Topics

QCX Inductance measurements #qcx #80m


Scott - N1ST
 

I'm doing some inductance measurements with an MFJ antenna analyzer.   Can someone please tell me what frequency I should be using when measuring L1-L3, and L4?


Manuel; DL2MAN
 

This depends on the band of your kit.
L4 should be middle of your band
L1-l3 should be some khz over your band since those are for low pass

73 DL2MAN


ajparent1/KB1GMX
 

Despite calibration I've found the MFJ259B I have insufficiently accurate.

The key things is that measuring at the right frequency is part of the
matter and then you have to take calibration into account.

However the AADE LCII seems to be by far the most accurate save for
my old RLC bridge.  

Allison
-------------------------------
Please reply on list so we can share.
No direct email, it goes to bit bucket due address harvesting in groups.IO


Jim Allyn - N7JA
 

I recently bought an LC meter from either Ebay or Banggood, I forget which.  It was cheap, maybe 20 or 30 bucks.  When I turn  it on it tells me it's a LC100-A  Rev. 4.8.  I believe it works at fairly low frequencies, but it does seem to give accurate results.  If you want to measure at specific (and higher) frequencies, get a NanoVNA.  I have several, the latest is the NanoVNA-H model, which is better than the earlier ones I bought.


DK
 

Sir,

Would you mind posting a link as to where you purchased your NanoVNA-H model?

I am unclear as to the various models available and would appreciate your input.

Thank you!

DK KD6TK

On Apr 26, 2020, at 1:58 PM, Jim Allyn - N7JA <jim@allynelectronics.com> wrote:

NanoVNA-H model


Dave VE3GSO
 

I have a NanoVNA H-4 unit purchased from an eBay seller. I looked for included adapters, loads, and cables. It has become a valued tool in my shack.

Dave

On Apr 26, 2020, at 18:52, DK <donaldphilbin@hotmail.com> wrote:

Sir,

Would you mind posting a link as to where you purchased your NanoVNA-H model?

I am unclear as to the various models available and would appreciate your input.

Thank you!

DK KD6TK

On Apr 26, 2020, at 1:58 PM, Jim Allyn - N7JA <jim@allynelectronics.com> wrote:

NanoVNA-H model


Jim Allyn - N7JA
 

On 4/26/20 3:52 PM, DK wrote:
Would you mind posting a link as to where you purchased your NanoVNA-H model?

I got mine here:

https://www.alibaba.com/product-detail/Hugen-NanoVNA-H-New-item-Original_62342877955.html?bypass=true

Some people have had difficulty buying with PayPal, but if you click the "Contact Supplier" link on the right side of the page, you can send a message to Maggie to arrange PayPal payment.

There is also a NanoVNA-H4, with a 4 inch screen, available here:

https://www.alibaba.com/product-detail/Original-Hugen-NanoVNA-H4-4-0_62455845943.html?fullFirstScreen=true

Again, click the "Contact Supplier" link on the right side of the page if you have any troubles, and Maggie will take care of you.

There are a lot of different vendors selling NanoVNA clones.  Some of them are OK, and some of them suck.  The first one I bought, I now know is classified as "Bad", but at least it wasn't one of those classified as "Worse."  My second NanoVNA, a -H model, was bought from Maggie on AliBaba, and the performance is WAY better than the first "Bad" one I bought.  In theory, all NanoVNAs are supposed to be good up to 900 MHz, but some of them lose accuracy well before that, while the -H versions are good up to 1500 MHz, and some say they are usable higher, up to 2.1 GHz.

There is also a NanoVNA-V2, also known as the S-A-A-2.  The designer of this one says it's good up to 3 GHz and usable up to 3.5 GHz.  One of the reviews I saw the other day said it was usable up to 4 GHZ.  They are available here:

https://www.tindie.com/products/hcxqsgroup/nanovna-v2/?pt=ac_prod_search

but they are out stock at the moment.  I signed up on the waiting list for whenever they get a new batch of them.

As long as you buy the -H, -H4, or -V2 model, you will love your NanoVNA!


Jim Allyn - N7JA
 

There is also a wonderful piece of software that will allow you to use your NanoVNA with a desktop or laptop computer running Linux, MacOS, or Windows. It's called NanoVNA-Saver, and it works with most NanoVNA versions.  You can get it here:

https://github.com/mihtjel/nanovna-saver

NanoVNA-Saver is free and open source.


geoff M0ORE
 

I rely on my N2PK VNA for HF work. Paul's hardware  and software from Dave, G8KBB, and you have lab class test equipment. Not available to buy, you have to build it from scratch.

