HP8753A measurement help required

[David]

Hi,

I have just purchased a HP8753A VNA and need some help setting the thing up.

I want to start off just measuring impedance of lumped components but I
cannot get any sensible readings. I have tried all sorts of Calibrations
from the operation manual but still no luck.

I have the HP85044A Test Set and the 50 Ohm Calibration set.

I am trying to connect a coaxial lead to the Test port on the Test Set
and so a 1 Port measurement. I have tried both RESPONSE cal and 1-Port
Cal and placed a short,oopen and 50 Ohm load at end of the coax and then
after calibration I place a leaded cap but do not get anything like I
see in RF books I Have.

Any help much appreciated.

Regards

David

 

[g]

David

For a rudimentary measurement, first select S11 under measure.

Leave test port 1 open.
Next select Cal and to perform a response calibration by
selecting "open"
Next under Format, select Smith Chart.

You can now place a DUT at the test port and see S11 directly or else,
by selecting marker, read the R +- jX at the marker position.

g

I have just purchased a HP8753A VNA and need some help setting the thing
up.

I want to start off just measuring impedance of lumped components but I
cannot get any sensible readings. I have tried all sorts of Calibrations
from the operation manual but still no luck.

I have the HP85044A Test Set and the 50 Ohm Calibration set.

I am trying to connect a coaxial lead to the Test port on the Test Set
and so a 1 Port measurement. I have tried both RESPONSE cal and 1-Port
Cal and placed a short,oopen and 50 Ohm load at end of the coax and then
after calibration I place a leaded cap but do not get anything like I
see in RF books I Have.

 

[David]

G,

Thanks for that.

The Test port is an "N" connector. How can I attach a capacitor to it ?

I tried setting up as you suggest and used a length of coax from Test
port to component.

When I select Smith chart I get what looks like child's scribble all
over the chart.

Regards

David

g wrote:

David

For a rudimentary measurement, first select S11 under measure.

Leave test port 1 open.
Next select Cal and to perform a response calibration by
selecting "open"
Next under Format, select Smith Chart.

You can now place a DUT at the test port and see S11 directly or else,
by selecting marker, read the R +- jX at the marker position.

g

I have just purchased a HP8753A VNA and need some help setting the
thing up.

I want to start off just measuring impedance of lumped components but
I cannot get any sensible readings. I have tried all sorts of
Calibrations from the operation manual but still no luck.

I have the HP85044A Test Set and the 50 Ohm Calibration set.

I am trying to connect a coaxial lead to the Test port on the Test Set
and so a 1 Port measurement. I have tried both RESPONSE cal and 1-Port
Cal and placed a short,oopen and 50 Ohm load at end of the coax and
then after calibration I place a leaded cap but do not get anything
like I see in RF books I Have.

 

[g]

David

The Test port is an "N" connector. How can I attach a capacitor to it ?

I'd suggest using a solder pot type N female. Connect the solder-N to
your test cable and calibrate with the DUT absent.

I tried setting up as you suggest and used a length of coax from Test
port to component.

When I select Smith chart I get what looks like child's scribble all
over the chart.

That probably indicates that it is measuring correctly. Your DUT is

being rotated (transformed) by the length of cable. Calibrating with
the cable and N fitting (sans DUT) first will eliminate that, leaving
your measurement plane located *at* the DUT instead of some distance
down your test cable from it.

g

 

[David]

G,

I connected a coaxial cable (about 300mm length) to the test port.

Sweep was set between 300kHz and 1.3Ghz

The measurement was set up for Smith Chart to measure S11

Auto Scale was applied

A 1-port calibration was performed. (Q: What do I use for a load at the
end of the flying coaxial lead. The precision Load I have is "N" type) I
used 2 x 100 Ohms resistors as "Load" for Cal.

I attached a 27pF leaded capacitor (with leads cut short as possible) to
end of coaxial cable.

When I looked at the response I saw a Circle that indicated the
component became inductive around 500MHz (I presume this is SRF).

The odd thing is that the capacitance reads only 3.1pF at 1Mhz and does
not read 27pF until 369 MHz ?


g wrote:

David
The Test port is an "N" connector. How can I attach a capacitor to it ?


