Hi - just wonder if anyone has any comments on the MFJ 974H tuner,
please. I am thinking of getting one to use with a 260' centre fed
antenna and balanced line. It seems the ideal tuner to use having a
direct balanced output and not one via a balun.

Many thanks,

Peter

Peter wrote:

Hi - just wonder if anyone has any comments on the MFJ 974H tuner,
please. I am thinking of getting one to use with a 260' centre fed
antenna and balanced line. It seems the ideal tuner to use having a
direct balanced output and not one via a balun.

There was some discussion about moving the balun from the output
of an unbalanced tuner to the input. It is generally accepted
that action will not improve things very much. The only difference
in that action and what MFJ has done is that, in the MFJ-974H,
there is some series capacitor impedance opposing the common mode
current. That series impedance varies with capacitor settings and
is therefore not constant.

The Johnson Matchboxes suppressed common mode current through link
coupling (no balun required). The MFJ-974H doesn't use link coupling
so the common mode current flows right through the tuning caps. And
the MFJ-974H does indeed have a balun function on the source side of
the network. It appears to be a w2du 1:1 choke balun. So the MFJ-974H
is not as good at choking common mode currents as the Johnson Matchbox
and not extremely superior to an unbalanced tuner with a w2du 1:1
choke balun on the output.

I'm not trying to discourage anyone but the MFJ-974H may not be an
extreme improvement over an unbalanced tuner with a w2du 1:1 choke-
balun on the output.
--
73, Cecil http://www.qsl.net/w5dxp