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Author Topic: Parasitic Suppressor Resistors in Amplifiers.  (Read 29070 times)
AG6K
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Posts: 1




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« Reply #30 on: October 01, 2011, 04:15:21 PM »

My question to Tom was  if you know the self resonant frequency of the
tube in question, would using a parallel resonant supressor with a high C to L ratio be something
that is worth investigating.

Absolutely. It is a good method for minimizing loss on desired frequencies while maintaining effective suppression at a prolematic frequency.
  
Quote
The goal would be to minimize reactive losses at 30 MHz

  reactances don't incur losses Tom. they change the phase relationship between E and I. 

and below by using a LC tuned circuit that
would provide a low impedance path at HF, and a very high impedance path at the parasitic frequency.
this would force the VHF energy through the resistor, killing the Q at the self resonant, possible
parasitic requency.

There will be a certain optimum dampening resistance. My parasitic suppressor page goes into all of this.



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AG6K
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Posts: 1




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« Reply #31 on: October 01, 2011, 05:24:46 PM »

OK, I am trying to follow this thread

It's really pretty simple.

Tube type HF amplifiers used by hams often have oscillations at frequencies other than the desired ones because there are unavoidable resonances in the circuit. Usually these are in the VHF region. A typical HF amplifier circuit looks different to VHF frequencies in such a way that the wiring itself becomes a tuned circuit.

  Amen Jim, well put. 

These "parasitic oscillations" or "parasitics" can't usually be completely cured by neutralization,

  Indeed, in fact they are unaffected by neutralization because neutralization is only at the operating frequency. 

bypassing or shielding. (Those things help, and are good practice, but most amplifiers need more).

  The capacitive feedback path for VHF parasitic oscillation exists inside the tube so dealing with it not a piece of angelfood cake with cream cheese icing. 

The usual cure is to insert one or more "parasitic suppressors" in the VHF oscillator circuit, in such a way that VHF oscillations can't start or be sustained.

  Correct, and a way to do this is to reduce VHF amplification by reducing VHF RL on the anode.  This can be done by using a low VHF-Q parasitic suppressor.

The typical parasitic suppressor is a small inductance in parallel with a noninductive resistor.

  There is no such thing as a non-inductive R, but there are low inductance resistors.

 The idea is that the inductor value is small enough that it is essentially a short-circuit at HF, yet large enough at VHF that the resistor is effectively in the circuit for VHF.

  good

The resistor introduces enough loss at VHF that parasitic oscillations can't start or continue.

  Well sort of, but a VHF suppressor's specific job assignment is to reduce amplification at the VHF resonance so that there will be not enough VHF amplification for VHF  parasitic oscillation.   

That's the theory. In practice, suppressing parasitics can take a bit of trading-off, particularly in amps covering the higher HF bands like 10 meters. This is because an inductor-resistor combination with values of L and R large enough to stop a parasitic may have some loss at HF too.

  good point.  There's a tradeoff to almost everything. 

... ... ...  cheers Jim. 
   
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AG6K
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Posts: 1




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« Reply #32 on: October 01, 2011, 05:40:30 PM »

OK, I am trying to follow this thread, but the one dude is putting everything in quotes, including his replies. That is not helping.

So how does one do it the right way?   tnx
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N2EY
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Posts: 5063




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« Reply #33 on: October 02, 2011, 04:45:22 AM »

OK, I am trying to follow this thread, but the one dude is putting everything in quotes, including his replies. That is not helping.

So how does one do it the right way?   tnx

Simple:

All quotes begin with a quote statement in brackets and end with a /quote statement in brackets.

Your own added verbiage has no such statement.

Look at your own post which I quoted and hit "modify" to see how it is done.

73 de Jim, N2EY
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AG6K
Member

Posts: 1




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« Reply #34 on: October 02, 2011, 05:53:36 AM »

OK, I am trying to follow this thread, but the one dude is putting everything in quotes, including his replies. That is not helping.

So how does one do it the right way?   tnx

Simple:

All quotes begin with a quote statement in brackets and end with a /quote statement in brackets.
like this Jim?

Your own added verbiage has no such statement.

Look at your own post which I quoted and hit "modify" to see how it is done.

73 de Jim, N2EY

[/quote]
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N2EY
Member

Posts: 5063




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« Reply #35 on: October 02, 2011, 06:18:48 AM »

OK, I am trying to follow this thread, but the one dude is putting everything in quotes, including his replies. That is not helping.

So how does one do it the right way?   tnx

Simple:

All quotes begin with a quote statement in brackets and end with a /quote statement in brackets.
like this Jim?

Your own added verbiage has no such statement.

Look at your own post which I quoted and hit "modify" to see how it is done.

73 de Jim, N2EY

[/quote]

Almost there. Note the extra /quote in brackets at the end.



