Triband_S_2L

Making a Left Circular 2401 MHz, Dual Circularity 1296/1269 MHz, and Dual Circularity 432/435 MHz Patch Feed for EME and AO-40

This tri band patch feed with dual circularity on the U & L bands is almost identical to the single left circularity triband version. The main differences are a number of extra holes punched for the extra connectors and tuning bolts. The placement of the connectors and tuning bolts was chosen for greatest circularity symetry.

If only single band dual circularity is desired, the unneeded U or L band RCV connector can be omitted along with its diametrically opposite frequency tuning bolt.

A single circularity triband patch feed system should not be converted to dual circularity as many of the U and L band disk holes will be in the wrong place.

A tri band (S, L, & U) circularly polarized patch feed for EME and AO-40 is shown in the picture at the left. It uses 6 disks carefully placed in an axial line. As shown in the picture at the right, all connections to this tri band patch come out the rear of the 432 reflector, along with 6 of the 7 tuning adjustments. Things will get a bit confusing at times, but just follow step by step to avoid a lot of scrap metal when things don't quite fit.

There is plenty of room on the back of the 432 reflector disk for EME preamps and relays. A DL2AM solid state 80 watt 1296 amp could also be mounted behind the 432 reflector.

Cutting out the 6 Disks

Start by cutting out the 6 disks. The 2401 MHz patch (the smallest disk, in the front) is 1/32" (1/16" would be easier to tap) brass for solderability. The 2401 MHz reflector, the two 1269 disks and the 435 MHz patch disks are made from 1/16" aluminum, and the 435 MHz reflector is made from 1/8" aluminum.

Cut the rearmost 435 MHz reflector to 16 1/2" diameter. Cut the 435 MHz patch in front of the 435 MHz reflector to 14" in diameter. Cut the 1269 MHz reflector to 6 5/8" diameter. Cut the 1269 MHz patch to 4 1/4" in diameter. The 2401 MHz reflector is next at 3 1/2" in diameter, and finally cut the 2401 MHz patch out of a piece of brass to 2 3/8" in diameter. I use K & S brass from a local hardware or hobby store rack.

Center Hole in All Six Disks

Drill a 3/16" hole in the center of the 6 disks which will be used for axial alignment of the disks when a 10-24 bolt, 3" long, is passed through the disks. Make a mark anywhere on the brass disk that is 11/16" out from the center hole. This will be the point of attachment of the 2401 MHz coaxial connector and the centering hole for the larger clearance holes in the bigger aluminum disks. Temporarily bolt the six disks together tightly with the brass disk on top. Now drill a 1/8" hole through the mark on the brass disk and the 5 aligned aluminum disks below the brass disk. Remove the 10-24 bolt and mark one side of each disk as "UP".

2401 MHz Patch Plate

Put a mark on the brass disk 1/2" clockwise from the 1/8" feed hole, also 11/16" out from the center hole. Drill a 1/8" hole in the brass 2401 MHz patch at this point. Then tap this hole with a 6-32 tap held perfectly perpendicular to the surface of the 2401 MHz patch. Screw in a 1/2" long 6-32 flat head bolt from the "down side". Put 1/4" wide hex 6-32 nut on the "UP" side of the bolt, with about 1/8" extending downwards. Finger tighten the nut to avoid stripping the threads in the brass disk. This screw will be used to tune for best received circularity and strongest received signal (hopefully the same point). Set the brass disk aside for now.

2401 MHz Reflector

Now the 2401 MHz reflector is drilled out to attach a type N male chassis connector. This design requires a connector set that is about 3 " long from the back of the 2401 MHz reflector to 1/2" or more from the back of the 435 MHz reflector. I achieve this with a type N male chassis connector, a type N double female connector, a type N double male adapter, and a type N right angle to the downconverter mounted behind the 435 MHz reflector. VE7BPB suggested using two short pieces of brass or copper tubing like a 50 ohm power divider design instead of all the adapters. Drill out the off center 1/8" hole previously drilled to 3/8" exactly centering the drill on the 1/8" hole. Some chassis connectors have a bottom taper that may require as much as a 1/2" hole for center pin clearance. This type N male chassis connector is attached from the "DOWN" side with four 4-40 flathead 3/8" long bolts inserted from the "UP" side. Holding the connector centered in the 3/8" (1/2") hole with the outer edge of the connector parallel with the outer rim of the 2401 MHz reflector, mark where the holes will be drilled. Drill four 1/8" holes at the marks. Then turn the 2401 MHz over and counter sink bevel the holes from the "UP" side so the four flathead screws will attach as flush as possible. Now attach the type N male chassis connector to the "DOWN" side of the 2401 MHz reflector using the four 4-40 flathead 1/2" long bolts and 4-40 1/4" nuts. Screw a type N double female adapter into the type N male chassis connector and a type N double male adapter into the female adapter. Looks very powerful at this point.

