[Hammarlund] Re: antenna connection

[Mike Taylor]

----- Original Message -----
From: "Mike Taylor" <reel2reel@hotmail.com>
To: <dcsfree@worldnet.att.net>
Cc: <hammarlund@mailman.qth.net>
Sent: Saturday, February 07, 2004 1:10 AM
Subject: antenna connection


> 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.
>