In the Argonaut, find the wire that runs from the
TX final to the antenna relay. (These are on different
boards if I remember, so there should be a length of
RG-174 running between the board plug connectors.
Unsolder one end and run it to one of the unused RCA
jacks on the back panel. Run another length of cable
from one of the other jacks back to the point where you
unsoldered it. Put a jumper or the attenuator between
the two jacks, and it will have no effect on the
legendary QSK, while putting the attenuator in just
the transmit side.
While a good step attenuator can be used for either
QRPp or foxhunting, you may want different ones for
each application. The resistor closest to the TX
will have to dissipate the most power, and since you
don't necessarily know which sections will be switched
in, it is probably best to wire all the attenuator
sections using 1- or 2-watt carbon or metal-film
resistors. Construction and, especially, shielding,
are not as important at HF, and you probably only need
up to 30dB of attenuation (unless you want to go below
1mW.)
For foxhunting (especially on VHF) the shielding of
the attenuator is most important - not just between
sections, but good commercial units have a shield
down the middle of each section to isolate the two
sides of each switch. But even the best commercial
shielded attenuators rarely give more than 60 or 70dB
of usable range - beyond that direct pickup through
the case of the receiver will be stronger than the
signal from the attenuator. This is why most serious
hunters that I know use an "offset" (or "active")
attenuator - this is a frequency converter with a
variable injection level, capable of providing over
100dB of attenuation. There are a number of designs
on the net. Personally I like to use a double balanced
mixer since it reduces the response to paging
transmitters and other stray signals.