Topband: Beverage Resistors

[DAVID CUTHBERT]

Dave,

metal film resistors do not have much thermal mass in the metal film. For a
short term overload such as lighting induced current the metal film can be
damaged as it reaches vaporization. Carbon composition resistors are a
favorite for Beverage antennas because the resistive element has
considerable thermal mass for both short term and long term energy input. It
takes roughly 40 joules to pop a 2 watt carbon comp resistor.

Wirewound resistors do not have much short-term thermal mass. The
contra-wound "non-inductive" wirewounds suffer from this same issue as well
as arcing between the two layers of wire turns.

Thick film on ceramic substrate resistors can take a good amount of short
term energy. However, the 1% types are often laser trimmed and these thin
slices in the resistive element tend to arc during high current/voltage
conditions, damaging the resistor. I would go with 5% resistors.

The ultimate low cost Beverage resistor is the Pulse-eater. The carbon comp
and the Ohmite surge rated ceramic core resistors are a good second choice.
If cost is no object the big pulse resistors from Globar are the ultimate.

     Dave WX7G

On Wed, Oct 14, 2009 at 7:05 PM, R. David Eagle <kb8nnu at yahoo.com> wrote:

> hello all...
>
> This question is for all you beverage experts out there - Can you use metal
> film resistors for the terminating resistors???  If not, what is the best
> kind to use that is worth its cost/benefit?
>
> Thanks again,
>
> Dave
> KB8NNU
>
>
>
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