[amsat-bb] 1/4 wave stub lesson learned.

[Andrew Rich]

When we installed the VOR in the Gold Coast I was moving the center pin in and out at 113 MHz !

Sent from my iPhone

> On 26 Jul 2017, at 8:26 am, Robert Bruninga <bruninga at usna.edu> wrote:
> 
> 1/4 Wave stub lesson learned.
> 
> 
> 
> I always wondered exacly where one measured a ¼ wave coax stub.. the
> shield, or the total connection length to the center coax?
> 
> 
> 
> ANSWER: The length of the center wire makes a difference.
> 
> 
> 
> We had poor second harmonics from our Cubesat VHF transmitter. Carefully
> built a prototype shorted ¼ wave stub and tweaked it to over 26 dB of a
> notch at the second harmonic.  But then to install it on the cubesat
> transmitter board, we couldn’t quite get the prototype coax to fit right at
> the transmitter connection and had to extend the center of the coax about
> 1/8”.
> 
> 
> 
> This detuned the stub by over 5 MHz at the 145 MHz operating frequency
> though the length of the shield remained the same.
> 
> 
> 
> Now I know. Everything counts!
> 
> 
> 
> Fortunately it detuned it lower so I have two more cuts available on the
> flight unit to bring it in…
> 
> 
> 
> Bob, WB4APR
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