开云体育

On Mon, Oct 10, 2022 at 05:53 PM, Brian Beezley wrote:

our antivirus program is probably keeping you from opening the ZIP file. Send
the file to to assure yourself that
it's virus-free and then disable your antivirus program.

I finally got it to download and then opened.
Is the L that is displayed before accounting for distributed capacitance?
Do I add one wire diameter to my core diameter to get "Core Dia" (i.e. center to center)
Do I measure width from center of outer wire to center of the opposite outer wire?
If I do the above and the calculate measured L with distributed capacitance it comes close.
268uh displayed, 238.5uh calculated with distributed capacitance, 237.3uh measured.
True L x C/C+Cd = The measured L
Q is almost 24% higher than I measure.

However, If the Q of my 260A capacitor is 10,000, at 1MHz, that is 0.151Ω, add that to 0.958Ω from the program and we have 1.107Ω.
Q =XL / R(loss)-- 237uh coil at 1MHz is 1491XL / 1.107Ω = 1346Q, this is just below what I measured at about 1380Q.


I got 100pf cap from Digikey that was supposed to have a Q of 10,000, I added it to my minimum 37pf of the 260A,
and found Q dropped just a few points with the 10,000Q 100pf added, telling me my 260A cap is not very much better than the10,000Q fixed cap I added.

Mikek

Mikek, I think this has gotten too far from the realm of NanoVNAs. I have sent you several private messages to try to take this discussion off-line, but I've not received a reply. If you want to continue, send me an email. My address is shown where you downloaded the program.

Brian

On Tue, Oct 11, 2022 at 02:14 PM, Brian Beezley wrote:

Mikek, I think this has gotten too far from the realm of NanoVNAs.

OK, no problem. Anyone that wants to email me about my last post, please do.
Thanks for the info about measuring Q of a cap, I'm building a circuit between forum exchanges, when
I get that working I'll pull out the 260A and see what I can find out about measuring cap Qs.
Thanks, Mikek
Just got your email 16 minutes ago.

Mike,

the *Internet Archive *seems to have captured /The Radioboard/, to be found at . Wait for a calendar to show, and then the Archive has various captures at different dates, so one can go back in time. It has also captured the "didn't pay" message to be found today.

The Crystal Set forum's most recent capture before things went south is at <>. (the equivalent for the website seems to be .)

HTH, 73, Stay Safe,

Robin, G8DQX

P.S: It's possible, likely even, that The Radioboard is awaiting revival on payment of a fee, if someone has the necessary cash.

On Wed, Oct 12, 2022 at 09:26 AM, G8DQX list wrote:

the *Internet Archive *seems to have captured /The Radioboard/, to be found at
. Wait
for a calendar to show, and then the Archive has various captures at different
dates, so one can go back in time.

Thanks for checking, but as far as I can tell, none of the individual posts are archived

It has also captured the "didn't pay"

message to be found today.

The Crystal Set forum's most recent capture before things went south is at

<

These are after it went South. I think Namecheap.com is trying to sell the URL.

. (the equivalent for the website seems to be

.)

This looks like a page setup by the original founder of TheRadiboard, Dave Schmarder, a few
of the links work, others say account suspended or take you to the wayback machine.
I'm afraid all the info is gone only to be experimented, discovered, built and rewritten in the future.
Mikek

I don't measure ultra-high Q inductors very often, but my favoured method is to use three ATC 800B porcelain caps in parallel to make up the resonating capacitance. Air spaced caps are generally inferior in my experience. It might be possible to find an air spaced cap that can compete with the (triple) ATC800B caps from a few MHz up into VHF, but I think it will be a very exotic and expensive capacitor. I've not tried comparing the Q of ATC800B vs air spaced down at 1 MHz though.

I have a large bare copper PCB with lots of 'triple 800B' caps on it and these cover from a few pF through to several hundred pF. I then connect up the test inductor to the chosen capacitance and then do a Q measurement.

If you have access to a good lab VNA it should be possible to do some comparative ESR measurements between various 100pF caps from about 20 MHz through to 100 MHz using a basic S11 measurement. It won't realistically be possible to do this much below about 20MHz, but the Q curve could be extrapolated to give some idea of the Q below 20 MHz. Due to the limitations of the VNA (when doing an S11 measurement), it can only give 'for indication only' results for the Q of the 100pF cap across 20MHz to 100MHz. However, I think that comparing the relative result between various 100pF cap types would still be useful/informative.

Using Excel for curve fitting is a good start, but you need to specify a mathematical curve equation to get the ball rolling. The graphing function of Excel can provide an idea of whether the relation between your X and Y varibles variables is Linear-Linear, Linear-Log, Log-Linear, and or Log-Log. That should suffice in most instances to give you an idea of what kind of equation you need to start with.

There are several freeware/shareware curve fitting software packages available. Google is your friend here. After trying several, my favorite by far is CurveExpert 1.4. Very easy to use, and once you specify your X and Y variables, it will run through dozens of simple and complex equations and give you an idea of which equation provides the best fit. You can download CurveExpert 1.4 from Software Informer at the following URL:




Good luck.

Ken -- WB?OCV

From: tuckvk3cca
Sent: Tuesday, October 11, 2022 03:41 AM
To: [email protected]
Subject: Re: [nanovna-users] Measuring Air Capacitor losses #general_vna

Excel does allow you to curve fit and then find an extrapolated value. It will provide you with the curve fitted formula.

It's probably not worth putting too much effort into the curve fitting algorithm below a few MHz because I think this is the region where the dielectric losses can begin to cause an increase in ESR with reducing frequency. Starting up at VHF and working downwards, the ESR of a ceramic cap typically falls with reducing frequency due to reduced metal losses but at some point, the dielectric losses cause it to start climbing up as the frequency is reduced. I'm not sure where this happens with a porcelain cap like the ATC 800B. In my experience the ESR of the 800B caps can still be seen to be falling down towards 10MHz but I'm not sure where the ESR will eventually start to climb again.