[Hammarlund] antenna connection

[Mike Taylor]

Wow, Dan...Lot's of stuff about baluns. Yes, what you're seeing is normal.
Try using a longwire on a C.B., scanner, or car radio and you'll get the
same thing when you use coax. If you hook a longwire antenna to the center
conductor of a coax connector, and screw on the outer connector on the
radio's coax jack, the sensitivity will go way down. This is because you are
trying to use a longwire antenna (which is unbalanced) into a balanced coax
input. With no ground plane connected to the coax braid on the antenna side,
the coax acts like an inductor. The  braid is shorting out with the center
conductor. Look at it like this: You're asking a radio signal to go into the
center pin of the coax connector, that's fine. But when you ask that RF to
travel through a wire that has a chassis ground braid surrounding it for
many feet, the inductance between the braid and center conductor (only a few
ohms) is the same as if you wrapped wire around your single wire antenna
lead-in. Screwing the outer coax connector on the SO-239 is the same as if
you took the wire wrapped around your lead-in and hooked it to chassis
ground. You won't hear much of anything. If you want to use the coax
connector, it's designed for 50 ohm antenna systems (such as a ground plane
antenna which is not practical below 15 meters). For a dipole or longwire
antenna, use the antenna screw terminals which are designed for 300 ohm
systems.  For a dipole antenna: connect to the two antenna terminals. For a
longwire antenna: connect to the first antenna screw, and jumper the second
antenna screw and ground screw together. (In either case, the ground screw
to a decent ground is good but not necessary). A longwire antenna can go to
the center of the coax connector but the braid should be connected to the
longwire at the antenna feed point and should not be screwed onto the
receiver's coax connector. Experiment with this and you'll get the picture.
73's Mike.