A few problems with the TX keying up there I think.
12.52utc UK pass - tx de-keyed before the 12.54utc image was complete.
14.27utc UK pass - tx keyed up half way through the 14.31utc image, the carrier then remained up until the next image at 14.33utc after which it dropped correctly.
David G8OQW
ISS Stuck Transmitter problem. July 15, 2010
The Problem:
A few problems with the TX keying up there I think. 12.52utc UK pass - tx de-keyed before the 12.54utc image was complete. 14.27utc UK pass - tx keyed up half way through the 14.31utc image, the carrier then remained up until the next image at 14.33utc after which it dropped correctly.
David, G8OQW ***
Hi David:
Your transmitter observations are completely expected.
A problem was discovered in August 2006, during Pavels V. mission on ISS. It appears that a last minute design change to the VOX box is causing RF on the power leads to cause the Transmitter Op-amp to get Stuck in the Transmitting mode. A second VOX box was sent to the ISS in 2008, which also succumbed to the same RF on the power lead problem.
What should happen:
SpaceCam sends out a short DTMF tone, to start the TX session, followed by a CW ID. The SSTV Audio from the Laptop keeps the VOX box in TX mode. A few seconds after the end of the SSTV image, the silence will cause the VOX box to drop the Transmitter signal.
Here is what is really happening:
SpaceCam sends out a short DTMF tone, to start the TX session, followed by a CW ID. The SSTV Audio from the Laptop keeps the VOX box in TX mode. The VOX box picks up RF noise from the Power leads, which are attached “Inside” the specially modified Kenwood TM-D700.
When the SSTV audio Stops, the RF noise is still saturating the Op-Amp in the VOX box. This causes the transmitter signal to be Stuck on the ON condition and keeps the Kenwood transmitting.
The Kenwood TM-D700 has a built in “WatchDog” timer, which will force the transmitter to turn off after a few minutes (usually set to a 3-minute value).
After each First-Start SSTV image, the TM-D700 transmitter may Stick on for a full three minutes or until the time value of the WatchDog timer is set for. The WatchDog timer will be reset when the Transmit control lead is finally released.
Based on your observations this is what is happening. If the Slide Show timer is set for 1 minute and the Watch Dog timer is set for 3 minutes, and Martin-1 is being used the following should be happening.
First start, Successful Martin-1 image. Total time for CW ID and Martin-1 image, approximately 120 seconds. The TM-D700 transmitter will stay ON, even though there is No new Image.
After a 1-minute delay, the Slide Show will start sending a second Martin-1 image. When the WatchDog timer reaches 3 minutes, it should abort the transmitter, which will cause the SSTV image to abort prematurely.
A fix for this problem has been presented to ARISS on multiple occasions. No action has been taken. Volunteers welcome.
http://www.marexmg.org/documents/PSUCUSBProjectPub1.doc
http://www.marexmg.org/fileshtml/futureprojects.html
73 WF1F
www.marexmg.org
--- On Thu, 7/15/10, David Barber david.barber@dbelectronics.co.uk wrote:
From: David Barber david.barber@dbelectronics.co.uk Subject: [sarex] MAI-75 - 15 July 2010 To: "'SAREX'" sarex@AMSAT.Org Date: Thursday, July 15, 2010, 11:05 AM A few problems with the TX keying up there I think.
12.52utc UK pass - tx de-keyed before the 12.54utc image was complete.
14.27utc UK pass - tx keyed up half way through the 14.31utc image, the carrier then remained up until the next image at 14.33utc after which it dropped correctly.
David G8OQW
Sent via sarex@amsat.org. Opinions expressed are those of the author. Not an AMSAT member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/sarex
ISS SSTV Home work:
Hi all:
Marex is always trying to improve our Manned space flight projects. I could use your help in analyzing the images coming from ISS.
Here are a few homework assignments for you.
Assignment #1: WatchDog timer: Try to video tape a full SSTV sequence from beginning to end. We have heard rumors that the transmitter may be getting stuck “ON” after sending an image, and then later aborts in the Middle of the “Next” image when the built-in Watchdog timer activates. Can you be the first to catch a full video sequence of this happening? See if you can calculate the setting of the TM-D700 Watchdog timer.
Assignment #2: Calculate Slide Show delay. Try to record 2 or more images in a row. Record the start of each image. If your images include the UTC time stamp you can also try to calculate if the clock on the laptop is set correctly (it may be on Russian time or UTC time).
The time between images, minus the image transmission time, will be the slide show delay time.
The original SpaceCam1 duty cycle goal was less than 40% transmitter time. A Slide Show delay of 3 minutes, with Robot-36 would put the transmitter in this range.
The current images from ISS on July 15, are using Martin-1, which requires approximately 114 seconds per image. The stuck transmitter VOX bug, keeps the radio running for up to 3 minutes at a time. This means, that if we want to keep the transmitter duty cycle to 40% or less, we need to increase the Slide show mode to 8+ Minutes.
When you have your results, send them and supporting images to: marexmg@comcast.net
Rename your images and use the following format New format: 0607311905wf1f.jpg
I removed the first two numbers of the year and the “Z” for UTC time. All dates are assumed to be in UTC dates. The images coming down from ISS using Marex SpaceCam1 will also have a time stamp embedded into the image. You can also use these numbers to generate you file names. If you are a Short Wave listener and do not have a call sign, just place your Initials after the time (0607311905abc.jpg)
If we break this down Year =06 Month = 07 Day = 31 Time = 1905 UTC Call sign = wf1f Description (optional) = Windows shot Image format = JPG
Image Quality Please do not put any text over lays on the images, Example, do not put web page or advertisements in the image. Your own call sign and date are acceptable.
Send all images directly to MAREX at Marexmg@comcast.net
Thank you for your support
WF1F, Miles
participants (2)
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David Barber -
MM