Cecil Moore wrote:
I'm considering putting up a 1/4WL vertical for 30m
with four slanted elevated 1/4WL radials. I looked
at all the bands, 40m-10m. Take a look at the
performance of this antenna on 10m where it is
an omnidirectional 5/8WL, 4.28 dBi at 10 deg.
Note the four radials are also 5/8WL.

Keep the 5/8WL vertical on 10m and shorten the
radials to 1/4WL (8.25').
0.57 dBi at 10 deg.
3.5 dBi at 24 deg.
4.4 dBi at 53 deg.

Looks like 5/8WL radials may work better for a
5/8WL vertical than 1/4WL radials.

Sure...Old news to me....
http://web.wt.net/~nm5k/acompari.htm

I've used that exact antenna...was designed mainly as a 5/8
for 10m, but also used it as a 1/4 on 30m.. I used 3/4 wave
radials the last time...."10m".
I also did the same thing on 40/17...My full size 40m GP
doubled as a 5/8 on 17m. I used a 24 volt relay to switch
in a loading coil for the 5/8...In modeling those,
I found the 5/8 should have more gain than the 3/4 radials,
but seems to me, the 5/8 radials would need to be tuned to
work properly...IE: think dual 5/8 radiators...One up, one
down...The 3/4 radials are a good match as is, being the
reactance is tuned out with that length...
BTW....Vuuuurrrrryyy important...If you dual band it, you
must use an ungrounded series matching coil. There can be
no dc connection to ground, if you want it to work on 30m.
MK