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IMD performance of D4D

Adam Rong
 

Folks,

One of potential customers asked about the IMD performance and I think it is a good question. I have to clarify here when I wrote spurious suppression of -50dBc. It is actually for harmonics of 2nd and 3rd and other parasitic oscillations. If we check closely near the carrier frequency with a spectrum analyzer, the IMD products of 3rd, 5th are quite strong. The measured IMD 3rd is not good, which will generate strong overtone in waterfall spectrum and cause nearby channel interference. During design phase, I have noticed it but I have to balance the RF output from the design simplicity with this spec. I also noticed that the carrier leakage without audio modulation is strong too, and it is even higher than the 3rd IMD products.

Those are the facts and I hope you can understand and help improve if you can. Thank you.

--
Thanks,
Adam Rong

Adam Rong
 

Gang,

Compared with 2nd and 3rd harmonics, the adjacent channel IMD products are higher. I did try to attenuate the input audio and it will improve but the result was not so satisfying. In this way, I have decided to remove C20 and C23 to change the LPF from elliptical to regular filter. It will improve the impedance matching with the antenna at the cost of higher 2nd harmonics. I will add this note into the full manual.

Beta testers, please remove C20 and C23 as well.

For serious builders, please follow this page to try:
https://pa3csg.nl/?page_id=40

Thanks,
Adam

Adam Rong
 

Gang,

Follow up on this IMD topic:

Two domestic customers reported that D4D won't work with automatic tuner very well. One customer fixed it by switching off power supply of the tuner, the other has no fix yet. I guess it is related with IMD products. The automatic tuner will detect signal frequency and tune to the best point, but with strong IMD products, the auto tuner just failed to work.

Thanks,
Adam

Jim
 
Edited

The D4D works great with my LDG Z-817 auto antenna tuner. 

73!

Jim - KH2SR

Jim
 

Should jumper wires be installed in place of C20 & C23 after they are removed?

Adam Rong
 

No. Otherwise it will short the coils.

Thanks,
Adam

在 2019年5月23日,上午4:57,Jim <KH2SR@...> 写道:

Should jumper wires be installed in place of C20 & C23 after they are removed?