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Re: Advice on antennas for working the LEO's



I continue to be amazed that folks have still not gotten this message:

USE A PREAMP!  It is the single most significant item for operating 
satellites --- succesfully!

Repeat after me:
If you cannot hear em - you can not work em!
If you cannot hear em - you can not work em!
If you cannot hear em - you can not work em!
If you cannot hear em - you can not work em!
If you cannot hear em - you can not work em!

OK, got it now! You can use a very simple antenna for LEO satellites 
--- IF YOU USE a PREAMP!
For AO-51 mode-U, I have used a 2m whip - 1/4 wavelength (20-inches 
high) with a 432-MHz preamp.
That's it!

You can run a small yagi for your 2m uplink, pointed 20 degrees 
elevation and either manually rotate it or use a cheap TV rotator.
I have used my 3-element Arrow antenna and 5w.
Bob Bruninga has explained this a "million" times --- I admire his patience!

So what is the most important part of a satellite station?
huh?
eh?
what?

a preamp

73's Ed - KL7UW

At 12:24 PM 2/22/2007, Amir K9CHP wrote:
>I'm working LEO sats with a Kenwood D7AG HT and an Arrow II antenna. I have
>settled on putting the Arrow on a light tripod in a way that allows me to
>aim it both in azimuth and elevation and adjust for polarization. In
>addition, I've added a Hamtronics pre-amp to the 70 cm receiving end of the
>antenna. It is powered by the smallest 12v  SLA battery I could lay my hands
>on. The amplifier is definitely the best addition to the system. I can now
>hear satellites at full scale quieting and tune for Doppler by ear and by
>looking at the scale. Recently, as I'm planning on a trip, I've gone back to
>work my Pryme AL-800 antenna, just to get more experience with it. Yes, I
>can work satellites with it and make contacts, but the difference between
>the Pryme and my regular setup is rather substantial.
>
>So Bruce, I'm definitely with you on pre-amps at the antenna.
>
>73' de Amir K9CHP Member ARRL, AMSAT #36083
>Cayuga County Highland SAR www.highlandsar.org
>1st Special Response Group www.1srg.org
>Apprentice Tracker Joel Hardin Professional Tracking Services
>http://www.jhardin-inc.com
>
>
>
> > -----Original Message-----
> > From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On
> > Behalf Of Bruce Robertson
> > Sent: Thursday, February 22, 2007 12:11 PM
> > To: Gary McKelvie
> > Cc: amsat-bb@amsat.org
> > Subject: [amsat-bb] Re: Advice on antennas for working the LEO's
> >
> > Quoting Gary McKelvie <garym@garym.org.uk>:
> >
> >
> > > Several people have suggested using a vertical antenna such as a
> > > colinear. I have actually already tried this and the results are very
> > > disappointing, which I put down to my location rather than anything
> > > else as where I am is not particularly that good certainly form a
> > > VHF/UHF point of view.
> >
> > Gary:
> >
> > We look forward to working you on this side of the pond. If I remember the
> > details of this thread correctly, one of your design goals for this system
> > is to not require preamps. I would venture to say that most every antenna
> > design or recommendation pertaining to satellite work assumes low-noise
> > preamps as close to the antenna as possible. This might explain the
> > difference between your experience and others' with vertical antennas.
> >
> > What I love about this aspect of the hobby is the experimentation. Though
> > my antennas are down right now, there have been many silent mid-Atlantic
> > passes of VO-52 where I have amused myself by testing the minimum signal
> > required for reception, used varying antennas, and switched in and out a
> > preamp or two. Just me and an orbiting radio laboratory; thank you, ISRO!
> >
> > Conducting such experiments with my pair of FT-817s and TS-2000 suggests
> > that a preamp is terribly important, especially for 70cm downlink
> > operation. In fact, my 70cm preamp is an indoor model, and it *still*
>makes
> > a crucial difference. I think this is because the NF of these radios'
> > preamps is just not devised for small-signal work. To put it more
>strongly,
> > I would rather spend an evening doodling around on 70cm with a (indoor)
> > preamp and a coathanger-and-bnc vertical than I would with my 8 element
> > rotating outdoor beam and no preamp!
> >
> > Your high-gain, narrow bandwidth antennas will make up for this, of
>course.
> > But other beginners might be interested to know that by using preamps and
> > shorter, wider bandwidth antennas it is possible to have exceedingly
> > enjoyable LEO satellite operations with a single, azimuth-only TV-type
> > rotor. The approach offers some advantages: such short antennas are also
> > easier to build from scratch materials, easier to put up on in the air;
>and
> > the wide beamwidth of the antenna makes it possible to manually control
>the
> > rotor without too much fuss. The advantage of your az/el system is that it
> > will be closer to HEO-ready when P3E and SSETI are launched next year.
> > However, I venture to say that you really will need preamps then.
> >
> > I started out using HRD, but like others, I have found that recent
>versions
> > do not track SSB/CW correctly, and it seems that Simon's focus is now on
> > the latest digital Swiss Army Knife. If you have difficulties of this
> > nature, try the demo of SatPC32 or other dedicated programs.
> >
> > Again, for others with a different set of resources, there's a great
> > discussion of why a fixed-elevation rotor system works well at:
> > http://web.usna.navy.mil/~bruninga/rotator1.htm
> > I would advise that homebrewers begin avoiding circular polarization and
> > the mechanical challenges that entails. Many of us have had good luck
> > building the so-called 'cheap yagis':
> > http://www.wa5vjb.com/yagi-pdf/cheapyagi.pdf
> > My 70cm one is 8 elements; I found my 4 element 2m to be a bit
> > under-powered for receiving AO-7, but I had fun with it for 2 years!
> >
> >
> > 73, Bruce
> > VE9QRP
> >
> >
> > _______________________________________________
> > Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author.
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>
>_______________________________________________
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