开云体育

I was interested in the performance of the output signal. So at first I measured the output power:
10 MHz -12,13 dBm
50 MHz -12,57 dBm
100 MHz -13,21 dBm
200 MHz -14,85 dBm
300 MHz -7,92 dBm
400 MHz -8,07 dBm
500 MHz -8,25 dBm
600 MHz -8,90 dBm
700 MHz -8,57 dBm
800 MHz -8,76 dBm

Frequency Offset:
Set to 100 MHz measurement was 99,999 908 MHz which is an offset of 92 Hz. Excellent !!!

Output Spectrum:
Spectrum is fine up to 270 MHz with harmonics at least 20dB down
However above this frequency there is a strong subharmonic or spurious 12dB higher than the wanted signal. See picture enclosed. I have no idea how this may influence our measurements. In the pictures some sent to the group I can not see negative results.
This probably explains why output power is higer at 300MHz and above.

Ernst

I believe that's exactly how they have extended the range of this instrument to 900MHz: by using the harmonics.
otherwise Si5351 is only rated up to 200-300MHz. This is the same principle used in EU1KY antenna analyzer

You know, of course, that the signal out is a square wave.
According to the schematic, the Si5351 feeds the output directly through the resistor bridge..

You are right. But frankly speaking I do not understand why the spurious do not influence the test results. I am lacking the theory behind.

Just by curiosity I made a phase noise measurement of the output signal. For comparison the overlay in the picture is my 10MHz rubidium standard which shows the measurement limits of my system.

BTW the images attached are so compressed that often it is very hard to read any text. Can this be modified by the moderator of the group?

"You are right. But frankly speaking I do not understand why the spurious do not influence the test results. I am lacking the theory behind."

If the system is linear, the harmonics can be separated and filtered out. Usually with DSP processing.

But if the harmonics start to enter nonlinear region of component, mixer for example, filtering does not work completely.

One of your countrymen, Michael Knitter has an English-language presentation where he describes, in detail, how the harmonics are handled internally by the FA-VA5 antenna analyzer that he designed. It should answer you questions. He also wrote a article for QEX magazine, July, 2015, where more of the math is shown.

Sorry, but gave you wrong reference date for QEX article.

It is titled "DG5MK IV Meter, An Accurate Antenna Analyzer" by Michael Knitter in the May, 2017 issue of QEX.

Thanks for info, George. Thats what I was looking for.

Have searched the net, but did not find a copy of the QEX 2017/05. Do you know any source for this reference?

QEX is a magazine published by the ARRL for communications experimenters. The articles and papers in it are much more technically-oriented than most of what is in the QST ARRL magazine. One must be an ARRL member to access the QEX files and maybe even a QEX subscriber (I am one - I don't know if an ARRL member can access the QEX files without having a QEX subscription).

I haven't tried to access any QEX papers in a while. The papers as published in the physical magazine are limited in length and so, make available more technical details, software, schematics, etc., etc., there are a bunch of additional files for many of the papers on the ARRL/"QEXfiles" web pages. It appears that the original text of the published papers is not available but the supplemental files referenced above are.

Remember that the magazines published by the ARRL are all copyrighted and so it is not strictly lawful to pass PDF copies of them around, at least to non-subscribers. I'm guessing that that is the reason that one cannot just download PDF copies of the articles.

I will look to see if I can find my paper copy of the 2017 May/June issue of QEX. I think I unpacked my QST and QEX magazines a while back.

As an aside, QEX is a pretty good technical publication.

DaveD

"Have searched the net, but did not find a copy of the QEX 2017/05. Do you know any source for this reference?"

Try searching for, or emailing, the author. Often they will provide a copy to you as a courtesy.

Also try searching for related material to FA-VA5 antenna analyzer. It should be easy to find on web.

He has also written material showing how to connect his unit to DG8SAQ VNWA software.
(Very powerful software but with a steep learning curve.).