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Folks,
Please use the SEARCH feature of the forum.?
There is a thread called: voltage sensing diode
Look for it?/g/nanovna-users/message/5526
It's D2 beside the battery connector



On Sun, 23 Aug 2020 at 6:15 PM, Gary O'Neil<n3go@...> wrote: Hi Steve;

Gee... I can attach pix with any of my 3 iPads, 2 iPhones, and my iPod. My gripe is that I can’t use them for much more than lethargic web browsing once Apple obsoletes their support. :-(? I could give everybody in our club a NanoVNA or two for what I have tied up in i-Hardware. <sigh>

I have the version 3.1 board. There is a vacant diode footprint marked D2 as I recall. The anode is wired directy to the battery + side connection pad on the board, so it should be easy for you to find. The cathode side is marked, but it may not appear exactly obvious. That pad is wired to a blind via on the board. The early schematic(s) do not show it connected. One of the developers awhile back posted a comment that it was wired but not populated, and it’s purpose was for a battery level indicator anticipated for a future upgrade.

More recently, somebody posted that a 1N4148 would fill the bill, so I gave it a try, and it seems to function as intended.

If you are unsure of what you see in yours, i can disassemble mine again, and snap a Photo for you.

--
73

Gary, N3GO

you will see the resonant point move towards your desired center

frequency, it may not be much of a change, maybe a few MHz.

I'm sure you mean a few KHz. Should be clear from context, but just in case
somebody is confused...

Hi Steve;

Gee... I can attach pix with any of my 3 iPads, 2 iPhones, and my iPod. My gripe is that I can’t use them for much more than lethargic web browsing once Apple obsoletes their support. :-( I could give everybody in our club a NanoVNA or two for what I have tied up in i-Hardware. <sigh>

I have the version 3.1 board. There is a vacant diode footprint marked D2 as I recall. The anode is wired directy to the battery + side connection pad on the board, so it should be easy for you to find. The cathode side is marked, but it may not appear exactly obvious. That pad is wired to a blind via on the board. The early schematic(s) do not show it connected. One of the developers awhile back posted a comment that it was wired but not populated, and it’s purpose was for a battery level indicator anticipated for a future upgrade.

More recently, somebody posted that a 1N4148 would fill the bill, so I gave it a try, and it seems to function as intended.

If you are unsure of what you see in yours, i can disassemble mine again, and snap a Photo for you.

--
73

Gary, N3GO

You said that you are attached to the "facade of my balcony". Your antenna will be affected by the building structure and the fact that you are close to the ground. Both of these will affect the feedpoint impedance and gain of the antenna.

Roger

On 8/23/20 1:42 PM, ea3iji@... wrote:

Hey,
I've just received my nanovna this week, and started to optimise the length of my half wavelength dipole wire, it's just two 5 meters wires connected with a 1:1 balun and attached to the facade of my balcony to work at in the 20meter band.
I start cutting the cable until I reached the minimum SWR measured in the Nanovna. but to my surprised I ended up with 4,25m, far from the theoretical 5 meters, Have I done something wrong????
Sorry if the it is a stupid question, I'm just a newbie.
Thank you!!!!

Not a stupid question..

Lower than expected isn't unusual - all manner of things around the antenna "loading it down" will tend to reduce the resonant frequency.

What I do is fold or crumple the excess length (because if you go too short, or move the antenna, and you need it longer, you can just uncrumple some).


If you're hanging it off a balcony, I wouldn't be surprised if it tunes low. Brick, Stucco, Wood, etc, all have an epsilon lower than free space.

Crumple til it's resonating in band, be happy, and move on.

Be glad you've got something like NanoVNA to see it.

Thanks Steve!
Bob

Are you using bare copper wire or wire with an insulating cover copper wire like house wiring? Generally when I build an antenna, I start with the following formula taken from the ARRL Handbook: Length (ft) = (492 x 0.95) / f(MHz), where the f(MHz) is the center frequency of the dipole. Once I know the length, I add a couple of additional feet of wire to each end. From there I get the antenna up in the air to take the first measurements to get a reference starting point. Hopefully, the resonant point will be higher than the center frequency you want for the dipole. If so, then you need to bring the antenna down and cut a couple of inches from each end of the wire. Place the antenna back up in the air and recheck your reading, hopefully, you will see the resonant point move towards your desired center frequency, it may not be much of a change, maybe a few MHz. Time to bring the antenna back down and cut some more off the end, and recheck the SWR and resonant point. As you get closer to your center frequency, start cutting a shorter amount of wire off the end. Instead of 2-4 inches, now only cut 1 to 1/2 inch off. If it turns out you went below your center frequency, you will need to start over with new wire or add wire to your existing antenna.