1269 MHz Patch Plate

The 1269 MHz patch plate gets two more holes on its "UP" side. Draw a line from edge to edge, through center & the 1/8" feed hole previously drilled for the 2401 MHz feed hole. Now draw two lines 45 degrees off from the edge to edge line just drawn. Put a mark on each line 1 5/16" out from the center, on the side opposite the 2401 feed hole. This will be the 1269 MHz patch's two feedpoints. Bolt the center of the two 1269 MHz disks together with "UP" up, patch on top. Then temporarily lock the two plates' orientation together by putting a short 4-40 bolt through the 1/8" holes drilled in each. Now drill a 5/32" holes at the mark on the two lines for attaching the 1269 MHz coaxial center pins.

Unfasten the two plates and drill a 3/8" hole centered on the 1/8" alignment hole. Dig out your old 1" Greenlee tube hole punch and punch a 1" hole in both the 1269 MHz reflector and 1269 MHz patch plate for the 2401 MHz feed to pass through. Set the 1269 MHz patch plate aside.

1269 MHz Reflector

Orient the 1269 MHz reflector disk with "UP" upwards, and the 1" hole down. The 5/32" holes drilled in the previous section should be at the top. Place a mark between the two 5/32" holes, also 1 5/16" out from the center. This hole will be used for the circularity adjusting bolt. Drill a 3/16" hole at this mark. Now draw two lines across the top of the disk, starting at a 5/32" feed hole continuing through the center hole to the opposite edge. 2" out from the center, place a mark on each line for the frequency adjusting screw. Drill a 3/16" hole at these marks too. Tap out the three 3/16" holes with a 1/4-20 tap, keeping the tap perpendicular to the surface of the plate.

Drill out the two 5/32" holes to 3/8"(1/2" for some connectors) for the type N female chassis connectors, making sure you keep the 3/8" (1/2") holes centered to the 5/32" holes. Then, while holding each female chassis connector centered in the hole and the edges parallel with the rim of the disk, mark the four holes that are used to attach each connector. Drill the eight holes with a 1/8" drill. From the "UP" side counter sink bevel the 8 holes so that the eight 4-40 flathead 3/8" long bolts will lie flush.

Attach the type N female chassis connectors to the "DOWN" side of the 1269 MHz reflector plate using eight 4-40 flathead 1/2" long bolts and 4-40 1/4" nuts. From the "UP" side of the 1269 MHz reflector plate screw in a 3" long 1/4-20 flathead bolt into each of the two 1/4-20 tapped holes diametrically opposite the two connectors from the "UP" side. Leave extended about a 3/8" high and place a 1/4-20 nut on the "DOWN" side of each bolt to lock it in place after calibration. Finger tighten only, to avoid stripping the threads in the plate.

Make a special circularity adjusting bolt by soldering a 1 1/8" diameter piece of brass to the flat head of a 3" long 1/4-20 flathead bolt. The larger capacity permits greater spacing need by the higher EME powers that may be used. From the "UP" side of the 1269 MHz reflector plate screw in this special circularity adjusting bolt into the 1/4-20 tapped hole between the two connectors from the "UP" side. Leave extended about a 3/8" high and place a 1/4-20 nut on the "DOWN" side of each bolt to lock it in place after calibration.

435 MHz Patch Plate

The 435 MHz patch plate gets two more holes on its "UP" side. Draw a line from edge to edge, through center & the 1/8" feed hole previously drilled for the 2401 MHz feed hole. Now draw two lines 45 degrees off from the edge to edge line just drawn. Now put a mark on each line 3 3/4" out from the center, on the side opposite the 2401 feed hole. This will be the 435 MHz patch's two feedpoints. Bolt the center of the two 435 MHz disks together with "UP" up, patch on top. Then temporarily lock the two plates' orientation together by putting a short 4-40 bolt through the 1/8" holes drilled in each. Now drill a 5/32" holes at the mark on the two lines for attaching the 435 MHz coaxial center pins.

Unfasten the two plates and drill a 3/8" hole centered on the 1/8" alignment hole. Dig out your old 1" Greenlee tube hole punch and punch a 1" hole in both the 435 MHz reflector and 435 MHz patch plate for the 2401 MHz feed to pass through. Set the 435 MHz patch plate aside.

435 MHz Reflector

The disk with the most holes will be this 435 MHz reflector. Orient the disk with "UP" upwards, and the 1" hole down. The 5/32" holes drilled in the previous section should be at the top. Place a mark between the two 5/32" holes, also 3 3/4" out from the center. This hole will be used for the circularity adjusting bolt. Drill a 3/16" hole at this mark. Now draw two lines across the top of the disk, starting at a 5/32" feed hole continuing through the center hole to the opposite edge. 6" out from the center, place a mark on each line for the frequency adjusting screw. Drill a 3/16" hole at these marks too. Tap out the three 3/16" holes with a 1/4-20 tap, keeping the tap perpendicular to the surface of the plate.

435 MHz Circularity and Frequency Adjusting Bolts

Attach the type N female chassis connectors to the "DOWN" side of the 435 MHz reflector plate using eight 4-40 flathead 3/8" long bolts and 4-40 1/4" nuts. From the "UP" side of the 435 MHz reflector plate, screw in a 1 1/2" long 1/4-20 flathead bolt wit a 1 1/8" diameter brass disk soldered to its head into each of the two 1/4-20 tapped holes diametrically opposite the two connectors from the "UP" side. Leave extended about a 3/8" high and place a 1/4-20 nut on the "DOWN" side of each bolt to lock it in place after calibration. Finger tighten only, to avoid stripping the threads in the plate.

Make a special circularity adjusting bolt by soldering a 1 1/8" diameter piece of brass to the flat head of a 1 1/2" long 1/4-20 flathead bolt. The larger capacity permits greater spacing needed by the higher EME powers that may be used. From the "UP" side of the 435 MHz reflector plate screw in this special circularity adjusting bolt into the 1/4-20 tapped hole between the two connectors from the "UP" side. Leave extended about a 3/8" high and place a 1/4-20 nut on the "DOWN" side of each bolt to lock it in place after calibration.

Assembling the Tri Band S, L & U Patch

In reverse order, or "bottom up" sequence, place a 3" long 10-24 bolt through the center hole in the 435 MHz reflector plate from the "DOWN" side. Fasten with a 10-24 hex nut and firmly tighten. Now put another 10-24 nut on the the 10-24 bolt and adjust so that a 1" space between the plates will result. The center conductor of the type N female chassis connectors have to extended. I cut the head off two brass 6-32 bolts to 1 1/2" long and sharpen the cut off end on a grinder so that the end result is about 1 1/4" long. I tin this sharpened end and the center conductor of the type N female chassis connector. Holding the sharpened end on the center conductor, I solder the two together with this center conductor extension standing up straight, perpendicular to the surface of the 435 MHz reflector, on each connector.

The next thing to do is mounting the four 1" nylon spacers to the 435 MHz reflector "UP" side. These nylon spacers are 1" long, 1/2" in diameter, and have an 1/8" hole bored through the center. I tapped the hole out to 8-32 on either end of each spacer and attached them to the 435 MHz reflector using four 1/4" long 8-32 bolts.

Screw in the circularity adjusting 1/4-20 bolt with the 1 1/8" brass head into the 1/4-20 tapped hole nearest the 435 MHz reflector plate's type N connector, from the "UP" side. Screw it in so that the head stands about 3/4" off the surface of the reflector.

Screw in the frequency adjusting 1/4-20 flathead bolts with the 1 1/8" brass heads into the 1/4-20 tapped hole diametrically opposite each type N connector on the 435 MHz reflector, from the "UP" side, so that its head is near the surface of the reflector at minimum capacitance.

Place the 435 MHz patch plate on the center mounting bolt and align the patch plate so the 1" holes match and the feed screws goes through the 5/32" feed holes in the patch plate. The holes in the top of the spacers should also appear. After appropriate adjustments are made if needed, remove the patch plate, put a 5/16" wide 6-32 hex nut on each brass screw coming from the type N connectors and a 10-24 nut on the center bolt so the patch plate will be spaced 1" from the reflector, put back the patch plate and add another 10-24 nut, a 6-32 nut on each connector extension, and four 8-32 bolts into the 1" nylon spacers to hold the patch plate firmly in place. The 435 MHz patch plate should be spaced 1" from the 435 MHz reflector all around and the brass screws should not be pulled up, potentially breaking the solder joints. You should have three 1" holes lined up for passing the 2401 MHz and 1269 MHz adapters through, and three 1/2" holes lined up for passing the 1269 MHz Circularity and Frequency adjusting bolts through.

