[AMPS] Re: PA Measurments

Larry Molitor w7iuv@axtek.com
Fri, 15 May 1998 04:45:58 +0100

At 22:25 5/14/98 -0500, you wrote:
>While I don't agree with Tom on a lot, I do agree with him here.
>Clip leads COULD very easily be used on 160 meters.  Certainly not at VHF 
>though.  Tom is not saying that.

Jon, I cuda sworn that my original post refered to the problem of doing a
VHF characterization of a two-port network designed for HF, I.E. a pi-net
on your 4-1000 or some such. If it did, then Tom twisted that around and
confused the issue. If I screwed it up, then consider this an apology to
all concerned.

>The size of the connector relative to wavelength at 160 is so small that 
>it really doesn't matter.  And BNC connectors are spec'd WELL up into the 
>GHz range.  
>I've also never seen an APC-7 connector at Radio Shack!
>I've done plenty of quick and dirty measurements on amps even at 800 MHz 
>and get good results doing it the quick and dirty way.  IMHO, you only 
>really need to worry about reference planes and so forth when the 
>connector begins to be a significant size relative to the wavelenght (ie. 
>GHz ranges).  
>Is using high quality connectors going to give better results?  SURE.  
>But how much accuracy do you really need at HF or even just to prove a 
>point for that matter?  So your phase angle of S21 is off by a couple 
>degrees.  And you magnitude of S21 is off by .2 dB.  Big wup!  Unless you 
>are trying to get that accurate, don't worry about it.

It's really a matter of perspective. Life gets tuff over here on my planet
sometimes. Imagine if you will, that you are tasked with demonstrating a
Final Acceptance Test on deliverable product to a customer representitive
who has no technical background. Imagine further if you will, that said
customer happens to be a nit-picker and has to power to with-hold payment
for said product. Imagine just a little further that if payment is
with-held, your management team looses their year-end bonus package. Now
just to spice it up a little further, you happen to know that there is no
design margin on one certain parameter and that the product is within a
half db or so of failing. No need to spend a half hour doing traceable cal,
if it fails, just look the customer straight in the eye and say "0.2db -
big wup!" 



Larry - W7IUV

FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm