Re: My second BITX40 has arrived!
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john, the reason i elected to put the dds into the VFO injection is that, even a very small signal will drive the transistor to limiting. So, all drive levels will be the same out of the VFO transistor. The actual drive level is set by the 10K resistor to the buffer amplifier. - f
On Wed, Dec 7, 2016 at 11:31 AM, iam74@... [BITX20] <BITX20@...> wrote:
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L4 is in the center of the board, next to C93. How do you know? Tune to a frequency and put your finger next to it. The VFO will change frequency violently.
If you are going to use a DDS, the VFO MUST be disabled. The easiest way to do this is to remove L4 from the board. Personally I would have put the DDS entry into the space between Q8 and Q9. Then the removal of C72 would have made the VFO irrelevant. (This is the easiest way to modify the BITX v.3)
Incidentally, even if you decide to remove C72 and insert the DDS here, L4 must still be removed to disable the VFO. The quarters are too close and there will be interference with the VFO running.
The DDS level must be adjusted to one that satisfies the mixer --- even if that involves an attenuator or another amplifier.?
john
AD5YE
---In BITX20@..., wrote :
I am finding the sensitivity to be very poor with the DDS.? Did your sensitivity improve when you removed L4? And, is L4 the coil that is right next to the DDS jack?? I can't see the markings on the board and can't find a high-res image of the board. ?
When you "removed" the coil, did you short it or just remove it altogether?
tnx de AC3K
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