[Top] [All Lists]

[AMPS] Setting the record straight--Dick Ehrhorn

To: <>
Subject: [AMPS] Setting the record straight--Dick Ehrhorn
From: (
Date: Sat, 21 Jul 2001 12:54:08 EDT
In a message dated 7/21/01 11:34:47 AM Eastern Daylight Time, writes:

>  on 7/18/01 12:03 PM, 2 at wrote:
>  > 
>  > /\  Designing an unconditionally-stable HF/MF amplifier is more difficult
>  > than designing a stable amplifier for VHF.   Although I have heard
>  > reports thereof, I have never seen parasitic damage in a VHF or UHF
>  > amplifier.  
>  I gotta throw my 2 cents in on this one because this statement is just not
>  completely accurate.

Two cents is more than your statement is worth, because you don't know 
whether Rich has heard reports thereof nor do you know whether he has seen 
parasitic damage in a VHR or UHF amplifier as he states.  He says that he has 
not, so one might conclude that you are calling him a liar.
>  Building a stable amplifier that has high gain becomes increasingly
>  difficult the higher ones goes in frequency.  Things such as layout issues,
>  bypassing and genuine parasitics become critical.  When I say "genuine
>  parasitics" I don't mean the kind Rich talks about.  I am talking about the
>  inherent, real world, stray inductances and capacitances in components.

Please explain the difference between "genuine parasitics" and Measure's 
parasitics" since you are so well versed in theory.

>  Rich's statement could argued to be correct only because generally we hams
>  build our HF/MF amplifiers to be pretty broad banded in their coverage.
>  Sure we may have different tuned circuits for different bands, but the
>  amplifier in general covers a very large percentage bandwidth.  For
>  simplicity's sake let's say the HF band is from 1 to 30 MHz, centered at 15
>  MHz (I know it starts higher than 1 MHz).  An amp designed to cover this
>  basically is designed for nearly 200% bandwidth! (Percentage bandwidth is
>  defined as the total bandwidth covered divided by the center frequency *
>  100).  Our bandwidth is 30MHz - 1 MHZ = 29 MHz. %BW = (29/15)*100 which is
>  approximately 200%.
The above statement is ludicrous and shows how well you understand radio 

>  That's significant and that's what makes designing plate chokes, suppressor
>  chokes, etc. a real art.
>  Now take a UHF amplifier design at 435 MHz.  Even if we wanted to cover the
>  entire 70cm band from 420 to 450 MHz, we only have a percentage bandwidth 
>  6.8%!  Yet no one designs the UHF amplifiers to have even that much
>  bandwidth.  It would be rather difficult.  Amazing, how we are covering
>  approximately the same total bandwidth - 30 MHz.
>  A UHF amplifier with the same bandwidth as our HF amp would literally cover
>  from nearly DC to 900 MHz!
>  My point is we have to compare apples to apples.  An HF amp with a 
>  of 6.8% would be MUCH easier to stabilize than a UHF amplifier with 6.8%
>  bandwidth.

Your comparison is apples to lemons.  Does your wunderkin 4-1000A amplifier  
which you built using clever techniques, operate on the following frequencies 
in YOUR stated bandwidth: 4-6.99 Mhz, 7.3-13.99 MHz, 14.3-20.99 MHz and 
21.5-27.99 MHz?
>  Rich's statement as blanket fact is just not true.

Not only are your statements untrue, some might call them unintelligent.

>  73,
>  Jon
>  NA9D

FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>