Re: Pushing the QCX (T1 question) #qcx

Alan
 

Simple problem, Coupling C then resistor with parallel diode to ground. Fet gate goes to ground with no drive, drive loss is Vf of diode.  DC restoration circuit  used in  AC coupled video amplifiers from 70 years back .

 

Alan

G8LCO

 

Sent from Mail for Windows 10

 

From: Alan G4ZFQ
Sent: 27 August 2018 08:38
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] Pushing the QCX (T1 question) #qcx

 

> ;-)   I think a narrow BPF improves the performance.

 

Hans,

 

Yes, I do not dispute that. But may I suggest the difference would not

usually be noticed without careful comparison.

 

>>> I would suggest isolating IC3 pin 3 with a capacitor.

> It won't work... if you capacitatively couple IC3 pin 3 to the PA gate,

> then the peak-peak squarewave will be 5V BUT, it will be centered on 0V.

 

Oh yes, I see...

But it seems there have been a couple of cases where PA device failure

has resulted in 12V  being sent back through IC3. One of those affected

have reported failure of the Si5351 and another has said IC2 required

replacing.

If that really is the case then I'm wondering how to buffer IC3 to avoid

this rare occurrence.

 

73 Alan G4ZFQ

 

 

 

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