wrote in news:1166596897.289275.21440@
48g2000cwx.googlegroups.com:

Today I was making some measurements with my MFJ-259B. From the manual,
I read:
....

What concept am I screwing up here?

Scott, your measurments are all over the place like a wild woman's
whatchamacallits.

Is the broadband detector in the MFJ being influeced by RFenergy received
by the antenna? That will make the readings worthless. Just try a quality
reflectometer (eg a Bird 43) and see if the readings are consistent with
the '259... if they aren't ask yourself why.

My experience (like others reported in the thread) is the MFJ259B is
potentially misleading on 2m.

As for your original question, MFJ's hint is useful, but visualise where
your observations mapped on a Smith chart, and assumption of one of the
two possible signs for the reactance will often seem less sensible or
even inconsistent. Additionally, it you calculate the load impedance
(considering the line's characteristics) at the load end of the line, and
consider readings at several nearby readings, again one of the two
possible sign assumptions for reactance will seem less likely to be true.

(Pity you can't plug in a line type and length and the analyser calculate
the impedance at the load end of the line, may be do it now? The
calculator at http://www.vk1od.net/tl/tllc.php will perform the calcs for
you.)

I see advice that you use an integral electrical half waves of coax or
just a foot of coax. Neither eliminates impedance transformation by the
coax when you sweep 4MHz as you have done.

Owen


-Scott, WU2X

Here are the values I measured:


Freq R X SWR
--------------------------------------
144 44 2 1.1
144.25 46 4 1.1
144.5 55 7 1.1
144.75 60 7 1.2
145 68 0 1.3
145.25 78 0 1.4
145.5 79 0 1.4
145.75 73 11 1.5
146 63 21 1.5
146.25 53 23 1.5
146.5 46 21 1.5
146.75 40 18 1.5
147 37 10 1.5
147.25 35 8 1.4
147.5 37 6 1.3
147.75 41 10 1.3
148 48 15 1.3
148.25 59 19 1.4
148.5 75 16 1.6
148.75 90 0 1.7
149 96 6 1.9