开云体育

TU all for such wonderful comments, all helping me to visualize the concept of RETURN measurement.
I think when we add the word return LOSS it bothers me.
A double-negative is always problematic: so RL = -20 dB ????
Is that the same as saying a GAIN of 20 dB?
I did make an error in saying RETURN LOSS is -20 dB.
That is not what I was thinking (but I did write it that way).
I am thinking the RETURN signal is 20dB weaker than the FORWARD signal.
And yes, the log (ratio) types of measures do not include the word "loss".
Maybe if I say my "hearing loss is 20 dB at 1000 Hz" that makes it clear.
I would not say my "hearing loss is -20 dB"
Again, the double-negative
Or, would I say my signal is -2 S units fainter than my neighbor's signal? No.
I am new to all of the VNA stuff. I've only had this Nano VNA tool for 10 months and have done a meager job of learning the fundamentals, and learning some really basic concepts that I should have mastered decades ago.
My background is in astrophysics and physics - not in engineering or electronics.
But I've been a ham since 1958 and should be more aware of the vocabulary, if not the meaning of the formulas involving logarithms.
Again - interesting discussion. It has helped me.
I will likely continue to plot the RETURN LOSS graphs with negtive values, but I will stop myself from saying a RETURN LOSS is a negative number.
I'm convinced now.
The other topic I am struggling to really grasp is when plotting the PHASE (S11) of say a dipole antenna, that when the reactance changes from negative to positive, at resonance, the graph is SO SO steep. That amazed me. The PHASE graph is much sharper than the SWR graph. But then the RETURN LOSS graph is also much sharper than the reflection coefficient (rho) graph.
Maybe that is why engineers like these graphs where the resonance and loss is so obvious.
As hams, I often measure SWR with a crude (cheap) meter.
Generally I don't fret if the SWR is 2:1 or less. My radio seems content with that.
I never realized that a gazillion different impedance values can result in the same SWR of 2:1
Or said another way, if I know the SWR, do I know the impedance? NO!!!!
When I see that now on a Smith Chart - say a circle with rho=0.33 I can see the RIM of that circle can represent many different R,X values - all with the same SWR of 2:1
Why is that not taught more clearly in ham radio study guides?
Maybe the thought is that a Smith Chart is way too complicated for rookies.
No. I think reading about the Smith Chart taught me the difference in SWR and impedance.
De k3eui Barry