[amsat-bb] Re: [amsat-ne] Cornell Satellite Team Needs Help
rogerkola at aol.com
Mon Apr 21 03:38:32 PDT 2008
I am currently manually forwarding our posts to amsat-bb at amsat.org until you get you access. Then the discussion should shift over there.
The boards or reflectors will not pass attachments so if you have any, please post on your website and insert URL's for our access.
Please point out your antenna location in the pictures you provide.
My responses are inserted between your text....Roger WA1KAT
----- Original Message -----
From: Nathaniel S. Parsons
To: Roger Kolakowski ; gs at cusat.cornell.edu ; tc at cusat.cornell.edu ; Dan Oltrogge
Sent: Monday, April 21, 2008 12:11 AM
Subject: Re: [amsat-ne] Cornell Satellite Team Needs Help
Thank you very much for the quick response. I have a few more questions, though (inline, below). I've copied a few of my team's mailing lists so they can get involved, too.
On Sun, Apr 20, 2008 at 11:29 PM, Roger Kolakowski <rogerkola at aol.com> wrote:
I have forwarded your email to the entire AMSAT population as the amsat-ne
reflector does not get used much and I don't think it is directed through
the amsat-bb at amsat.org main reflector.
Thank you very much. I'm in the process of joining those reflectors, but I'm waiting for moderator approval.
In your ridge design test I think I would have used the radio with a simple
quarter whip to set a baseline for the antenna. This would help isolate your
problem by having a 0 dB gain level to your receiving system.
Once you set that, you can start testing antennas.
>Ah, that's a good idea! I just need a little >clarification. If I understand you correctly, you think >we should do some (or all) of the following:
>1. Take a 6.89" piece of antenna wire, attach a UHF >connector to it, and stick it on a TH-D7. (is this how >you make a whip antenna? I really should get my hands >on that antenna handbook...)
Yes, however use the same connector that is on the radio and have the vertical rod insulated from the outer shield with some sort of plastic sleeve where they "might" make contact. (I have not checked you 1/4 wave math)
>2. Take this out to the hilltop where we had the >satellite
>OR the rooftop where we had the ground station (which?)
>3. Transmit from one and/or the other station (which?)
You are trying to confirm that your control station will work both ways with alternating antenna systems at the "satellite" Both ways won't hurt.
>adding attenuators one side and/or the other (which >one?) until the signal cuts out, and this is our >baseline.
Add Attenuation at the base as initially this is your variable. Your Satellite is your "control."
>4. Repeat, substituting the whip for the other station.
Not necessary...your "base" will never have this configuration
>5. Go back to the non-baseline setup with the same amount of attenuation.
Go to the setup where the "satellite" 1/4 wave antenna is replaced by your "designed" antenna and remeasure
>If we can't get signal, then we know one of the >antennas has negative gain, which is bad.
If you can't get signal, your "satellite" antenna arrangement is exhibiting less "gain" toward the "base" than a 1/4 wave whip. Not good.
>Then, add attenuators until signal is lost again, this >being how much gain we have in that direction.
In relationship to 1/4 wave.
>6. If step 5 works, take off 3 dB of attenuation, and >rotate until signal is lost again, to experimentally >determine the gain pattern.
Remember, you are not in "free space," local objects, height above the ground, etc will skew any true pattern, but it won' hurt to try.
I'm not sure how you are deploying such an elaborate antenna without damage
during launch and the design is intricate enough that pictures would help.
>We have no deplyables. As for pictures, I've attached >one, and our .EZ model. To be more specific, the loop >is epoxied to the same plastic that the solar panels >are. What the model does not show is that there is >another antenna on the bottom of the satellite, and, >for the first stage of the mission, there will be two >identical satellites stacked together. For a better >idea, see the "Documents" section of the web site for a >video of our planned mission.
>Also, since we are spin-stabilized, deployables are a >bad idea, especially ones that radiate energy.
Without reviewing your EZ-NEC calculations, have you taken into account that the epoxied antenna will be extremely close to the metalic frame and the solar cells?
If your antenna is only on one axis will you be shielded in all other directions so that any spin will shadow the earth?
Directionality of the antenna comes to mind, interaction with the cube's
surface is a consideration.
I agree that it is a consideration, but I'm not sure what tools or equations to use to consider them. What about a poor matching circuit? One idea on this side is to try swapping in and out various capacitors to iterate towards a better one. Do you think that would work? I know that the TH-D7 will dial back its power if it sees a high SWR...
Many of the Annapolis' satellites used metal tape measure strips rolled up
for launch and released into quarterwave whips in orbit as simple antennas.
Unfortunately, we don't have this option, since we are spin-stabilized, and antennas that dissipate energy would get us spinning the wrong direction.
Having the test transceiver external to the cube for the ridgeline test also
brings up some questions as to the duplication of your space cube's actual
We didn't have any electronics in the prototype structure, but we thought having all that metal was enough. We can certainly put the boards in to see if it will have any effect, though.
I would suggest setting a direct, line-of-site baseline with a traditional
antenna and radio first.
I agree, I'm just a little fuzzy on the specifics (see above).
----- Original Message -----
From: "Nathaniel S. Parsons" <nsp25 at cornell.edu>
To: <nsp25 at cornell.edu>
Sent: Sunday, April 20, 2008 9:32 PM
Subject: [amsat-ne] Cornell Satellite Team Needs Help
>> We had a the satellite's antenna attached to a structural prototype of
> the satellite, and brought it to a hill roughly 4km from our ground
> antenna. We stuck attenuators on the ground station, between the
> antenna and the pre-amp in order to simulate the path loss we would
> experience in space (LEO, 330x685, 9.1 degree inclination), and
> transmitted from the satellite. By our calculations, we needed
> roughly 57 dB of attenuation in order to be confident that we could
> hear the satellite while it was at the edge of the horizon, but we
> lost signal after 10 dB. It is possible we made mistakes in the design
> or construction of the satellite's antenna, or in the configuration of
> the ground station, so I would greatly appreciate if you could look
> over what we have and did, and see if you could point out what we've
> done wrong, what we can do to further test this, and what potential
> solutions are. If anyone is in the Ithaca area, I would be more than
> willing to show you our setup.
> On each satellite, we have two square loop antennas made of 12-gauge
> copper wire, 8.3125 cm per side, corner fed. At the feed point of the
> antenna, we have a matching circuit as follows:
> According to our EZNEC model, this comes pretty close to matching
> impedence with our 50-ohm, RG316 coax, 1/2 wavelength long, which
> feeds into a Kenwood TH-D7AG, modified to fit in a metal box suitable
> for flight. For the test, we didn't use the flight radio, but
> connected the same antenna to an unmodified TH-D7 held outside the
> prototype structure (if that has any significance).
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