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Ian Jackson · December 23rd 06, 08:32 AM posted to rec.radio.amateur.antenna

In message . com,
writes

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

Driving the diode with a wideband RF amplifier would have the following
advantages:
(a) allow a lower level of RF sample to be used (higher tap-off ratio).
(b) further minimise the possibility of diode distortion products from
getting back into the RF through-signal.
(c) drive the diode at a higher level, thus improving the RF-in to
DC-out linearity.
Do any SWR meters do this?
Ian.
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