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The 4302 or the newer 4312 (which seems
hard to find) are the modules I'm thinking of. I think the 4302
was mentioned in ZL1AXG's article.
The placement between the LPF and the
pre-driver puts the ATTN in the antenna path on RX which is
presumably 50 ohm and I assume is also 50 ohm on TX considering
the by-directional LPF.
This placement, to non-engineer me,
looks like the ideal "effector" location for an RX AGC scheme,
ahead of any active devices. Or it could just be setup as a
manual RF gain control on RX. It is also looks like a very
straight forward way to control drive levels per band on TX,
either via pre-sets or an ALC setup.
I'm also thinking that this approach
should be largely free of "unintended consequences".
In any case it looks like an enjoyable
73 Jack KZ5A
On 4/19/2019 5:10 AM, Tom, wb6b wrote:
On Thu, Apr 18, 2019 at 04:26 PM, Jerry Gaffke wrote:
You could easily control that attenuation from a
These may be a little overboard for the purpose but I have one of
each of these digitally controlled attenuators that I bought to
build up my tool set for making RF measurements.
This one had the part number of the attenuator chip ground off.
Depending on the manufacture of the part, the specified low
frequency cutoff could be 9Khz, 1Mhz or 10Mhz. For HF measurements
a possible 10Mhz cutoff is an issue.
However, the construction with the machined aluminum body is
This one specifies the part number in the description and the
number on the attenuator chip matches. It is a 9Khz to 4Ghz
attenuator. It doesn't have a display, so would be a better choice
for installing into the uBitx.
You can also buy the current version of the Peregrine attenuator
chip from Digikey, mount it on a SMD adaptor board and add it to
your uBitx IF chain. But, the modules are easier to work with.
These parts have an actual 50 ohm impedance (when the other end is
50 ohm terminated). It might be that the 50 ohms is a bit more
load that the IF chain was designed for.