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HI-Z EVALUATUTION - MEASURED DATA COMPARISON with HP 8753C

 

OK.....I just had to do it. NANOVNA-F measured data compared to the HP
8753C measured data. Subjects are:

1) 220-ohm 1/8-watt 10 %
2) 470-ohm 1/8-watt 5 %

Both VNA's were calibrated SOL. Measurements were made by placing the
cursor at the designated frequencies and reading the complex impedance from
the Smith Chart (HP) and Saver (NANOVNA - F). I cut the resistor leads as
short as possible and inserted them into their respective female connectors
(NANOVNA-F: SMA Port 01.........HP 8753C: BNC at end of 50-ohm cable where
cal. standards were placed). In both cases, the reflection measurement
method was utilized. Measured data follows:

*Frequency (MHz) * *220-ohm*
*470-ohm*
*NANOVNA-F * *HP 8753C*
*NANOVNA-F* *HP 8753C*

49.5 197.3 - j15.9 209 - j19.7
456.1 - j20.5 464.8 - j17.1
144.0 206.9 - j20.6 109 - j19.7
451.4 - j58.2 466.9 - j17.8
299.6 198.1 - j18.7 193 -
j9 415.3 - j105.1 429.2 - j17.2
403.9 186.9 - j17.1 190 - j6.7
405.2 - j108.5 406.3 - j115.6
700.0 182.2 - j17.2 188.5 - j8.9
320.1 - j174.0 413.1 - j178.3
955.0 180.2 - j18.0 181.2 - j2.2
265.2 - j192.7 273.9 - j153.4

Draw your own conclusions.

My Own Conclusions: PRETTY DARN GOOD....NO.....EXCELLENT.....comparing $60
to $25,000++ (in its day).

I do not own a Rig Expert but have used
a couple. I'll take the NANO's any day over far more $$$ for "the
others".

And, these are portable. The HP 8753C
is anything but portable!!!!

Dave - W?LEV
 

Sorry your table is all over the place can work out which is which.

Go higher than 1-2K ohms, think you will start to see the difference.
 

for 144MHz in HP8753C column you have a typo I think...

--
Regards,

Slawek/SP9BSL
 

High Z is hard to obtain at RF. For parallel twin lead with #16 wire, the spacing is 0.3 inches for 300 Ohms. The spacing for 1000 Ohms is 105 inches!
 

My tube amplifier takes exception to your statement:

"High Z is hard to obtain at RF. "

The amp wants to know who do you think has been talking on 40 meters for
the last 30 years?


And the 450 ohm ladder line does not agree with your concepts of
transmission line either.

But I told them that I would talk to you on their behalf. So please be more
open to all the work they do, OK ? :)
All done now, I hope they settle back down. (-:

Nels
NE7LS

On Mon, Feb 17, 2020, 6:52 AM W1RS <Deflatermaus@...> wrote:

High Z is hard to obtain at RF. For parallel twin lead with #16 wire, the
spacing is 0.3 inches for 300 Ohms. The spacing for 1000 Ohms is 105
inches!
 

I'll tell you what I have done to test high impedance RF.

I built myself a fixture PCB, you can see if here:



One of the parts of the fixture PCB is a ZIF socket connected to two SMA
female connectors. It is very useful for measuring leaded components.

I calibrated the VNA (the one I designed and built) using the ZIF socket
lever up for open circuit, a very short wire between two holes for short
circuit, and a 1/4 watt 51 ohm resistor for load. The leads were trimmed
to minimize the inductance of the resistor.

At 1-30 MHz, I then could measure the impedance of a 10k ohm resistor. The
results were accurate over the entire frequency range, between about 9800
to 10200 ohms.

At 1-600 MHz, I could measure the impedance of a 1k ohm resistor. The
results were between about 950 and 1050 ohms over the entire range up to
about 550 MHz, where the resistance dipped slightly to about 900 ohms.

Because I only use the SI5351A up to 200 MHz (as that's all its speced
for), 600 MHz is the maximum frequency I can test with the third harmonic.
Fifth harmonic and up tends to be useful mainly just for crude antenna
measurements.

On Mon, Feb 17, 2020 at 9:52 AM W1RS <Deflatermaus@...> wrote:

High Z is hard to obtain at RF. For parallel twin lead with #16 wire, the
spacing is 0.3 inches for 300 Ohms. The spacing for 1000 Ohms is 105
inches!
 

In calibration for measurement and in measurement at RF frequencies, high-Z
is far more difficult than a short or proper 50-ohm termination. Take 144
MHz and assume you are attempting to measure 1 kohm. There will always be
present roughly 0.5 to 1 pf in the measurement. At 144 MHz, 0.5 pF =
-j2210 ohms. This is over twice the real part even at 0.5 pF - a very
small capacitor.

True, the output impedance (if you will, resistance plus a small amount of
several pF of capacitance) of an HF tube amplifier is very high, between
1000 and 4000 ohms (+/-). The pi-L network between the tube plates and the
output to the antenna feedline matches that high-Z (and renders pure
resistance) to 50-ohms. That impedance is not measured with a VNA but
rather but by using standard Ohm's Law based calculations specifically
tailored for determining the values of the matching network to enable
maximum power transfer.

