[Amps] Plate modulation from power supply ripple?

[TexasRF at aol.com]

Makes one wonder if the receive mixers and product detector would provide  
the mixing process to produce hum sidebands.
 
This is an interesting aspect of rf design that I personally have never  
studied or experimented with.
 
73,
Gerald K5GW
 
 
 
 
In a message dated 10/3/2013 10:49:25 A.M. Pacific Daylight Time,  
garyschafer at comcast.net writes:

 
AM modulation is a  multiplication (mixing) process. Without a switch 
(amplifier driven into  cutoff) there is no multiplication of the signals.   
The variation in  plate voltage due to power supply ripple will be seen in 
the output as  addition and subtraction of the main signal and ripple 
voltage but at a very  low level if the amplifier is linear.  No side bands are 
created as they  are in an AM signal. 
73 
Gary   K4FMX 
 
 
  
____________________________________
 
From:  TexasRF at aol.com [mailto:TexasRF at aol.com] 
Sent: Thursday, October 03, 2013 10:44  AM
To: ww1c at outlook.com;  garyschafer at comcast.net;  amps at contesting.com
Subject:  Re: [Amps] Plate modulation from power supply  ripple?
 
Hi All, even if the  plate current did not change, wouldn't the changing 
plate voltage result in  changing power input and corresponding changes in 
power  output?
 

 
That sounds like  modulation as well.
 

 
Taking this to an  extreme, removing the filter C altogether, any hum 
modulation then? How  much?
 

 
73,
 
Gerald  K5GW
 

 

 

 

 

 
 
In a message dated  10/3/2013 8:35:17 A.M. Pacific Daylight Time, 
ww1c at outlook.com  writes:

Hi Gary, All
I  was thinking about your statement and looking a typical tube anode  
characteristics (curves).If I read this correctly, change in plate voltage  does 
cause a change in plate current.Is this not plate modulation?  I  am not 
sure if the operating class changes this.Perhaps I need to simulate  this 
too...
Thanks
MarkkuWW1C

> From: garyschafer at comcast.net
> To:  ww1c at outlook.com; amps at contesting.com
> Subject: RE: [Amps] Plate  modulation from power supply ripple?
> Date: Wed, 2 Oct 2013 12:36:06  -0500
> 
> You don't hear the ripple because it does not  modulate the linear 
amplifier.
> If you were to run the amplifier in a  non-linear mode such as class C 
then
> it would plate modulate  it.
> 
> 73
> Gary  K4FMX
> 
> >  -----Original Message-----
> > From: Amps  [mailto:amps-bounces at contesting.com] On Behalf Of Markku
> >  Oksanen
> > Sent: Wednesday, October 02, 2013 12:40 AM
> >  To: amps at contesting.com
> > Subject: [Amps] Plate modulation from  power supply ripple?
> > 
> > 
> > All
>  > I was simulating (with LTspice) a three phase power supply where  the
> > secondary is in star configuration with full wave  rectification. You 
can
> > get also a second voltage from this by  connecting to the center of the
> > star, this voltage is half of  the full wave rectified voltage and is
> > only half wave rectified  (per phase), 3 pulse in stead of 6 pulse for
> > the higher  voltage.
> > It turns out that even relatively high value (tens of  uF) filter
> > capacitors would leave some 10% of ripple on the  lower voltage.  Now 
the
> > question is: How much plate  modulation this make?  The ripple frequency
> > is 150 Hz and  to me this looks like your regular high level, plate
> > modulated  AM transmitter.  Why do we not hear this on a typical signal
>  > if it is there?
> > 
> > MarkkuWW1C
> >  _______________________________________________
> > Amps mailing  list
> > Amps at contesting.com
> >  http://lists.contesting.com/mailman/listinfo/amps
> 

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