On 26/04/2020 20:27, ajparent1/KB1GMX wrote:
Despite calibration I've found the MFJ259B I have insufficiently accurate.

The key things is that measuring at the right frequency is part of the
matter and then you have to take calibration into account.

However the AADE LCII seems to be by far the most accurate save for
my old RLC bridge.  

Allison
-------------------------------
Please reply on list so we can share.
No direct email, it goes to bit bucket due address harvesting in groups.IO


John Kirby
 

Scott,

Your orignal frequency question has been well answered
      Good on DL2MAN


Allison notes, the MFJ 259 is not a 'labority' standard and ...
...""The key things is that measuring at the right frequency is part of the matter and then you have to take calibration into account.""


I have a different opinion of the MFJ 259
Plus a technique on how to measure inductance you may like to try

From a frequency stand point ...
I find the 259 can be as accurate as you ham shack receiver when beat against it (the shack RX) and WWV or CHU

From an L/C meter stand point ...
Measurement accuracy depends on THE 'standard component' plus  frequency accuracy (ham shack RX)

For example...
How to measure  inductive reactance  (XL) in Ohms then calculate inductance (L)  in Henrys
First we will need to know the 'value' of the 'standard'  C  (capacitor) within a decent accuracy I call 'spot on'

So,  how do we define or 'create' a STANDARD  capacitor using and the 259 and ham shack receiver

There is an empirical measurement technique to find capacitive reactance (XC in Ohms) and then C in Farads  with way more than enough accuracy for ham radio home brew

An empirical measurement suggests (to me at least) an error free result that works like example below using ... money, marbles or chalk, for obvious reason I prefer marbles

You put 73 marbles into a bag
I put more marbles in the bag
You open and count 88 marbles total
How many marbles did I put in the bag?
By observation    88 - 73 = 15
In this case 15 references the difference or 'DELTA' measurement technique

Now let's work with capacitors and units of microFerad (uF) = (10E-6
Farad)

Capacitors connected in parallel are like resistors connected in series, their values add.  A 75 Ohm resistor in series with a 25 Ohm resistor makes a total of 100 Ohms. (Not knowing your electronic background I introduced resistance as reinforcement) Like wise a 75 uF cap in parallel with a 25 uF cap equals 100 uF total

Now lets create a STANDARD capacitor then use it to measure inductance with a very high confidence of accuracy

Suppose we do not know the value of two junk box capacitors called capA and capB  ...BUT... (just like marbles) we can calculate the DELTA between two measurements

Set the MFJ frequency to the band of interest, any number, for example  7.12345 mHz ... accuracy, stability and drift do not matter at this point

My 259 measures junkbox capA at 525 Ohms (capacitive reactance (XC)) of course accuracy is unknown and does not matter at this point

Keep all leads as short as possible

Now connect junkbox capB parallel to capA and my 259 indicates total XC at 850 Ohms

Note agan, we have no idea the true value or accuracy of these first two measurements  . . . YET!
BUT by DELTA C arithmetic we now know capB = 325 Ohms

junk box capB = deltaC = (Cmax) - (Cmin)
 (850) - (525) = 325

At this point ... regardless of the accuracy of your 'meter' we know three things
1) the frequency band of interest (40 meters)
2) the 'DELTA value' of junkbox capB = XC = 325  Ohms  'spot on '
3) and ... capA may OR maynot be  525  Ohms +/- any % ....at this point it does not matter because capB at 325 Ohms 'spot on' becomes our STANDARD C for inductance measurements

Return capA safely to the junkbox

Now by having a 'spot on' STANDARD C (capB) we can measure inductive reactance (XL) and then calculate inductance (L)

Connect the unknown inductor in series with only capB from MFJ coax connector and MFJ ground keeping leads short as possible

Turn the 259 frequency dial until the IMPEDAMCE meter dips at zero Ohms

The dip or "null" will be fairly sharp (because at resonance a series tank circuit creates a dead short circuit) the dip at zero Ohms indicates resonance

Next ZERO BEAT the ham shack receiver to the MFJ 259 dip frequency, CW mode works best

My shack receiver indicates 7.65432 mHz or (7.654 E+6 for arithmetic purpose)

At this point we know several things
1) my  L/C  'tank circuit' is resonant at 7.65432 mHz
2) at resonance  XL = XC
3) therefor  XL =  XC =  325 Ohms = junkbox capB
4) from the equation ... XL = 2pi f L  (reactance in Ohm)  we can calculate L (inductance in Henery) by ...
 
