>
> Regards
> Bryan  VK3KEZ
>
>
> On 8 Jan 2019, at 3:02 pm, Bruce Raymond <bruce at raymondtech.net 
> <mailto:bruce at raymondtech.net>> wrote:
>
>> 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
>>>
>>>
>>> _______________________________________________
>>> hfsig mailing list
>>> hfsig at lists.tapr.org
>>> http://lists.tapr.org/mailman/listinfo/hfsig_lists.tapr.org
>>
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