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I found the center conductor and dielectric and after putting them back in the VNA is responding correctly through out its full range. Sometimes a little poking around can solve a huge problem.

On 12/6/21 7:01 PM, Nicholas wrote:

A little embarrassing but I think I found the problem. I checked the SO-238 to BNC male adapter I was using and THE CENTER CONDUCTOR IS MISSING! It likely got lost on a piece of coax that I was using at one point. I am going to find it and put it back in. That would certainly result in an open no matter what antenna I use!

A classic problem is when someone "stretches" a piece of coax to make it reach (or when pulling through a conduit or around something else), and the center conductor pulls back within the shield, taking the center pin with it.

A little embarrassing but I think I found the problem. I checked the SO-238 to BNC male adapter I was using and THE CENTER CONDUCTOR IS MISSING! It likely got lost on a piece of coax that I was using at one point. I am going to find it and put it back in. That would certainly result in an open no matter what antenna I use!

The cable tests correctly at DC with a multimeter with the braids connected and the center conductors connected correctly. The setup I have is exactly the same as when it was working correctly but just out of curiosity, what test are you talking about that might get me closer to a solution.

When I have a problem like this, when something working suddenly stops, my
first impression would be that a connection/cable has a problem. So I
check each carefully. Sometimes a cable is broken right inside the
connector, and works fine until it is bumped; or a connector isn't reliable
when disconnected from one setup and moved to another. So I always check
those issues carefully first. Of course, I also check that the nano
input/output isn't broken by doing a simple test that I have seen work
before.
In this case you seem to have indicated (without including details) that it
gives you an 'open' indication after you changed your setup, so it could
well be that it is indeed open because of a bad cable or connection.

I calibrated it for the upper edge of the AM band, 1600 to 1700 KHz and it worked really well before with the calibration done in this range. For some reason with calibration done in the same range it is not working at all suddenly. I have never exceeded the specifications for transmitter input power being very careful about where I set that for a transmitter under test and I have followed the directions for calibration exactly including some extra steps which would be useful the ISOLAT and THRU calibration steps to be exact. It is just confusing to me why this would suddenly happen.

What frequency range are you calibrated for? Perhaps recalibrate for a narrower range spanning the AM broadcast band, say 200 kHz to 2500 kHz.? Good luck.

Ken - WB?OCV

Show quoted text

What frequency range are you calibrated for? Perhaps recalibrate for a narrower range spanning the AM broadcast band, say 200 kHz to 2500 kHz.? Good luck.

Ken - WB?OCV

Those creations will likely work adequately for HF frequencies and below.
But at VHF and above, the leads and composition of the resistors will cause
some issues due to the parasitic inductance.

I checked it elsewhere and it does not seem to be responding at all below 50 MHz so it is not just the AM broadcast band but also HF and to an extent low VHF as well.

try these out,, i too have been trying to get better cal kit just for the nanovna, i made set of
so239 (see my post "Calibration, Compensation, DIY Parts Hacking!...... My First Post!") and i think
its ok but i still want to order these( ) and see if my tinkering is ok, plus having a factorie cal set will let me build more stuff knowing i have more then one standard to rely/test on on.. good
luck
KK6DBR

Thanks for a great reference, Roger. There's much to be learned in that video.

73, Ralph Bolt, K?RO

Thanks Jim. I tried it with good success.

73, Ralph Blt, K?RO

It was working perfectly in the AM broadcast band before both the S21 and S22 connectors so I don't think that is the problem. The nearest AM radio station to me is about six miles away and I am using the upper edge of the band but that is a reasonable possibility.

On 12/5/21 9:43 AM, Nicholas wrote:

For some strange reason my NanoVNA is now not responding correctly to any antenna designed for the AM broadcast band and instead is showing it as an open. I have confirmed the calibration using the test loads and it looks perfect so I am not sure what is going on here.

Could your antenna be picking up significant amounts of signal and overloading the input of the VNA?

For some strange reason my NanoVNA is now not responding correctly to any antenna designed for the AM broadcast band and instead is showing it as an open. I have confirmed the calibration using the test loads and it looks perfect so I am not sure what is going on here.

On 12/4/21 6:59 PM, Nicholas wrote:

One big reason why I got the device is to determine an unknown impedance on a transmitter and to adjust it to 50 ohms to drive antennas better. What method would I use for that, the transmitter by the way is a part 15 compliant AM one built from a kit with a maximum output of 100 mW and a continuously variable output control from 0 to 100 mW. This has been bugging me for quite a while but I have found the device very useful for looking at antennas.

it is? difficult to measure the output impedance of a high power amplifier (S22) in a meaningful way, because it really means you are feeding a signal into the output (like a salmon swimming upstream).? And it's not clear that that's the measurement you want.

One way to do it is to measure the output into varying loads (generically, called a load pull measurement), which you could do with a NanoVNA, and some sort of output coupler. From measuring the output signal with different loads, you can calculate the output Z.

Consider the amplifier as a Thevenin equivalent of a ideal voltage source in series with a output impedance Zout. The output voltage of the amplifier (which is what the VNA measures) is Vout = Videal*Zload/(Zout+Zload).? So if you measure the Vout with a couple or three Zload, you can calculate Zout.

I think the question was about finding Zeenko's store, so here is the link:


On Fri, Dec 3, 2021 at 9:49 AM 贵é濒颈虫 ?ngel <felixangelperiago@...>
wrote:

Hello Erik.

Zeenko's NanoVNA H4 is not a good NanoVNA?
I have a Nanovna but i want to buy an H4.

Regards
贵é濒颈虫

El vie., 3 dic. 2021 12:16, Erik <dl1ecd@...> escribió:

Looking for an approved vendor Aliexpress (Zeenko Store) without success.
Where to buy a NanoVNA H4 HW rev 4.3?
--
73 de dl1ecd, Erik

One big reason why I got the device is to determine an unknown impedance on a transmitter and to adjust it to 50 ohms to drive antennas better. What method would I use for that, the transmitter by the way is a part 15 compliant AM one built from a kit with a maximum output of 100 mW and a continuously variable output control from 0 to 100 mW. This has been bugging me for quite a while but I have found the device very useful for looking at antennas.

On Sat, Dec 4, 2021 at 06:38 AM, Ralph Bolt, K?RO wrote:

I understand how to use the Nano-VNA to measure a crystal's frequency.

Can I use the same configuration to measure the resonant frequency of a
parallel capacitor and inductor?

There are several ways to measure parallel L/C resonance with a VNA. Some are described half way down in this article.



Roger