450 ohm ladder line is a real differential transmission line as is 300-ohm
TV twin lead as are long parallel close-spaced ribbons of copper strip as
are parallel copper traces on opposing layers of a PC board. I use
parallel open wire transmission line between my home brew L-network
matching network (a.k.a., "antenna tuner" - it does NOT 'tune' the
antenna!!) and the feed point of my 450-foot long doublet. Works great as
a relatively lossless transmission line and withstands high SWR with
insignificant additional loss.

Dave - W?LEV

On Mon, Feb 17, 2020 at 3:47 PM Nels Nelsen <nels.nelsen@...> wrote:

My tube amplifier takes exception to your statement:

"High Z is hard to obtain at RF. "

The amp wants to know who do you think has been talking on 40 meters for
the last 30 years?


And the 450 ohm ladder line does not agree with your concepts of
transmission line either.

But I told them that I would talk to you on their behalf. So please be more
open to all the work they do, OK ? :)
All done now, I hope they settle back down. (-:

Nels
NE7LS

On Mon, Feb 17, 2020, 6:52 AM W1RS <Deflatermaus@...> wrote:

High Z is hard to obtain at RF. For parallel twin lead with #16 wire,
the
spacing is 0.3 inches for 300 Ohms. The spacing for 1000 Ohms is 105
inches!





--

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

Here is another similar set of data:

I think it supports Dave's general conclusion for resistors like 470 Ohms. This was done with a HP8714B VNA that is functionally very similar to the 8753.

However, it also shows more data points. This gives a look that again shows that the fine little nanoVNA is quite fine up to 300 MHz, good but noisy up to 900 MHz and (not shown here) challenging up to 1500 MHz. Nothing really new, but worth keeping in mind.

The spike at 225 MHz for the nano-VNA is repeatable and is an error. Others have seen this.

I did a quick look at a 5100 Ohm resistor, and neither the 8714 nor the nanoVNA was doing well with this. The 8714 was better in the 5 to 100 MHz range.

I have a N2PK VNA that makes very high quality measurements up to 60 MHz. It has an RF I-V adaptor

and

If you want to measure high or low impedance values, this box adds to the accuracy. But, to use this with the nanoVNA would require firmware changes and also the connection to a digital control line, that might be challenging.

73, Bob W7PUA
 

Nels, I should have said Hi-Z broadband transmission lines. Of course the tube amp situation is as Dave stated. I went to to calculate the spacing for the ladder line.
I was amazed at how rapidly it increases with the impedance. The line-to-line capacitance requirements just get really small. According to the equations presented,

300 Ohms --> 0.3 "
450 Ohms --> 1"
700 Ohms --> 8.5 "
1000 Ohms --> 105"

I'm very impressed with the nanoVNA, but with the 50 Ohm bridge design, I would not expect to achieve good accuracy at measuring at greater than 10 times the bridge Z, especially at higher frequencies.
 

Robert,

please take a look at my 9.8k Ohm measurements. With the S21 method, the
results are acceptable.
/g/nanovna-users/message/11027

For a lower resistor, results are much better (S21 method):
[image: image.png]

Using an external bridge with a reference higher than 50 OHm would improve
measurements, but some difficult calculations are needed.
/g/nanovna-users/topic/64426024#8601

Ady YO2NAA

On Tue, Feb 18, 2020 at 4:53 PM W1RS <Deflatermaus@...> wrote:

Nels, I should have said Hi-Z broadband transmission lines. Of course the
tube amp situation is as Dave stated. I went to
to calculate the spacing
for the ladder line.
I was amazed at how rapidly it increases with the impedance. The
line-to-line capacitance requirements just get really small. According to
the equations presented,

300 Ohms --> 0.3 "
450 Ohms --> 1"
700 Ohms --> 8.5 "
1000 Ohms --> 105"

I'm very impressed with the nanoVNA, but with the 50 Ohm bridge design, I
would not expect to achieve good accuracy at measuring at greater than 10
times the bridge Z, especially at higher frequencies.



image.png

 

Hi to W1RS,
I don't know you very well but
I hope you understand my post was mostly jest. I figured any one with a
"W" call sign would understand.
Nice meeting you,
I hope to talk more about non-50 ohm measurements.
I have a lot of 300 - 450 ohm ladder line work to do. And I am just
starting out with a VNA. So I will be asking for help.
I also want to take a closer look at the "some what popular" wide band low
Z to high Z -"half wave"- end fed toroid transformer and see if there is
room for improvement. I have used a bob-tailcurtain on 80meters in the past
and had amazing results. I have also used the half of a bob-tail and I
recommend it. Some People have no idea what can be done on 80m day after
day with less than 100 watts right thru a sunspot minimum. Those are my
ambitions, more later. I am just starting out with using a VNA an still
have lots of reading to do.

Nels Nelsen
NE7LS

On Tue, Feb 18, 2020, 6:53 AM W1RS <Deflatermaus@...> wrote:

Nels, I should have said Hi-Z broadband transmission lines. Of course the
tube amp situation is as Dave stated. I went to
to calculate the spacing
for the ladder line.
I was amazed at how rapidly it increases with the impedance. The
line-to-line capacitance requirements just get really small. According to
the equations presented,

300 Ohms --> 0.3 "
450 Ohms --> 1"
700 Ohms --> 8.5 "
1000 Ohms --> 105"

I'm very impressed with the nanoVNA, but with the 50 Ohm bridge design, I
would not expect to achieve good accuracy at measuring at greater than 10
times the bridge Z, especially at higher frequencies.

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