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K9FV
Member

Posts: 494




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« Reply #36 on: October 02, 2011, 06:57:44 AM »

Quote from: AG6K
So how does one do it the right way?   tnx

Note the
Quote from: ag6k....
that appears at top of reply window.
then verbiage of their quote you wish to use. then the

Be sure to put your words after the last [/quote] and this will allow your text to appear separate from quoted text.

 Mr Measures, from your last post I think you have the idea, but maybe this will help.

73 de Ken H>

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AG6K
Member

Posts: 1




Ignore
« Reply #37 on: October 02, 2011, 01:32:07 PM »

OK, I am trying to follow this thread, but the one dude is putting everything in quotes, including his replies. That is not helping.

So how does one do it the right way?   tnx

Simple:

All quotes begin with a quote statement in brackets and end with a /quote statement in brackets.
like this Jim?

Your own added verbiage has no such statement.

Look at your own post which I quoted and hit "modify" to see how it is done.

  I CLICKED MODIFY AND THERE WERE NO CLUES.  MAYBE IT DOESN'T WORK WITH APPLE COMPUTERS?


73 de Jim, N2EY

[/quote]
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AG6K
Member

Posts: 1




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« Reply #38 on: October 02, 2011, 01:55:15 PM »

Quote from: AG6K
So how does one do it the right way?   tnx

Note the
Quote from: ag6k....
that appears at top of reply window.
then verbiage of their quote you wish to use. then the

Be sure to put your words after the last
and this will allow your text to appear separate from quoted text.

 Mr Measures, from your last post I think you have the idea, but maybe this will help.

73 de Ken H>


[/quote]

  tnx Ken.  So when I want to place comments within certain parts of a quote I have to type [/quote] before and after each comment I write ?
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N2EY
Member

Posts: 5063




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« Reply #39 on: October 02, 2011, 02:01:04 PM »

In the interest of legibility I will try to explain the quoting process. If you already know how this works, please go on to the next posting.

----

When someone writes a posting and someone else replies by hitting "quote", an editing box appears with the original verbiage plus what I call "quote control phrases".

The quote control phrases are encased in brackets []. The beginning of a quote has the verbiage "quote author = ........." with lots of stuff about the author, topic number, message number, date, etc. with the whole thing encased in brackets. The end of a quote has just the word "/quote" encased in brackets.

eham sees those quote control phrases and puts the quotes in shaded boxes to differentiate the quote from the reply. However, you have to tell it when to start and stop by cutting and pasting the correct phrases in the correct places.  

For example, here's what a quote looks like when eham before processes it, with the brackets []replaced by braces {} so you can see the quote control phrases:

{quote author=AG6K link=topic=77773.msg542975#msg542975 date=1317516030}
So how does one do it the right way?   tnx
{/quote}

See the beginning and ending quote control phrases? If you replace the braces by brackets, they disappear because eham recognizes them.

Here's what it looks like after eham processes it (brackets used):
So how does one do it the right way?   tnx

When you just stick your own verbiage into a quote without an end-of-quote control phrase, eham doesn't know the quote is over and so makes your words part of the quote.

eham permits multiple/nested quote levels but tfirst get the basic working.

It has nothing to do with Apple or PC.

73 de Jim, N2EY
« Last Edit: October 02, 2011, 02:11:54 PM by N2EY » Logged
W8JI
Member

Posts: 9748


WWW

Ignore
« Reply #40 on: October 02, 2011, 02:01:58 PM »

Proper protocol would be to go to the site talk forum for help, and not totally ruin a running useful thread with unreadable posts and noise.   :-)
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AG6K
Member

Posts: 1




Ignore
« Reply #41 on: October 02, 2011, 02:50:58 PM »

In the interest of legibility I will try to explain the quoting process. If you already know how this works, please go on to the next posting.

----

When someone writes a posting and someone else replies by hitting "quote", an editing box appears with the original verbiage plus what I call "quote control phrases".

The quote control phrases are encased in brackets []. The beginning of a quote has the verbiage "quote author = ........." with lots of stuff about the author, topic number, message number, date, etc. with the whole thing encased in brackets. The end of a quote has just the word "/quote" encased in brackets.

eham sees those quote control phrases and puts the quotes in shaded boxes to differentiate the quote from the reply. However, you have to tell it when to start and stop by cutting and pasting the correct phrases in the correct places.  

For example, here's what a quote looks like when eham before processes it, with the brackets []replaced by braces {} so you can see the quote control phrases:

{quote author=AG6K link=topic=77773.msg542975#msg542975 date=1317516030}
So how does one do it the right way?   tnx
{/quote}

See the beginning and ending quote control phrases? If you replace the braces by brackets, they disappear because eham recognizes them.

Here's what it looks like after eham processes it (brackets used):
So how does one do it the right way?   tnx

When you just stick your own verbiage into a quote without an end-of-quote control phrase, eham doesn't know the quote is over and so makes your words part of the quote.

eham permits multiple/nested quote levels but tfirst get the basic working.

It has nothing to do with Apple or PC.

73 de Jim, N2EY
tnx Jim.  cheers
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