05-14-2001, 03:15 PM
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Mike, K4IZN, has set up a low cost S-Band station for working AO-40. He has several homebrew antennas and a modified down converter. Here are the details…
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http://www.qrz.com/pics/dsc_008.jpg
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CONVERTER RECOMMENDATION: The Drake 2880 is a fun project for someone who likes to tinker and try to get "something for nothing". It is
much better than no equipment at all for S-band !!!. I do not think an unmodified 2880 is worth more that $75 especially without a 2 meter crystal. If you want to enjoy "armchair" copy or you get more pleasure from making contacts than tinkering then I recommend a commercial down converter. I think the SSB UEK-3000SAT is the best unit available. It sells for $460 from SSB USA (”).
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Mount it at the antenna feedpoint and run RG-58U from it to the RX in the shack (then turn the RF gain down and enjoy).
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http://www.qrz.com/pics/dsc_002.jpg
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DRAKE 2880: I bought my unmodified 2880 about 2 years ago from an individual for $35 (including a new crystal). I don't have a current source for the Drake. If you know of a source, please post a response. All the modifications for this unit are available at <a HREF=http://members.aol.com/k5oe/> Jerry, K5OE: Home Brew Amateur Antennas</A> site. Look under the Drake 2880 mods section. Similar units made for TV service are not as easy to modify and/or do not perform as well. Check with someone that has successfully modified a unit of the type you are considering before you buy it!
PERFORMANCE: The 2880 with no external pre-amplifier is a very marginal performer. I can copy CW stations very well. SSB stations are very difficult to copy. Signals are just barely above the noise level. A better antenna than the helix would improve this situation. I have plenty of projects to look forward to. By the way, I tried to copy the MB with a few green trees obstructing the path and signals were too degraded to copy!!!
HELIX: My antenna design is very similar to one described by K5OE, Jerry on his web site, see above. Look at the section on his 13cm double helix. I built a right hand single helix with different dimensions. All the wire I used is scrap type NM copper (used for electrical wiring). The PVC is 1 5/8" outside diameter plumbing pipe. Two 18" long sections are needed. They are joined together with a straight coupling after winding the helix and installing the reflector.
The helix is 12 turns of #12 bare wire spaced 1 1/4" per turn. The wire is first close wound on the pipe and then stretched to the correct total length of 15 inches to give it a tight fit and uniform spacing. The helix is held in place by small plastic ties that pass through holes (just under and to each side of the wire) in the pipe and around the wire. A tie is placed at each end and also the middle of the helix.
The ring reflector is made from #10 copper wire with the insulation left in place except for just enough space to join the ends together. A piece of hookup wire is wound over both ends of the exposed wire which is "butted" together and solder is blended into the joint. The pipe coupling is installed such that the reflector ring lies against its edge around the pipe. This holds the ring "squarely" and gives it good mechanical stability. The ring is positioned about 1/4" from the end of the helix.
The coax is type RG-11U and is about 12" long. The N connector was installed before making the connections to the antenna. I removed about 1" of the coax jacket, exposed 1/2" of center conductor, and trimmed off the shield so that 1/4" of it is exposed. Hookup wire is wrapped around the ring reflector butt splice and the other end is wrapped around the coax shield. The ring and shield are pulled together and everything is soldered. The center conductor of the coax is bent to align with the helix and soldered to the end of the helix conductor. Some sources recommend reducing the space of the first turn of the helix. I have not seen any performance improvement from this.
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<TD VALIGN="TOP">After completing the pipe assembly and attaching the converter I placed a mast bracket at the balance point on the pipe. I have no test equipment to determine the feedpoint impedance of this antenna but I do know that for receiving AO-40 it works! POINT IT CAREFULLY.
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http://www.qrz.com/pics/dsc_001.jpg
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Hope to see you on AO-40.
