Removing DDS generated noise noise from a QRP transceiver

Adding a DDS VFO to a QRP transceiver can improve frequency stability and provide digital frequency readout. However it can also generate noise that affects reception. Video demonstrates how noise in a Bitx transceiver was found and cured with three added parts.
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[@cwguy8960]

Nice job - the end result is impressive! I love it when you find a simple and effective cure for noise.

[@mohinderkaur6671]

a low dropout regulator would be smaller and more effective. holtek parts like HT7533 may work. A C multiplier may help too

[@edwinklaver]

Thanks Peter. I was having the noise problem with my CDV. You filter worked great.

[@TheFretman2]

I bought a cheap Chinese DDS VFO and man it has a nasty output. The DDS VFO inputs into and also shares a power supply with a DC receiver. This little filter circuit removed most of the noise. I still hear some hum, but I think that once I've got the receiver in a metal enclosure, most of that will go away. Thanks!

[@mumrah42]

Great information for tracking down noise! I added this to my bitx40 and got rid of noise coming in from my switching power supply as well as from the DDS. I did hear the DDS noise coming in over the actual DDS line (not power line) but that was easily remedied with an inline filter capacitor (I used 220uF)

[@Paul_VK3HN]

Good A/B test proves the DC filter's effect. Might be worth experimenting with a 1mH RFC in place of the resistor.

[@vk3ye]

Thanks Paul - I did try a lower value ferrite but it had no effect. Besides resistors are cheaper and I had the box of them close at hand!

[@MidlifeRenaissanceMan]

I know this goes back to the before times, but I was wondering if you had considered the customary 0.1uF ceramic caps in parallel with the electros to compensate for the higher frequency stuff

[@Paul_VK3HN]

Wow this is a conversation in slomo. I would definitely parallel a 100nF. Not sure why it may have been left off. You cant have too many 100nF caps!​@@MidlifeRenaissanceMan

[@DavidGillooly]

Excellent demonstration of a good engineering practice!

[@owenvinall9970]

Excellent video and explanations thanks Peter. Vk5fkov

[@bradenglettkd8zm69]

fantastic information!

[@raafatalheety826]

Good video 73

[@alessandrowyatt6271]

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[@zevbraylon5978]

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[@OldF1000]

A PI filter in a power supply goes to show There is no school like old school ; )

[@WA8QFE]

Good job ! WA8QFE