Re: zBitx +-2 MHz transmit spurs? --> SHOWSTOPPER for transmitting
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GM Gordon,?
I still believe it could be a power issue - the 3.3v regulator does not appear to be properly filtered per the manufacturer Datasheet. The other possibility is that the output of the 5351 is loaded too much under transmit conditions. The effect could even be combined.?One or both of these problems could occur only when the circuit is loaded (transmitting).? I'd measure the 3.3V regulator output under both receive and transmit conditions. If that varies more than a little bit, there may be an issue on the regulator side. Substituting the 5351 with a signal generator could give an indication if the 5351 might be involved.?
I suspect a combination effect.?
Lee KX4TT
On Wednesday, April 16, 2025 at 08:27:27 AM EDT, Gordon Gibby KX4Z via groups.io <docvacuumtubes@...> wrote:
Well that tells us even more.. Not due to the power supply. Unlikely to be produced BEFORE the crystal filter (it would screen it out) Has to be coming in AFTER the filter Dependent on the existence of some desired signal level for existence.? Not just being picked up "as is" from another wire.? ? ? Hence, possibly an IMD product with some other signal in the box.? ?
Gordon KX4Z
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Lee