[NLRS] Checking out performance of a satellite ground station

[James Klassen]

I haven’t tried this, but I am just thinking along the lines of estimating
coax loss at various frequencies by measuring the return loss of a length
of coax that is shorted or open at the far end.

What would happen if return loss was measured at 145Mhz and 290Mhz using
the assumption the antenna impedance should show a low return loss (high
SWR) at the second harmonic?

Would the difference in return loss between the two frequencies give an
idea of if the power is being lost in the coax (hence high return loss and
low indicated SWR across a wider range of frequencies/low Q) vs making it
to the antenna (which should have a relatively narrow resonance peak/high
Q)?

Or for that matter just measuring the 2:1 SWR bandwidth and seeing if it
matches predictions for the antenna type?  Anything wider would likely
indicate losses.

On Tue, May 3, 2022 at 10:30 Jon Platt via NLRS <nlrs at mailman.qth.net>
wrote:

> That some of the coax connectors were not weather sealed may not be good.
> I have seen cases where there has been water in the feedline but that the
> SWR was still low, so SWR alone may not be an indicator.   My only thought
> would be to borrow a Time Domain Reflectometer (TDR) that can see any bump
> in impedance along the feedline.  I do not own a TDR but perhaps someone on
> the list here may.  Otherwise a visual inspection by moving the connector
> and seeing if moisture is present can work too.   Good luck.
> 73, JonW0ZQ
>
>
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