          L = XL / 2 pi f
             = 325 / (6.28 X  7.6543E6)
             = 325 / 4.8069E7
             = 6.76E-6
          L = 6.76 uH
 
5) from the reactance equation  XC =  1 / 2Pi f C   we can find the value of junkbox capB in Farads by ...
      
          C = 1 / (2pi  f  XC)
              =  1 /  (6.23 X 7.65432E6 X 325)
              =  1 /  1.562E10
              =  6.40 E-11
              =  64 E-12
          C  =  64 pF


Most common ham radio powers of 10 
kelo    abbreviated  k  equal  E3
meg   abbreviated  m equal  E6
gig      abbreviated  g  equal E9

micro  abbreviated  u  equal   E-6
nano   abbreviated   n  equal  E-9
pico    abbreviated   p  equal  E-12

By observation one can see, that maybe except for frequency, accuracy to a fine degree is not a big thing for home brew ham radio experiment

Examples above put component values well within any first cut 'ball park' figure

The coil you are winding must mate with a capacitor to serve any purpose
Capacitors selected for most kits now days may only have a tolorence of +/- 5% at best so a turn or two on or off an inductor will make the circuit function to your delight

If you change the way you look at things,
        the things you look at change

72 73 74  P^3
John
N3AAZ


Ed Kwik
 

One of the best posts I have seen
Ed
AB8DFHAM


George Korper
 

John, wow. You have shown the QCX to be a "quantum" ready rig. 
Really, really good exercise! 

On Mon, Apr 27, 2020, 3:41 PM John Kirby <n3aaz_qrp_1@...> wrote:
Scott,

Your orignal frequency question has been well answered
      Good on DL2MAN


Allison notes, the MFJ 259 is not a 'labority' standard and ...
...""The key things is that measuring at the right frequency is part of the matter and then you have to take calibration into account.""


I have a different opinion of the MFJ 259
Plus a technique on how to measure inductance you may like to try

From a frequency stand point ...
I find the 259 can be as accurate as you ham shack receiver when beat against it (the shack RX) and WWV or CHU

From an L/C meter stand point ...
Measurement accuracy depends on THE 'standard component' plus  frequency accuracy (ham shack RX)

For example...
How to measure  inductive reactance  (XL) in Ohms then calculate inductance (L)  in Henrys
First we will need to know the 'value' of the 'standard'  C  (capacitor) within a decent accuracy I call 'spot on'

So,  how do we define or 'create' a STANDARD  capacitor using and the 259 and ham shack receiver

There is an empirical measurement technique to find capacitive reactance (XC in Ohms) and then C in Farads  with way more than enough accuracy for ham radio home brew

An empirical measurement suggests (to me at least) an error free result that works like example below using ... money, marbles or chalk, for obvious reason I prefer marbles

You put 73 marbles into a bag
I put more marbles in the bag
You open and count 88 marbles total
How many marbles did I put in the bag?
By observation    88 - 73 = 15
In this case 15 references the difference or 'DELTA' measurement technique

Now let's work with capacitors and units of microFerad (uF) = (10E-6
Farad)

Capacitors connected in parallel are like resistors connected in series, their values add.  A 75 Ohm resistor in series with a 25 Ohm resistor makes a total of 100 Ohms. (Not knowing your electronic background I introduced resistance as reinforcement) Like wise a 75 uF cap in parallel with a 25 uF cap equals 100 uF total

Now lets create a STANDARD capacitor then use it to measure inductance with a very high confidence of accuracy

Suppose we do not know the value of two junk box capacitors called capA and capB  ...BUT... (just like marbles) we can calculate the DELTA between two measurements

Set the MFJ frequency to the band of interest, any number, for example  7.12345 mHz ... accuracy, stability and drift do not matter at this point

My 259 measures junkbox capA at 525 Ohms (capacitive reactance (XC)) of course accuracy is unknown and does not matter at this point

Keep all leads as short as possible

Now connect junkbox capB parallel to capA and my 259 indicates total XC at 850 Ohms

