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Full 10M (and above) coverage for EPT6900XX chassis

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Old 09-02-2011, 10:27 PM
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Default Full 10M (and above) coverage for EPT6900XX chassis


I have been contemplating modifying my radios wiith the EPT6900XX chassis (General Grant, Superstar SS158EDX, RCI 69FFC2 etc.,) to allow full coverage to 29.700 on 10M. This small modification will simply shift the entire range from the original 24.265MHz - 29.655MHz up to 24.705MHz - 30.095MHz, thus allowing full coverage to 29.700MHz on 10M, while still covering the 12M band.

I would simply change out the existing X2 crystal (15.360MHz) to 15.800MHZ. I don't believe alignment would be required.

(I'm also working on a scheme to allow 100KHz repeater splits. This might require another crystal either diode or relay switched in TX.)
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Old 09-02-2011, 10:57 PM
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Originally Posted by VA3ES View Post

I would simply change out the existing X2 crystal (15.360MHz) to 15.800MHZ. I don't believe alignment would be required.

(I'm also working on a scheme to allow 100KHz repeater splits. This might require another crystal either diode or relay switched in TX.)
Uhhhhhh . . . . I definitely would re-align it . . .
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Old 09-02-2011, 11:06 PM
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Uhhhhhh . . . . I definitely would re-align it . . .
Really? All I'm doing is shifting the range up by 440 KHz. I would be doing that by simply changing bands, and we don't align the radio when changing bands.

I'll check it out anyway... RX sensitivity and TX power anyway... just to be sure!
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Old 09-03-2011, 02:05 AM
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Remember; this is the reference oscillator we are talking about here . . .
I'm sure you have seen the freq expansion boards for Cobra 29's that use multiple crystals. The better expansion boards also include a separate trimmer capacitor for each crystal so that it stays in tune when flipping to a different band/crystal.

Yes; I would make sure that the voltage is also correct when shifting the core freq of the PLL, as it will shift some. Doubtful that it will become unlocked; but then again - it might too. Depends where the voltage is set. Then I would re-tune the reference oscillator to ensure that is on target. Guess it all depends on how much accuracy you demand from your gear.
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Last edited by Robb; 09-03-2011 at 02:29 AM.

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Old 09-03-2011, 05:03 AM
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Quote:
Originally Posted by Robb View Post
Remember; this is the reference oscillator we are talking about here . . .
I'm sure you have seen the freq expansion boards for Cobra 29's that use multiple crystals. The better expansion boards also include a separate trimmer capacitor for each crystal so that it stays in tune when flipping to a different band/crystal.

Yes; I would make sure that the voltage is also correct when shifting the core freq of the PLL, as it will shift some. Doubtful that it will become unlocked; but then again - it might too. Depends where the voltage is set. Then I would re-tune the reference oscillator to ensure that is on target. Guess it all depends on how much accuracy you demand from your gear.
Actually, we will be checking to make sure the VCO voltage is within tolerance. I'm not sure that a trimmer is required for the X2 reference, as there is none to begin with. Besides, we can net the frequencies as required with the coils, according to the manual. Nothing that any competent tech wouldn't do.
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Old 09-03-2011, 08:02 AM
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Quote:
Originally Posted by Robb View Post
Uhhhhhh . . . . I definitely would re-align it . . .
Me Too.


Quote:
Originally Posted by VA3ES View Post
Really? All I'm doing is shifting the range up by 440 KHz. I would be doing that by simply changing bands, and we don't align the radio when changing bands.

I'll check it out anyway... RX sensitivity and TX power anyway... just to be sure!
you don't realign when changing bands because its already aligned within that bandwidth, but if you shift it all up 440 khz then its going to be out of tune on the top end which it wasn't previously aligned for,

bare in mind many of these chassis are working at their bandwidth extreme already, when you move past the previous tuning you may get the vco refusing to lock, as well as uneven tx power/rx sensitivity.

even if i was moving a 40 ch set from mid band (fcc) to high band to cover 27.555 i would retune it.
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Old 09-03-2011, 08:12 AM
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I had Richard Byrd do this for my DX2517. He did do a full alignment. Power on 10 meters is a little lower than 11. More like 25-30 watts instead of 35-45 on 11. That is just a limitation of the chassis. No problems with the VCO on this unit.

I have it connected to a sound card IX and have run SSTV on it. PSK31 is a problem because of drift. People have to chase me all over the waterfall, lol.
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Old 09-03-2011, 11:00 AM
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[...] you don't realign when changing bands because its already aligned within that bandwidth, but if you shift it all up 440 khz then its going to be out of tune on the top end which it wasn't previously aligned for, [...]
OK, OK!! You guys have convinced me! Sheesh! Such sticklers for accuracy and precision! (Actually, I hope I can actually get the extra 440 KHz bandwidth out of it. In fact, all I really need is the extra 45 odd KHz, but that extra 300 KHz is a bonus for receiving purposes.)
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