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No, not necessarily. Some types of these do not short both conductors together and even if they do, there's no guarantee that the potential of the feedline will be the same as that of your device until they have been equalized. The feedline and antenna may all be at ground potential, but you and your device may have accumulated a static charge, which should be dissipated before making the connection.

Yeah, longer would be better, and there's no need to cut a specific length to make the measurement. Any reasonable length you have lying around can be used as long as you can measure its physical length with adequate relative accuracy. 1% is good enough. I've used arbitrary lengths I had on hand ranging from around 10' to over 50'. (I have a 100' tape measure). Set the max frequency of the measurement scan range appropriate to the length being measured. Higher for shorter lengths and lower for longer lengths.

On 8/14/21 6:41 AM, S Johnson wrote:

I have an idea for finding the velocity factor of any cable. Please let me know if this could work.

The NanoVNA can measure cable lenth accurately if the cable’s VF is known and can be input into the calculations. Most people either just guess at the VF or look up the cable’s manufacturer specs. But here is the idea for either unknown cable or for those wanting to confirm the manufacturers number. Using the cable of interest, make up a one meter length of cable, with the connectors you plan to use in the actual antenna system, and then use the NanoVNA to measure that, inputting different VF’s until the Nano shows 1 meter long. Then you’ll know the VF factor exactly.

Exactly.? Or you can put in 100 for the VF, measure the length, and compare the measured length to the actual physical length.? VF = physical length/VNA length@100 VF

I'd use more than a meter long piece, so the "connectors and fixtures" are a smaller fraction of the cable length.

I have an idea for finding the velocity factor of any cable. Please let me know if this could work.

The NanoVNA can measure cable lenth accurately if the cable’s VF is known and can be input into the calculations. Most people either just guess at the VF or look up the cable’s manufacturer specs. But here is the idea for either unknown cable or for those wanting to confirm the manufacturers number. Using the cable of interest, make up a one meter length of cable, with the connectors you plan to use in the actual antenna system, and then use the NanoVNA to measure that, inputting different VF’s until the Nano shows 1 meter long. Then you’ll know the VF factor exactly.

I would always discharge an antenna coax before measuring, just to be on the safe side. However, I would assume that if one has an unun, balun, or matching transformer between the antenna an receiver end of the coax the antenna already has a path to ground and is in all likelihood self-discharging. Please correct me if I'm wrong, but this is something to consider. Safest practice would be to short the coax regardless.? 73
Ken --? WB?OCV

I always connect my coax from all antennas to ground when not in use. No problems with static then and I can measure them any time I need/want to. Well, as long as I've just disconnected them from their normal grounded resting place.

--
Phil KE3FL

On 8/13/21 1:27 PM, Donald Hellen wrote:

Andrew . . .

On Thu, Aug 12, 2021 at 08:15 PM, Andrew Kurtz wrote:

Doesn’t that phrase “1 port device” suggest a single input? My antenna
has a single wire going outside; where would I find some other signal to
attach to the outer conductor of the small SMA on the VNA? Please don’t
reply if you want to tell me I am an idiot and still not help me out.

The single port needs two wires to function.



It does seem perhaps a little confusing, but the article above shows a port with two wires into a "black box" circuit. Think of it like this. A single port device might have only an input. A two port device might have an input and an output.

Donald KX8K

This is true, and one of the wires connecting one port to the other might be "inside the VNA" (i.e. the chassis ground)

On 8/13/21 1:03 PM, Fred Moore wrote:

Just a quick question. How many ohms would you suggest for that bleeder?

Megohms.

I used to use scrap black vacuum hose - it was UV resistant and happened to be conductive, and best, it was cheap.


Now, I'd probably just use a 1 Meg resistor if I had one.