Note agan, we have no idea the true value or accuracy of these first two measurements  . . . YET!
BUT by DELTA C arithmetic we now know capB = 325 Ohms

junk box capB = deltaC = (Cmax) - (Cmin)
 (850) - (525) = 325

At this point ... regardless of the accuracy of your 'meter' we know three things
1) the frequency band of interest (40 meters)
2) the 'DELTA value' of junkbox capB = XC = 325  Ohms  'spot on '
3) and ... capA may OR maynot be  525  Ohms +/- any % ....at this point it does not matter because capB at 325 Ohms 'spot on' becomes our STANDARD C for inductance measurements

Return capA safely to the junkbox

Now by having a 'spot on' STANDARD C (capB) we can measure inductive reactance (XL) and then calculate inductance (L)

Connect the unknown inductor in series with only capB from MFJ coax connector and MFJ ground keeping leads short as possible

Turn the 259 frequency dial until the IMPEDAMCE meter dips at zero Ohms

The dip or "null" will be fairly sharp (because at resonance a series tank circuit creates a dead short circuit) the dip at zero Ohms indicates resonance

Next ZERO BEAT the ham shack receiver to the MFJ 259 dip frequency, CW mode works best

My shack receiver indicates 7.65432 mHz or (7.654 E+6 for arithmetic purpose)

At this point we know several things
1) my  L/C  'tank circuit' is resonant at 7.65432 mHz
2) at resonance  XL = XC
3) therefor  XL =  XC =  325 Ohms = junkbox capB
4) from the equation ... XL = 2pi f L  (reactance in Ohm)  we can calculate L (inductance in Henery) by ...
 
          L = XL / 2 pi f
             = 325 / (6.28 X  7.6543E6)
             = 325 / 4.8069E7
             = 6.76E-6
          L = 6.76 uH
 
5) from the reactance equation  XC =  1 / 2Pi f C   we can find the value of junkbox capB in Farads by ...
      
          C = 1 / (2pi  f  XC)
              =  1 /  (6.23 X 7.65432E6 X 325)
              =  1 /  1.562E10
              =  6.40 E-11
              =  64 E-12
          C  =  64 pF


Most common ham radio powers of 10 
kelo    abbreviated  k  equal  E3
meg   abbreviated  m equal  E6
gig      abbreviated  g  equal E9

micro  abbreviated  u  equal   E-6
nano   abbreviated   n  equal  E-9
pico    abbreviated   p  equal  E-12

By observation one can see, that maybe except for frequency, accuracy to a fine degree is not a big thing for home brew ham radio experiment

Examples above put component values well within any first cut 'ball park' figure

The coil you are winding must mate with a capacitor to serve any purpose
Capacitors selected for most kits now days may only have a tolorence of +/- 5% at best so a turn or two on or off an inductor will make the circuit function to your delight

If you change the way you look at things,
        the things you look at change

72 73 74  P^3
John
N3AAZ


Roger Hill
 

Hi John.

 

Please explain for me.

If cap B has a reactance of 325 ohms at 7.12345, why do you use 325 ohms as the reactance at 7.65432?

At this point we know several things
1) my  L/C  'tank circuit' is resonant at 7.65432 mHz
2) at resonance  XL = XC
3) therefor  XL =  XC =  325 Ohms = junkbox capB

 

Surely the reactance of Cap B changes with frequency? So should you not use 7.12345 in the equation below FIRST, to get C, then use C in the calculation of L from the resonant frequency? I.e I think it is off by about 6%

5) from the reactance equation  XC =  1 / 2Pi f C   we can find the value of junkbox capB in Farads by ...
      
          C = 1 / (2pi  f  XC)
              =  1 /  (6.23 X 7.65432E6 X 325)
              =  1 /  1.562E10
              =  6.40 E-11
              =  64 E-12
          C  =  64 pF

 

Or is my old brain missing something obvious?

73

Roger

G3YTN


---
***************************
Roger Hill
***************************

On 2020-04-27 16:41, John Kirby wrote:

Scott,

Your orignal frequency question has been well answered
      Good on DL2MAN


Allison notes, the MFJ 259 is not a 'labority' standard and ...
...""The key things is that measuring at the right frequency is part of the matter and then you have to take calibration into account.""


