amdx wrote:

If I wind a transformer using the specified A sub L and then use that
transformer in a receive antenna where the voltages are very small, wouldn't
I be low on the curve and cause the transformer to function poorly
especially at the lowest frequency of the design?

Mike

PS Thinking about a Flag antenna, which has a small output signal.

Mike,


I think you are focusing on non-issues and not consider things that are
really important.

First, I would not use a 43 core on a low frequency receive antenna.
This is especially true with an ungrounded antenna that has
exceptionally low signal output, like a Flag.

There are very few antennas in the world that are perfectly UNbalanced
or perfectly balanced. Even what we consider an unbalanced antenna can
cause feed system problems. When the antenna has very low signal
output yet occupies a large spatial area, you are especially looking at
problems.

The flag has low common mode impedance, and fairly high differential
mode impedance. It is neither balaunced nor unbalanced, it is in that
soupy world of something that requires equal and opposite currents at
the feed without perfect voltage balance. It is not a balanced antenna,
and not an unbalanced antenna.

When that is combined with the very low signal output, you have to pay
particular attention to the transformer design.

You really can't use a transmission line transformer because it will
not have enough isolation. You need a primary-secondary transformer
with isolated and slightly seperated windings. You really don't want a
material that requires 30 or 40 turns, because extra wire will increase
stray capacitance from primary to secondary.

You almost certainly want to move into a binocular core with fairly
high permeability at the lowest frequency, like a 73 material. Unless
you have a few volts of RF from a closeby station, flux density is not
an issue.

You want to keep primary/secondary capacitance down near a dozen pF or
less if possible, and have NO direct path for common mode currents.

http://www.w8ji.com/k9ay_flag_pennant_ewe.htm

73 Tom