[Antennas] Re: B&W

[Dave Kelley]

At 04:01 AM 7/22/2002 -0400, you wrote:
>New on the list.
>I just picked up a B&W 5-30 mhz dipole and would like a few pointers.
>First I can get
>up to 30 foot on the ends and 40 foot in the center if I REALLY have to.
>I have a
>MFJ 949D tuner if anyone recommends it. It will be oriented north and
>south almost true
>and I have a huge lake about 200 yards from the south end. What can I
>expect in results?
>Any help or other suggestions will be appreciated.
>de
>Jim  k6tit

Jim,

I'm not intimately familiar with the B&W dipole, but I think I can give you
a few pointers so you know what performance to expect.

The reason you may have heard disparaging remarks about the antenna
is because it is designed to be a compromise.  The antenna uses a 
resistor to help it to maintain an input impedance close to 50 Ohms (and
hence an SWR below 2:1) across the specified frequency band.
Although its broadbanding effect is desirable, the resistor also absorbs
a significant amount of power. Thus, you won't radiate as strong a signal
with this antenna as with other (less broadband) designs.  As long as
you're aware of the compromise and are willing to accept the power loss
in return for a no-tune, broadband, easy-to-use antenna, then don't let
anyone make you think twice about your decision.  If it's a compromise
you're willing to make, then the B&W is the right antenna for you!

The radiation pattern of the antenna should be very close to that of a 
dipole of the same length.  That is, the antenna should radiate most
strongly in the broadside direction (perpendicular to the wire) at the
lower frequencies. At the higher frequencies there may be some 
lobing.  In other words, there may be several directions of maximum
radiation interspersed with radiation nulls. There will be very little 
radiation off the ends of the antenna at all frequencies, depending
on how V-shaped or not the antenna is laid out.  The lake will probably
have no noticeable effect on the performance of the antenna; nearby
surrounding objects, such as your house, will be more important in
that regard.

The tuner shouldn't be necessary as long as the SWR of the antenna
is below about 1.5:1 on the bands you're interested in using. This 
assumes that you're using a rig manufactured in the last 20 years or
so.  If you use an older rig (characterized by load/tune controls that
must be adjusted every time you change bands), then you can get by
with a much higher SWR (up to 3:1 or more?), since the load/tune
controls essentially act as a built-in tuner.

I hope this information helps you out (and other owners of this or
similar antennas).

73,
Dave NB4J

--
Dave Kelley, NB4J
Lewisburg, PA
Union County