Re: LF: DK7FC's 2nd VLF TX test...

[Andy Talbot <andy.g4jnt@googlemail.com>]

If you go the the extent of UT synced FSK, then you'll gain another 3dB by using BPSK.   FSK is an orthogonal signalling mode, where you test the power level in one slot (frequency bin) against that in the other slot.   When correlated over a symbol period, the resule will be either 1 for teh correct tone, or 0 for th eotehr tone    However, BPSK compares the voltage amplitude between the two states, so you're now testing for what amounts to 1 or -1.    Hence 3dB advantage for synchronous BPSK versus synchronous FSK.  

 

Normally you don't see the benefit in simple amateur signalling protocols  as the need for carrier and bit timing recovery degrade the process, so for casual signalling FSK wins - hence the power  of K1JT's JTxx and WSPR modes.

 

But, by introducing GPS locked and timed signalling, operating both ends coherently, the latter issues go away and you should be able to get the full theoretical advantage of synchronous signalling.

 

Andy
www.g4jnt.com

Thanks for the info on the DDS VFO, now I recall you mentioned
it in an earlier post.   I wondered whether it would do FSK.
The QRSS mode is very poor, a most inefficient use of the
channel capacity - literally a waste of time.  Dual frequency
Morse code would be much better, but better still an efficiently
encoded digital signal sent with UT synchronous FSK.

Probably Spectrum Lab already has everything you need for
this, including the ability to sync the carrier frequency to
an external frequency standard.

> i plan to get the permission for a 300m vertical antenna!