...I heard mentioned on eham here several times in the past on other forums that the best place for a choke on the coax is one quarter wavelenght down or away from the feedpoint...
Just goes to show that you can't trust everything you hear on the internet!
Actually, this isn't a bad location for a SECOND choke if you need one.
With the choke 1/4 the way down the feedline, you have effectively a 1/4 wave radial
wire connected to the feedpoint. That's about the best
you can do to encourage
current to flow in it instead of the antenna. If you are using an antenna with a poor
ground anyway (such as a ground plane with inadequate radials, or and end-fed half
wave, etc.) then the added radial may improve the SWR due to increased
currents on the feedline.
Since chokes aren't perfect, if the objective is to minimize currents on the feedline,
it is best not to encourage them in the first place. That's why the choke goes as
close to the antenna is possible.
A choke at a high impedance point in a feedline isn't as effective as one at a low
impedance point. Putting a second choke 1/4 wave after the first means that only
one of them will be at a high current point, and the other second will attenuate
any currents that make it past the first one. But if you have that much common
mode current that you need two chokes, you probably need to rethink your