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Given my limited work with a NanoVNA I ask:

It appears the calibration routine (so far I have only needed for one port) is done without regard to any parameters being set.
Once it is done and saved you can reload it later and use it again.

Questions:
When would be a case that requires a new calibration vs just reloading one that has been saved?
Is it better to do a new calibration each time you fire up the nano rather than used a saved one?
What makes a calibration worth saving? ie. how should they be labeled?

TNX

On 7/15/21 5:54 AM, Richard Clemens wrote:

Given my limited work with a NanoVNA I ask:

It appears the calibration routine (so far I have only needed for one port) is done without regard to any parameters being set.
Once it is done and saved you can reload it later and use it again.

Questions:
When would be a case that requires a new calibration vs just reloading one that has been saved?
Is it better to do a new calibration each time you fire up the nano rather than used a saved one?
What makes a calibration worth saving? ie. how should they be labeled?

Reasons to recalibrate (as opposed to use a saved cal set):

1) A different test setup, where the "reference plane" for the measurements is different.? For instance, if you have test port cables with different length, and you do the cal at the end of the cables.

2) If the frequency span of the measurements is different than the frequency span of the calibration.? The NanoVNA does some interpolation, but if you did a cal from 0-50 MHz and now you're measuring a DUT from 200-300 MHz, the measurement might be iffy. Likewise if you did a cal from 0-900 MHz, and the measurement is from 20-30 MHz.

3) You can't remember what you did for a cal before

4) The temperature or something else has changed significantly. I don't know how temperature sensitive the NanoVNA is, but things like the bridges and detectors will change somewhat with temperature.? The oscillator frequency also changes, although I would expect that to be a 10s of ppm sort of thing, so unless you're measuring crystals or 2kHz wide filters at 30 MHz, you probably wouldn't see it.

Think of the NanoVNA as being somewhat like a RF Ohmmeter.? When you turn on the ohmmeter you check to see that it reads infinity with the leads apart, and zero with the leads shorted.? Same sort of thing.? Check to see that it reads appropriately with open and load, and if it looks ok, it probably is.? (If you store it with the load on CH0, then when you turn it on, you'll see the good match, and then when you disconnect the load to connect the DUT, you'll see the reflection match, so that's a easy way to check.

On Thu, Jul 15, 2021 at 09:27 AM, Jim Lux wrote:
Very helpful -- however when I do a calibration with nanovna-saver's tool it does not ask for a frequency range when starting the process - confusion...

2) If the frequency span of the measurements is different than the frequency
span of the calibration.? The NanoVNA does some interpolation, but if you did
a cal from 0-50 MHz and now you're measuring a DUT from 200-300 MHz, the
measurement might be iffy. Likewise if you did a cal from 0-900 MHz, and the
measurement is from 20-30 MHz.

In starting the cal process, it is assumed you have previously set the
desired frequency range.

Dave - W?LEV

On Thu, Jul 15, 2021 at 11:37 AM Richard Clemens <rich.clemens@...>
wrote:

On Thu, Jul 15, 2021 at 09:27 AM, Jim Lux wrote:
Very helpful -- however when I do a calibration with nanovna-saver's tool
it does not ask for a frequency range when starting the process -
confusion...

2) If the frequency span of the measurements is different than the

frequency

span of the calibration. The NanoVNA does some interpolation, but if

you did

a cal from 0-50 MHz and now you're measuring a DUT from 200-300 MHz, the
measurement might be iffy. Likewise if you did a cal from 0-900 MHz, and

the

measurement is from 20-30 MHz.

--
*Dave - W?LEV*
*Just Let Darwin Work*

I am of the practice of ALWAYS doing a calibration. This comes from many scars of debugging ‘unexpected’ results which, ultimately, turned out to be calibration problems.

Calibration just doesn’t take that long. I consider it insurance against my own forgetfulness.

Ward

This is a timely thread as I just received my -F this week. My HF antennas
all have PL-259 connectors. To connect them to the NanoVNA, I already have
SO-239 to SMA Male (like these
<>). I don't have PL-259 open,
short, and loads (though obviously open & short would be trivial to build)
and I'm wondering for HF frequencies (up to 30MHz), would the calibration
done on the port (using the supplied calibration connectors) be acceptable,
or I should I get an SMA female to PL-259 (like this
<>)
and calibrate at the female SMA?

The final result (during calibration) would look like: SMA
open/short/load->SMA female to PL-259->SO-239 to SMA male->S11 on NanoVNA.

Is this overkill, and would that last adapter invalidate any
calibration when it's removed to plug in the actual antenna?

73,
David, K2DBK
k2dbk.com
twitter: @k2dbk


On Thu, Jul 15, 2021 at 3:39 PM ward harriman <ward.harriman@...>
wrote:

I am of the practice of ALWAYS doing a calibration. This comes from many
scars of debugging ‘unexpected’ results which, ultimately, turned out to be
calibration problems.

