What kind of feedline are you using for the UHF antenna? This is meant as an open question to all related to this. Do you *really* need a preamp because you are using something lossy and noisy like most braided shield feedlines?

73 de Pat --- KA9SCF. Amsat #35741

Hi Pat, Just a couple of thoughts,

You need a preamp to strengthen the signal from the satellite to 1) overcome any change of Polarity which may occur during reception.

2) to strengthen the signal to be stronger than any noise picked up in the transmission line - which could compete with a week signal.

3) to overcome any losses in the transmission line and it's connectors which can be significant.

Personally I use a high quality, low Loss, well shielded transmission line, and a Pre-amp (capable of switching when RF is applied) and with a gain of at least 25 db and a very low noise factor < 0.9db

I do get good results.

Robin Haighton VE3FRH Immediate Past President AMSAT Canadian Representative to ARISS Past President BARC Member ARRL, RAC, RSGB, AMSAT-NA, AMSAT-UK.

-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Patrick Green Sent: Friday, August 17, 2007 9:15 AM To: Amsat BB Subject: [amsat-bb] Re: eggbeater II antenna performance oscar 50-52

What kind of feedline are you using for the UHF antenna? This is meant as an open question to all related to this. Do you *really* need a preamp because you are using something lossy and noisy like most braided shield feedlines?

73 de Pat --- KA9SCF. Amsat #35741

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At 10:20 PM 8/17/2007, Bruce Robertson wrote:

... Do I remember correctly that designs such as this are less circularly polarized at the low elevations than they are overhead? If so, have you considered the Lindenblad by Tony, AA2TX? http://www.arrl.org/qst/2007/08/monteiro.pdf

If you're building either antenna specifically for VO-52, you might consider making it LHCP, which I believe is the polarization of the 2m signal transmitted by Hamsat. (Tony reports that his RHCP design nonetheless receives VO-52 well.)

A low noise preamp at the antenna will make a huge difference also at 145 MHz.

Dear Friends,

I have designed, built and used both "Eggbeater" and Lindenblad (omni-directional) antennas for LEO satellites. (You can find my "Eggbeater" design in the 1998 AMSAT-NA Space Symposium Proceedings.)

Both antennas are perfectly reasonable for LEO satellites. The performance differences between them are subtle and may not easily be noticed in a simple A/B test.

The "Eggbeater" (i.e. full-wave loop turnstile) antenna is horizontally polarized at the horizon and at low elevation angles. At elevation angles above around 50-60 degrees, the vertical component starts to become significant and the antenna becomes elliptically to circularly polarized. Directly overhead, the antenna is circularly polarized.

The Lindenblad is circularly polarized at the horizon and at low elevation angles. As the elevation angle increases, the vertical component decreases and the axial ratio becomes bigger (i.e. the circularity gets worse.) A Lindenblad has a null directly overhead although in actual use, it is pretty hard to detect this and of course the satellites are almost never directly overhead anyway.

When the satellite antenna is circularly polarized (i.e. like AO-51,) there is virtually no overall performance difference between the antennas although the instantaneous signals levels may differ.

But, when the satellite has a whip antenna, the Lindenblad will provide less fading at low elevation angles due to its ability yo accept any linear angle of polarization whereas the "eggbeater" will show a deep fade if the incoming polarization is nearly vertical.

Many of the current analog satellites use circularly polarized antennas, so there would not be a great deal of difference between the two antennas on these satellites.

The Lindenblad has one other advantage and that is that work reasonably well for terestrial FM repeaters so you can get away with having only one omni antenna at your station for each band.

73 to all, Tony AA2TX