VNA Recommendations

[hendorog]

ZND is aggressively priced, even less expensive than the portable ZVL, but still more expensive than a USB VNA  

Could you share some idea of the prices?

[loxodes]

ZND is aggressively priced, even less expensive than the portable ZVL, but still more expensive than a USB VNA  

Could you share some idea of the prices?

It looks like the 8.5 GHz ZND goes for about 20k USD.. (https://www.microlease.com/us/products/rohde-schwarz/rf-network-analyzers/znd8?basemodelid=111969&bestbuyonly=1)

[tatus1969]

The MiniVNA seems to get fairly positive feedback elsewhere.

I am using it and am not very happy with it. IMO it has two big problems:
- the entire's signal path frequency response is not very flat, they heavily rely on compensation there. You can even see sawtooth residues from that
- the signal gen's output impedance over frequency is also not very flat. As this cannot be compensated, this is my main concern.
Anyhow, for that low price a great tool.

[Performa01]

...
- the signal gen's output impedance over frequency is also not very flat. As this cannot be compensated, this is my main concern.
Anyhow, for that low price a great tool.

The vast majority of these instruments generally don’t have a perfectly matched input/output impedance over the entire frequency range.

The usual cure is to introduce some fixed inline attenuator with 6 or 10dB, which improves the return loss by 12 or 20dB respectively. Of course, this is at the cost of input sensitivity / output power, but that shouldn’t be a big concern for most applications.

[tatus1969]

thanks for the tip, will consider that next time running into that problem. Doesn't help for reflection measurements with the miniVNA's built in directional coupler though. Just want to say that this one is good for hobbyists but I would not recommend using it in any more professional tasks.

[hendorog]

ZND is aggressively priced, even less expensive than the portable ZVL, but still more expensive than a USB VNA  

Could you share some idea of the prices?

It looks like the 8.5 GHz ZND goes for about 20k USD.. (https://www.microlease.com/us/products/rohde-schwarz/rf-network-analyzers/znd8?basemodelid=111969&bestbuyonly=1)

Thanks for that. By the way, how are you getting on with your VNA project?

[loxodes]

Thanks for that. By the way, how are you getting on with your VNA project?

(for context, hendorog is talking about my open hardware VNA: http://github.com/loxodes/vna)

The VNA works from 500 MHz to 3.5 GHz with about +/- .5 dB of accuracy, 40 dB or so of dynamic range, and a dozen points per second. I'm waiting on the next revision of some boards to push the maximum frequency up to 6 GHz and improve the accuracy and dynamic range.

The current topology relies on a broadband I/Q demodulator with an output that goes down to DC (an ADL5380), and I don't know of any of those above 6 GHz. I haven't decided how I'm going to push it past that, but I'll probably end up ditching the I/Q downconverer and doing that in software like Henrik Forstén's VNA. I'm playing with the AD9864 to handle the sampling and downconversion with a BeagleBone PRU for high speed IO. The LTC5548 mixer/doubler could enable operation up to 14 GHz off my existing synthesizer, I'm waiting on a test board for that.

I wouldn't recommend that anyone reproduce what I'm doing yet, Henrik Forstén's VNA is a better option for a DIY VNA at this point. When I'm done I hope to have something an order of magnitude slower, less accurate, and cheaper than a commercial VNA.

[hendorog]

The VNA works from 500 MHz to 3.5 GHz with about +/- .5 dB of accuracy, 40 dB or so of dynamic range, and a dozen points per second. I'm waiting on the next revision of some boards to push the maximum frequency up to 6 GHz and improve the accuracy and dynamic range.

The current topology relies on a broadband I/Q demodulator with an output that goes down to DC (an ADL5380), and I don't know of any of those above 6 GHz. I haven't decided how I'm going to push it past that, but I'll probably end up ditching the I/Q downconverer and doing that in software like Henrik Forstén's VNA. I'm playing with the AD9864 to handle the sampling and downconversion with a BeagleBone PRU for high speed IO. The LTC5548 mixer/doubler could enable operation up to 14 GHz off my existing synthesizer, I'm waiting on a test board for that.

I wouldn't recommend that anyone reproduce what I'm doing yet, Henrik Forstén's VNA is a better option for a DIY VNA at this point. When I'm done I hope to have something an order of magnitude slower, less accurate, and cheaper than a commercial VNA.

Thanks, and congrats on the good results.

I made something similar using an ADL5380 and a MAX2871 PLL. It worked but the accuracy wasn't great.
The plan is to add a second receiver for a reference, a second PLL and move to mixers instead of the ADL5380.

The 2nd PLL will be used to shift the phase - ala N2PK VNA - which removes the need for IQ demod, permits harmonic cancellation and DC offset cancellation.