In RDF navigation the more "fixes" one has the smaller the
ccccircle of confussion. For a variety of reasons, measurement
erros, propagation anolomies etc, the bearing is seldom perfect.
These imperfections create a difussed "circle" that the calculated
powiton lies witihin. Moer sighting/bearings gives smaller errors,
but using home built equipment one shouldn't expect world class
accuracy.

As a basic check pick a non NDB,make your measurements,
being carefuyll to note the GPS reading for each, and see how
close you come to hitting the transmitters location.

I su pect that yoru antenna will be far from accuarte with some
imbalance. that will be hard to quantify exactly. As a fun project,
that will teach you a lot about navigation go for it, but as a serious
attempt I suspect you will be dispointed.

Even at NDB low fRF frequencies, there are too many things
that will cause transmission path errors. I live about 15 miles from
the Lexington Blue Grass Fild NDB and even with a barrowed
mil grade RDF setup it's apparent bearing changed by several
degrees the month I had the unit. The NDB in Frankfort and Mt.
Steerling "wondered" all over the place. with sudden randon sshifts
up up to +/- 5 degrees. The pilot who loaned me the unit told me that
the closer to the earths surface you got with a LF RDF the more error
you
pikced up. At 5000' the error was very small. This was 25 years ago
and I suepct not much has changed.

This was an aircraft RDF and at that time still was within the
calibration cycle.

Good luck and have fun.

Terry