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Hi Larry,
When I disconnect the battery and plug the USB in the LED blinks as if it is charging.

sorry for double post, didn't realize my other one went though.

Just make sure, as others have pointed out, that you don’t have any other wires (power supply, USB to computer,, etc) connected to the nanoVNA.

73, Willie N1JBJ

On 2/17/22 5:52 AM, WB2UAQ wrote:

We're measuring impedance here. No matching transformer is needed. Just a 1:1 high common mode Z balun. From the Z's measured you determine the characteristics of the balanced transmission line OR and that includes its electrical length. Let's not over complicate things here.

Considering that the NanoVNA is smaller than a lot of HF baluns for balanced lines, I don't think you need the balun, either (until you get up to where the NanoVNA is a significant fraction of a wavelength - maybe don't use it for UHF TV twinlead.

On 2/16/22 11:28 PM, Bob Ecclestone VK2ZRE wrote:

I'm wondering if the correct way to measure the length of window line
with a NanoVNA is fundamentally different than that of measuring coax.

I'm following the method described by Arie
(/g/nanovna-users/message/26832). I have 5.175m of "JSC
1320 300 Ohm Ladder Line 300 Ohm 20 AWG / 7 Strands Bare Copper". That's
a quarter wavelength of 20.7m, or a frequency of 14.5MHz.


First things first, a FULL ELECTRICAL wavelength at 14.5MHz is 300/14.5 ~= 20.7m. A quarter wave ELECTRICAL length is 5.172m.
To find the PHYSICAL length for a quarter wave stub at 14.5MHz, MULTIPLY the ELECTRICAL length by the cable VF.
The Spec Sheet for 1320 TV Ladderline is 0.82. Therefore the PHYSICAL length required is 5.172*0.82 = 4.241m.

If you now want to prove this, you can use the NanoVNA, BUT it is best if you use a broadband matching transformer and measure the 300 Ohm ladderline in balanced mode.
If you try measuring the ladderline directly on the 50 Ohm unbalanced S11 input of the NanaVNA, you will get unreliable results as you have already discovered. Possible reasons are mentioned in other posts in this thread.

It is unclear why you'd get unreliable results for measuring *electrical length* without a balun - given that the NanoVNA is tiny, and isolated from other things. That is, the "unbalanced-ness" of the VNA is irrelevant when looking at a piece of balanced transmission line, unless there's some weird layout that has the transmission line laying next to the VNA.

The 300 ohms (or 100-120 ohms looking at twisted pair) means that one can't directly use the S11 or R+jX values, but the *distance* measurements should be just fine. The impedance of a balanced line with the other end open goes through the same cycle (at the same frequencies) of apparent short (at 1/4 wavelength), to apparent open (at 1/2 wavelength), to apparent short (at 3/4 wavelength), etc.

What wouldn't be necessarily valid is loss measurements (which is a handy feature of a VNA measurement, not only do you wind up with the length of the cable, but you get the loss at various frequencies)

We're measuring impedance here. No matching transformer is needed. Just a 1:1 high common mode Z balun. From the Z's measured you determine the characteristics of the balanced transmission line OR and that includes its electrical length. Let's not over complicate things here.

Hi Brady,
Did you try disconnecting the battery and powering the Nano from a USB source?
Sometimes when the battery gets too low, the CPU can get into a weird state (assuming you have the battery sense diode installed).

(also, please don't double-post - if you need to, please delete the previous post so we can keep forum somewhat clean)
Thanks,
Larry

Hi All,

My Nano VNA-H4 was sitting for a while, and after charging will not turn on. I checked the battery voltage, it is fully charged. The red LED works, not sure what to do next. Any help would be appreciated.

Agree with Kevin. Very good explanation.

John, wa3jrs

Bob, thank you so much for your very detailed answer. It'll take me awhile to get the ferrite and build the test jig, but I'll let the group know of my results. Thank you, again, for so generously answering my question.

-Kevin
KC3KZ

I have the same looking unit with the same firmware. It says it is supposed to go to 3ghz but mine only allows 2.413ghz as top end.
Have you tested yours to 3ghz?