I have a different opinion of the MFJ 259
Plus a technique on how to measure inductance you may like to try

From a frequency stand point ...
I find the 259 can be as accurate as you ham shack receiver when beat against it (the shack RX) and WWV or CHU

From an L/C meter stand point ...
Measurement accuracy depends on THE 'standard component' plus  frequency accuracy (ham shack RX)

For example...
How to measure  inductive reactance  (XL) in Ohms then calculate inductance (L)  in Henrys
First we will need to know the 'value' of the 'standard'  C  (capacitor) within a decent accuracy I call 'spot on'

So,  how do we define or 'create' a STANDARD  capacitor using and the 259 and ham shack receiver

There is an empirical measurement technique to find capacitive reactance (XC in Ohms) and then C in Farads  with way more than enough accuracy for ham radio home brew

An empirical measurement suggests (to me at least) an error free result that works like example below using ... money, marbles or chalk, for obvious reason I prefer marbles

You put 73 marbles into a bag
I put more marbles in the bag
You open and count 88 marbles total
How many marbles did I put in the bag?
By observation    88 - 73 = 15
In this case 15 references the difference or 'DELTA' measurement technique

Now let's work with capacitors and units of microFerad (uF) = (10E-6
Farad)

Capacitors connected in parallel are like resistors connected in series, their values add.  A 75 Ohm resistor in series with a 25 Ohm resistor makes a total of 100 Ohms. (Not knowing your electronic background I introduced resistance as reinforcement) Like wise a 75 uF cap in parallel with a 25 uF cap equals 100 uF total

Now lets create a STANDARD capacitor then use it to measure inductance with a very high confidence of accuracy

Suppose we do not know the value of two junk box capacitors called capA and capB  ...BUT... (just like marbles) we can calculate the DELTA between two measurements

Set the MFJ frequency to the band of interest, any number, for example  7.12345 mHz ... accuracy, stability and drift do not matter at this point

My 259 measures junkbox capA at 525 Ohms (capacitive reactance (XC)) of course accuracy is unknown and does not matter at this point

Keep all leads as short as possible

Now connect junkbox capB parallel to capA and my 259 indicates total XC at 850 Ohms

Note agan, we have no idea the true value or accuracy of these first two measurements  . . . YET!
BUT by DELTA C arithmetic we now know capB = 325 Ohms

junk box capB = deltaC = (Cmax) - (Cmin)
 (850) - (525) = 325

At this point ... regardless of the accuracy of your 'meter' we know three things
1) the frequency band of interest (40 meters)
2) the 'DELTA value' of junkbox capB = XC = 325  Ohms  'spot on '
3) and ... capA may OR maynot be  525  Ohms +/- any % ....at this point it does not matter because capB at 325 Ohms 'spot on' becomes our STANDARD C for inductance measurements

Return capA safely to the junkbox

Now by having a 'spot on' STANDARD C (capB) we can measure inductive reactance (XL) and then calculate inductance (L)

Connect the unknown inductor in series with only capB from MFJ coax connector and MFJ ground keeping leads short as possible

Turn the 259 frequency dial until the IMPEDAMCE meter dips at zero Ohms

The dip or "null" will be fairly sharp (because at resonance a series tank circuit creates a dead short circuit) the dip at zero Ohms indicates resonance

Next ZERO BEAT the ham shack receiver to the MFJ 259 dip frequency, CW mode works best

My shack receiver indicates 7.65432 mHz or (7.654 E+6 for arithmetic purpose)

At this point we know several things
1) my  L/C  'tank circuit' is resonant at 7.65432 mHz
2) at resonance  XL = XC
3) therefor  XL =  XC =  325 Ohms = junkbox capB
4) from the equation ... XL = 2pi f L  (reactance in Ohm)  we can calculate L (inductance in Henery) by ...
 
          L = XL / 2 pi f
             = 325 / (6.28 X  7.6543E6)
             = 325 / 4.8069E7
             = 6.76E-6
          L = 6.76 uH
 
5) from the reactance equation  XC =  1 / 2Pi f C   we can find the value of junkbox capB in Farads by ...
      
