VS: [WSJTX] Q65 and non-linear RF power amplifiers #Q65


Reino Talarmo
 

Hi Steve,

Non-linear amplifier is fine in principle. Only requirement is that it can deal with the smooth amplitude change during power-up and power-down phases or those are prevented by an extra configuration setting. Unfortunately I don’t remember what it is, an additional configuration file. There was discussion on that issue during 2.4.0 release candidates.

73, Reino OH3mA

 

Lähettäjä: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] Puolesta Steve Kavanagh via groups.io
Lähetetty: 07 June 2021 18:34
Vastaanottaja: main@WSJTX.groups.io
Aihe: [WSJTX] Q65 and non-linear RF power amplifiers #Q65

 

I don't see anything in the Quick Start guide that makes me think there would be a problem with non-linear  (Class C, E, etc.) power amps in Q65.  Am I correct?

73,
Steve VE3SMA


Bill Somerville
 

Hi Reino, and Steve,

the option to disable waveform ramp up and down is only for the FST4(W) modes, this was due to a particular design of non-linear PA suffering failure when presented by a slowly rising input signal. The feature is FST4(W) specific because the way that waveform is generated is specific to that those modes.

The release note information from WSJT-X v2.3.0 (2021-2-2) for that particular enhancement was:
 - FST4/W: Disable envelope  shaping at start and  end of transmission
   when environment variable FST4_NOSHAPING=1. Works for fst4sim too.
73
Bill
G4WJS.

On 07/06/2021 22:24, Reino Talarmo wrote:

Hi Steve,

Non-linear amplifier is fine in principle. Only requirement is that it can deal with the smooth amplitude change during power-up and power-down phases or those are prevented by an extra configuration setting. Unfortunately I don’t remember what it is, an additional configuration file. There was discussion on that issue during 2.4.0 release candidates.

73, Reino OH3mA

 

Lähettäjä: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] Puolesta Steve Kavanagh via groups.io
Lähetetty: 07 June 2021 18:34
Vastaanottaja: main@WSJTX.groups.io
Aihe: [WSJTX] Q65 and non-linear RF power amplifiers #Q65

 

I don't see anything in the Quick Start guide that makes me think there would be a problem with non-linear  (Class C, E, etc.) power amps in Q65.  Am I correct?

73,
Steve VE3SMA



Steve Kavanagh
 

Thanks for the clarification, Bill and Reino.

Is the Q65 ramp amplitude shape and timing documented somewhere?  I couldn't find it in the User Guide or the Quick Start Guide.

Does it vary with sub-mode?

Why is it needed? Reduction of "key-clicks" at the start and end of transmissions?

73,
Steve VE3SMA


Peter Hall, VK6HP
 

Hello Steve,

I was the poster who raised the issue with the FST4(W) waveforms in this forum and in the RSGB LF group.  You can see the later part of the discussion here:

https://wsjtx.groups.io/g/main/topic/79269122#20188

The problem arises because, at some point in the chain, the analog drive signal has to be converted to digital form, preferably with as little jitter as possible.  Typical squaring circuits have a dead or indeterminate band - however tiny - and, with very slow envelopes, produce erratic pulse drive to the (very widely used) Class D or E PAs, the designs of which typically requires a well-tempered pulse train.  As you see from the previous discussion there are several solutions possible, the most satisfactory being the setting of the environment variable as outlined by Bill.

I haven't tried Q65 yet but can do so in the next week.  Whether there's a problem will depend on the how slow the envelope rise and fall is.  I agree it'd be handy to have some descriptions or, better yet, sketches of the various WSJT mode signals.

73, Peter.


Steve Kavanagh
 

Hi Peter

Yes, I saw your posting earlier...an interesting thread.  I am not sure I understand what the reasons are for the ramp up and down.  My interest in Q65 is really for VHF and up, where Class D and E amps are mostly impractical (though getting closer over time as technology improves), but running a Class C amp (or class A or AB in hard saturation) is easy.  I'm guessing there would be no equivalent issue with the ramps in this case, though I suppose there might be a momentary increase in dissipation.  But it would be helpful to know the waveform and what one gives up by eliminating the ramps.

74,
Steve VE3SMA