Good Luck

David S

You don't change the SWR by changing the length of the cable.? It's the dipole itself that needs adjustment.
Your goal is to adjust the dipole length for minimum reactance at the operating frequency.? This usually coincides with lowest SWR but not exactly.? Cable length is immaterial.
Perhaps you are coupling some metal near the ends of the dipole and that is adding to the dipole electrical length.
73, Bob

First you must include the velocity factor of the wire - typically .95.? That brings the length down to 4.75.? Also, as the wire gets closer to the ground, the ground capacity makes the wire look longer..? 4.25M sounds? a little low.? Are the wires near any metal?

Dave - WB6DHW

Hey,
I've got a halfwavelengh dipole hanging on the facade of my balcony, it's two 5 meters wires connected through a 1:1 balun to work in the 20m band. I tried to optimise the length by cutting wire to go to the minimum SWR measured on the nanovna, but to my surprised I ended up with only 4,25m wires, far from the theoretical 5m.
I'm just a newbie so I might have done something wrong but I don-t know what, can anybody give me a hint??
Thanks in advance!!!

Hey,
I've just received my nanovna this week, and started to optimise the length of my half wavelength dipole wire, it's just two 5 meters wires connected with a 1:1 balun and attached to the facade of my balcony to work at in the 20meter band.
I start cutting the cable until I reached the minimum SWR measured in the Nanovna. but to my surprised I ended up with 4,25m, far from the theoretical 5 meters, Have I done something wrong????
Sorry if the it is a stupid question, I'm just a newbie.
Thank you!!!!

On Sat, Aug 22, 2020 at 10:17 PM, Bill Cody wrote:

Newbie NanoVNA-H4 user here with some questions:

1) My unit arrived a couple days ago with firmware version 0.5.0. Is this the
latest for the H4 model?
2) Has anyone using macOS with Parallels running Windows 10 been able to flash
the firmware? I get the unit in DFU mode successfully, the DfuSe Demo windows
app successfully sees the VNA, and I successfully load a DFU file into the
app, however when I click "Upgrade" the app just sits there with 0% progress.
The Device Manager shows all the correct entries in both DFU and normal mode,
and NanoVNA-Saver works fine in Windows.

Thanks!

Here is the latest 'official' firmware update for the H4, it comes from Hugen's own repository.

On Fri, 31 Jul 2020 at 09:53, Gabriel Tenma White <OwOwOwOwO123@...>
wrote:

Here are the designs under way and future plans for VNA hardware
improvements:


Some of our engineers are now working for another company on a new product
lineup:

- A full two port 3GHz VNA with 100dB dynamic range across the band. I
don't know if this will feature a display.

3 GHz full 2-port would be great if it had 4 receivers, which would allow
unknown thru calibration. That’s a massive advantage.

But without a display I would personally not buy.



Dave.


--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...

Telephone 01621-680100./ +44 1621 680100

Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United
Kingdom

Hi Bob,
There is a document in the hardware mods section of the forum's files that tells how it was done..?
/g/nanovna-users/files/Hardware%20Mods/NanoVNA%20new%203.2%20LCD%20display%20Herman%20ON1BES.pdf



On Sun, 23 Aug 2020 at 4:40 PM, Bob Albert via groups.io<bob91343@...> wrote: Steve, can you point me toward that display, and any instructions to retrofit?
Thank you.
Bob K6DDX

Steve, can you point me toward that display, and any instructions to retrofit?
Thank you.
Bob K6DDX

Ok, I just read the Whole msg: you've reflowed around the ribbon cable.

Did you do a continuity check from the digitizer input pins on the uP to the solder pads?

It's not a software issue. Either the input pins to the uP are bad or you have an open trace (via?) To the display connector.

If your ohmmeter has less than 3v at the leads, try measuring the resistance during touch, at the input pins to the uP with the VNA OFF.

If I remember correctly, there is a forum post with firmware to test the touchscreen.