Fred - N4CLA

On Fri, Aug 13, 2021 at 1:42 PM John Nightingale via groups.io <if455kc=
[email protected]> wrote:

As a matter of routine, consideration should be given to installing a

bleeder across the antenna's lead in the station to drain static
accumulation and never mind if it's a "grounded" antenna. A permanent
bleeder like that does not affect reception or transmission. For the
present purpose it would not affect v.n.a. observations. In urban areas
particularly, diode and gas discharge devices can cause problems; old
fashioned "R" is all that's required.

John
at radio station VE7AOV.

+++++


On 2021-08-13 8:27 a.m., Jim Lux wrote:

On 8/13/21 8:12 AM, David Eckhardt wrote:

When connecting any length of coax to any sensitive measurement
instrument,
I ALWAYS first grab the end of the coax and effectively short the end
with
a finger or hand. If there has been a recent lightning storm, you
might be
surprised and the discharge might surprise you in an undesirable manner.
The cylindrical capacitor that makes up the coaxial cable can hold a
charge
for a very long time.

Blowing dust, snow, or rain, are even more of a charging hazard than
the field from a passing thunderstorm. Continuous charging. It
charges until something breaks down, so you get a buzz or continuous
clicking. A sort of relaxation oscillator.

If your antenna is fed with coax, it appears as a single "wire". However,
in reality, it consists of two conductors: 1) The single inner conductor,
and 2) The outer braid. Fields are conducted to/from your transceiver
within the coaxial or cylindrical volume within the inner makeup of the
coaxial cable between the inner surface of the braid and the outer surface
of the central conductor.

If you have just a single wire as with a T, Windom, or traditional Marconi
antenna the single wire would go to the center of the source port (Ch 0).
This will enable a single-port measurement or Z11. When making
measurements with this setup, do not hold the VNA or place it near any
conducting surface as that will bias the readings.

Dave - W ?LEV

On Fri, Aug 13, 2021 at 8:27 PM Donald Hellen <donhellen@...>
wrote:

Andrew . . .

On Thu, Aug 12, 2021 at 08:15 PM, Andrew Kurtz wrote:

Doesn’t that phrase “1 port device” suggest a single input? My antenna
has a single wire going outside; where would I find some other signal to
attach to the outer conductor of the small SMA on the VNA? Please don’t
reply if you want to tell me I am an idiot and still not help me out.

The single port needs two wires to function.



It does seem perhaps a little confusing, but the article above shows a
port with two wires into a "black box" circuit. Think of it like this. A
single port device might have only an input. A two port device might have
an input and an output.

Donald KX8K

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

I have a 1 MΩ permanently connected across the output of my transmatch.
When the feedline is disconnected from the transmatch (most of the time), I
have a 50 Ω resistor paralleled with a 70 volt breakdown spark gap. Both
are 5-watt resistors.

Dave - W?LEV

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

Andrew . . .

On Thu, Aug 12, 2021 at 08:15 PM, Andrew Kurtz wrote:

Doesn’t that phrase “1 port device” suggest a single input? My antenna
has a single wire going outside; where would I find some other signal to
attach to the outer conductor of the small SMA on the VNA? Please don’t
reply if you want to tell me I am an idiot and still not help me out.

The single port needs two wires to function.



It does seem perhaps a little confusing, but the article above shows a port with two wires into a "black box" circuit. Think of it like this. A single port device might have only an input. A two port device might have an input and an output.

Donald KX8K

Just a quick question. How many ohms would you suggest for that bleeder?

Fred - N4CLA

On Fri, Aug 13, 2021 at 1:42 PM John Nightingale via groups.io <if455kc=
[email protected]> wrote:

As a matter of routine, consideration should be given to installing a

bleeder across the antenna's lead in the station to drain static
accumulation and never mind if it's a "grounded" antenna. A permanent
bleeder like that does not affect reception or transmission. For the
present purpose it would not affect v.n.a. observations. In urban areas
particularly, diode and gas discharge devices can cause problems; old
fashioned "R" is all that's required.

John

at radio station VE7AOV.

