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ND6T BiTX40 2nd harmonic solution

 

I was reading the BiTX Hacks blog this morning and saw where Bill Meara had posted some information from Don, ND6T, about the 2nd harmonic at 14.4++ MHz on the BiTX40. I noticed this problem last month on both of the BiTX40 rigs that I've been playing with so I believe the issue to be universal. I wanted to first finish tweaking some of the features that I was incorporating into both an AD9850 DDS VFO and an Si5351 VFO before tackling this issue. I finished those projects to my satisfaction yesterday and came down to the shop this morning to look at the LPF to see if I could adjust it to drop the second harmonic. Before getting started I read the blog and lo and behold - Don already had the solution. I installed a .1uF 100V cap across L7 in both of the BiTX40s and the second harmonic dropped from -28dB to -60dB with no noticeable effect on the output. Many thanks to Don for saving me a lot of effort. --73-- Mike -- W0MNE
 

Did you mean 100pF not 0.1uF?

Cheers Alf vk2yac


mikedoty via Groups.Io wrote:

I was reading the BiTX Hacks blog this morning and saw where Bill Meara had posted some information from Don, ND6T, about the 2nd harmonic at 14.4++ MHz on the BiTX40. I noticed this problem last month on both of the BiTX40 rigs that I've been playing with so I believe the issue to be universal. I wanted to first finish tweaking some of the features that I was incorporating into both an AD9850 DDS VFO and an Si5351 VFO before tackling this issue. I finished those projects to my satisfaction yesterday and came down to the shop this morning to look at the LPF to see if I could adjust it to drop the second harmonic. Before getting started I read the blog and lo and behold - Don already had the solution. I installed a .1uF 100V cap across L7 in both of the BiTX40s and the second harmonic dropped from -28dB to -60dB with no noticeable effect on the output. Many thanks to Don for saving me a lot of effort. --73-- Mike -- W0MNE
 

Absolutely correct, Alf - 100pF and NOT .1uF.? The mind and the fingers on the keyboard aren't always in sync:-)? Thanks for catching that.

Mike --? W0MNE

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