[amsat-bb] Fw: Re: Ridge Test Results
rogerkola at aol.com
Tue Apr 22 05:01:03 PDT 2008
----- Original Message -----
To: G0MRF at aol.com
Cc: rogerKola at aol.com
Sent: Tuesday, April 22, 2008 7:22 AM
Subject: RE: [amsat-bb] Re: Ridge Test Results
Thanks for the copy Nate.
No need to reply to what follows, but it may be useful. I'll look out for the next update.
Congratulations, That's really good progress for just a couple of days.
I think 45dB will take you just to about 600km, but really there's room for improvement yet.
The photo's show the antenna very well. A couple of thoughts.
It looks like it is mounted on FR4 PCB and this is an inch or so from the main structure. Is there another antenna on the other side? - The RF will not pass through the satellite.
The FR4 will affect the properties especially if you have applied glue at a voltage node on the antenna.
Also, I see one side is very closely coupled into a track running from the solar cells. That will not help.
My guess is that the antenna will be really bad on the VNA. - Remember when testing that the VNA will show you return loss. You will know if the return loss is between 0dB and 6dB that the antenna does not work. But please be aware that even if you see a 'good' return loss e.g. 15 to 30dB, Then that may not indicate that the energy from your transmitter is being radiated. - After all, a 50 Ohm resistor has a wonderful return loss, but does not radiate. Look for a nice dip at your design frequency.
If you have to replace the antenna then a whip / steel tape would be OK but needs to work against part of the structure. - Which looking at your satellite will be difficult to do.
A good solution may be to make a dipole from two solid metal rods and fit them to the same spot where your antenna is at present. - But clear of other objects. Say 1 inch above the surface. Another choice would be a folded dipole, but you will need to match that from apx 200 to 300 ohms, back down to 50 ohms.
If you decide on the simple (but reliable) dipole, mount the elements off the PCB material and only support them at the center not at the ends. The ends are a high voltage point and anything near them or touching will affect the performance.
I think your original estimate of 57dB is spot on. Well done.
Path loss for 3.18km = -95.26dB
Path loss for 2000km = -151.23
Difference from ridge to space = 56dB
So you have to find another 12dB + some margin for loss due to spin or pointing angle.
1) It could be that the rubber duck is only 50% efficient. - So that could be 3dB off the total. But your new antenna may no be much better.
2) You have not mentioned ground station feeder loss. Without the preamp that will be added to the total. On 70cms you could be looking at 4 - 6dB.
So, possibly only 6 or 7dB to find !!!
Your TS2000 has an S meter. On SSB or CW the sensitivity is as follows. This is very approximate, but it may help. This is with RF gain at max and no pre-amp.
S1 = - 113dBm at antenna.
S3 - 110dBm
S5 - 107
S7 - 102
S9 - 93dBm
>From what you have said so far 0.5W of carrier from the ridge should give a little over S9 when in SSB or CW. If you can check this with a lab sig generator and your TS2000 you will be able to do some really good measurements on your system.
I have one final thought on the missing dBs. Or the lack of 9600.
You mention that you have not been able to use 9600 and you are still not 100% reliable on 1200.
It could be that you need to optimize the modulation level on the transmitter. That is very important because if the modulation is too high. - i.e. if the volume going into the radio is too high, then the bandwidth on FM will be much greater then necessary. The reason this is important, is that if the transmitted bandwidth of the signal exceeds the width of the filters in the receiver, then the demodulated audio will be distorted and you will never recover the data. (I think something like this happened to CAPE 1)
So, spend a little time optimizing the transmitter either by experimentation, or by calculating the bandwidth and then attaching the transmitter to a spectrum analyzer to make the adjustment. - There probably isn't time, but the proper way would be to generate a test signal at 9600 and then examine the recovered audio for distortion / linearity.
Give the TS2000 a try with OSCAR 51 on 435.300 (starting 10kHz high for Doppler and finishing 10k low)
April 1 - April 30
FM Repeater, V/U
Uplink: 145.920 MHz FM, NO PL Tone
Downlink: 435.300 MHz FM
9k6 Digital L/U BBS and Telemetry
Uplink: 1268.700 MHz FM
Downlink: 435.150 MHz FM
From: G0MRF at aol.com [mailto:G0MRF at aol.com]
Sent: 22 April 2008 08:44
Subject: Fwd: [amsat-bb] Re: Ridge Test Results
In a message dated 22/04/2008 05:39:41 GMT Standard Time, nsp25 at cornell.edu writes:
I'm sorry we didn't get in touch, but my cell phone died while we were out
Were were listening on 146.610, but didn't hear anything except the time.
Maybe we weren't using it correctly?
If you could get all of that material tomorrow, that would be excellent. We
do have access to sanding paper, a file, and a grinding wheel, though.
On Mon, Apr 21, 2008 at 11:26 PM, F. Kevin Feeney <fkf1 at cornell.edu> wrote:
> Were you transmitting in just one direction or from TS to D7 and then from
> D7 to TS?
Via packet, only TS to D7 (some were sent the other way, but we were told
having attenuators on the RX side would give us unreliable data). By voice,
both directions, and while that signal was fuzzy at higher attenuation, it
never completely cut out. For the packets, we always received them on the
radio, but the number recorded was the amount passed on to the computer.
> Why list the power settings in each radio if you are only transmitting
> from the TS2000 to the D7? That confused me.
Just for completeness.
> How successful have you been at running the radios in 9600 baud mode in
> previous testing? If you don't have many weeks of positive results in that
> mode at this point with whatever antennas, I'd be very wary of committing to
> a launch.
Not very. We could complete the mission at 1200 baud, though, it would just
take longer to move data back and forth.
> so what are the power listings for each radio telling us? To me I think
> I'm seeing that your circularly polarized antenna isn't quite as good in
> horizontal mode as in vertical? You have to have less attenuation in place
> to get two good packets per two tries for the same power settings in
> horizontal as for vertical. looks like about a 15 db difference? (30 vs 45?)
> That says your circular antenna "circularity" is suspect. Is it a helix?
> Crossed yagis with phasing harness? Is it up in the air off the support
> structure? Are the feedlines trailed out the back of the antenna, or do they
> come down through the elements to the mast?
I'm sorry that I wasn't clear, but all our rotations were in the direction
of the other station. So, if an observer were looking at us from the side,
So we didn't really test the circularity of the ground antenna, but the gain
pattern of the rubber duck.
> Wait - were you testing the loop during any of this? I thought all of the
> measurements were made with the rubber duck only in three orientations,
> vertical, horizonatal and 45 degree. Where is the loop data shown?
The loop data is the 10 dB figure mentioned in my first email. Under these
same conditions on Friday, the loop only worked up to 10dB.
Also, I can use a network analyzer tomorrow at 2PM. Is it worth analyzing
the square loop antenna at this point?
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