73
Mike K4IZN
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<TD VALIGN="TOP">
Mike, K4IZN, has set up a low cost S-Band station for working AO-40. He has several homebrew antennas and a modified down converter. Here are the details…
</TD>
<TD>
http://www.qrz.com/pics/dsc_008.jpg
</TD>
</TR>
</TABLE>
CONVERTER RECOMMENDATION: The Drake 2880 is a fun project for someone who likes to tinker and try to get "something for nothing". It is
much better than no equipment at all for S-band !!!. I do not think an unmodified 2880 is worth more that $75 especially without a 2 meter crystal. If you want to enjoy "armchair" copy or you get more pleasure from making contacts than tinkering then I recommend a commercial down converter. I think the SSB UEK-3000SAT is the best unit available. It sells for $460 from SSB USA (”).
<TABLE>
<TR>
<TD VALIGN = "TOP">
Mount it at the antenna feedpoint and run RG-58U from it to the RX in the shack (then turn the RF gain down and enjoy).
</TD>
<TD>
http://www.qrz.com/pics/dsc_002.jpg
</TD>
</TR>
</TABLE>
DRAKE 2880: I bought my unmodified 2880 about 2 years ago from an individual for $35 (including a new crystal). I don't have a current source for the Drake. If you know of a source, please post a response. All the modifications for this unit are available at <a HREF=http://members.aol.com/k5oe/> Jerry, K5OE: Home Brew Amateur Antennas</A> site. Look under the Drake 2880 mods section. Similar units made for TV service are not as easy to modify and/or do not perform as well. Check with someone that has successfully modified a unit of the type you are considering before you buy it!
PERFORMANCE: The 2880 with no external pre-amplifier is a very marginal performer. I can copy CW stations very well. SSB stations are very difficult to copy. Signals are just barely above the noise level. A better antenna than the helix would improve this situation. I have plenty of projects to look forward to. By the way, I tried to copy the MB with a few green trees obstructing the path and signals were too degraded to copy!!!
HELIX: My antenna design is very similar to one described by K5OE, Jerry on his web site, see above. Look at the section on his 13cm double helix. I built a right hand single helix with different dimensions. All the wire I used is scrap type NM copper (used for electrical wiring). The PVC is 1 5/8" outside diameter plumbing pipe. Two 18" long sections are needed. They are joined together with a straight coupling after winding the helix and installing the reflector.
The helix is 12 turns of #12 bare wire spaced 1 1/4" per turn. The wire is first close wound on the pipe and then stretched to the correct total length of 15 inches to give it a tight fit and uniform spacing. The helix is held in place by small plastic ties that pass through holes (just under and to each side of the wire) in the pipe and around the wire. A tie is placed at each end and also the middle of the helix.
The ring reflector is made from #10 copper wire with the insulation left in place except for just enough space to join the ends together. A piece of hookup wire is wound over both ends of the exposed wire which is "butted" together and solder is blended into the joint. The pipe coupling is installed such that the reflector ring lies against its edge around the pipe. This holds the ring "squarely" and gives it good mechanical stability. The ring is positioned about 1/4" from the end of the helix.
The coax is type RG-11U and is about 12" long. The N connector was installed before making the connections to the antenna. I removed about 1" of the coax jacket, exposed 1/2" of center conductor, and trimmed off the shield so that 1/4" of it is exposed. Hookup wire is wrapped around the ring reflector butt splice and the other end is wrapped around the coax shield. The ring and shield are pulled together and everything is soldered. The center conductor of the coax is bent to align with the helix and soldered to the end of the helix conductor. Some sources recommend reducing the space of the first turn of the helix. I have not seen any performance improvement from this.
<TABLE>
<TR>
<TD VALIGN="TOP">After completing the pipe assembly and attaching the converter I placed a mast bracket at the balance point on the pipe. I have no test equipment to determine the feedpoint impedance of this antenna but I do know that for receiving AO-40 it works! POINT IT CAREFULLY.
</TD>
<TD>
http://www.qrz.com/pics/dsc_001.jpg
</TD>
</TR>
</TABLE>
Hope to see you on AO-40.
73
Mike K4IZN