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Re: Helical array (was ... well never mind)

On 1999-05-21 kf4fdj@AMSAT.Org said:
   >CC: amsat-bb@AMSAT.Org

   >gets my attention, and I am sure it will get the attention of other
   >operators on this reflector.
   >Are you a current operator?  What type of station do you have at

 Mainly Operate Mode A and Pacsat, not as active as I would like to be.
 In the Elementry school I teach part-time at we are running electives
 based on Space themes. DO-17 was fun when it was running and the kids
 enjoyed decoding telemetry. MIR never ceases to please the students,
 The school board has provided a small room to setup as a "SHACK" I
 am planning on canvassing the local clubs for equipment donations.
 I have some surplus radio gear here, Two Meter All Mode/70 Cm
 transverter, Power supplies, etc. Thats why we are looking at trying
 to cobble together the antennas/mounts/amps for free or next to it.
 Some people have e-mailed me suggesting Mode B setup as well.

   >Both Ramsey, and Hamtronics sell preamp kits
   >that are adequate for mode J work.  A 3 db noise figure, although
   >marginally usable on 2 meters, will fail miserably on 70 cm.  Most
   >modern, mast mounted GasFet preamps have noise figures around .5 db.
   >On 2 meters, a noise figure of 1.5 db will work nicely.  Go for as
   >low a figure as you can on 70 cm.

 I had looked at the Hamtronics Helical resonators, The area I live in
 is a small town with very little RF pollution in 2/70cm bands. I could
 likely get away without the bandpass filter/amp. I just thought I could
 rework the TV Amp in/out and maybe get the noise down to 1 db or less.

   >Hard line is 75 ohm TV coax.  Is that what you mean?  The garden
   >variety 75 ohm line you use at home would certainly handle the
   >power, but is so lossy, a run of any length would introduce so much
   >thermal noise to your system, it could render it useless.  Ladder
   >line could be used for longer runs with proper baluns at both ends,
   >and the loss/cost ratio is good.  At a minimum, I would recommend
   >9913 coax.  How much do you need for the school setup?  I might be
   >willing to finance that part of your school install.  I have a
   >partial spool of 9913 in my garage.

 The local Cable TV operator had to replace a few bays from a bad storm
 during the winter. They said I could take it and use it if I wanted,
 after looking at it I can say that there is no way I can route it into
 the schools "SHACK" the stuff has almost no bending radius. I estimate
 we need about 60 feet of 9913 to go from the shack up onto the school roof.
 And anything you could offer would be most welcome! Barring that I had
 considered using that RG-6 stuff that is used for satellite dish LNB
 Feeds. Though I am told its not the best way to go.

   >There are some operators who have made interfaces for the Alliance
   >rotator.  Message Bill Briles, W0OQC, he made one a few years ago.
   >Jeff Griffin, KB2WQM, is currently working on one.  I like the idea
   >of using a basic stamp type controller for the Alliance rotator.
   >Mark Hammond, KC4EBR helped develop one.  Try contacting him.  All
   >3 of these operators have AMSAT aliases.
   >I hope to work you soon on one of the birds!
   >73, Mike

 Thanks Mike, I will do that! and I will keep you informed on the progress
 of the installation and kids elective.



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