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Re: Feedback on downlink on VO-52


I have to throw in my 2 cents.

I'm not sure why you would be getting any desense.  I have virtually the 
same setup.
I have not had any indications of desense with my installation.
I'm using an IC-910H, separate feedlines, mast mounted preamps, and yagi 
Feedlines are 9913F7 ultraflex and are about 60' long plus connections from 
the preamps to the antennas.
I have a 2  meter CP KLM (oldie), a 1.2 GHz looper, and a 435 KLM.
Separation between the 2 meter and the 70 cm antennas is about 8 feet.
I do use an elevation rotor and so the antennas can be aimed quite 
Normal power output is usually about 5 watts unless the satellites have a 
very low pass.
Using more than 25 watts would be pretty unusual with most satellites.
I live in Phoenix, AZ, and am surround by mountains, some within walking 
so in most directions I have an elevated, rugged horizon.

The first question that I would ask is how much power are you running on the 
And then, how far apart are the antennas?

I use the CI-V interface with SATPC32 to control the doppler.  It works 
You just have to make sure the address in the radio matches what you have 
set in the software configuration files.
For SSB I have the frequency updated whenever it gets off by 20 or more Hz. 
For FM I'm using 300 Hz.
Maybe overkill on SSB, but it's better than having the tone jumping up and 
down all the time.
As George said, do the CAT interface first, expecially if you plan to be 
doing SSB or CW.
Once you have that set up, you can tweek your downlink on the CAT display 
when you first transmit.
After that, your uplink and downlink should pretty well track with each 
The fun comes when you have to follow someone who has no doppler control.

I don't think you are going to find any easy way to interface the Channel 
Master rotor to a computer interface.
Generally the interfaces expect a voltage between 0 and 5 volts representing 
the azimuth of the antenna.
A higher indicator voltage can be scaled down to the 0 to 5 range if you can 
find something suitable.
Most ham rotors have separate wiring for the indicator potentiometer in the 
rotor and that can be easily scaled
and used with computer interfaces.

Hope this helps.  I can set a picture of my antenna installation if that 
would help.


Message: 13
Date: Tue, 01 Apr 2008 10:12:03 -0500
From: Ronald Nutter <rnutter@networkref.com>
Subject: [amsat-bb] Re: Feedback on downlink on VO-52
To: George Henry <ka3hsw@earthlink.net>, "amsat-bb@amsat.org >>
AMSAT-BB" <amsat-bb@amsat.org>
Message-ID: <47F250C3.7020801@networkref.com>
Content-Type: text/plain; charset=UTF-8; format=flowed

I am using seperate antennas and feedlines.  For the time being, I am
using a Channel Master antenna to turn the antennas.  I have a pvc pipe
rig setup with the antennas at an angle of 25 degrees due to the clutter
in the neighborhood I have to clear to see the sats.  I hope to have a
tower in the future but with being laid off from my job, cant really
have any expenditures right now.

I have the cat interface for the IC910H but havent looked into how to
set it up yet.


George Henry wrote:
> -----Original Message-----
>> From: Ronald Nutter <rnutter@networkref.com>
>> Sent: Mar 31, 2008 10:40 PM
>> To: AMSAT-BB <amsat-bb@amsat.org>
>> Subject: [amsat-bb]  Feedback on downlink on VO-52
>> Thanks to the help of several on this listserv, I was able to get a
>> contact on VO-52 until I lost coordination on keeping the rotor turned
>> and the IC910H tweaked the right way on the VFO's.  I had problems
>> finding my downlink because of what I think is desensing on the 2M 
>> downlink.
>> Can I resolve this by putting a filter on the 2M receive to stop the
>> desensing like I would on the UHF receive on the FM birds ?  If not, is
>> there another way to fix the problem ?
>> Thanks to W0EOZ for putting up with me while I was trying to figure
>> things out.  Hopefully my next contacts will last a bit longer <G>.
>> Ron
> Are you using separate 2 meter and 70 cm antennas with separate feedlines, 
> or diplexing onto a single feedline to a single antenna?  First thing to 
> do is reduce your uplink power as much as possible while still being 
> heard.  If you are diplexing to a single feedline, you only have about 
> 60dB or so of isolation, so too much uplink power can exceed that.  You 
> should be able to work VO-52 with 25 watts or less...
> I have never experienced desense on 2 meters from my 70 cm uplink...  only 
> the reverse, which can be cured with separate feedlines and antennas, 
> ample separation between the antennas, and the diplexer-as-filter trick 
> found at <http://www.amsat.org/amsat-new/articles/Mode-J/>
> And I strongly recommend buying or building a CAT interface and letting 
> your tracking program take care of tuning the radio (and turning the 
> rotors, if you buy or build a rotor interface as well).  The demo version 
> of SatPC32 is fully functional except for saving your station parameters, 
> and can be downloaded from <www.dk1tb.de/indexeng.htm>.
> If you like it, register it:  all proceeds go directly to AMSAT.  A CAT 
> interface PC board with the harder-to-find chips included is available 
> from <www.farcircuits.net> and only costs about $20 to build.  The 
> FOD-Track rotor control PC board is also available from Far Circuits, and 
> will cost $45 - $50 to build.  The LVB Tracker is available thru the AMSAT 
> store, and has the advantage of being able to operate without a computer 
> attached... nice for mobile ops!
> Go for the radio control first:  that'll free you up to deal with the 
> rotors manually, and they demand far less attention than tuning does.
> 73,
> George, KA3HSW

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