Traps and advertising claims
Mon, 17 Feb 1997 16:54:53 -0500
> We can talk about models and manufacturers claims and theory and how
>things "seem" until the cows come home and get tangled in the beverages, but
>until we start making some real, meaningful measurements we probably won't
>be any closer to the truth.>
Then K8DO said:
>We actually do have some real measurements that reveal very low power losses
>in good traps, performed by measuring temperature rise for a given power
>input over a given time, using a KT34XA... At this moment my
>Al-what's-his-name disease is kicking up and I do not remember who reported
>that...or on which reflector...
Interesting idea, and I had also assumed that if there is loss, then power
is lost as heat.
But then Mr. Cebik writes:
"The loss of gain due to the use of traps or other forms of loading
elements does not necessarily mean loss of power in the sense of
conversion into heat. Hence, a low-Q trap does not turn it into a
resistor. Rather, it turns it into an inefficient trap, which allows
significant power beyond the trap point. Low Q will also mean a higher
resistance, but in relationship to the reactance of the components, and
this may also create a higher power loss, but usually not to the point of
self-destruction. The reduction of gain on 20 meters of a 20-15-10 meter
trap beam is in part due to the fact that at 20 meters, the traps act as
inductive loads in the elements, reducing effective radiation from the
element to the degree that coil loads can be considered to be almost
non-radiating substitutes for what would otherwise have been at that point
a linear radiating element segment."
This is food for thought, and if this is the effect that low-Q traps have,
then measuring temperature rise in the traps won't tell the whole story.
This might explain why a computer model shows significant loss (ie. nearly
3 dB) but the traps still don't burn up. Comments, anyone? Still seems to me
that the only way to really know is to compare the antennas, either on
receive or using a field strength meter.
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