As you have suggested, this 4'th harmonic is a problem when running the VFO at 5mhz. ?On the Raduino, one possible fix is to run the VFO on the high side, at 19mhz ?But with a vfo at 19mhz for operating 7mhz LSB, the crystal filter does not have so steep a skirt on the carrier side where we need maximum attenuation. ?So your fix at 4.8mhz might be the best solution. ?On the new uBitx, I'd like to think the extra crystals in the filter will allow us to not worry so much about crystal filter skirts.
On Wed, Mar 15, 2017 at 10:09 am, Jerry Gaffke wrote:
Raj: ?Thanks for the clarification. ?And yes, this might apply to digital VFOs as well. ?The mixer is having trouble with images from the fourth harmonic on both analog and digital vfo's. ?A square wave from a digital VFO should have no even harmonics, so quite possible that your fix will also help out on the Raduino too.
On Wed, Mar 15, 2017 at 08:06 am, Raj vu2zap wrote:
My passion is analog VFO, but I guess it would apply to other digital VFO's on 4.8-5 Mhz!
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