August 2007 - Eagle (INACTIVE)

Teamspeak conference tonight
by Jim Sanford 14 Aug '07

14 Aug '07

All: If there's any interest, I WILL be on at 2100 EDT. I see one other check in. Agenda would be Symposium and general status update. I've just been too busy to send out agenda before now, sorry. Way too many balls in the air right now. As always, anything else anyone wants to discuss... 73, Jim

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Proposed 70 cm Receiver plan - Let's get this project going!
by Juan Rivera 10 Aug '07

10 Aug '07

All, The 70 cm Receiver has been stuck in a rut for too long. Now that I've completed my Symposium presentation I'd like to get it back on the tracks and moving forward again. Here's the way I see it: Passband Ripple - we want to understand this problem before proceeding with the next upgrade revision so we don't end up with another prototype that still has excessive ripple. John will design a new PCB that will act as a test fixture for the 199 MHz 1st IF string. Parts will be distributed to John, Bill Ress and to me. We will all work this problem in parallel. The PCB will also contain test fixtures for any other portions of the receiver that we want to characterize independently of the receiver. The various fixtures can be cut apart once the PCB is fabricated. I'd suggest that the proposed analog replacement 10 MHz reference be included. I'll run that in my temperature chamber. CAN-Do Module - No one has volunteered to work the power supply issue so I'll do it. It's my belief that the existing step-down converter is running at a much lower efficiency that anyone realizes. I'll test this theory and report back. It appears to be a generic characteristic of this type of converter that the efficiency drops off towards zero at very low output currents. As I've discussed in my logs, this one is only putting out 11 milliamps. This could also explain the motorboating that I have observed. So far I have not found any other switching step-down converter that is optimized for this low output current. This problem needs to be resolved now since it impacts the design of the enclosure. If we go to an analog regulator the CAN-Do conducted and radiated EMI problem will be completely eliminated. If we stay with a switching step-down converter then we may either need to move to a two-compartment enclosure or vacate the front third of the existing enclosure to escape the CAN-Do radiated EMI. The Enclosure - I put forth a recommended enclosure requirement calling for a worst case PCB flex of 0.0084" in any one-inch segment. No one has made an argument against this. I do not believe that the current sheet metal enclosure with attached self-clinching standoff mounts and three separate heat sinks can meet this proposed requirement over the proposed temperature range which extends down to -60*C. With the current design that attaches the CAN-Do module to the main PCB via the 40-pin header and then fixes the CAN-Do module to the front panel, there is no room for any flexing or twisting between the base plate and front panel since those induced stresses will be transferred directly to the solder joints on the 40-pin header. The sheet metal vs. milled enclosure questions needs to be resolved. Low temperature Operation - The minimum operating temperature of the SAW filters is -35*C and the minimum storage temperature is -40*. For the IC's the minimum operating temperature is -40*C and the minimum storage temperature is -65*C. These temperatures are not just guesses on the part of the manufacturer. They are a function of the difference in thermal coefficient of expansion between the various internal parts of the devices. Operation below the minimum operating temperature will cause premature failures to develop in short order. The worst case scenario would be to power up the Receiver after is had cold soaked to -60*C. The silicone would heat up very quickly and begin to expand. The thermoplastic case material would lag behind and expand at a different rate causing large internal stresses. I have not seen a final word on the minimum temperature that the Receiver will see in orbit. If it really is -60*C then I propose that a space-rated thermal switch in placed in series with the DC power to prevent activation below -40*. Even this thermal switch proposal side-steps the SAW filters which cannot withstand -60*C. The proposed work around of splitting the receiver into two sections adds complexity which reduces reliability. A way needs to be found to keep the receiver from dropping below -40*. External EMI from the primary power source - The next revision of the Receiver needs to include EMI filtering and possible shielding to deal with radiated and conducted EMI from all sources. These sources need to be identified and characterized so that the Receiver can be designed properly. It makes no sense to press on with the next revision upgrade until this is sorted out. Receiver Requirements vs. ATP - The ATP contains tests for which there are no requirements. We need to harmonize these two documents and do a new peer review for both. Let's get these items resolved!! 73, Juan - WA6HTP

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updates
by Jim Sanford 08 Aug '07

08 Aug '07

Team: A few weeks back, I requested updates for the Journal article, due now. I've received info from Juan Rivera, Bill Ress, Bdale Garbee, Marc Franco, and Bob Davis. Everybody else, please send me something before 1800 9 August, when I will start writing. This is the last Journal before Symposium, so it is our chance to provide reasons for members to come. Thanks 7 73, Jim wb4gcs(a)amsat.org

