power formula for vswr?
 

If I know only the power in dbm is there a formula to arrive at
vswr without conversion first to watts or volts?

outbound = +63dbm (2kw)
reflected = +36dbm (4w)

This is a waveguide system with a dummyload connected in
the event the numbers seem improper.

I would like to use the formula when we connect the real antenna.

power formula for vswr?
 

Gudmundur wrote:
If I know only the power in dbm is there a formula to arrive at
vswr without conversion first to watts or volts?

outbound = +63dbm (2kw)
reflected = +36dbm (4w)


Take the formula for calculating vswr from P in watts, previously converting
the dBm into W.
You'll get the following vswr=(1+10^(0.5*(Pout-Pref)))/(1-10^(0.5*(Pout-Pref))).


Regards,
Pawe³ Stobiñski, SQ9NRY

power formula for vswr?
 

Pawe³ Stobiñski wrote:
Gudmundur wrote:

If I know only the power in dbm is there a formula to arrive at
vswr without conversion first to watts or volts?

outbound = +63dbm (2kw)
reflected = +36dbm (4w)


Take the formula for calculating vswr from P in watts, previously
converting the dBm into W.
You'll get the following
vswr=(1+10^(0.5*(Pout-Pref)))/(1-10^(0.5*(Pout-Pref))).


Regards,
Pawe³ Stobiñski, SQ9NRY


SWR = -1?

power formula for vswr?
 

John - KD5YI wrote:
SWR = -1?

Right, a little oversight. Swap Pout for Pref.


Regards,
Pawe³ Stobiñski, SQ9NRY

power formula for vswr?
 

Sort of ...

The Return Loss is 63dBm - 36dBm = 27dB (that's very good!)

Converting to reflection coefficient, Gamma = 10^(-27dB/20) = 0.0447

Then, VSWR = (Gamma + 1)/(Gamma-1) = 1.09 : 1

No volts or watts but, to be honest, Gamma is a voltage ratio ... :-)

Hope that helped,
Darrell ...

"Gudmundur" wrote in message
...
If I know only the power in dbm is there a formula to arrive at
vswr without conversion first to watts or volts?

outbound = +63dbm (2kw)
reflected = +36dbm (4w)

This is a waveguide system with a dummyload connected in
the event the numbers seem improper.

I would like to use the formula when we connect the real antenna.