[amsat-bb] Re: Advice on antennas for working the LEO's

[Amir K9CHP]

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 at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
> Behalf Of Bruce Robertson
> Sent: Thursday, February 22, 2007 12:11 PM
> To: Gary McKelvie
> Cc: amsat-bb at amsat.org
> Subject: [amsat-bb] Re: Advice on antennas for working the LEO's
> 
> Quoting Gary McKelvie <garym at 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
> 
> 
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