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[AMPS] Power Handling of Resistors

To: <amps@contesting.com>
Subject: [AMPS] Power Handling of Resistors
From: 2@vc.net (measures)
Date: Tue, 7 Mar 2000 09:08:19 -0700
>
>In a message dated 3/7/00 12:36:39 AM Eastern Standard Time, 
>jono@enteract.com writes:
>
>>  Some of you questioned my technical sanity when I suggested dumping some 
>VHF power into a 5 Watt resistor and seeing if it can handle the power.
>>  
>>  My original quote:
>>  > If anyone doubts me, take your two meter radio and a let's say a 5 Watt
>>  > resistor and hook them up.  Key up your radio (at full power) and let it 
>> go immediately.  You won't damage the resistor nor even make it warm.  And
>>  > you'll likely have keyed into it for at least 250 to 500 mS which is much
>>  > longer than Rich's 10s of mS.
>
>So what is your point Jon?
>>  
>>  Well, I decided to put my money where my mouth is.  I took 2 of Rich's 100
>>  Ohm 3 Watt resistors (6 Watt total dissipation), put them in parallel and
>>  soldered them to a PL-259.  I then hooked them up to the output of my 2
>>  meter setup which consists of an FT-847 and a Mirage amp which puts out
>>  about 160 Watts.
>
>And........
>>  
>>  The resistors measured 52.1 Ohms before I applied power.  After a short CW
>>  dah at full power output (160 W), I measured the resistors again - 51.2 
>Ohms
>>  - within the error of my power meter.  Did a little longer dah again.  The
>>  resistors still measured 51.2 Ohms.  Lastly, I did a 2 second keydown.  The
>>  resistors started turning a little brown, were quite warm, but were STILL 
at
>>  51.2 Ohms.
>>  
>>  I feel my point was proven.
>
>Wow....this is rocket science or is this from the General class question 
>pool?

When a point is truly proven, silence is good form.   .  .  
>>  
>>  So the question is:
>>  
>>  Rich claims that suppressor resistor are damaged by a nearly instantaneous
>>  output of VHF energy due to an "oscillation."  This "oscillation" occurs so
>>  fast that the panel meters on the PA don't have time to respond.  This, as
>>  W8JI said, is probably on the order of nano-seconds or even a few
>>  milliseconds at MOST.
>>  
>>  If these same resistors can handle 160 Watts of VHF energy for 2 seconds,
>>  how much could they really handle in less than a thousandth of the time?  I
>>  doubt enough to be damaged as Rich claims.
>
>This is the point where ignorance overtakes (overshadows) common sense.  (1) 
>Apparently Jon hasn't the slightest idea of the magnitudes of difference 
>between the amount of energy stored in the power supply of a multi-kilowatt 
>power supply hooked to 220 VAC mains and a toy desk top 160 watt amp.

Excellent point.  One of the great entertainments on the AMPS group is 
specious poop.  

cheers

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