Hi all,

I need some advice (moral support?) as to the correct interpretation of
an MFJ259B output when testing traps as its handbook gives no guidance
for trap testing. Intuitive interpretation leads one up the garden path?
A commercial and home-brew trap gave the same results. Tests were done
as
follows:
(All measurements were verified by an additional external freq. counter)

A 50 ohm carbon resistor was used in series with the hot output which
connected to a 2-turn 55mm dia loop of wire that was loosely coupled to
a
trap for 40m; the other end of the loop going back to the MFJ ground.
The total loop alone measures R=51 X=14.
Tuning the frequency with the trap in-situ resulted in 3 points of
interest:

a) 7.00 MHz R=51 X=0
b) 7,08 MHz R=60 X=14
c) 7,20 MHz R=120 X=42

Which is the actual parallel resonance of the trap? My guess is point
(b)
where no reactance is added or subtracted by the "load" and the trap is
not
seen by the MFJ.
This is an in-between point that has no sharp tuning like points (a) and
(c)

I also assume point (a) is where the loop and trap combination present a
pure high dynamic impedance to the MFJ output.

The same test with a dip-meter and its associated coil only showed a dip
at point a) which I consider close but incorrect. The trap is admittedly
series-resonant and absorbs maximum power from the dip-meter but I
contend
that testing open-ended traps may be deceptive as they seem to exhibit
both
a series and parallel resonance not far apart.

Terminating the open end eliminates point (c) altogether as I proved
with a
swept measurement using an IFR analyzer: There is only a minimum
response
visible on the scope display around 7,20 MHz (c) which must be a
parallel
resonance as the trap is in series with the IFR input. However, the
proximity
of the trap body to the faceplate could influence the frequency but NOT
the
fact that the series resonance has totally disappeared.

Any comments will be welcome!
Thanks
Hans ZS6KR