          C = 1 / (2pi  f  XC)
              =  1 /  (6.23 X 7.65432E6 X 325)
              =  1 /  1.562E10
              =  6.40 E-11
              =  64 E-12
          C  =  64 pF


Most common ham radio powers of 10 
kelo    abbreviated  k  equal  E3
meg   abbreviated  m equal  E6
gig      abbreviated  g  equal E9

micro  abbreviated  u  equal   E-6
nano   abbreviated   n  equal  E-9
pico    abbreviated   p  equal  E-12

By observation one can see, that maybe except for frequency, accuracy to a fine degree is not a big thing for home brew ham radio experiment

Examples above put component values well within any first cut 'ball park' figure

The coil you are winding must mate with a capacitor to serve any purpose
Capacitors selected for most kits now days may only have a tolorence of +/- 5% at best so a turn or two on or off an inductor will make the circuit function to your delight

If you change the way you look at things,
        the things you look at change

72 73 74  P^3
John
N3AAZ


George Korper
 

And what about stray capacitance? 


On Tue, Apr 28, 2020 at 9:02 AM Roger Hill <rhill@...> wrote:

Hi John.

 

Please explain for me.

If cap B has a reactance of 325 ohms at 7.12345, why do you use 325 ohms as the reactance at 7.65432?

At this point we know several things
1) my  L/C  'tank circuit' is resonant at 7.65432 mHz
2) at resonance  XL = XC
3) therefor  XL =  XC =  325 Ohms = junkbox capB

 

Surely the reactance of Cap B changes with frequency? So should you not use 7.12345 in the equation below FIRST, to get C, then use C in the calculation of L from the resonant frequency? I.e I think it is off by about 6%

5) from the reactance equation  XC =  1 / 2Pi f C   we can find the value of junkbox capB in Farads by ...
      
          C = 1 / (2pi  f  XC)
              =  1 /  (6.23 X 7.65432E6 X 325)
              =  1 /  1.562E10
              =  6.40 E-11
              =  64 E-12
          C  =  64 pF

 

Or is my old brain missing something obvious?

73

Roger

G3YTN


---
***************************
Roger Hill
***************************

On 2020-04-27 16:41, John Kirby wrote:

Scott,

Your orignal frequency question has been well answered
      Good on DL2MAN


Allison notes, the MFJ 259 is not a 'labority' standard and ...
...""The key things is that measuring at the right frequency is part of the matter and then you have to take calibration into account.""


I have a different opinion of the MFJ 259
Plus a technique on how to measure inductance you may like to try

From a frequency stand point ...
I find the 259 can be as accurate as you ham shack receiver when beat against it (the shack RX) and WWV or CHU

From an L/C meter stand point ...
Measurement accuracy depends on THE 'standard component' plus  frequency accuracy (ham shack RX)

For example...
How to measure  inductive reactance  (XL) in Ohms then calculate inductance (L)  in Henrys
First we will need to know the 'value' of the 'standard'  C  (capacitor) within a decent accuracy I call 'spot on'

So,  how do we define or 'create' a STANDARD  capacitor using and the 259 and ham shack receiver

There is an empirical measurement technique to find capacitive reactance (XC in Ohms) and then C in Farads  with way more than enough accuracy for ham radio home brew

An empirical measurement suggests (to me at least) an error free result that works like example below using ... money, marbles or chalk, for obvious reason I prefer marbles

You put 73 marbles into a bag
I put more marbles in the bag
You open and count 88 marbles total
How many marbles did I put in the bag?
By observation    88 - 73 = 15
In this case 15 references the difference or 'DELTA' measurement technique

Now let's work with capacitors and units of microFerad (uF) = (10E-6
Farad)

Capacitors connected in parallel are like resistors connected in series, their values add.  A 75 Ohm resistor in series with a 25 Ohm resistor makes a total of 100 Ohms. (Not knowing your electronic background I introduced resistance as reinforcement) Like wise a 75 uF cap in parallel with a 25 uF cap equals 100 uF total

Now lets create a STANDARD capacitor then use it to measure inductance with a very high confidence of accuracy

Suppose we do not know the value of two junk box capacitors called capA and capB  ...BUT... (just like marbles) we can calculate the DELTA between two measurements

Set the MFJ frequency to the band of interest, any number, for example  7.12345 mHz ... accuracy, stability and drift do not matter at this point

My 259 measures junkbox capA at 525 Ohms (capacitive reactance (XC)) of course accuracy is unknown and does not matter at this point

Keep all leads as short as possible

Now connect junkbox capB parallel to capA and my 259 indicates total XC at 850 Ohms

