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Tracking Gen for a Tek 494P.
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I have purchased a Tek 494P off Ebay yesterday. ( It is still in transit). What I must have is a tracking gen to go with her. I looked through the 494P manual but could not determine what it is. ( I am bit slow at understanding) Besides I might not be able to buy one even if I can find one.
So the big question. What will work as a substitute? Where could I find information on how to build one if possible? My current interest is in the 2 to 3 GHz range only, but might go to around 10 GHz. Even a block diagram will help. I could jury rig something to work. Any help is welcome. Thanks Azzy. |
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Azzy,
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The basic method of making a tracking generator is to mix a frequency equal to the first IF with the first Local Oscillator to produce a signal equal in frequency to the analyzer input frequency. This is somewhat complicated in the 494P by the fact that the first IF frequency is somewhat variable (since the second local oscillator is sometimes swept). For the 0-1.8GHz band, the first IF is about 2.072 GHz. For most of the higher bands the first IF is 829MHz. For a simple 2 to 3 GHz tracking generator you could use an external 829MHz source (approximate frequency), buffer amplifiers for the first LO output and a mixer. You would need to operate at sweep widths that did not sweep the second local oscillator. Fancier tracking generators would include signal leveling and would include the second LO oscillator to allow proper operation with narrow sweeps: Take a look at what John Miles did for the 0-1.8GHz band: <<>> --John Gord --- In TekScopes@..., "Asadullah" <mirasad31415@...> wrote:
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Hi John,
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Thanks for the link. it's very useful. Although I wish he had provided some more details. Typical of good engineers, he assumes that the reader already knows the skipped details. At least now I see that there is no particular adjustment or problem with the the actual first and/or second IF frequency. Could I replace his varactor with a trimmer. This only when the first Lo alone is swept. I wonder if he really needed all the complexity. I will cook something up though my scrap box is not as well stocked as his. Also, pehaps from my position, it might be better to have a level controlled VC oscillator, as the tracking gen, controlled by a phase comparator, comparing a fixed xtal osc( crytal at a submultiple with some tunability) running at the first IF, with mixture of the S/A first local osc with the tracking gen followed by a narrow band pass filter at the first IF frequency. Azzy --- In TekScopes@..., "johncharlesgord" <johngord@...> wrote:
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