[AMPS] Setting the record straight--Dick Ehrhorn

[2]

>This is enough Dave, lets not start it all over again!
>Thanks Will, K6NDV
>
Dave/Mike ? made some valid points, Will.  Please see below.

>-----Original Message-----
>From: owner-amps@contesting.com [mailto:owner-amps@contesting.com]On
>Behalf Of Wt8r@aol.com
>Sent: Saturday, July 21, 2001 9:54 AM
>To: na9d@speakeasy.net; amps@contesting.com
>Subject: Re: [AMPS] Setting the record straight--Dick Ehrhorn
>
>
>
>In a message dated 7/21/01 11:34:47 AM Eastern Daylight Time,
>na9d@speakeasy.net writes:
>
>>
>>  on 7/18/01 12:03 PM, 2 at 2@vc.net 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.
>
/\  liar is a bit strong.  

>>  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.
>
/\ the last part of this sentence is (beginning with "since") detracts 
from the impact.  Understating  works way better than overstating.  

>>  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
>theory.
>
/\  and mathematics.  Remove "is ludicrous and"  -  and you have a better 
torpedo.  

>>  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 
of
>>  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 
bandwidth
>>  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.
>
/\   ditto


-  R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.  
end


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