[Elecraft] OT: Checking coax jumpers before soldering

[ab2tc]

Hi,

The terminated loss in a coax is half of the return loss looking into the
unterminated cable. RL is easily calculated using the formula:

RL = 20 * log (VSWR+1)/(VSWR-1) (dB)

The reason for the factor of two is that the wave has traveled the cable
twice before being measured as return loss. But it is true that high SWR is
diffucult to measure accurately so the method isn't used much. E.g. the
LP100A is pegged at VSWR = 9.99 so cannot determine losses less than 0.87dB.
The LP100A can also display the return loss directly but unfortunately that
value is also pegged at the 1.74dB value corresponding to that SWR.

AB2TC - Knut


DL6OAP wrote
> That kind of chart is e. g. in the ARRL antenna book (I have two older
> editions but am sure it is in both of them). Since the measurement assumes
> that the fraction of the power that is put into the line and not being
> converted into heat in the coax is completely reflected at the far end, it
> should work equally well with shorted or open end. I have a MiniVNA
> network analyzer that relies on this method for determining the electrical
> length and the loss of coax. Normally I leave the end open. 
> However, I am not sure if it works very well with short pieces of low loss
> coax because of the difficulties of precisely determining a high s.w.r.
> 
> 73, Ralf, DL6OAP
> 
> Am 12.11.2013 um 14:47 schrieb "Charlie T, K3ICH" <

> pincon@

> >:
> <sni>





--
View this message in context: http://elecraft.365791.n2.nabble.com/OT-Checking-coax-jumpers-before-soldering-tp7580727p7580765.html
Sent from the Elecraft mailing list archive at Nabble.com.