I'm wondering if the correct way to measure the length of window line
with a NanoVNA is fundamentally different than that of measuring coax.

I'm following the method described by Arie
(/g/nanovna-users/message/26832). I have 5.175m of "JSC
1320 300 Ohm Ladder Line 300 Ohm 20 AWG / 7 Strands Bare Copper". That's
a quarter wavelength of 20.7m, or a frequency of 14.5MHz.


First things first, a FULL ELECTRICAL wavelength at 14.5MHz is 300/14.5 ~= 20.7m. A quarter wave ELECTRICAL length is 5.172m.
To find the PHYSICAL length for a quarter wave stub at 14.5MHz, MULTIPLY the ELECTRICAL length by the cable VF.
The Spec Sheet for 1320 TV Ladderline is 0.82. Therefore the PHYSICAL length required is 5.172*0.82 = 4.241m.

If you now want to prove this, you can use the NanoVNA, BUT it is best if you use a broadband matching transformer and measure the 300 Ohm ladderline in balanced mode.
If you try measuring the ladderline directly on the 50 Ohm unbalanced S11 input of the NanaVNA, you will get unreliable results as you have already discovered. Possible reasons are mentioned in other posts in this thread.

To match 50 Ohm to 300 Ohm, the impedance ratio is 300/50 = 6. The turns ratio for the transformer is the square root of the impedence ratio, sqrt(6) = 2.45.
So let us use 8 turns on the 50 Ohm Primary and (8*2.45) = 19.5 turns on the 300 Ohm Secondary.
The half turn is convenient as we end up with the primary at one end and the secondary at the other end of the ferrite core.

To make the matching transformer, use a binocular "balun" ferrite core. I have used a 14mm (9/16") long, 13.2mm wide ferrite with two 3.8mm (5/32") holes.
It is best if the primary and secondary windings are bifilar wound.
It is even better if the smaller 8 turn primary is wound in the centre of the 19.5 turn secondary.

As the power levels used here are quite low, the thickness of the wire is not critical. The main thing is that you can fit 28 "turns" of wire down each hole.
You will need about 1200-1500mm (4-5ft) of fine enamelled copper wire for a 14mm (9/16") binocular balun core.
Take your wire, fold it over, mark one leg at each end so you can identify it later and twist the legs together lightly. About 1 twist per cm, 2 twists per inch is fine.

It is difficult to describe what to do next, but what we want is to start with 5.5 turns of the secondary wire only, then 8 turns of the double bifilar wire, and finally 5.5 turns of the secondary wire only to finish up.
Unwind about 250-300mm (10"-12") of the unmarked leg so you can pass 5 full turns of the marked leg only through both holes of the ferrite and then pass it through the hole you started at to give 5.5 turns.
Now twist the unmarked leg around the marked leg to start your bifilar combined winding.
Make 8 complete turns with the twin bifilar wire and finish at the same end you started the 8 bifilar turns.
Separate the two legs and wind the marked leg ONLY through the ferrite another 5.5 times. You should finish at the same end you started with the single wire.

The "single" wire end is your 300 Ohm secondary, the bifilar 8 turn end is your 50 Ohm primary.

Mount the finished transformer on a piece of pcb or perf board. Attach a female SMA connector to the 8 turn winding and some terminals at the 300 Ohm end to attach your ladderline.
I am not being too prescriptive here. Use your imagination and your ingenuity to make a neat, relatively robust piece of test adaptor for you VNA test kit.

FINALLY, connect your SMA test lead to the transformer SMA connector and terminate the 300 Ohm terminals with a NON-INDUCTIVE 300 Ohm SMT or metal film resistor/s.
Now do a Short/Open/Load Calibration over the frequency range of interest and save to one of your Calibration memories.

You can now run your test on your ladderline. It should be relatively accurate as the Calibration Plane is at the 300 Ohm Terminals of the Transformer.

I used a similar transformer design when I was a design engineer working on early VDSL Broadband Network deployment. This used multiple carriers from 2MHz-35MHz on 100 Ohm Cat 5 cable.
I used a 10 turn primary and 14 turn secondary for the 50/100 transformer. The system was very sensitive to cable balance and the transformer worked well.