I'd suggest using a solder pot type N female. Connect the solder-N to
your test cable and calibrate with the DUT absent.

I tried setting up as you suggest and used a length of coax from Test
port to component.

When I select Smith chart I get what looks like child's scribble all
over the chart.

That probably indicates that it is measuring correctly. Your DUT is
being rotated (transformed) by the length of cable. Calibrating with
the cable and N fitting (sans DUT) first will eliminate that, leaving
your measurement plane located *at* the DUT instead of some distance
down your test cable from it.

g

 

[g]

David

A 1-port calibration was performed. (Q: What do I use for a load at the
end of the flying coaxial lead. The precision Load I have is "N" type) I
used 2 x 100 Ohms resistors as "Load" for Cal.

Not much point in using a load for measuring a low loss/reactive
component like a capacitor. Just use the Response:Open cal and nothing
else. That should leave you seeing a high impedance after the cal and
before the device is connected.

I attached a 27pF leaded capacitor (with leads cut short as possible) to
end of coaxial cable.

When I looked at the response I saw a Circle that indicated the
component became inductive around 500MHz (I presume this is SRF).

Perhaps. Or maybe you tried to do a full S11 cal rather than response
only? You really don't need the load to get pretty close for measuring
a reactance. Using a load will help your accuracy for well matched
devices. Using open gives you a measurement for small capacitances and
using a short for small inductance. You can do an open:short:load cal
if you have all standards in the same connector type for which you have
a defined cal kit in the instrument. Otherwise just use response cal.

The odd thing is that the capacitance reads only 3.1pF at 1Mhz and does
not read 27pF until 369 MHz ?

What do you see before you attach the DUT? Should look pretty much like
a dot on the right side of the Smith Chart and read out as a high Z with
perhaps a small capacitance portion. This represents the modeled
fringing capacitance of an "open".


g

 

[David]

G,

Thanks heaps, I am starting to actually measure something now. It was
frustrating as I was looking forward to receiving the VNA but found once
it arrived that I didn't actually know how to use it

When I do the Open only Response cal I get a dot on the Resistance line
on right hand side. R is jumping around but reads several "K" Ohms.

When I connect now a 22pF leaded cap it shows 22p at low freq and starts
increasing above 30MHz. The response curve of the component crosses the
Resistance line at around 350MHz and the cap looks inductive above this.

By 150MHz this leaded cap is 150pF. No wonder I had problems building
prototypes using leaded components at VHF in the past. I did not realise
the capacitance changes so much with frequency.

Do I use this same methodology if I want to measure SMD caps and
inductors ? Just attach the cable to PCB without component and cal for
open than solder in the cap or for inductor, form a short to gnd plane ,
cal and then replace short with inductor ?

Finally, What would I do to measure an RF IC in place on a PCB ? I have
a SA605 Receiver IC that should have input impedance that looks like
around 1K Ohm in par with 2.5 pF. As this is capacitive, would I do
something like solder coax to pcb pad and have coupling cap to IC
removed for OPEN cal and then insert the coupling cap to device to
measure impedance.

g wrote:

David

A 1-port calibration was performed. (Q: What do I use for a load at
the end of the flying coaxial lead. The precision Load I have is "N"
type) I used 2 x 100 Ohms resistors as "Load" for Cal.


Not much point in using a load for measuring a low loss/reactive
component like a capacitor. Just use the Response:Open cal and nothing
else. That should leave you seeing a high impedance after the cal and
before the device is connected.

I attached a 27pF leaded capacitor (with leads cut short as possible)
to end of coaxial cable.

When I looked at the response I saw a Circle that indicated the
component became inductive around 500MHz (I presume this is SRF).


Perhaps. Or maybe you tried to do a full S11 cal rather than response
only? You really don't need the load to get pretty close for measuring
a reactance. Using a load will help your accuracy for well matched
devices. Using open gives you a measurement for small capacitances and
using a short for small inductance. You can do an open:short:load cal
if you have all standards in the same connector type for which you have
a defined cal kit in the instrument. Otherwise just use response cal.
The odd thing is that the capacitance reads only 3.1pF at 1Mhz and
does not read 27pF until 369 MHz ?

