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Wednesday, June 13, 2012

SolderSmoke Podcast #144 FDIM SPECIAL!

Venus glides across the sun's face during its previous transit, seen from Flagler Beach Pier in Florida.
Photograph by Jim Tiller, Daytona Beach News-Journal/AP

June 13, 2012


SolderSmoke podcast #144 is available for download: 


http://soldersmoke.com/soldersmoke144.mp3


--A CQ from the Rolling Thunder!
--The Transit of Venus.
--JA DX on 17 
--Kick Panel Finale: 
--Workin' on the Workbench (and test gear)
--Billy's Computer Project:  Success! 
--SPECIAL REPORT FROM FDIM
--MAILBAG: Urban legends, Hot Iron, Dry Joints 
--Bluegrass Music

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

6 comments:

  1. Hi Bill,

    Oh, wow. There's no way I'd turn you in to "The Man", man.

    I just don't want you to get hassled by him. That or some curmudgeony "OO" who thinks he or she is "The Man".

    Far out and 73.......
    Steve Smith WB6TNL
    "Snort Rosin"

    ReplyDelete
  2. I'm sad to report you have not yet quite digested the 80M 20M issue. Us Drake TR-4 geeks know that the local oscillator (VFO) runs at 5-5.5 MHz. The IF is 9 MHz. So, if you look at the combination math, you'll see how it plays.
    RF input (3.5 MHz-4.0 MHz) plus the VFO (5.0 MHz - 5.5 MHz) gets you a 9 MHz result.
    RF input (14.0 MHz - 14.350 MHz) MINUS the VFO (5.0 MHz - 5.5 MHz) also gets you the 9 MHz result.

    Since you invert the sense of the mixer, you capture the opposite sideband. It happens to work especially well in this case, since the convention is LSB on 80 and USB on 20.

    It's all about the math!!
    73,
    Steve
    W1KF

    ReplyDelete
  3. Hi Steve,

    Indeed, it is all about the math and that is why the sideband does not change with the 9 MHz I.F./5 MHz LO scheme regardless of sum or difference mixing. Here is the math:

    20 Meters

    USB gen output, mod.=1KHz 9.001 MHz LO (VFO) +5.200 MHz
    ---------
    SUM 14.201 MHz

    75 Meters

    USB gen output, mod.+1KHz 9.001 MHz LO -5.200 MHz
    ---------
    DIFFERENCE 3.801 MHz

    Both outputs are USB

    Now the opposite sideband:

    LSB gen output, mod.=1KHz 8.999 MHz LO (VFO) +5.200 MHz
    ---------
    SUM 14.199 MHz

    75 Meters

    USB gen output, mod.=1KHz 8.999 MHz LO -5.200 MHz
    ---------
    DIFFERENCE 3.799 MHz

    Both outputs are LSB

    The above is simplified because in reality the DSB carrier is not placed in the center of the filter passband however the math works the same. Also, I used 1KHz modulation for simplicity. The whole voice spectrum, .300 - 3 KHz can be inserted and the result will be the same: No sideband inversion.

    73.......Steve Smith WB6TNL
    "Snort Rosin"

    ReplyDelete
  4. Sorry, the formatting got fouled up in transit. It was all straight and pretty when I pushed the "Send" button. Honest. :-)

    73.......Steve Smith WB6TNL

    ReplyDelete
  5. I'll trust you about the formatting, but I think I'll take issue with the math, because we seem to have crossed assumptions. You see, the Drake TR line does not change LO. It's fixed at 9.000 MHz. There are separate USB and LSB crystal filters. In that context, I think you'll find the math changes just a bit. If we set the VFO to 5.2 MHz, and add the USB 1 KHz signal, we get something at 5.201. Now, the math is:

    9.000 - 5.201 = 3.799 (LSB)

    9.000 + 5.201 = 14.201 (USB)

    Would you agree, or do you think I missed something?

    73,
    Steve
    W1KF

    ReplyDelete
  6. No need to respond. Your are, in fact, completely correct. I'm the one who made the mistake. The VFO does not have the 1 KHz signal on it, the 9MHz does, as you've noted. Clearly, I am not thinking clearly. Or at least, I wasn't until your post made me think it through a few more times.

    Well, that, and walking over to the TR-4, and playing with it for a minute.

    Are there any remedial math courses you can suggest??

    Bill, thanks for hosting our discussion!

    73,
    Steve
    W1KF

    ReplyDelete

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