Put another 10-24 nut on the center screw, placed so a 1/2" spacing from the front of 435 MHz patch plate to the back of the 1269 MHz reflector plate occurs. Place the 1269 MHz reflector on the center hole, with the type N male long chassis connector with type N double female adapter extending through the center of the 1" holes in the 435 MHz reflector and 435 MHz patch plate and the two 1269 MHz tuning bolts extend through the 1/2" holes in the 435 MHz reflector and 435 MHz patch plate. Now put another 10-24 nut over this center screw to lock the orientation perfectly centered.

Put a 5/16" wide 6-32 nut on the 6-32 brass bolt extension from the type N male long chassis 1269 MHz connector and screw it down so that its top surface is 3/8" from the surface of the 1269 MHz reflector. Put another 10-24 nut on the center screw, placed so there will be 3/8" of separation between the top of the 1269 MHz reflector plate and the back of the 1269 MHz patch. Place the 1269 MHz patch plate on the center hole, with the 6-32 brass bolt extension from the type N male long chassis 1269 MHz connector coming through the 5/32" hole in the 1269 MHz patch plate. Put another 10-24 nut on the center 10-24 bolt to hold the 1269 MHz patch plate solidly to the tri band patch feed assembly, checking to see that you have 3/8" spacing all around on the 1269 MHz reflector to 1269 MHz patch plate. Add a final 5/16" hex 6-32 nut on the brass center feed bolt and you have the 1269 patch section assembled.

Put another 10-24 nut on the center screw, placed so a 1/2" of 1269 MHz patch plate to the back of the 2401 MHz reflector plate separation occurs, and place the 2401 MHz reflector on the center hole, with the type N male long chassis connector with double female and double male adapters extending through the center of the 1" holes in the 1269 MHz patch plate, 1269 MHz reflector plate, 435 MHz patch plate, and 435 MHz reflector plate. Now put another 10-24 nut over the center screw to lock the orientation perfectly centered.

Put another 10-24 nut on the top of the last nut, snug it up and verify that you have 1/4" spacing. If your nuts are not exactly 1/8" thick like mine, then use washers to achieve 1/4" spacing between the 2401 MHz reflector and the 2401 MHz patch plate. Align the 1/8" hole in the 2401 MHz patch plate with the center conductor underneath. Add a final 10-24 nut to the center bolt to lock the 2401 MHz patch plate to the assembly. You can use a small wire to bridge a gap if your center conductor is short, but I usually just form a solder bridge between the center conductor and the 2401 MHz 1/8" feed hole.

At this point you should have an interesting stack of six disks that looks like it might not only communicate with the moon directly but get a QSL card from the Man on the Moon!

Attach this S, L, & U tri band patch in place of the C Band Chaparral feed horn as detailed above. Connect a 435 MHz coax to the type N female connector at the back of the 435 MHz reflector plate, a 1269 MHz coax to the type N male adapter coming from the back of the 1269 MHz reflector plate, and put a downconverter on the type N male long connector. An AIDC 3731 is shown in the picture at the right. Attach a coax line with a type F male connector to the down converter.

Calibration

I find that if I have exactly followed the dimensions and set the 7 alignment bolts as will be detailed, the patch will work very close to perfect without further tuning.

2401 MHz

Loosen the 6-32 locknut on the 2401 MHz patch plate and turn the front screw so that it is spaced .020" or the thickness of 3 "bingo" postcards above the reflector.

1269 MHz

Loosen the 1/4-20 locknut on the two frequency tuning bolts (diametricly opposite the 1269 MHz coax connectors). Turn each 1/4-20 flathead bolt so that it is as far from the 1269 MHz patch plate as possible. Loosen the 1/4-20 locknut on the circularity tuning bolt coming through the 435 MHz reflector plate and nearest to the 1269 MHz type N connectors, and turn the bolt so that it is just touching the back of the 1269 MHz patch. Note the position of the slot on this flathead bolt and turn the bolt back exactly 1 turn (.05") or 7 "Bingo" postcards separation. These setting will be very close, but you can use the diametricly opposite frequency 1/4-20 bolt to trim each of the two 1269 MHz patches to exact frequency. I achieved an almost perfect match when these bolts are 2 turns back (.1") or 21 "Bingo" postcards separation from touching the rear of the 1269 MHz patch. If you have any asymetry, you can balance it out with different settings for the two frequncy bolts.