What do you see before you attach the DUT? Should look pretty much like
a dot on the right side of the Smith Chart and read out as a high Z with
perhaps a small capacitance portion. This represents the modeled
fringing capacitance of an "open".


g

 

[g]

David wrote:

G,

Thanks heaps, I am starting to actually measure something now. It was
frustrating as I was looking forward to receiving the VNA but found once
it arrived that I didn't actually know how to use it

And you're only using about 1% of it at this point, there's lots more,

particularly if you have time domain! &gt

When I do the Open only Response cal I get a dot on the Resistance line
on right hand side. R is jumping around but reads several "K" Ohms.

That's right. If you look carefully at 3 GHz you may notice that it is

starting to rotate clockwise around the edge. That's the modelled
fringing capacitance of the "open" standard you have selected as part of
the Cal kit you are using.

When I connect now a 22pF leaded cap it shows 22p at low freq and starts
increasing above 30MHz. The response curve of the component crosses the
Resistance line at around 350MHz and the cap looks inductive above this.

By 150MHz this leaded cap is 150pF. No wonder I had problems building
prototypes using leaded components at VHF in the past. I did not realise
the capacitance changes so much with frequency.

The capacitance almost certainly doesn't change this much. You're seeing

the actual component characteristics which are closer to series
connected RLC. The L is "tuning out" the C on the way to series
resonance. When you cross the horizontal axis, you are at resonance and
all that is left is the ESR of the DUT.

Do I use this same methodology if I want to measure SMD caps and
inductors ? Just attach the cable to PCB without component and cal for
open than solder in the cap or for inductor, form a short to gnd plane ,
cal and then replace short with inductor ?
Yes, basically. For a really refined measurment you would use cal

standards designed for the environment you are measuring in (PCB).
However for many purposes, a simple resopnse cal in situ but sans DUT is
enough. You use the cal device(s) most appropriate for the DUT since the
measurement effectively is comparing the known cal with the unknown DUT.
If you have a situation such as you mention where the DUT looks both
capacitive (low freq) and inductive (higher) you may want to use more
than a single device for the response cal.

Finally, What would I do to measure an RF IC in place on a PCB ? I have
a SA605 Receiver IC that should have input impedance that looks like
around 1K Ohm in par with 2.5 pF. As this is capacitive, would I do
something like solder coax to pcb pad and have coupling cap to IC
removed for OPEN cal and then insert the coupling cap to device to
measure impedance.
Same thing, but use a thru cal device. You'll have to figure out how to

connect the test ports together in the measurement environment. Maybe
just use a couple of semirigid cables soldered to the PCB and connected
by a piece of microstrip.


The goal is to make the test fixture as much like the
application/measurment environment as possible and find cal standards
that give you as much information about the desired paramater as possible.

I think Agilent might have some VNA basics app notes on their web site.
Have you looked?

g
>

 

[David]

G,

Thank you for all the helpful information you have given me.

I also looked at a document from Agilent that explains how to make Test
Fixtures to use as standards using microstrip.

Another site shows actual "N" connectors and SMA that are shorted, open
and a Load (2 x 100R) and then another where the DUT is soldered across
the back of the connector.

g wrote:

David wrote:
G,

Thanks heaps, I am starting to actually measure something now. It was
frustrating as I was looking forward to receiving the VNA but found
once it arrived that I didn't actually know how to use it

And you're only using about 1% of it at this point, there's lots more,
particularly if you have time domain! &gt

When I do the Open only Response cal I get a dot on the Resistance
line on right hand side. R is jumping around but reads several "K" Ohms.

That's right. If you look carefully at 3 GHz you may notice that it is
starting to rotate clockwise around the edge. That's the modelled
fringing capacitance of the "open" standard you have selected as part of
the Cal kit you are using.

When I connect now a 22pF leaded cap it shows 22p at low freq and
starts increasing above 30MHz. The response curve of the component
crosses the Resistance line at around 350MHz and the cap looks
inductive above this.

By 150MHz this leaded cap is 150pF. No wonder I had problems building
prototypes using leaded components at VHF in the past. I did not
realise the capacitance changes so much with frequency.

The capacitance almost certainly doesn't change this much. You're seeing
the actual component characteristics which are closer to series
connected RLC. The L is "tuning out" the C on the way to series
resonance. When you cross the horizontal axis, you are at resonance and
all that is left is the ESR of the DUT.


