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Can I use NanoVNA and RF wideband amplifier together? #newbie #applications #improvement

 

Hi,

My name is Godwin. I am new to NanoVNA. I want to use it to identify the presence of simple RF antenna tags in the vicinity.
I design the RF antenna tags and print them in conductive ink. Different antenna patterns produce different resonant profile response from the VNA (see attached pic).
Suppose a passive RF antenna tag with resonant frequency at 500 MHz is there. When I bring an interrogator antenna (20mm magnetic field probe connected to CH0) near it, the VNA shows a dip (in S11) at that particular frequency.
But the working range is always very small (usually less than a cm). Suppose if my RF tag lies about 10-15 cm away (both reader and tag are coplanar, distance is only along their central axis), how to make it work?

1. Is it possible to improve the 'read range' for this method by amplifying the signal ?
2. If yes, how to safely do it without damaging the VNA and the antenna. I came across some cheap RF wideband amplifier. But I am not sure how to connect them together.
3. What other additional components (amplifier? / attenuator? / RF power generator?) are needed to implement this ?

Any help/suggestion is appreciated.
Thanks!
Godwin.

NanoVNA_example_RF_Antenna_prototypes.jpg

 

On Fri, May 19, 2023 at 04:09 AM, <godpon@...> wrote:

Suppose a passive RF antenna tag with resonant frequency at 500 MHz is there. When I bring an interrogator antenna (20mm magnetic field probe connected to CH0) near it, the VNA shows a dip (in S11) at that particular frequency.
But the working range is always very small (usually less than a cm). Suppose if my RF tag lies about 10-15 cm away (both reader and tag are coplanar, distance is only along their central axis), how to make it work?

1. Is it possible to improve the 'read range' for this method by amplifying the signal ?
2. If yes, how to safely do it without damaging the VNA and the antenna. I came across some cheap RF wideband amplifier. But I am not sure how to connect them together.
3. What other additional components (amplifier? / attenuator? / RF power generator?) are needed to implement this ?

------------------------------------------------------------------------------------------------------------------

Your setup appears to function like a wideband DIP meter which depends on mutual coupling between two coils (your tag and the loop antenna). This method depends on close proximity of the coils and the only way I can see to improve the read range is to maybe increase the area of the loop receive antenna (similar to the use of a Helmholtz coil).

I'd love to hear if anyone else has a different suggestion.

Herb
 

Hello Godwin. Along the same lines as Herb's post.

You can try the following. Make sure the amplifier in use is specified to be unconditionally stable. Otherwise you run the risk of damage to the vna. You can connect the output port or the input port of the amplifier to the vna, S11 one port. And a sense antenna, small loop or patch to the other port of the amplifier. The idea is to look for changes in the amplifier reflection coefficient as measured on the vna, S11vna. This follows from the equation describing the change in the amplifier reflection coefficient with variations in the load. Variations in the load, is the Gamma sense antenna as coupled to the tag.

S11vna = (S11amp + S12ampS21amp Gamma sense antenna)/ (1-S22amp Gamma sense antenna)


If you turn the amplifier around, the same equation applies changing just the subscript ports.
Ideally, S12 is small, BUT not too small for this to function.

Regards, Alan
 

49-year RF engineer here. Given the original poster's apparent level of experience, suggesting to have them add an amplifier sounds like a recipe for disaster to me.
73, Don N2VGU
 

Understood Don.

Godwin should insure that the amplifier in use is stated on the data sheet... unconditional stabilty is met.

Perhaps you can suggest cautionary steps that should be taken prior to connecting an active device to these vna tools.

Regards,
 

No advice to give on your RF ID detector, but I have spent most of my career testing high-power amplifiers with VNAs, so I can offer a few basic rules:

1. ALWAYS assume the amplifier may put out its maximum power, when arranging your amplifier output attenuation. Even if you maintain a low drive level, attenuate output of amplifier to at least 6 dB below the damage threshold of the equipment to which you’re connecting it.

2. Always attenuate on output of amplifier, rather than input, because… noise.

3. Dynamic range is going to be your limitation in calibrating any amplifier test, if desired. Let’s say your amp has 60 dB of gain, and you want to test its gain compression, so you might need 25 dB sweep range. But you’re calibrating without the amp in the loop, so even if you manage to get the power centered in your VNA dynamic range, you need at least 85 dB of range. I know this one might not be relevant to your specific test, but the subject says “can I use NanoVNA and RF Wideband amplifier together?”

4. Do watch amplifier stability, as already noted by another. This is part of the reason for my rule #1.

I’ve spent many countless hours with 10,000 watt amplifiers connected to $200k VNA’s, and have never blown one up myself, but I’ve seen it done numerous times.
 

YET

:-)

On 21/05/2023 12:15, Thomas wrote:
I’ve spent many countless hours with 10,000 watt amplifiers connected to $200k VNA’s, and have never blown one up myself
 

Hi,

Should add that the nanoVNA, is not the best tool for amplifier testing.
The output is square wave, so there is quite a bit of power in the
harmonics.
And worse for amplified testing, on once you go above 300MHz, it go into
harmonic mode.
So at 600MHz the output is 200MHz, and the nano is measuring on the third
harmonic. So unless you have a high pass filter when working above 300MHz,
your amplifier will be saturated by the fundamental frequency, and it can
look as it performs badly at higher frequencies.

So before using the nano with an amplifier, read a lot, and understand how
it works and its limitations.

Regards,
Askild

On Sun, 21 May 2023, 13:16 Thomas, <thomas@...> wrote:

No advice to give on your RF ID detector, but I have spent most of my
career testing high-power amplifiers with VNAs, so I can offer a few basic
rules:

1. ALWAYS assume the amplifier may put out its maximum power, when
arranging your amplifier output attenuation. Even if you maintain a low
drive level, attenuate output of amplifier to at least 6 dB below the
damage threshold of the equipment to which you’re connecting it.

2. Always attenuate on output of amplifier, rather than input, because…
noise.

3. Dynamic range is going to be your limitation in calibrating any
amplifier test, if desired. Let’s say your amp has 60 dB of gain, and you
want to test its gain compression, so you might need 25 dB sweep range.
But you’re calibrating without the amp in the loop, so even if you manage
to get the power centered in your VNA dynamic range, you need at least 85
dB of range. I know this one might not be relevant to your specific test,
but the subject says “can I use NanoVNA and RF Wideband amplifier together?”

4. Do watch amplifier stability, as already noted by another. This is
part of the reason for my rule #1.

I’ve spent many countless hours with 10,000 watt amplifiers connected to
$200k VNA’s, and have never blown one up myself, but I’ve seen it done
numerous times.
 

There are NanoVna V2s for higher frequencies.

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