1269 MHz Patch feed for the AO-40 L Band Uplinks

This patch is a scaled up version of the S band patch feed. Here are the 1269 MHz dimensions.

The reflector is 6 1/2" in diameter, made from a piece of 1/16" thick aluminum. A 1/8" hole is drilled in the center for the center 4-40 mounting bolt. 1 5/16" out from the center is a 3/8" hole through which the center conductor of a type N female connector extends. The type N connector, on the side of the reflector away from the patch, is attached to the reflector plate by four pan head 4-40 bolts with the heads on the side of the reflector facing the patch plate. The type N center conductor has a 3/4" length of a 6-32 brass bolt soldered to it for connecting to the 1269 MHz patch plate. Put a 1/4" size 6-32 nut on the brass bolt threads, outside spaced 3/8" from the reflector.

The 1269 MHz patch plate is 4 1/4" in diameter, and was made from 1/16" thick aluminum plate stock like the reflector. I drilled three holes in this patch plate. The first hole is a 1/8" hole in the center of the patch plate, the second hole is a 5/32" hole drilled 1 5/16" out from the center (mates to the type N center conductor on the reflector), and the third hole is a 3/16" hole, 1" clockwise from the type N hole, also 1 5/16" out from the center hole. I then carefully tapped this 3rd hole with a 10-24 tap.

I put a 3/4" long pan head 4-40 bolt through the center hole of the reflector from the side away from the patch, and fastened the center bolt to the reflector with four 1/4" wide 4-40 nuts. This provides the 1269 MHz patch spacing, which is about 3/8". You can trial fit the patch to the reflector, verifying that the second hole in the patch plate just fits over the brass bolt extending from the center conductor of the type N connector. The third hole, tapped to 10-24, should be clockwise from the 2nd hole for LHCP. If counter-clockwise from the 2nd hole, the patch becomes RHCP. Since the dish reflection inverts polarity, the desired RHCP dish needs the clockwise LHCP location for the third hole.

I made the adjustable bolt capacitor much larger for greater spacing since it will be used for transmitting. I soldered a nice shiney new penny to the centered head of a 3/4" long 10-24 flat head bolt. If the patch doesn't work out, you can always unsolder the penny.

Now carefully screw the 3/4" long flat head 10-24 bolt & penny into the threaded third hole on the patch, from the side of the patch that will be facing the reflector. Leave the coin head about 1/4" above the patch surface for now. Attach a 10-24 nut on the other side of this tuning bolt to act as a tuning lock. Finger tighten only as this 10-24 flat head bolt is riding on just a few threads. If you strip the plate threads, you can always put a second nut on the coin side of the patch plate, but it will be tougher to adjust.

Fasten the patch to the center bolt with another 4-40 nut, fastening the type N center conductor's 6-32 bolt extension to the 2nd hole in the patch with another 1/4" size 6-32 nut. . I experimentally determined that the best SWR for this 1269 MHz patch feed resulted when the flat head of 10-24 bolt and penny was spaced the thickness of six postcards (direct mail "Bingo cards") from the surface of the reflector (.042"). Lightly snug up the tuning lock nut when this spacing is achieved. Later, if you are happy with the performance, you can seal everything with some fingernail polish.

The picture at the left shows my test system used in the development of this 1269 MHz circular patch feed system. The handie-talkie is an ICOM 4 band thingie, an IC-T81A. One of its features is one watt of output from 1240 MHz to 1300 MHz, making it a dandy low power test signal source. The red cable has an SMA male connector on one end and a type N male on the other, delivering a real 3/4 of a watt to the SWR bridge.

The SWR Bridge is a dual needle Diawa CN 801-S which operates between 900 MHz and 2500 MHz. It has two input power ranges, 2 watts and 20 watts.

A short length Andrew 50 ohm hardline jumper and a 90 degree type N adapter connects the Diawa to the 1269 MHz patch. A 3" piece of RG-62 size coax outer sheath provides a non-conducting tuning tool to sneak up on the minimum SWR without so much hand capacity effect. I have been able to easily set the circular patch to less than a 1.2:1 SWR.

In the background is a 1264 MHz signal source described above, with the 1264 MHz vertical plugged in, and the 435 MHz and 145 MHz verticals on the table. The vertical antenna provides a rough test of circularity by twisting it around the perpendicular axis in front of the patch.

On a later model of this 1260 MHz circular patch feed I added another adjustable 3/4" long flat head 10-24 bolt for frequency adjustment. The bolt was located on the axial line extending from the type N connector through the center. The 10-24 tapped hole is placed near the edge at 2" from the center of the 1269 MHz patch.

Is it Worth it?

A 45 element loop yagi for 1269 MHz from Directive Systems claims 20 db of gain, and is linear polarized. It's a nice looking antenna, costing about $150. The 1269 MHz circular patch, however, in front of a 7 1/2' dish at a conservative 50 % efficiency will produce 27 db of gain, and the circular polarization is good for another 3 db over linear polarization into AO-40. For $10 worth of parts for the 1269 MHz circular patch feed! Now I carefully count my dbs, and 10 dbs gain is like attaching a 100 watt amplifier to the 10 watt output of your 1269 MHz rig and your signal will have less QSB too.

Even a 4' dish with this 1269 MHz circular patch feeding it is 4 db stronger than the linear 45 element loop yagi.

I run about 1 watt output from the 1269 module in my ICOM 910H. The measured output at the 1269 MHz patch feeding my 10' dish is 1/3 of a watt. Often this is too much power for the satellite, so I have to reduce power to about 1/10th of a watt at the patch feed. The 1269 MHz circular patch attached to the support arms of a 7 1/2 dish in place of the C band Chapparal feed that the TVRO dish originally had.