I use an ICOM T81 as a 1 watt signal source into a Diawa 801S dual needle UHF SWR bridge for final tuning each 1269 MHz connector for the best match over the range of 1269 MHz to 1296 MHz, optimizing at 1296 MHz..

435 MHz

Loosen the 1/4-20 locknut on the two frequency tuning bolts (diametricly opposite the 435 MHz coax connectors). Turn each 1/4-20 flathead bolt so that it is as far from the 435 MHz patch plate as possible. Loosen the 1/4-20 locknut on the circularity tuning bolt coming through the 435 MHz reflector plate and nearest to the 435 MHz type N connectors, and turn the bolt so that it is just touching the back of the 435 MHz patch. Note the position of the slot on this flathead bolt and turn the bolt back exactly 2 turns (.1") or 14 "Bingo" postcards separation. These setting will be very close, but you can use the diametricly opposite frequency 1/4-20 bolt to trim each of the two 435 MHz patches to exact frequency. I achieved an almost perfect match when these bolts are 3 turns back (.15") or 21 "Bingo" postcards separation from touching the rear of the 435 MHz patch. If you have any asymetry, you can balance it out with different settings for the two frequncy bolts.

I use an AEA 140-425 Graphic Analyzer to final tune each 435 MHz connector for the best match over the range of 432 MHz to 435 MHz, optimizing at 432 MHz.

Attaching the Downconverter

I don't want any coax loss between the 2401 MHz patch and the downconverter, so I plug the AIDC 3731 downconverter directly into the type N adapters. There are two mounting configurations that I have used. I generally screw the AIDC 3731 input directly into the type N double male adapter coming out the back of the dish. This will result in the downconverter sticking out perpendicular to the 435 MHz reflector which is not so good mechanically, but I have never encountered any problem. I use this system on my 10' dish. Another option is to use a type N right angle adapter and tie wrap the downconverter to 1/4" holes drilled in the 435 MHz reflector. This is much stronger mechanically but introduces the slight loss of another coax adapter. I use this system on my 14' dish. To stabilize the AIDC 3731 downconverter, I remove the 12 V regulator inside it, never remove voltage from the downconverters, and put 1" pipe insulation around the AIDC 3731 to prevent Sunlight/shadow drift.

Mounting the tri band circular patch on your BUD

I drill six 1/4" holes at the edge of the 435 MHz reflector for mounting the tri band circular patch to the dish arms. The holes are in a pattern spaced 120 degrees for 3 arm support systems and 90 degrees for 4 arm support systems. The objective is to put the feed exactly in the center of the dish with the brass 2401 MHz patch at exactly the focus point of the dish.

The original Chapparal feed is about 7" in diameter and the 435 MHz reflector is 16 1/2" in diameter, so if you use the original feed mounting poles spread further apart, your feed will be too far away. There are two techniques for bringing your new feed system into focus. You can attach the feed arms to a special support that holds the tri band circular patch at the correct place, or you can cut the tubes off so the spacing is correct. I calculated that the tubes were 4 1/4" too long, so after cutting off 5" and putting both ends inside a larger tube 3/4" apart, the feed system focused in just perfectly but if not, I could space the tubes for perfection.

Sources for the type N connectors

Some people have e-mailed me telling me that they were unable to located some of the type N connectors and adapters used on these multi-band circular patch feed systems. I got the type N male chassis connector, long, from Radioshack.com, but they went out of business last Summer, and I have been unable to find any more. I now use the short standard version which works fine. Pasternack (949) 261-1920 has these connectors (PE4131) for $8 each as well as the double male (PE 9007) and the double female (PE 9006) also at $8 each. Their type N female chassis connector (PE4013) is $5 each. Hangar 19 in Texas may also have these connectors and adapters at more reasonable prices (around $3 to $4 each). Avoid the cheap plastic insulated type N connectors. They melt when soldered, and sometimes result in a patch impossible to tune for low SWR.

Does it work?

???More about this later.......