Re: New MGM Modes on Beacons


Mike Lavelle K6ML
 

Andy,

Sorry, that was my mistake.   I mixed up ISCAT (which is unfortunately being deleted... it’s still being used for microwave aircraft scatter) with JT4 (which is alive and well).    In the last part quoted, I was not writing that JT64 was retired, just QRA64 (the parens only applied to QRA64).  

While I’m at it, my comment about which modes use hard vs Gaussian keying (and my quote from Joe that modes over 4 bits were hard keyed) was focused on microwave modes, so ignored FT8, which, as your writeup mentions does use Gaussian. 

I also agree with your statements about frequency multiplication amplifying spurs by 20 dB per decade (same as phase noise and FM noise) being a serious issue by at microwaves and even worse at millimeter waves.  Working at 122 GHz, with a 12,200x multiplication factor, I have managed to produce some awful spectra with serious spurs, FM and PN.   John Miles (KE5FX) suggested on his excellent website that a great way to find out how truely awful a VHF source can be is to use it as the reference input to a microwave ‘brick’ and then look at the multiplied spectrum at microwaves.   ‘Clean’ oscillatros can shown to be quite ‘dirty’ using this technique.        

It looks like translation loops (PLLs with mixers) may be a good solution to spurs, etc, at SHF/EHF.    

I don’t see a problem with using frac-N with MFSK ... the requirement is CPFSK, which PLLs do meet... the VCO waveform is not discontinuous, just not elegantly shaped FM.... and if the PLL loop bandwidth is low (but still at at least 10-20x the baud rate), the low pass filtering produces smooth keying.


Mike K6ML

Mike K6ML

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