Do I use this same methodology if I want to measure SMD caps and
inductors ? Just attach the cable to PCB without component and cal for
open than solder in the cap or for inductor, form a short to gnd plane
, cal and then replace short with inductor ?
Yes, basically. For a really refined measurment you would use cal
standards designed for the environment you are measuring in (PCB).
However for many purposes, a simple resopnse cal in situ but sans DUT is
enough. You use the cal device(s) most appropriate for the DUT since the
measurement effectively is comparing the known cal with the unknown DUT.
If you have a situation such as you mention where the DUT looks both
capacitive (low freq) and inductive (higher) you may want to use more
than a single device for the response cal.


Finally, What would I do to measure an RF IC in place on a PCB ? I
have a SA605 Receiver IC that should have input impedance that looks
like around 1K Ohm in par with 2.5 pF. As this is capacitive, would I
do something like solder coax to pcb pad and have coupling cap to IC
removed for OPEN cal and then insert the coupling cap to device to
measure impedance.
Same thing, but use a thru cal device. You'll have to figure out how to
connect the test ports together in the measurement environment. Maybe
just use a couple of semirigid cables soldered to the PCB and connected
by a piece of microstrip.


The goal is to make the test fixture as much like the
application/measurment environment as possible and find cal standards
that give you as much information about the desired paramater as possible.

I think Agilent might have some VNA basics app notes on their web site.
Have you looked?

g

 

[Pierre-François]

Hi Dave,

Do you know this site?:
http://www.vnahelp.com/products.html
It could help you!

pf


"David" <dhuisman@bigpond.net.au> a écrit dans le message de news:
W7_li.6799$4A1.2315@news-server.bigpond.net.au...

G,

Thanks heaps, I am starting to actually measure something now. It was
frustrating as I was looking forward to receiving the VNA but found once
it arrived that I didn't actually know how to use it

When I do the Open only Response cal I get a dot on the Resistance line on
right hand side. R is jumping around but reads several "K" Ohms.

When I connect now a 22pF leaded cap it shows 22p at low freq and starts
increasing above 30MHz. The response curve of the component crosses the
Resistance line at around 350MHz and the cap looks inductive above this.

By 150MHz this leaded cap is 150pF. No wonder I had problems building
prototypes using leaded components at VHF in the past. I did not realise
the capacitance changes so much with frequency.

Do I use this same methodology if I want to measure SMD caps and inductors
? Just attach the cable to PCB without component and cal for open than
solder in the cap or for inductor, form a short to gnd plane , cal and
then replace short with inductor ?

Finally, What would I do to measure an RF IC in place on a PCB ? I have a
SA605 Receiver IC that should have input impedance that looks like around
1K Ohm in par with 2.5 pF. As this is capacitive, would I do something
like solder coax to pcb pad and have coupling cap to IC removed for OPEN
cal and then insert the coupling cap to device to measure impedance.

g wrote:
David

A 1-port calibration was performed. (Q: What do I use for a load at the
end of the flying coaxial lead. The precision Load I have is "N" type) I
used 2 x 100 Ohms resistors as "Load" for Cal.


Not much point in using a load for measuring a low loss/reactive
component like a capacitor. Just use the Response:Open cal and nothing
else. That should leave you seeing a high impedance after the cal and
before the device is connected.

I attached a 27pF leaded capacitor (with leads cut short as possible) to
end of coaxial cable.

When I looked at the response I saw a Circle that indicated the
component became inductive around 500MHz (I presume this is SRF).


Perhaps. Or maybe you tried to do a full S11 cal rather than response
only? You really don't need the load to get pretty close for measuring a
reactance. Using a load will help your accuracy for well matched devices.
Using open gives you a measurement for small capacitances and using a
short for small inductance. You can do an open:short:load cal if you
have all standards in the same connector type for which you have a
defined cal kit in the instrument. Otherwise just use response cal.
The odd thing is that the capacitance reads only 3.1pF at 1Mhz and does
not read 27pF until 369 MHz ?

What do you see before you attach the DUT? Should look pretty much like a
dot on the right side of the Smith Chart and read out as a high Z with
perhaps a small capacitance portion. This represents the modeled fringing
capacitance of an "open".


g