Building a LS dual-band patch for AO-40
W0LMD did the real work here,
and to him, I gratefully give credit and thanks. His pages on dishs
and dish feeds
are very useful and helpful.|
Nonetheless, I found the original
instructions difficult to follow, so I wrote up my own pictorial form which
may be at least easier to visualize. Let's start with a parts list, that
way you can at least know what you need. Then there'll be lots of pictures
explaining what to do.
Note: Click on pictures on this page to enlarge.
What you'll need
1 - 10"x14" galvanized sheet metal (in roofing department), cut as follows
6 5/8" diameter disk: Rearmost 1269 MHz reflector
4 3/8" diameter disk: 1269 MHz patch
3 1/2" diameter disk: 2401 MHz reflector
2 3/8" diameter disk: 2401 MHz patch
1 - 1 3/4" 10-24 (or 10-32) bolt
3 - 10-24 (or 10-32) nuts
1 - 1/2" steel (or nylon) spacer
2 - 1/4" nylon spacers
1 - 1/2" 6-32 flat head brass bolt
1 - 6-32 brass nut
8 - 1/2" 4-40 flat-head bolts
8 - 4-40 nuts
2 - 1" long 1/4-20 flathead brass bolts
2 - 1/4-20 brass nuts
tin snips or aircraft shears
assorted drill bits up to 3/8"
1/2" countersink (and/or grinder to enlarge holes)
1" Greenlee chassis punch (or hole saw for soft metal)
nutdrivers (for 4-40 and 10-32 bolts)
soldering iron (not too small) and/or tapping tools
hack saw [optional]
compass for drawing circles [optional]
Cutting and drilling
Cut out four disks from roofer's sheet metal as listed in parts list. You
might want to drill a small hole in the center, and use that to draw your
circles. Precision is nice, but not a stiff requirement and you can touch
things up with a file. I couldn't find my compass, so i just used string
with the drill bit i just used as a center
Drill a 3/16" hole in the center of each of the 4 disks which will be used for
axial alignment of the disks. If you're following me closely, then you may
just be enlarging existing center holes.
On the 2401 MHz patch, drill two 1/8" holes, each 11/16" from center and
1/2" apart. Choose the more accurately drilled and select which side to
use such that this hole is on the counterwise side of the center hole.
Screw all four disks together with 10-24 bolt and drill 1/8" hole through
the remaining three disks using that hole as a guide.
Unscrew the disks and tap the other 1/8" hole to 6-32 thread (but if
the metal is thin, expect to solder a nut to this point facing away
from the reflectors and don't bother with a tapping tool).
Please see the K5MAN
S patch engineering drawing for details if the above instructions aren't clear.
On 2401 MHz reflector, enlarge the 1/8" hole to 3/8" for male N-connector
(you may need 1/2" for some connectors). Position connector and drill four
1/8" holes using the connector as a template (countersinking if reflector
is thick enough for this to make sense). Attach connector with four 1/2"
4-40 bolts and corresponding nuts.
Bolt together 1296 MHz patch and reflector, and drill 5/32" hole, 1 5/16"
from center and 90° clockwise from 1/8" hole. Drill 1/8" hole out
to 3/8" for male N-connector.
Unfasten patch and enlarge both 3/8" holes to 1" using a Greenlee chassis punch
(the device that some of the old-timers used to use for tube sockets).
Again, see K5MAN L patch engineering drawing for details if these instructions aren't clear.
Drill holes in reflector to accomodate your choice
of mount (see original W0MLD instructions for Chaparral mount), unless you're just using your
downconverter's N-connector to support the feed (what I did). That may be
risky if the uplink feed isn't safely secured and someone yanks on the cable.
On 1269 MHz reflector, drill 3/16" hole, 1 5/16" from center and 1"
clockwise from 5/32" hole, for circularity bolt. Drill another 3/16" hole,
2" from center and 180° from 5/32" hole, for the frequency bolt. Tap
both out with 1/4-20 tap. Drill 5/32" hole out to 3/8" (or 1/2") for female
Position connector and drill four 1/8" holes using the
connector as a template (countersinking if reflector is thick enough for
this to make sense). If you have no tapping tools but patience and a hot
enough iron, then you can solder the nuts to the reflector instead (that's
what I did).
Hints and putting it together
Assembly should be fairly straightforward with pictures to guide you. The
N connectors are pretty obvious, and you don't solder the nuts as shown
here unless you're not using a tapping tool (and/or if your sheet metal
This shows things as they are attached to each disk prior to finally
Before attaching things, you may want to consider a few hints which may save
you time later.
Check to make sure the spacing is uniformly 1/2" between the 2401 MHz patch
and reflector, then solder the center pin of the male N-connector, which
should be barely produding above the 2401 MHz patch to the patch itself, as
shown above. After you do this, you won't be able to access the area between
the 2401 MHz patch and its reflector, but you should still be able to
separate the two patches and fix other things if necessary.
I couldn't find the right size of 1/2" spacer, but one size was close enough
that it was simply a matter of drilling out the spacer to make the 10-24 bolt
fit through it. By using spacers instead of nuts between the patches and
their respective reflectors, you can take things apart if something goes wrong
This concludes the assembly phase. For now, please see the last several
paragraphs of the
instructions for information about calibration (tuning). You will
probably hear the beacon with a small offset-fed dish without calibration,
but this will improve reception and is necessary before attempting to
transmit with this device. One of the major reason people use too much
power on AO-40 is that they can't hear very well, so concentrate on getting
the reception part working well first.
Again, we gratefully acknowledge
W0LMD, who did the real work
here. See some of his other pages on
and other interesting topics for more project ideas.