+++++


On 2021-08-13 8:27 a.m., Jim Lux wrote:

On 8/13/21 8:12 AM, David Eckhardt wrote:

When connecting any length of coax to any sensitive measurement
instrument,
I ALWAYS first grab the end of the coax and effectively short the end
with
a finger or hand. If there has been a recent lightning storm, you
might be
surprised and the discharge might surprise you in an undesirable manner.
The cylindrical capacitor that makes up the coaxial cable can hold a
charge
for a very long time.

Blowing dust, snow, or rain, are even more of a charging hazard than
the field from a passing thunderstorm. Continuous charging. It
charges until something breaks down, so you get a buzz or continuous
clicking. A sort of relaxation oscillator.

You are correct in connecting this single series tuned "filter" between the
two ports. The coaxial braid is taken care of inside the VNA. Usually,
these "filters" would be mounted inside in some sort of conductive
enclosure. Then, you would have a coax in and a coax out. You're fine
with the single series tuned circuit.

Dave - W?LEV

On Fri, Aug 13, 2021 at 6:55 PM Andrew Kurtz via groups.io <adkurtz=
[email protected]> wrote:

Gee, I sent this with a picture that didn’t come through! Picture a
home-made coil, 3 turns on 1/2” diameter, with a little capacitor soldered
to one end… No coax or coax fittings anywhere...

On Aug 13, 2021, at 2:40 PM, Andrew Kurtz via groups.io <adkurtz=

[email protected]> wrote:

You folks have been very helpful! You can tell that I am a rank

beginner, but I still think we sometimes talk past each other. Here is a
100MHz band-pass filter, simply an inductor and a capacitor in series. I
can attach one end to the CH0 center pin and the other end to the CH1
center pin. So what do I attach to the outer conductor(s)? It could be
simply attach them to each other (which I would assume happens inside the
VNA already)…? Since the VNA is calibrated, I would think it “knows” what
signal to send out CH0 based on doing just what it did during calibration,
without “needing” some ground. It would then compare that known output to
the reflection it gets at CH0 and the transmission it sees at CH1…?

Conversely, you say every filter you have has a coax connector at each

end. So, what is connected to the outer conductor, since the filter only
needs one entry point and one exit point? Mine works fine… (I have an
entirely home-made receiver — a crystal set — on which I have heard maybe
40 stations from 610 kHz to 24 MHz and from all over the world. This
filter sends some strong local FM signals to ground just before my
detector.)

On Aug 12, 2021, at 1:30 PM, Zack Widup <w9sz.zack@...> wrote:

Every filter has a ground path. How would you connect a filter with only
one lead? Is it going to be used like that in a circuit? All the

filters

I've built have a BNC, N or SMA connector for input and output. The

input

connects to the CH0 connector and the output connects to the CH1

connector.

I use the SMA cables supplied with the NanoVNA and any needed adaptors.
Simple components have two leads. However you do it, connect one lead to
the center pin of CH0 and the other lead to ground. I've used two

alligator

clips on wires soldered to the ends of a small piece of coax connected

to

the CH0 connector for lower frequency measurements. You may need a test

jig

for higher frequencies.

Zack

On Thu, Aug 12, 2021 at 12:18 PM Andrew Kurtz via groups.io <adkurtz=
[email protected]> wrote:

Yes, this does make sense… except what then do you connect to the outer
connector when analyzing a filter or some other simple component. The
center pin on CH0 goes in, and there is nothing left to connect to the
outer conductor.

Andy

On Aug 12, 2021, at 11:45 AM, Zack Widup <w9sz.zack@...> wrote:

I look at that as sort of like trying to apply DC power through only

one

lead. I always use connections through both the center connector and

shield

of the NanoVNA.

