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All the valid points and suggestions (tinyVNA, SDR, cheap receiver), just to add WHY nanonVNA is not a valid solution :)

Those three above "listen" to the signal and show something on screen are create audio that you can hear.

nanoVNA, on the other side, creates the signal and measures what comes back after reflecting from device being tested (1 port), or what passes through tested device (2 port measurement).

nanoVNA will "record" something if you use it in the way you want, but results will be very unpredictable :)

Rich

I did some 2 port measurements on inductors and capacitors in this video. Perhaps this might give you some ideas to get started?



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VE6WGM

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VE6WGM

First: for the application in the uBITX the 2 dB dip is no problem. But if you want to try and improve, change the number of turns (up or down) on L5 AND L7 and try tuning the capacitors again. If the dip gets worse, try changing L5 and L7 the other way. This action changes the matching to the filter to optimize it. I have no idea if adding a capacitor in the ground lead is a good idea, but I am almost certain that the filter unit should be well grounded and adding a capacitor will give a path around the filter and ruin the response.

Second: in your application in the uBITX, you don't need the improved steepness that using two units will achieve. I believe the original application for using two units to create a 4 pole filter is in two way FM radios at VHF and UHF frequencies. In this application the radio needs the extra filter performance because this filter is the ONLY filtering and it is setting the ultimate bandwidth of the radio to reject adjacent channel interference. In the uBITX, this filter at 45 MHz is a roofing filter and the ultimate bandwidth filtering happens further along in the signal path at the crystal filter. From reviewing a few data sheets, it seems that when intended for 4 pole filters, they are sold as matched sets, with a marking as noted above for the pins to be connected together in the middle of the filter. Shipping them in matched pairs suggests that they are somehow matched at the factory; I would guess they are matched to be precisely on the same frequency, though the polarity marking suggests to me that something more complex may be involved.

Think i'll go the SDR way as i allready have one. Now just getting/making a directional antenna. My son had brought his world receiver about a month ago and the interference is all over the frequencies. We suspect some converters of solar panels in the neighbourhood.

I read about i think the tinyVNA. Don't know the differences between the two. I bought my nanoVNA to tune the SWR of my antenna. Now i'm discovering other possibilties.

Here's a spreadsheet that shows how the source and RxLO PLLs are programmed to use different harmonics.?? I've also included \the source code from si5351.c that actually implements it.

You can enter a desired frequency in the yellow highlighted cell to see what happens.? That frequency is compared against the threshold (and multiples) to decide which set of harmonics to use (highlighted in green, according to how it works out), and in turn, that determines what the PLLs in the SI5351 are programmed for.

There's a matrix that compares the Source and RxLO frequencies, and all the harmonics, and you can see that only one of them is 5kHz (which is highlighted in red).

You can also change the "threshold" frequency (normally 300 MHz).

On 5/7/22 7:52 AM, Jon MacGahan via groups.io wrote:

I'm just learning about the Nano-VNA; I don't actually own one yet. I understand that the source is a square wave, which contains odd-order harmonics. Suppose I want to measure return loss on some device that has a narrow-band response. It has very good return loss at F but very bad return loss at 3*F, 5*F, etc. Does the Nano-VNA somehow filter the reflected signal so that it only responds to F, not 3*F, etc. I.e., does the Nano-VNA processing include something like a digital filter that eliminates the harmonics? Otherwise the return loss response would be corrupted by the harmonics.

It's not done with digital filters, it's done with clever choice of harmonics for the receiver LO. The analog and digital bandwidth of the receiver is less than 1 kHz.

The transmit signal has fundamental, 3rd, 5th, etc.

The LO is generated so that it's 5 kHz away at a *different* harmonic, i.e., the transmit will be on the 3rd, and the LO will be on the 5th. So the LO harmonics don't line up with the transmit harmonics.

As a result, the NanoVNA receiver doesn't even see the "wrong" harmonics of the source.

Try it out with an excel spreadsheet where you can set the harmonic numbers and Synthesizer frequencies, it's really quite clever.

(Of course I am assuming that I am operating the Nano-VNA at a low frequency - not operating on the harmonics.)

Please disregard my previous post. I found the answer.

I'm just learning about the Nano-VNA; I don't actually own one yet. I understand that the source is a square wave, which contains odd-order harmonics. Suppose I want to measure return loss on some device that has a narrow-band response. It has very good return loss at F but very bad return loss at 3*F, 5*F, etc. Does the Nano-VNA somehow filter the reflected signal so that it only responds to F, not 3*F, etc. I.e., does the Nano-VNA processing include something like a digital filter that eliminates the harmonics? Otherwise the return loss response would be corrupted by the harmonics.

(Of course I am assuming that I am operating the Nano-VNA at a low frequency - not operating on the harmonics.)

Hello,

thanks for the information.
But the question is nothing extraordinary and simple:

Suppose you have just tested with the nanovna 2 filters 2 poles 45mhz. They look identical.
If you want a 4 pole filter, how do you plug them in. (They are often serial with the 2 center legs connected to a capacitor to ground)
The question is: You serialize them in the order of the nanovna test or you reverse the direction of the 2nd filter?
or how is the black dot determined if the question is asked differently?

Simple no?

cdt

TenTec had their "Patented Jones Filter" which worked very well. It was more for a variable bandwidth, but some of the techniques may apply here.

Schematic at:

Minor point, but QRM is interference from other stations. QRN is interference from noise.

On my V2Plus4 it needs to be entered in percent. e.g. A velocity factor of 0.73 should be entered as 73.

Hello,

Jim, yes i known that
But i have 5 filters 45R15AZ. No black dot.
My question is:
How after testing then with a nanovna select the 2 betters, and the best combinaison to connect them?

cdt

OK, I'll add a small correction to that last post

...measurement accuracy...the nominal value of an inductor or capacitor is highest at 0+j50 ohms or 0-j50 ohms, respectively.

Just so people don't get their knickers in a twist. ;-)

Regards,
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VE6WGM

The reason why people make measurements at +/- 90 degrees on the smith chart is because the measurement accuracy using the shunt configuration when trying to measure the nominal value of an inductor or capacitor is highest at 0+j50 ohms.

"Nowhere in the references above does it indicate that measurements are made at a 90 degree reflection coefficient angle which is the 12 o'clock position of the Smith chart. In fact you can see from my graphs (that used your s1p file) that good results are obtained at reflection coefficient angles over a wide range.

I think part of this "90 degree belief" is that the S11 refection coefficient phase is sometimes confused with the phase of the impedance Z. Somehow this leads to the belief that measurements of inductors have to be made at 90 degrees. This subject has been discussed several times in this group. I just noticed that Owen Duffy (who writes technically thorough articles on the NanoVNA and other electronic subjects) just wrote an analysis of the s1p file you posted and it is interesting reading."

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VE6WGM

Mini-Circuits has TONS of applications literature, and like their products, it's pretty much all top-notch. Look here:



and here:

The black dots connect together in the middle of the pair.

Yet another splitter document. This one is from Mini-Circuits:
RT