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Old 29th June 2020, 01:57 AM   #691
benb is offline benb  United States
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Join Date: Apr 2010
Geez. I suppose for the price I could work with an upper limit of 1.5gHz. If I get a 5G design job I'll have to look for something else.

Seeing that I start to wonder how Agilent/Keysight/Tek/whoever-they-are-thesedays stay in business.
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Old 29th June 2020, 11:29 PM   #692
AnalogJoe is offline AnalogJoe  Mexico
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Join Date: May 2019
Quote:
Originally Posted by Tubelab_com View Post
I got one of these "Nano VNA's" last week.

NanoVNA-H Portable Vector Network Analyzer 10KHz-1.5GHz MF HF VHF UHF Antenna | eBay

I can confirm that it works as expected with a few known loads that were lying around. I have an HP 8753C, but it is rather impractical for some outdoor antenna experiments. I will do a comparison between the large, heavy and expensive HP and the $80 handheld unit in a couple weeks when I get back from a road trip.
Try using the software Nano VNA Saver
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Old 29th June 2020, 11:30 PM   #693
AnalogJoe is offline AnalogJoe  Mexico
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Join Date: May 2019
Quote:
Originally Posted by benb View Post
Geez. I suppose for the price I could work with an upper limit of 1.5gHz. If I get a 5G design job I'll have to look for something else.

Seeing that I start to wonder how Agilent/Keysight/Tek/whoever-they-are-thesedays stay in business.
Just saw a Keysight PNA on e-bay for $380,000 used!, the thing can go up to 65GHz but still you can buy a house with that!
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Old 4th July 2020, 02:42 PM   #694
w5jag is offline w5jag  United States
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Join Date: Feb 2007
Location: Arkansas
Quote:
... The tiny Inductors are Murata LQW18A series High Q 0603. (those that look blue-ish.) The shortwave inductors are 1210 or 18?? from Coilcraft or EPCOS/TDK. They are not yet on the board.
I am not geting satisfactory results using SMD inductors in HF filters as constructed on these SMD prototype boards. I'm guessing that at some frequency the pads are going to have undesirable stray capacitance to ground, but it dosn't seem to be an issue at HF ( so far ). I'm doing something wrong, but I don't know what it is.

I built a chebyshev 3 pole low pass filter, - 3 dB cutoff predicted to be 30 MHz. In fact, the same low pass filter built point to point on the perforated board in the early up conversion experiments, so a known to work filter. I built it with 0805 ceramic caps, and the generic 0805 cheap china inductors that can be seen in the picture. I terminated each end with a 47 ohm 0805 resistor to force an impedance match. The calculator is at wa4dsy.net

As measured with the RP, the result was dismal. It had a low pass characteristic, but nowhere near what the filter program predicted, the roll off began about 10 MHz early and was very weak, even by three pole standards, really just a gentle slope. To eliminate the crap cheap china generic inductors as the problem, I built another with good quality EPCOS/TDK inductors ( surplus, but from a reputable vendor - I'm sure they are genuine parts ) but the results were still terrible. Better, but still terrible.

I removed the Epcos inductors, and subtituted inductors I wound on T-25 (red) cores, and remeasured. The 30 MHz predicted -3dB cutoff measured at 28.75 MHz. The program predicted -10 dB at 40 MHz, and I measured -15 dB. 50 MHz was predicted as -15 dB and I measured - 20 dB. I could probably tweak the toroids to get -3 dB at the predicted 30 MHz, but the point is that the toroids work, the SMD parts don't, and I don't understand why or what I am doing wrong.

So far I've fooled around with molded conformal inductors, SMD parts, and toroids, and the only thing that works as predicted in a filter circuit are toroid cores. As I've stated before, I'm aware of Q, but am not going to pretend I understand it. I would have expected the Epcos parts to be sufficiently high Q, maybe not like a toroid, but good enough to behave in circuit somewhat like predicted.

I think I am about ready to join the starter VNA club. I can't find anyone stateside that sells the VNA module for the Red Pitaya, so I may get one of the nano vna's. It seems there are several different variants of those.
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