Note agan, we have no idea the true value or accuracy of these first two measurements  . . . YET!
BUT by DELTA C arithmetic we now know capB = 325 Ohms

junk box capB = deltaC = (Cmax) - (Cmin)
 (850) - (525) = 325

At this point ... regardless of the accuracy of your 'meter' we know three things
1) the frequency band of interest (40 meters)
2) the 'DELTA value' of junkbox capB = XC = 325  Ohms  'spot on '
3) and ... capA may OR maynot be  525  Ohms +/- any % ....at this point it does not matter because capB at 325 Ohms 'spot on' becomes our STANDARD C for inductance measurements

Return capA safely to the junkbox

Now by having a 'spot on' STANDARD C (capB) we can measure inductive reactance (XL) and then calculate inductance (L)

Connect the unknown inductor in series with only capB from MFJ coax connector and MFJ ground keeping leads short as possible

Turn the 259 frequency dial until the IMPEDAMCE meter dips at zero Ohms

The dip or "null" will be fairly sharp (because at resonance a series tank circuit creates a dead short circuit) the dip at zero Ohms indicates resonance

Next ZERO BEAT the ham shack receiver to the MFJ 259 dip frequency, CW mode works best

My shack receiver indicates 7.65432 mHz or (7.654 E+6 for arithmetic purpose)

At this point we know several things
1) my  L/C  'tank circuit' is resonant at 7.65432 mHz
2) at resonance  XL = XC
3) therefor  XL =  XC =  325 Ohms = junkbox capB
4) from the equation ... XL = 2pi f L  (reactance in Ohm)  we can calculate L (inductance in Henery) by ...
 
          L = XL / 2 pi f
             = 325 / (6.28 X  7.6543E6)
             = 325 / 4.8069E7
             = 6.76E-6
          L = 6.76 uH
 
5) from the reactance equation  XC =  1 / 2Pi f C   we can find the value of junkbox capB in Farads by ...
      
          C = 1 / (2pi  f  XC)
              =  1 /  (6.23 X 7.65432E6 X 325)
              =  1 /  1.562E10
              =  6.40 E-11
              =  64 E-12
          C  =  64 pF


Most common ham radio powers of 10 
kelo    abbreviated  k  equal  E3
meg   abbreviated  m equal  E6
gig      abbreviated  g  equal E9

micro  abbreviated  u  equal   E-6
nano   abbreviated   n  equal  E-9
pico    abbreviated   p  equal  E-12

By observation one can see, that maybe except for frequency, accuracy to a fine degree is not a big thing for home brew ham radio experiment

Examples above put component values well within any first cut 'ball park' figure

The coil you are winding must mate with a capacitor to serve any purpose
Capacitors selected for most kits now days may only have a tolorence of +/- 5% at best so a turn or two on or off an inductor will make the circuit function to your delight

If you change the way you look at things,
        the things you look at change

72 73 74  P^3
John
N3AAZ


Evan Hand
 

Roger,
I would agree that the impedance would be different.  The way around it would be to start with finding the resonant frequency of the capB and L, then perform the difference test using that frequency with capA to find the impedance of capB at the resonance of the LC circuit. 

I believe that for Ham use, the difference between 7.1234 and 7.65432 would not be significant (less than 10%).  That was why picking a frequency in the band of interest.  The differencing process will still work.

Good post John!  I had not thought of this way to measure an unknown L/C value.

73
Evan
AC9TU


Roger Hill
 

Hi Evan:

Yeah, I reckon it is about 6% off, with the frequencies given, and I agree it does not matter in this instance. I was verifying  the 'in principle' process, and that as stated, it would introduce errors, which could be eliminated.

73

Roger

G3YTN

---
***************************
Roger Hill
***************************


On 2020-04-28 10:28, Evan Hand wrote:

Roger,
I would agree that the impedance would be different.  The way around it would be to start with finding the resonant frequency of the capB and L, then perform the difference test using that frequency with capA to find the impedance of capB at the resonance of the LC circuit. 

I believe that for Ham use, the difference between 7.1234 and 7.65432 would not be significant (less than 10%).  That was why picking a frequency in the band of interest.  The differencing process will still work.

Good post John!  I had not thought of this way to measure an unknown L/C value.

