[amsat-bb] Preamps and Polarization Switches

Jim Jerzycke kq6ea at verizon.net
Fri Jul 1 23:57:00 UTC 2016

Hi, Fred

I'm using an M2 2M7 2 meter beam, and an M2 420-450-11 70cm beam, with 
an SSB Electronic preamp on each. Prior to dedicating these antennas to 
satellite work, they were my "weak signal" terrestrial antennas. I have 
them mounted on the cross boom at 45* to the boom so that they're 90* to 
each other. I have a"reverse connected" diplexer ahead of the preamp on 
the 70cm antenna, and I use a 2 meter band-pass filter at the 2 meter 
output of the rig. These things have eliminated the 70cm desense I used 
to have when transmitting on 2 meters.

I ran separate DC power leads to the preamps after I blew out the preamp 
power switching transistor in my FT-847 by not checking to see if my 2 
meter bandpass filter was DC grounded!

The antennas are linear polarized, and work extremely well, although I 
do occasionally notice a some fade on certain satellites. It's nothing 
that really bothers me, and it saved me a ton of $$ compared to having 
switchable CP antennas. Switchable polarization is "nice" to have, but 
IMO, unless you have some compelling reason that requires 100% copy, 
it's not worth the significant cost premium.

I'm have a "used" Yeasu G-5400B Az/El rotator set I got from a friend 
who bought it new, and then never used it. I built a Fox Delta kit 
that's a clone of the LVB Tracker, so by using SatPC32, I have full 
rotator control and Doppler correction.

I use Davis RF "Bury Flex" cable, although there are other very good 
"RG-8 sized" cables available. The DX-400 cable from DX Engineering is 
another good quality cable I've used at VHF/UHF with good results.

By all means, start with the antennas, and add things as your budget allows.

73, Jim  KQ6EA

On 07/01/2016 10:13 PM, Fred Castello wrote:
> Newbie here and I am trying to put together a station.  I have a question about preamps.  I am making the following assumptions but please correct me or outline your station feeds if I am incorrect in my assumptions:
> Most experienced operators are using moderate to high gain yagi antennas, circular polarized.  I am thinking of purchasing the M2 LEO pack.  I am assuming that most folks are using RF protected preamps to keep from blowing them up on transmit.  It would be easier if one knew that they were always going to transmit on 2 meters (for instance) and one could place the NON RF protected preamp on 70 cms.  However, since there is a mix of V/U and U/V birds, it would seem the only way to get preamps up at the antenna where they belong is to use RF protected preamps ( with weather and RF protection, significantly more expensive).  Is there a role for diplexers here rather than running expensive RF protected switching?  Also, I know from my listening on my Elk Antenna that change in polarization can make a pretty significant difference in adequate reception.  So, it would also seem that there is a need with these type of antennas (M2 LEO) to have a polarization switching (cost for both
>    antennas almost matches the original cost of the antennas).  Do most operators have these switchable polarization switches.  My shack is about 60 feet from the top of the roof, so I will have to deal with those losses in spite of using good cable.  I was thinking of just starting with the antennas (no preamps, no polarization switching) and see how things go.  Any thoughts or advice would be much appreciated.
> Best
> Fred Castello, KF4FC
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