Zack W9SZ

On Thu, Aug 12, 2021 at 10:40 AM Andrew Kurtz via groups.io <adkurtz=
[email protected]> wrote:

All discussions of the NanoVNA suggest that the pin on the SMA

connector

attached to channel 0 is the only connection needed to look at

reflection

(S11). However, when I also connect my antenna ground to the outer
conductor, I get results which are WAY closer to expectation. For

example,

on an end-fed long wire antenna, just connecting the inner pin shows
reactance to always be capacitive from 0.5 MHz to 20 MHz. When I

add a

RF

ground to the outer conductor (which nothing I read suggests is the

right

thing to do), suddenly reactance cycles between capacitive and

inductive,

with X = 0 at all increments of 1/4 wavelength, as expected. Please
clarify the role of the outer conductor on either port.
Thanks.

Andy

<100M pass filter.jpeg>

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

Gee, I sent this with a picture that didn’t come through! Picture a home-made coil, 3 turns on 1/2” diameter, with a little capacitor soldered to one end… No coax or coax fittings anywhere...

This is a video of what voltages an antenna can present to equipment. Poor video, but worth watching.

73, Joe, K1ike

You folks have been very helpful! You can tell that I am a rank beginner, but I still think we sometimes talk past each other. Here is a 100MHz band-pass filter, simply an inductor and a capacitor in series. I can attach one end to the CH0 center pin and the other end to the CH1 center pin. So what do I attach to the outer conductor(s)? It could be simply attach them to each other (which I would assume happens inside the VNA already)…? Since the VNA is calibrated, I would think it “knows” what signal to send out CH0 based on doing just what it did during calibration, without “needing” some ground. It would then compare that known output to the reflection it gets at CH0 and the transmission it sees at CH1…?

Conversely, you say every filter you have has a coax connector at each end. So, what is connected to the outer conductor, since the filter only needs one entry point and one exit point? Mine works fine… (I have an entirely home-made receiver — a crystal set — on which I have heard maybe 40 stations from 610 kHz to 24 MHz and from all over the world. This filter sends some strong local FM signals to ground just before my detector.)

As a matter of routine, consideration should be given to installing a

bleeder across the antenna's lead in the station to drain static
accumulation and never mind if it's a "grounded" antenna. A permanent
bleeder like that does not affect reception or transmission. For the
present purpose it would not affect v.n.a. observations. In urban areas
particularly, diode and gas discharge devices can cause problems; old
fashioned "R" is all that's required.

John

at radio station VE7AOV.

+++++


On 2021-08-13 8:27 a.m., Jim Lux wrote:

On 8/13/21 8:12 AM, David Eckhardt wrote:

When connecting any length of coax to any sensitive measurement
instrument,
I ALWAYS first grab the end of the coax and effectively short the end
with
a finger or hand.? If there has been a recent lightning storm, you
might be
surprised and the discharge might surprise you in an undesirable manner.
The cylindrical capacitor that makes up the coaxial cable can hold a
charge
for a very long time.

Blowing dust, snow, or rain, are even more of a charging hazard than
the field from a passing thunderstorm.? Continuous charging. It
charges until something breaks down, so you get a buzz or continuous
clicking. A sort of relaxation oscillator.

On Fri, Aug 13, 2021 at 05:21 PM, Syd wrote:

Fooling around with this kit

Hello Syd,
When you have read the beginner guide, have a look at:
/g/nanovna-users/wiki/16592

73, Rudi DL5FA

I use my wedding ring to short the coax... Or make sure I touch the coax shield and center... You can still get a static discharge from the antenna at the base.

73, and thanks,
Dave (NK7Z)

ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources

Syd,

I suggest you read this document which will get you more familiar with the NanoVNA. It is in the files section of this group

/g/nanovna-users/files/Absolute%20Beginner%20Guide%20to%20The%20NanoVNA/Absolute_Beginner_Guide_NanoVNA_v1_6.pdf

Also read the Wiki for this group which is full of great information. You can also search the group for info on topics of interest. There are some very knowledgeable people in this group who have contributed to posts in the past.

Roger