[600MRG] Checking SWR

[John Langridge]

Hi Tom,

While some have physical meters at their operating position, probably
a larger number of us are using scope match, which monitors voltage
and current on the line and displays two sine waves which can be
superimposed to represent 50 +j0 ohms. Varying magnitudes and phases
display less than optimal values for R and X.   There are so many
scopes on the used market that this can solve the problem in a very
inexpensive and reliable manner.

One problem which can result from using an MFJ meter / tuner is that
the sense ferrite is not designed for MF/LF and can heat to the Curie
point very quickly destroying its ability to read anything.   That
problem occurred at my station many years ago with an MFJ 949E
tuner/meter/dummy load.  The meter always read 2:1 SWR no matter what
the load condition.  On one test the ferrite finally gave up the
smoke, to the point where the wire burned off of the core.    SO it
comes down to saying be careful when using meters outside of their
spec'ed operating range.

73!

John KB5NJD..




On 3/17/19, Tom Costa <tomcosta1953 at gmail.com> wrote:
> After finishing my amplifier, I was looking for a way to keep an eye on the
> SWR.
> I found that my old MFJ Versa Tuner II, MFJ-941B, seemed to work on 630
> meters.
> I’ve been experimenting with it for about a week and it does seem to do a
> good job showing the relative SWR.
> I’ve compared it to the built-in SWR display on the Monitor Sensors
> transverter and reads the same.
> I don’t trust it for actual power output measurements but for monitoring
> forward and reverse it works fine.
> My amp is setup for a meter but I had to order a 500uA meter and the MFJ
> does fine in the meantime.
> I’ve not seen much info on using or modifying existing meters for 630 meters
> so I thought I’d just throw this out there.
> 73
> Tom
> N9RU
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