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Passband Ripple - Latest Modifications and Test Results
by Juan Rivera 07 Aug '07

07 Aug '07

John, Per your request I have modified the input coupling to the 2nd Mixer as follows: * Remove C37 * Replace L15 and L16 with 16 ohm resistors * Install 0.27 µH inductors from pins 2 and 3 of U8 to ground I then retested the IF passband ripple by sweeping a 1 MHz span centered on 10.7 MHz. The output level was reduced by 3 dB but there was no change in the ripple. Click HERE <http://www.juanr.com/pages/hobbies/ham_radio/Eagle/passband_ripple.htm> to view my log. I think we need to look outside of that coupling area since weve pretty much replaced every component. Lets replace both SAW filters next. What do you think? 73, Juan

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Receiver Spec vs. ATP, a few Suggestions and a Question or Two
by Juan Rivera 06 Aug '07

06 Aug '07

John, I took a few minutes to look over your new specs and compare them against the Acceptance Test Procedure. I've got a number of tests in the ATP for which there are no specs: * Image rejection * Internally generated spurs * Local oscillator leakage * Input and Output VSWR Items that need to be addressed that aren't in either document: * EMI conducted susceptibility * EMI radiated susceptibility * Short and long-term frequency stability I also take issue with the -60C minimum power-down temperature. I think this is unrealistic just from a CTE mismatch perspective. The reliability of anything subjected to that wide a temperature spread is going to suffer. A way must be found to raise that temperature. I have a few thoughts... The CAN-Do switching step-down converter is only supplying 11 milliamps. If we take a slight efficiency hit we could just go to a simple linear regulator and completely eliminate the radiated and conducted EMI emission problem from CAN-do. That eases the EMI filtering and shielding requirements for every single payload. That seems like a good trade-off to me. Rather than worry about trying to conduct heat through a PCB why not just go to externally mounted regulators for the CAN-Do and the Receiver right on the case itself. We're not that pressed for space. That eases the heat sink and the associated thermal gap filler issues. EMI will still be an issue, but only for external sources instead of one that is inside the enclosure itself. That strikes me as a huge bonus. Why not design a single-sided PCB with the regulators hanging over the edge and the whole assembly, PCB and regulators, mounted directly to the enclosure. Stick it in with the CAN-Do module in a separate cell. Filter all the signal and power through the common bulkhead. I'm also curious as to why you are specifying two different types of SMA connectors. 73, Juan - WA6HTP

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This weekend at Central States VHF Society
by Tom Clark, K3IO 02 Aug '07

02 Aug '07

This year's CSVHFS meeting wound up tonite in San Antonio. Among the many AMSAT folks in attendance were W4MO, W7LB, W5IU, W3XO, N4HY, K5SDR, W5SXD, N6TX, KL7UW and K3IO. There were no satellite specific papers presented this year, but the world of DSP and SDR was very much present. K5SDR presented his new SDR5000 radio. KL7UW (with the SDR-IQ) and W5LUA (with the Softrock-40) reported on the use of SDR receivers for various VHF/UHF/Microwave tasks. AMSAT highlights of the meeting came at Saturday Night's banquet. K3IO accepted a financial contribution from CSVHFS for AMSAT. And then the crowning glory: Bob McGwier, N4HY was presented the 2007 John Chambers Memorial Award for technical achievement, recognizing his many SDR and AMSAT activities. Bob joins previous AMSAT Chambers Award recipients W0LER, W0PN, W3GEY & K3IO. Congratulations to Bob -- 73 de Tom, K3IO

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Journal update
by Jim Sanford 01 Aug '07

01 Aug '07

Gents: I need your input NOW. I have to write an article this week for submission.. Please tell me what you have done, what you are doing, and what you are going to do. I can speak from memory to U-rx., S2-Rx, and CAN-Do!. In need inputs from IHU, Power, structure, and lab. Thanks & 73, jim wb4gcs(a)amast.org

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Intelsat
by Robert McGwier 01 Aug '07

01 Aug '07

Yes, we are talking with Intelsat. They have told us there is no reason to keep this is a big secret. Just do not spread it around all over the place until we have our deal set. Bob -- AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair "If you're going to be crazy, you have to get paid for it or else you're going to be locked up." Hunter S. Thompson

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