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Old December 23rd 06, 03:03 AM posted to rec.radio.amateur.antenna
[email protected] nm5k@wt.net is offline
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First recorded activity by RadioBanter: Jul 2006
Posts: 757
Default IMD products from VSWR meters


Antonio Vernucci wrote:
Because active SWR meters do not usually suffer
from this effect, they can normally be left in without causing such
problems

Can anyone clearly explain what is an "active" SWR meter? I would presume that
the line is decopled from the diode by means of an amplifier. Is that what they
mean?

73

Tony I0JX


In this neck of the woods "active" usually means the meter has
peak reading circuitry that requires power to operate. In general,
as far as ordinary peak reading meters, this is the most accurate
type as far as trying to read voice peaks. The better ones use
fast acting LED's as the meter.
A "passive" meter is one that uses capacitors to give the meter
a "hang time" to sort of read peaks. But it's not as accurate, and
almost always reads low. "20-25% worth" for the average meter.
The cross needle meter in my MFJ-989C is an example of a
passive meter circuit. I call it "psuedo peak reading". :/
I also built a passive circuit into my old green cube heathkit
meter. It has a switch on the back to switch the caps in or out.
Naturally, the passive meters require no power to operate.
MK