Jim:

I have a number of HP and Narda N-type attenuators. If, for example, I use
a 30 dB attenuator (60 dB RL) within its rated frequency range as a load
for cal., where is the measurement plane? I have the "precision" HP cal.
standards, but I'm just curious.

Dave - WØLEV
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My guess is that the reference plane for a load begans at the start of the
resistave element. Note that a 60dB RL is theoretical for a 30dB
attenuator but it will likely not be nearly that good. Check the specified
VSWR for the attenuator.

On Tue, Jul 23, 2024 at 12:59 AM W0LEV via groups.io <davearea51a=
gmail.com@groups.io> wrote:

> Jim:
>
> I have a number of HP and Narda N-type attenuators. If, for example, I
> use a 30 dB attenuator (60 dB RL) within its rated frequency range as a
> load for cal., where is the measurement plane? I have the "precision" HP
> cal. standards, but I'm just curious.
>
> Dave - WØLEV
>
> <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail>
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The measurement plane is where you perform the calibration, the exact point where the calibration resistor and calibration short are placed in the circuit for calibration purposes.   In the ideal world, the DUT would be connected in the circuit to the exact point were the calibration standards had been connected.

ke8plm

On Mon, 22 Jul 2024 18:44:03 +0000
"W0LEV" <davearea51a@gmail.com> wrote:

> Jim:
>
> I have a number of HP and Narda N-type attenuators. If, for example,
> I use a 30 dB attenuator (60 dB RL) within its rated frequency range
> as a load for cal., where is the measurement plane? I have the
> "precision" HP cal. standards, but I'm just curious.

It will be at the input of the 30dB pad in the normal place for an
N-type connector. The reflection from the open end will, as you say, be
60dB lower and will not be easy to see so will perturb the measurement
very little. A precision cal standard is unlikely to have an inherent
return loss of 60dB, I would expect somewhere around 40-45dB. The
original cal documents should tell you if you have them.

--

Brian G8SEZ

I have used 1 or 2db attenuators when tuning duplexers for work at the ends of the cables (calibrated out) to insure a good match at the duplexer. I was also using an Agilent FieldFox to do the measurements

It does not matter where the 50-ohm load is so long as the surge or
characteristic impedance of the line to the load and the load are in
agreement. This is because the line would have no standing waves, thus
would look dimensionless.

I would still terminate the attenuator. Even a loose load, say 55 ohms,
would be better than a wide open. No point in having things worse than
they have to be.

The open and the short measurement location matters because of the large
reflection from that point. The load distance, as long as the cable
between the load and the load agree, is meaningless.

73 Tom



On 7/22/2024 2:44 PM, W0LEV wrote:
> Jim:
>
> I have a number of HP and Narda N-type attenuators.  If, for example,
> I use a 30 dB attenuator (60 dB RL) within its rated frequency range
> as a load for cal., where is the measurement plane?  I have the
> "precision" HP cal. standards, but I'm just curious.
>
> Dave - WØLEV
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The question might be “what’s the physical offset of the termination” and that’s something that *might* be given in a data sheet, but likely not. It’s a “measure it and see”. It would be difficult to measure, since it’s not like you can get a good reflection.

> On Jul 23, 2024, at 9:02 AM, Brian Morrison via groups.io <bdm=fenrir.org.uk@groups.io> wrote:
>
> On Mon, 22 Jul 2024 18:44:03 +0000
> "W0LEV" <davearea51a@gmail.com> wrote:
>
>> Jim:
>>
>> I have a number of HP and Narda N-type attenuators. If, for example,
>> I use a 30 dB attenuator (60 dB RL) within its rated frequency range
>> as a load for cal., where is the measurement plane? I have the
>> "precision" HP cal. standards, but I'm just curious.
>
> It will be at the input of the 30dB pad in the normal place for an
> N-type connector. The reflection from the open end will, as you say, be
> 60dB lower and will not be easy to see so will perturb the measurement
> very little. A precision cal standard is unlikely to have an inherent
> return loss of 60dB, I would expect somewhere around 40-45dB. The
> original cal documents should tell you if you have them.
>
> --
>
> Brian G8SEZ
>
>
>
>
>

If you are referring to the location of the reference plane of an S11 calibration, it is dominated by the location of the short and open.  The exact location of the load is of low importance if it is not reflecting much signal.
--John Gord

On Mon, Jul 22, 2024 at 09:59 PM, W0LEV wrote:

>
> Jim:
>
> I have a number of HP and Narda N-type attenuators.  If, for example, I
> use a 30 dB attenuator (60 dB RL) within its rated frequency range as a
> load for cal., where is the measurement plane?  I have the "precision" HP
> cal. standards, but I'm just curious.
>
> Dave - WØLEV
>
> (
> http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail
> ) Virus-free. www.avg.com (
> http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail
> )
>
>
>
>
>
> (
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> ) Virus-free. www.avg.com (
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>
>

Thanks, Jim, and everyone. Jim, that pretty much sums up my reasoning. I
just threw the question out as a matter of curiousity. And, yes, with no
reflection - a matched line - , it doesn't matter.

Dave - WØLEV

On Wed, Jul 24, 2024 at 6:00 AM Jim Lux via groups.io <jimlux=
earthlink.net@groups.io> wrote:

> The question might be “what’s the physical offset of the termination” and
> that’s something that *might* be given in a data sheet, but likely not.
> It’s a “measure it and see”. It would be difficult to measure, since it’s
> not like you can get a good reflection.
> > On Jul 23, 2024, at 9:02 AM, Brian Morrison via groups.io <bdm=
> fenrir.org.uk@groups.io> wrote:
> >
> > On Mon, 22 Jul 2024 18:44:03 +0000
> > "W0LEV" <davearea51a@gmail.com> wrote:
> >
> >> Jim:
> >>
> >> I have a number of HP and Narda N-type attenuators. If, for example,
> >> I use a 30 dB attenuator (60 dB RL) within its rated frequency range
> >> as a load for cal., where is the measurement plane? I have the
> >> "precision" HP cal. standards, but I'm just curious.
> >
> > It will be at the input of the 30dB pad in the normal place for an
> > N-type connector. The reflection from the open end will, as you say, be
> > 60dB lower and will not be easy to see so will perturb the measurement
> > very little. A precision cal standard is unlikely to have an inherent
> > return loss of 60dB, I would expect somewhere around 40-45dB. The
> > original cal documents should tell you if you have them.
> >
> > --
> >
> > Brian G8SEZ
> >
> >
> >
> >
> >
>
>
>
>
>
>

--

*Dave - WØLEV*

On Wed, 24 Jul 2024 15:42:11 +0000
"W0LEV" <davearea51a@gmail.com> wrote:

> Thanks, Jim, and everyone. Jim, that pretty much sums up my
> reasoning. I just threw the question out as a matter of curiousity.
> And, yes, with no reflection - a matched line - , it doesn't matter.
>

The reference plane of an N-type connector is at the forward edge of the
inner shield structure in the male connector that mates with the shield
of the female connector. It's done this way so that the sliding contact
between the male centre pin and female centre pin is taken out of the
equation. More expensive N-type connectors don't have slotted female
centre connector pins as these slots become increasingly inductive with
frequency. They also define the pin mating dimensions more accurately.

There's a diagram of N-type connectors in the document here:

https://www.slideshare.net/slideshow/n-type-connector/13009968

Probably some better diagrams are available at manufacturer sites.

As with all of these connectors the detail of the connector coefficients
only becomes important in the highest part of the rated frequency
range. The nanoVNAs don't appear to have a way to define custom
calibration kit parameters in the way that a seriously expensive VNA
does.

--

Brian G8SEZ