WISPY is a full 2-way WSPR transceiver but there may be occasions when just a simple WSPR TX is needed. This is the (current) schematic of the WSPR TX beacon for 10m, but the very same schematic with a different crystal and values should work on any HF band. On lower bands the doubler could be removed and a simple on-frequency crystal substituted. The doubler approach was the cheapest way for 10m WSPR.
The schematic needs rationalising and some further simplification, so treat this (as always) as a design starting point.
Hello Roger !
ReplyDeleteI'm happy to see this kind of QRP schematic for the WSPR. Actually, people don't know how to use WSPR has they are always with power around 5 to 10 W or more !!!!
I remember this modulation is based on phase shifting. So why not using the final transistor in a class C ?
73, from Thierry.
Thierry,
ReplyDeleteWith a normal SSB WSPR signal a class C PA is fine.
When the signal is a DSB one (two tones being emitted as in this design) then any non-linearity will result in a signal that will splatter over many tens of kHz either side of the carrier.
73s Roger
Hello Roger,
ReplyDeleteon wiki they said it's a 4 tone FSK. But I still do not understand why class C PA is not suitable here.
Because here, there is no amplitude modulation, just frequency modulation, class C should be ok even if it's DSB or SSB. Am I wrong ?
Thierry,
ReplyDeleteIf you put two FSK signals spaced about 2.5kHz apart into a non-linear amplifier then the transfer characteristic (non linear) will result in additional signals (intermod products) spaced at 2.5kHz intervals either side of the original ones. This is why a 2-tone test is done to check linearity of an SSB PA). With a single FSK signal this will not happen but with DSB there are TWO FSK signals present and this will be an inevitable outcome unless a linear PA is used.
Of course ! Thank you for the explanation, in fact it's like a two tone test because there is always two tones present, one in LSB and an other one in USB.
ReplyDeleteI didn't think to that and that is why it was confusing to me :))
73 from Thierry.