Calibration just doesn’t take that long. I consider it insurance against
my own forgetfulness.

Ward

On 7/15/21 5:48 PM, David Kozinn, K2DBK wrote:

This is a timely thread as I just received my -F this week. My HF antennas
all have PL-259 connectors. To connect them to the NanoVNA, I already have
SO-239 to SMA Male (like these
<>). I don't have PL-259 open,
short, and loads (though obviously open & short would be trivial to build)
and I'm wondering for HF frequencies (up to 30MHz), would the calibration
done on the port (using the supplied calibration connectors) be acceptable,
or I should I get an SMA female to PL-259 (like this
<>)
and calibrate at the female SMA?

It's all about "length vs wavelength" so.. a cm or so of adapter against 10m wavelength? Not going to make a big difference at HF (1cm is 0.3 deg of phase at 30MHz)

I use a SMA to SO-239 pigtail about 12" long - good strain relief, no worry about snapping the SMA off the board.

It's not that hard to build some cal standards - Open is easy, nothing :) - Short isn't too tough (shove some copper foil tape into an PL-259, or just solder a short between center pin and outside.? 50 ohm load is likewise easy for HF - non-inductive resistor on a PL-259.

The final result (during calibration) would look like: SMA
open/short/load->SMA female to PL-259->SO-239 to SMA male->S11 on NanoVNA.

Is this overkill, and would that last adapter invalidate any
calibration when it's removed to plug in the actual antenna?

73,
David, K2DBK
k2dbk.com
twitter: @k2dbk


On Thu, Jul 15, 2021 at 3:39 PM ward harriman <ward.harriman@...>
wrote:

I am of the practice of ALWAYS doing a calibration. This comes from many
scars of debugging ‘unexpected’ results which, ultimately, turned out to be
calibration problems.

Calibration just doesn’t take that long. I consider it insurance against
my own forgetfulness.

Ward

Hi David, I had a similar problem and used the SMA to PL-259 and PL-259 to
SMA adapters. I guess you know that the PL-259 connectors are no where near
a 50 ohm environment (around 30 ohms I think). But at 30MHz this should not
be a problem. Pete

On Thu, Jul 15, 2021 at 8:49 PM David Kozinn, K2DBK <dkozinn@...>
wrote:

This is a timely thread as I just received my -F this week. My HF antennas
all have PL-259 connectors. To connect them to the NanoVNA, I already have
SO-239 to SMA Male (like these
<>). I don't have PL-259 open,
short, and loads (though obviously open & short would be trivial to build)
and I'm wondering for HF frequencies (up to 30MHz), would the calibration
done on the port (using the supplied calibration connectors) be acceptable,
or I should I get an SMA female to PL-259 (like this
<

)

and calibrate at the female SMA?

The final result (during calibration) would look like: SMA
open/short/load->SMA female to PL-259->SO-239 to SMA male->S11 on NanoVNA.

Is this overkill, and would that last adapter invalidate any
calibration when it's removed to plug in the actual antenna?

73,
David, K2DBK
k2dbk.com
twitter: @k2dbk


On Thu, Jul 15, 2021 at 3:39 PM ward harriman <ward.harriman@...>
wrote:

I am of the practice of ALWAYS doing a calibration. This comes from many
scars of debugging ‘unexpected’ results which, ultimately, turned out to

be

calibration problems.

Calibration just doesn’t take that long. I consider it insurance against
my own forgetfulness.

Ward

50 ohm PL259 O239 connectors are readily available. Agree that if the discontinuity is very short compared to a 1/4 wave it make little/no difference. Going from a 50 ohms, through a 30 ohm PL259, and then back into a 50 ohms, the reflection from 50 into 30 is opposite and equal to that from 30 into 50. If the distance between them is very short compared to 1/4 wavelength, they essentially cancel. A PL259 it's maybe a cm or two compared to 250 cm for a 1/4 wavelength at 10m.

You can look inside HF amplifiers, tuners and other HF equipment and see RF being conducted around inside with simple wires, not transmission lines. That works because the lengths are short compared the the wavelengths involved.

That doesn’t address the point.

I always do the calibration with the NanoVNA by itself, not connected to a
computer. I have saved several band segments that I frequently use (say, 45
to 55 MHz, 140 to 150 MHz, 420 to 450 MHz) with the calibration done for
each of those segments and, for what I do, I haven't needed to re-calibrate
each time.

73, Zack W9SZ

On Thu, Jul 15, 2021 at 12:37 PM Richard Clemens <rich.clemens@...>
wrote:

On Thu, Jul 15, 2021 at 09:27 AM, Jim Lux wrote:
Very helpful -- however when I do a calibration with nanovna-saver's tool
it does not ask for a frequency range when starting the process -
confusion...

