Great advice Don. (Nice website too.)
One little point I would add to comments about listening to whether you hear
band noise when connecting that antenna, is that if you're performing this
test at VHF, or even the high end of the HF, the actual
connection/disconnection of the antenna should be from the back panel of the
radio, not via an antenna switch with some undetermined length of coax.
What can happen is that sometimes simply connecting an open length of coax
to the antenna input may change the audible noise coming from the receiver's
speaker. I haven't tried this with my K3s, but I've observed this effect
with other * radios, especially ones which depend on good input impedance
matching for their antenna inputs.
This effect is related to the length of the coax relative to the frequency
you're listening to, so I doubt if it would be noticeable below, say 10 or
15 M with a few feet of line to an antenna switch.
73, Charlie k3ICH
*I specialize in the restoration of the Collins 51S-1 receivers, and have
noticed this effect with them. The 51S-1's sensitivity is quite susceptible
to degrading from an unmatched antenna. During an alignment, I see a
small, but noticeable difference in the antenna input coil adjustments from
using a matched 50 Ω signal generator versus leaving the antenna input open
and relying on the calibrator signal for peaking.
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