73...Bob VK2ZRE

Charlie, I sent you details by email.

On Sun, Feb 13, 2022 at 03:37 PM, Alan Brown wrote:

Trying to use log mag and not working now.
I think I overload S21 with more then 10db.
What is the fix anyone now?
I’m hoping some simple right at the port

The front end of CH1 just contains some resistors and SA612 mixer. Try looking there for damage first....

Shown here >>>

Full schematic here >>

Roger

That would be great. Much appreciated Danny.

I also recently purchased the AURSINC SAA-2N v2.2 which I believe to be the same internally.

I loaded DiSLord's "V2 480x320 v1.1.00.bin" and had some difficulty getting the screen re-inverted but got it figured out in a few minutes.

I can't find the forum post where I downloaded it now but if you want that I can give you a link to my copy of it.

Danny

I recently purchased a NanoVNA V2 because it has the extended frequency range to 3GHz.
The firmware version is well over a year old (see attached photo) and was wondering if there are any recommended firmware upgrade versions for the NanoVNA V2.

Any suggestions on how to upgrade the firmware are greatly appreciated.

-Charlie

On 2/16/22 6:16 AM, Alan Brown via groups.io wrote:

I’m no wiser after these posts.
S21 does not work as not able to calibrate it.
It has gone bad. Overload.
Is there a fix? I’m measuring gain of a LNA as I have done many times and now the port is bad.
I don’t remember breaking it but I probably did as just takes a few seconds not thinking.
I was about to order a new H4 and this one will work for things I don’t need S21 port for.
What is it I’d have to change is the VNA, resistor chip etc??

This is a H4? Original NanoVNA RF design, just with a bigger screen? The first thing after the CH1 input is a resistive pad (I can't remember how many dB, but something like 17-20 dB). I would have thought that's pretty robust against a momentary overload. How much did your LNA put into it? The next thing in the chain is the mixer, but that should be able to handle 0dBm without damage and probably more - it's a bipolar Gilbert cell, and the inputs drive the bases of an NPN transistor.? This isn't some delicate CMOS or MOSFET. So, did you put more than ~100mW in?? Or worse yet, hook it up to the supply voltage without a DC block (e.g. if your LNA expects a bias T or something like that) - 12V across the 56 ohm input resistor is ~200mA or 2.5W - That teeny, tiny SMT resistor won't handle that.? After that goes open, the 12V is then across the 240 ohm series resistors and ultimately the SA612 input

You could probably measure the resistors in the pad to see if one or more is cooked.

OTOH, if it's a NanoVNA2, I believe they have an RF switch as the first thing after the connector, and those are fairly sensitive to overload.

I’m no wiser after these posts.
S21 does not work as not able to calibrate it.
It has gone bad. Overload.
Is there a fix? I’m measuring gain of a LNA as I have done many times and now the port is bad.
I don’t remember breaking it but I probably did as just takes a few seconds not thinking.
I was about to order a new H4 and this one will work for things I don’t need S21 port for.
What is it I’d have to change is the VNA, resistor chip etc??

Has anyone wound a high common mode impedance 1:1 balun with 50 ohm coax and calibrate at the output end of the balun?

I made a balun years ago for use with GR Z bridges (GR 1606 and 916) for this purpose with good results.

I didn't wind the coax on a ferrite toroid at the time. I wound the coax on a length of PVC pipe and with a variable cap across the coax (shield to shield) I tuned it to resonance for the frequency of the test. The common mode Z is very high and higher than a ferrite-cored balun.

Obviously this would not work for a swept frequency test but should work with a broadband ferrite-cored balun.

What I wanted to say here is:

A quarterwavelength at 500 kHz = 150m electrical.
A 1/4 wave physical cable with VF=0.78 would then be 150 x 0.78 = 117m long or with a VF of 0,66:? 150 x 0.66 = 99m
So sweeping from 500 kHz up will be sufficient for coax upto 100m long or so.
For longer cables one has to start with a lower frequency.

Arie


Op 12-2-2022 om 01:47 schreef Bob Ecclestone: