If you can't find suitable fixed attenuators at the local swap meet, I
can highly recommend MiniCircuit's inexpensive HAT-series (with BNC
connectors, also available with N and SMA).
http://www.minicircuits.com/dg03-152.pdf for more details. These run
$9.95 each and are real bargains. If you are serious about RF work, a
set of these in the steps 1, 2, 3, 6 (x2), 10 (x2) and 20 dB (x2) is an
excellent investment. This will let you make up any attenuation value
from 1 dB to 78 dB in 1 dB steps. (granted, stringing all 9 attenuators
in series for 78 dB is a bit awkward, but you get the idea.)
I know Minicircuits has a UK distributor, not sure about VK-land.
Jack
Geoffrey Mackenzie-Kennedy wrote:
Evening Kevin,
A step attenuator capable of adding up to140db or so of loss is
certainly very useful when working with receivers, but would be quite
expensive I believe. If two step attenuators were used in cascade they
would have to be built and connected in such a way that ensures that
the attenuation in any sneak path around the attenuators at all
working frequencies is >> 140db, and that the switched pads that make
up the attenuators do not talk to one another via spurious paths.
But even with a perfect step attenuator, the crosstalk between the
coax cables connected to the attenuator must be considered. The
leakage from coax such as RG-174 or RG-58 would be enough I think to
provide a significant sneak path around a 140db attenuator, adding
measurement error particularly so if the cables are physically close
to one another. Double screened coax helps to reduce this problem.
Leakage from the signal generator must also be considered.
To get around these problems but still have a useful step attenuator
for single frequency tests, I use a compromise arrangement consisting
of a 90db step attenuator and two HP 11708A 30db fixed attenuators or
pads with N connectors, in a way slightly similar to what you are
suggesting. Having a fixed 30db pad right at the circuit / receiver
under test provides a reasonable 50 ohm source, likewise a load for
the step attenuator. The second 30db pad when used is placed at the
generator's output. The step attenuator includes five 1db steps which
I find to be very useful at times. Double screened coax all the way.
73,
Geoff
GM4ESD
----- Original Message ----- From: "kbgluxford" <[EMAIL PROTECTED]>
To: "Elecraft Reflector" <[email protected]>
Sent: Thursday, September 28, 2006 8:12 AM
Subject: [Elecraft] new mini-modules: applications
Wayne and list members,
The AT1 step attenuator looks very interesting. However, would we
not need an attenuator capable of 140 db or so for receiver testing?
Yes we could cascade four of them, but this would scarcely be very
cost effective. How about supplying the same circuit board and parts
but with a different set of resistors to enable increases in
attenuation in say, steps of 40 db, which would mean that we would
only have to buy two kits.
Best regards from Downunder
Kevin
VK3DAP / ZL2DAP
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