Building a LS dual-band patch for AO-40

Introduction

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

Parts:
  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

Tools:
  tin snips or aircraft shears
  electric drill
  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)
  tape measure
  medium screwdrivers
  nutdrivers (for 4-40 and 10-32 bolts)
  soldering iron (not too small) and/or tapping tools
  file
  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 point.
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.
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 N-connector. 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).
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.

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 is thin).

 This shows things as they are attached to each disk prior to finally assembly.

Before attaching things, you may want to consider a few hints which may save you time later.


One thing that is helpful is to put slots into the aligment screws on the 1269 MHz side. This was done with a mitre box and a hack saw. This should make alignment of the transmit side easier, where SWR really does count for something.

Another little detail that I discovered when I tried to put things together was that the male N-connector interfered with the nuts holding the center screw down.
So this little 'user modification' was required, which was to take an ordinary file and remove enough material so that the nut cleared the N-connector.
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 later.
My assembly method differs slightly from the original in terms of the use of spacers. We also start with the 1269 MHz reflector, the largest disk. The 10-24 bolt starts on the connector side and a 1/2" spacer goes on the bolt as shown. 1/2" of #12 copper wire is soldered to the N-connector [not shown here] before the next level is attached.
This is followed by the 1269 MHz patch, which is secured by a 10-24 nut as shown. The other end of the #12 jumper is now soldered to the top of this patch (and you won't be able to get to things underneath this patch after that.)
We add a 1/4" nylon spacer, secured by a 10-24 nut, and then the 2401 MHz reflector. This is where you find out for sure if need to file down your N-connector to make it fit.
We add another a 1/4" nylon spacer, then the 2401 MHz patch, and we secured the whole thing with a 10-24 nut. Becase we don't use a nut between the 2401 MHz reflector and its patch, we can still take things apart if necessary.
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.

Conclusion

This concludes the assembly phase. For now, please see the last several paragraphs of the original 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 dish feeds and other interesting topics for more project ideas.