Unwanted products produced in high frequency signals mixing to get a lower frequency

Hello, this might seem a bit silly question but I need to make sure.
Will this oscillator produce any unwanted mixer products below 30MHz?
https://www.zl2pd.com/img/SpanOsc/WideSpanOscSchematic.jpg

This calculator is useful to see what frequencies may be present.
The instructions are on the first sheet of the excel workbook, but basically you enter in red the LO and RF values, and also the range of values
that you are interested in monitoring.
Note that it won't tell you the amplitude, but it will tell you what frequencies are present.

sky_123 said:

This calculator is useful to see what frequencies may be present.
The instructions are on the first sheet of the excel workbook, but basically you enter in red the LO and RF values, and also the range of values
that you are interested in monitoring.
Note that it won't tell you the amplitude, but it will tell you what frequencies are present.

Click to expand...

It would really be helpful but I do not have excel installed...

neazoi said:

It would really be helpful but I do not have excel installed...

Click to expand...

Ok I have tried it. It does not show any spurs below 30 mhz. I choose the range to be 1-30mhz and it shows highlights almost all over the hf band. I may be doing something wrong there, I am a bit confused.

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neazoi said:

Ok I have tried it. It does not show any spurs below 30 mhz. I choose the range to be 1-30mhz and it shows highlights almost all over the hf band. I may be doing something wrong there, I am a bit confused.

Click to expand...

I have also tried this **broken link removed** which seems less confusing. what is the difference between lo side LO and hi side LO? does it mean that the local oscillator is below or above the products frequencies?

In the last link calculator, I put:
LO tuning range =48-78 (the range of my vco)
If center freq.=48 (my steady crystal frequency which I mix with the vco)
Spur search range = 1-30
IF bandwidth=1

When on high side LO, spurs are zero in 1-30mhz. When in lo side LO spurs do exist.

Does it mean that there will be no spurs at 1-30mhz when I downconvert the 48-78 down to 1-30MHZ?

The spreadsheet should be showing you spurs, see here:

Your actual mixer may result in low spurs, but the spreadsheet cannot predict that of course.
Also, bear in mind that the VCO signal will also have some (probably a lot!) of harmonic content.
You can filter that out of course beforehand.
I'm guessing you want to construct a test RF generator for 0-30MHz, right?
This will probably be fine, for normal use-cases. I was planning to build a sig-gen at some stage too,
but I was going to just construct many VCOs and filters, and just switch between them.
The mixer method may be better but I did not consider it for my limited frequency range need.

sky_123 said:

The spreadsheet should be showing you spurs, see here:
View attachment 77695
Your actual mixer may result in low spurs, but the spreadsheet cannot predict that of course.
Also, bear in mind that the VCO signal will also have some (probably a lot!) of harmonic content.
You can filter that out of course beforehand.
I'm guessing you want to construct a test RF generator for 0-30MHz, right?
This will probably be fine, for normal use-cases. I was planning to build a sig-gen at some stage too,
but I was going to just construct many VCOs and filters, and just switch between them.
The mixer method may be better but I did not consider it for my limited frequency range need.

Click to expand...

Ok I found the old DOS version of appcad more clear to me to understand so I calculated the spurious there. It considers harmonics from both the LO and the VCO. After I saw the results it was clear to me that I need Two LPFs on the VCO and the LOSC and also an LPF after the mixer to filter the sum products. A LO notch filter after the mixer will result in attenuating the LOSC signal as well.
Only then one can achieve very pure spectral quality through 1-30MHz.
The good thing when mixing high frequencies to generate lower ones is that filtering is easier and not critical.
On the other side, a direct 1-30MHz oscillator would require a variable (or many switched) LPF, which can be a nightmare especially in lower frequencies.