2) If the frequency span of the measurements is different than the

frequency

span of the calibration. The NanoVNA does some interpolation, but if

you did

a cal from 0-50 MHz and now you're measuring a DUT from 200-300 MHz, the
measurement might be iffy. Likewise if you did a cal from 0-900 MHz, and

the

measurement is from 20-30 MHz.

The need for calibration and how frequently, varies with the measurement. If you need great precision, like accurately measuring a 40-db return loss, you might need to carefully calibrate several times a day. If you only need to know the frequency of an S11 dip, like tuning a small loop antenna in the field where there is only a single adjustment, you don't even need to calibrate at all.
73, Don N2VGU

It is important to remember that "accuracy" and "precision" are two separate characteristics of any measurement.

DaveD

--
This email has been checked for viruses by Avast antivirus software.

Thanks for all the replies. It sounds like for the frequencies I'm looking at, there won't be much of a difference no matter which method I use.

@Lou W7HV: Could you point me to where I could pick one a low-power 50 ohm PL-259 as you mentioned? I looked and all I've found so far were dummy loads with a minimum rating for 10W, which is way more than what's needed for me. Same with looking for resistors, except for industrial supply places where I could get a resistor for $0.50 plus $7.00 shipping.

73,
David, K2DBK

On 7/16/21 9:12 AM, David Kozinn, K2DBK wrote:

Thanks for all the replies. It sounds like for the frequencies I'm looking at, there won't be much of a difference no matter which method I use.

@Lou W7HV: Could you point me to where I could pick one a low-power 50 ohm PL-259 as you mentioned? I looked and all I've found so far were dummy loads with a minimum rating for 10W, which is way more than what's needed for me. Same with looking for resistors, except for industrial supply places where I could get a resistor for $0.50 plus $7.00 shipping.

I've used 30w Caddock noninductive TO-220 package resistors for this kind of thing, but they *are* a few bucks each.


You're probably better off just buying some cheap metal film 50 ohm resistors and testing them for parasitic L. 50 ohms is low enough that it's probably not a "spiral", rather just a uniform film.

David, I have been following this thread and thought I might add something
that might help you. This link that I have attached should give you an
easy way of making your Short/Open/Load standards using SO-239 connectors.

Fred - N4CLA



On Fri, Jul 16, 2021 at 12:12 PM David Kozinn, K2DBK <dkozinn@...>
wrote:

Thanks for all the replies. It sounds like for the frequencies I'm looking
at, there won't be much of a difference no matter which method I use.

@Lou W7HV: Could you point me to where I could pick one a low-power 50 ohm
PL-259 as you mentioned? I looked and all I've found so far were dummy
loads with a minimum rating for 10W, which is way more than what's needed
for me. Same with looking for resistors, except for industrial supply
places where I could get a resistor for $0.50 plus $7.00 shipping.

73,
David, K2DBK

Thanks again everyone! I've watched several of W2AEW's videos but hadn't
seen this one yet.

73,
David, K2DBK
k2dbk.com
twitter: @k2dbk

There has been discussion about calibrating at the transmitter end of the transmission line. Is anyone doing the calibration at the antenna end of the transmission line?

It might be interesting to see the Smith Chart and SWR plot right at the antenna terminals. I have two HF antennas with easy access to the ends of the coax cables. A different set of calibration standards or adapters may be required.

73, Kent
AA6P

On Sun, Jul 18, 2021 at 04:14 PM, Kent AA6P wrote:

There has been discussion about calibrating at the transmitter end of the
transmission line. Is anyone doing the calibration at the antenna end of the
transmission line?

It might be interesting to see the Smith Chart and SWR plot right at the
antenna terminals. I have two HF antennas with easy access to the ends of the
coax cables. A different set of calibration standards or adapters may be
required.

73, Kent
AA6P

On several occasions I have done the calibration at the end of the transmission line where it connects to the antenna. It works very well but requires a lot of running back and forth between the antenna and the ham shack.

Roger

On 7/18/21 4:14 PM, Kent AA6P wrote:

There has been discussion about calibrating at the transmitter end of the transmission line. Is anyone doing the calibration at the antenna end of the transmission line?

It might be interesting to see the Smith Chart and SWR plot right at the antenna terminals. I have two HF antennas with easy access to the ends of the coax cables. A different set of calibration standards or adapters may be required.

7

I'm doing exactly that. I have a RCS-8V switch box at the antenna end with a short and a load hooked up, so I can do a cal, remotely.


cables is the response of the cables, with the calibration at the VNA.? new and old refer to a pair of antennas.

newantenna.png is one of the antennas (new) with the "calibration at VNA"? blue trace is without moving the cal to the end, orange trace is with the cal at the end.