I had an interesting experience with a touchscreen. It was actually a working nano v2 for which I bought a 3.2” screen with the same interface via Ebay.

On plugging it in, all worked except the touch, so I lumbered to the calibrate routine with painful negotiation of the jog and press. Several calibration attempts failed, until I tried touching the bottom right corner when it told me to press the top left, and likewise for the other corner ( then save in Config -at least on the v2).

All well, and it works fine with the slightly bigger screen which is easier to read and actually has a virtually identical footprint of the original except a bit of the board which has the pcb tabs for the sd card ( will saw it off), and the holes do not line up for the through standoffs but a tab of glue will do instead.

I cannot post before and after pics as I cannot attach on this forum with an Ipad.

Steve L. G7PSZ

Dear Gary,

Agree wholeheartedly.

My stable of nano devices consists of an original v2, a v2 with 3.2” screen (much easier to use) and a v2 with 4” screen and n connectors about to arrive.....and a tinysa.

But I do have an original nano, ( currently on loan to a friend). I am intrigued where you placed the diode to light up the battery icon. Could you point me to it please?

Out of interest, I got a 3.2” screen and it fits and works with the 2.8” v2 and although it does not line up with the holes to secure it, it hardly overlaps the vna circuit boards. The small increase in screen size transforms the device. Alas, working from an Ipad, I cannot attach pics.

Steve L. G7PSZ

Regarding this post from Gary from yesterday,
a few quick explanations that may be obvious to some.
Also a bit of what should be considered wild speculation on my part.


Some nanovna firmware uses the fundamental all the way to 300mhz,
but not all Si5351's are capable of doing this, varies from part to part.
For this reason, some firmware uses the fundamental only up to 250mhz.
The SiLabs datasheet claims a max of 225mhz.

I assume that at 301mhz the nanovna is using 3'rd harmonic out the S11 port
in all firmware versions.
The Fourier Expansion of a square wave says the 3'rd harmonic has
one third the amplitude of the fundamental.
The power at 1/3'rd the voltage is down by 20*log10(3) = 9.54 dB,
which is what Gary saw with his spectrum analyzer.
But had he checked at 100.3 mhz, he likely would have seen the much stronger fundamental.


Incidentally, the second port of the Si5351 driving a local oscillator into the bridge
is probably using the 5'th harmonic when operating at 301mhz:
/g/nanovna-users/topic/33122998#1743



Gary said:
Once again though, the drive current leves also alters the source impedance of the si5351ports

Has this been measured? I don't think that's necessarily so.
SiLabs says the Si5351 has a 50 ohm source impedance on the output.
They limit the current, which I assume means this could be modeled as reducing
the voltage source that drives the 50 ohm source impedance, all internal to the Si5351.

As I stated previously, with programmable Si5351 output current limits at 2,4,6,8 ma,
we get a range of 20*log10(8/2) = 12 dB, which could be quite useful.
Though this from post 16863 might also be useful:
could calibrate with a 3dB pad in the cable for the S11 measurement.
The round trip attenuation for the reflection would then be 6dB.

However, the local oscillator from the second Si5351 channel into the bridge
is still at the same power. I doubt this matters much.


Gary wrote:
The 900 MHz release version of eddy555’s firmware yields ~ -14 dBm up
through maybe 250 MHz or so, then drops off to around -20 dBm at 800 MHz.

Hmm, -20 dBm from 250 to 800 mhz? Or drops suddenly to -20 dBm at 800 mhz
when moving to the 5'th harmonic?

Perhaps edy555 is adjusting the Si5351 output current to be stronger when using harmonics?

With -14dBm for the fundamental, edy555 is 7dB weaker than Hugen's firmware.
Perhaps he is reducing the current by half and getting (nominally) 6dB weaker?,
Without hardware changes, there is not much else he could be doing.

Jerry, KE7ER

1: Try made calibration first
Use leveler select Config->Touch cal
Touch top+left screen side
Touch bottom+right screen side

After check work, use Config->Touch Test

If all good - Save config (Confog->Save)

In not work (hardware problem):
Touch screen use +/- X and Y I/O pins for measure position - check it
For get position used ADC
For work ADC need correct voltage on on CPU VDDA (pin 9, need ~3.3V) and ground on VSSA (pin 8)