73
Evan
AC9TU


John Kirby
 

Hi Roger,

No your brain is not missing anything
In fact a very astute observation
Brings out an interesting point too
Thank you

from first post set 259 = "7.12345 mHz is set to the band of interest, accuracy does not matter at this point"

Series tank (capB and test sample L) are resonant at 7.654 mHz
Test sample L = 6.76 uH at 7.654 mHz
capB = 64 pF at 7.654 mHz

capB = 68.8pF at 7.123 mHz

The closer the frequency ratio (7.123 to 7.654) the better
For this example both are in the same band, close enough for home brew

from first post " The coil you are winding must mate with a capacitor to serve any purpose
Capacitors selected for most kits now days may only have a tolorence of +/- 5% at best so a turn or two on or off an inductor will make the circuit function to your delight"

All junkbox caps are not suitable for this technique
When the frequency ratio does not suit band of interest
take  pEEk my junkbox capB

Thanks again Roger



George,

Stray capacitance is best handled by keeping all leads as short as possiable

Repeatable is best handled with a 'test fixture' image attached
Thanks

72 73 74  P^3
John
N3AAZ


Roger Hill
 

Cheers John.

Thanks for clarifying.

73
Roger
G3YTN

On 28 Apr 2020, at 12:16, John Kirby <n3aaz_qrp_1@...> wrote:
Hi Roger,

No your brain is not missing anything
In fact a very astute observation
Brings out an interesting point too
Thank you

from first post set 259 = "7.12345 mHz is set to the band of interest, accuracy does not matter at this point"

Series tank (capB and test sample L) are resonant at 7.654 mHz
Test sample L = 6.76 uH at 7.654 mHz
capB = 64 pF at 7.654 mHz

capB = 68.8pF at 7.123 mHz

The closer the frequency ratio (7.123 to 7.654) the better
For this example both are in the same band, close enough for home brew

from first post " The coil you are winding must mate with a capacitor to serve any purpose
Capacitors selected for most kits now days may only have a tolorence of +/- 5% at best so a turn or two on or off an inductor will make the circuit function to your delight"

All junkbox caps are not suitable for this technique
When the frequency ratio does not suit band of interest
take  pEEk my junkbox capB

Thanks again Roger



George,

Stray capacitance is best handled by keeping all leads as short as possiable

Repeatable is best handled with a 'test fixture' image attached
Thanks

72 73 74  P^3
John
N3AAZ


ajparent1/KB1GMX
 

John,

When I compare the MFJ to the HP4191A impednace analyzer then you see
the difference.

Its not frequency accuracy its the calibration of the hardware that reads the
measurement bridge.  Then you allow for the accuracy of the A/D and D/As
used (less than 10bits).  so you have limited accuracy and granularity
(precision).  For measuring things loosely the MFJ is fine.

A N2PK or Aim4170, and a handful of others are much more accurate.
Used correctly the NanoVNA can be very good.

However in a fight the HP 4191A is the arbiter.

L4/C30 tunes the class E stage along with the LPF (which presents a load to it)
which needs a cut off high enough to match the band but no so high as to have
second harmonic excessive.  And they all interact!

Allison
-------------------------------
Please reply on list so we can share.
No direct email, it goes to bit bucket due address harvesting in groups.IO


George Korper
 

Ok, good advice and I'm taking it. I have a spare fixture that was looking for a purpose!


On Tue, Apr 28, 2020 at 1:37 PM Roger Hill <rhill@...> wrote:
Cheers John.

Thanks for clarifying.

73
Roger
G3YTN

On 28 Apr 2020, at 12:16, John Kirby <n3aaz_qrp_1@...> wrote:
Hi Roger,

No your brain is not missing anything
In fact a very astute observation
Brings out an interesting point too
Thank you

from first post set 259 = "7.12345 mHz is set to the band of interest, accuracy does not matter at this point"

Series tank (capB and test sample L) are resonant at 7.654 mHz
Test sample L = 6.76 uH at 7.654 mHz
capB = 64 pF at 7.654 mHz

capB = 68.8pF at 7.123 mHz

The closer the frequency ratio (7.123 to 7.654) the better
For this example both are in the same band, close enough for home brew

from first post " The coil you are winding must mate with a capacitor to serve any purpose
Capacitors selected for most kits now days may only have a tolorence of +/- 5% at best so a turn or two on or off an inductor will make the circuit function to your delight"

All junkbox caps are not suitable for this technique
When the frequency ratio does not suit band of interest
take  pEEk my junkbox capB

Thanks again Roger



George,

Stray capacitance is best handled by keeping all leads as short as possiable

Repeatable is best handled with a 'test fixture' image attached
Thanks

72 73 74  P^3
John
N3AAZ