Re: New MGM Modes on Beacons


John Quarmby
 

Plenty of food for thought Andy, thank you very much. I'm thinking that upgrading existing beacons to retain low phase noise and spurs might be easiest by using a fixed RDDS for frequency control, with a baseband I/Q modulator driven from a PIC via DACs modulating the output of the RDDS to provide all the modes required.

The 13cm version of GB3MHZ (when it is working!) uses a Next Gen Beacon source running on 320.830MHz with FSK CW and PI4, mixed with 2GHz multiplied from the 1GHz Next Gen clock. Phase noise performance is quite respectable, and in band spurs are just about acceptable here 4km LoS from the beacon.

73

John G3XDY

On 16/03/2021 10:21, Andy G4JNT wrote:

[Edited Message Follows]
[Reason: A pile of silly typos corrected]

With the introduction of new modes within the WSJT-X suite that use Gaussian shift MFSK, the old technique of switching between several switched tones using either a DDS or Fract-N PLL is no longer valid
 
Although not yet really applicable to microwaves, where JT4, JT65/Qxxx and PI4 will continue to reign, it is worth thinking about ways to implement FST4 and FT8/4 ready for if and when new GFSK modes appear that are suited to uWave usage.
 
This paper summarises the situation to date, and suggests a few ways forward.
 
 
 
Andy
 

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