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Hmmm...
I wasn't replying to you, Steve.
I was replying to Brian,KI8KY who has a V1 Nanovna and who started this message thread.

Also...your snide remarks are not welcome in this forum

Dear Larry,

No I did not reflow the flexible connector. The v2 uses plug-in screens, - one reason I chose it. If you had read properly, I was describing an anomoly which no one else seems to have had, where the screen calibration ( possibly of any similar device) gave “upside down instructions” until the calibration had been achieved by navigating just with the toggle switches. It could possibly arise even if the connector was a type needing reflow.

I am sorry that the information was of no interest to you. I am sure your reflow station is calling.

Steve L. G7PSZ

Sorry guys, must have a brain freeze when I wrote part of my response, you are correct the longer the wire, the lower the frequency, so you would be starting off lower than where you want to be and work your way up to the frequency you want to operate at.

--
David S

I think this topic went off on how to measure the test signal levels or something along those lines. What that has to do with Q accuracy is beyond me as it is a ratio as you stated and as those familiar with this know. Maybe the Q was covered but I can't easily see how. I am a Nanovna user now that I am retired and don't have access to the big $ instruments where I used to work.

In regard to your question about measuring the accuracy of the Q returned by the Nanovna, I want to mention that this is a tough measurement to make accurately and get consistent results between instruments....even HP instruments until improvements were made in how the measurement is done. This became apparent when I worked for a company that had a lot of custom inductors made by outside suppliers and Q was not a good spec to use unless it was a one-sided spec stating that the Q had to be greater than some quantity and the Q had to be fairly low. The problem surfaced when the inductors were specified against measurements made using the old HP 4342 Q Meter and even the earlier Boonton Radio Corp Q meters from the 50's. The 4342 and the BRC-160 for instance would report the Q to be much higher than the more modern instruments. These older Q meters used a tuned-circuit method where the Q was calculated (using meters) to be the ratio of the voltage across the inductor to the applied voltage. The newer instruments used reflection methods (couplers to measure S11) or used 4 wire measurements. The problem is that the resistive part of the impedance is so low compared to the reactance that these instruments didn't have the resolution or the ability to determine R in the presence of a high reactance or could not resolve the phase angle accurately enough and consistent enough. ( a small change in phase makes a big shift in the small R)

Now for the Nanovna, I found the accuracy of high impedances to be questionable above a few hundred ohms making it difficult to determine the Q accurately. For instance, the last time I did a comparison, my old BRC-160 determines the Q of a particular inductor to be about 130 and the Nano came back with something in the 40's. To get around the problem with accuracy at Hi Z's and even low Z's, I use the S21 Series-Thru and the S21 Shunt-Thru methods. Accuracy has been good enough for my impedance matching and comparison things that I find my self doing.

Thanks Allison!!

Thanks David, that's basically what I did, except that I was only checing the minimum SWR, How should I do to find the resonance freq with nanovna??

Thanks for your answer Dave, in fact there is wire everywhere I guess, the fences of the balcony and I guees many other in the structure of the building.

When I trim an antenna I first measure the resonant frequency.? Then compute the ratio of that to the desired frequency.? Convert that to wavelength, divide by 4 (each side of a dipole is 1/4 wave) and that will give me the desired change.? To avoid overshooting, I will only change half that amount and then repeat the process.? Of course, in the stuck-in-the-mud USA, convert meters to inches.
You don't have to measure what you have.? The resonant frequency tells you that.
Bob K6DDX

Some antenna materials don't fold, bend, or mutilate.
Could cut long, measure the resonant frequency, then reduce in length
by a ratio proportional to FreqResonant/FreqTarget.

Jerry, KE7ER

Wire diameter, insulation proximity to other object including wood will all
make a dipole shorter at lowest SWR. Or otherwise said will load the dipole
and make it electrically longer than is is.

Antennas in attic will be shorter than out doors as will low antennas.

Allison
-----------------
No direct email, it goes to bit bucket due address harvesting in groups.IO

On 8/23/20 3:07 PM, davidb1stein@... wrote:
<snip> 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.

This is why you crumple or fold the wire back, makes it easier to make it longer.

Bob,
I think you have misinterpreted the question, but it was stated somewhat awkwardly. He refers to 5 meters of wire for the dipole elements and later calls them cable. Beginners mistake in terminology. Build long, tune shorter to resonance. Have fun.

73,
PJH, N7PH

Post cited "Hopefully, the resonant point will be higher than the center frequency you want for the dipole". The extra Dipole length (to allow trimming for better Resonance/lower SWR) results in a LOWER resonant frequency than the Target. Shortening Dipole then Raises Frequency towards desired center frequency. Regards, John

DiSlord,
Would it be easy to add an SPI flash chip like this to the board...
this one is discontinued but if there is an alternative chip, it would allow for not only additional bitmaps, but maybe dual-booting of alternate FW.?

Isn't this how the Nanovna F stores code?
Thanks,?Larry


On Sat, 22 Aug 2020 at 8:09 PM, DiSlord<dislordlive@...> wrote: Attach screenshot example from SD card

Also for test i use nanoVNA Saver, and it also can grab 401 point and 800x480 image

As i see H4 platform allow connect big display, only one slowdown - Smitch chart, render it little slow, better use bitmaps on external flash.

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