Re: Bitx40 75KHz Spurious, How to solve it. #bitx40

Tim Gorman
 

Your carrier is at 7.029Mhz. Did you have your mode set to CW?

If so, you aren't seeing "spurious" mixer products at 75khz, 150khz,
and 225khz. They are something else. Since their appear on both sides
of the carrier I would have called them some kind of IMD products but
I've never seen IMD go up as you move away from the carrier.

If you were in CW mode, the mixers aren't used to generate the carrier
frequency so you wouldn't see any spurious mixer products.

There is something else going on here.

Since harmonics are based on the carrier frequency the closest one you
would have would be at 14.058Mhz. It wouldn't show up on your scan.

It's very obvious that you are picking up something that is
harmonically related at multiples on both sides of the carrier.

I have to admit I'm not sure what your screen is telling me. It appears
it is scanning from 7.029Mhz to 7.049Mhz. That's only 20khz total from
screen-edge to screen-edge, not the 500khz that would be required to put
your unknown 75khz away from the carrier.

If your total scan is 20khz then your unknowns are at 3khz, 5khz, and
8khz. They wouldn't even be harmonically related.

Are you sure your "50.0KHZ/" on the screen isn't the video bandwidth or
something?

tim ab0wr

On Mon, 25 Jun 2018 00:09:11 -0700
jj1epe@... wrote:

Hi!

I built Bitx40 about 2 weeks ago.
 
I measured the spurious of Bitx40 by using the spectrum analyzer.
The level of spurious of harmonics were under 50db. So this is fine.
But the spurious at 75KHz was observed.
The spurious might be the multiple of 25KHz.
It would be much appreciated if you could advise  me the cause and
solution of this spurious of Bitx40.

In Japan, we must prove to the authority that the spurious of the
transceiver meets the criteria to obtain the certification of the
transceiver from the authority. So if i could not resolve this
spurious, I will not be able to use Bitx40 in Japan.

Thanks in advance,
Akira
JJ1EPE


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