Re: Best Way to Measure Antenna SWR
On Fri, Aug 11, 2023 at 12:36 PM, Bryan Curl wrote:
Mike,
Tell us more about your antenna.
What length is your EFHW?
Did your EFHW have a reflector stub of some length connected to the shield
side or is it fed straight to coax?
Any choke in the line at some point?
I wonder how common mode currents would contribute to the measurement.
73, Bryan, n0lif
Bryan The attached drawings should answer your questions. The wire was bent to fit my garden. Performance is very good, with 100W SSB QSOs from my QTH near London to the US midwest, South America and Indonesia. -- Mike G8GYW
|
Re: Nano VNA SAVER graphs of a 40m loop antenna
|
Re: Nano VNA SAVER graphs of a 40m loop antenna
So, it's just a tad too long to center on the band. But if you're a CW
operator, perfect.
Dave - W?LEV
toggle quoted message
Show quoted text
On Fri, Aug 11, 2023 at 3:16?PM Barry K3EUI <k3euibarry@...> wrote: I just put up a full one-wavelength (140 ft) 40 meter loop antenna for
NVIS over the MidAtlantic area.
testing with my 3 yr old Nano VNA reveals no surprises using Nano VNA
SAVER to make these graphs
SWR, RETURN LOSS (dB), PHASE (degrees) and Smith Chart
yes .... I know I plotted RETURN LOSS as a negative value - but then it
matches the shape of the SWR curve.
de k3eui barry
phila region
-- *Dave - W?LEV*
--
Dave - W?LEV
|
Thank you, Zack and Robin for the reply. I bought a NANO VNA and had second thoughts about using it to measure an AM radio station tower, given the presence of another local AM signal. I might make an LC trap to reduce level of the other local signal, but the impact of the trap on the measurement needs to be taken into account.
Most likely I will locate an operating impedance bridge, which I used many years ago to measure under power from a transmitter, at about 100 watts. Relatively safe, for the brief exposure at medium wave.
|
Nano VNA SAVER graphs of a 40m loop antenna
I just put up a full one-wavelength (140 ft) 40 meter loop antenna for NVIS over the MidAtlantic area.
testing with my 3 yr old Nano VNA reveals no surprises using Nano VNA SAVER to make these graphs
SWR, RETURN LOSS (dB), PHASE (degrees) and Smith Chart
yes .... I know I plotted RETURN LOSS as a negative value - but then it matches the shape of the SWR curve.
de k3eui barry
phila region
|
Adding to Zack's reply, the first active device that the input encounters is an SA612 mixer chip. The data sheet (from NXP) suggests that compression non-linearity starts at around -30 dBm, and is -1 dB at about -25 dBm input. Above about -18 dBm, the output is constant. The data sheet also shows the results for inputs up to around +3 dBm. So for accurate measurement the signal? to the chip should be held back to no more than -20 dBm.
The input circuit starts with a *20 dB attenuator pad* before the input to the mixer. This then translates to:
* compression starts around -10 dBm
* 1 dB compression around -5 dBm
* constant output at around 2 dBm
* maximum *safe* input is generally reckoned to be *+10 dBm*, due to
the unbalanced nature of the attenuator circuit used [nanoVNA H4
circuit for version 4.2 hardware]
* and an *absolute maximum input* would be *+20 dBm*, but for a
*very short time* only, due to the power dissipation in the input
shunt resistor, which is probably 1/16 W rated
In this case, *less* is very much *more*.
Also, adding to what Zack has said, measuring anything with the level of local signal that you suggest it going to be very tricky, and need a lot of either guile or brute force (= high power.) On the guild front you /might/ find it useful to use driving software such as nanoVNA Saver to allow taking & recording many independent measurements. But if the signal levels are too high, that it us unlikely to be enough. Assuming that the signals are away from your frequencies of interest, then using the minimum bandwidth possible may be helpful.
Thinking out of the box, it would, in principle, be possible to us a band-stop (or band pass) filter and calibrate the nanoVNA at the measuring plane, with the filter between that measuring plane and the nanoVNA.
Good luck, 73,
Robin, G8DQX (who last worried about MW transmitters and their aerials/antennas rather a long time ago!)
toggle quoted message
Show quoted text
On 11/08/2023 13:43, Zack Widup wrote: I believe it's 10 dBm (10 mW). Do you really mean 1000 kHz? That's in the
AM broadcast band. That's a vertical of almost 250 feet. That will probably
produce way too much overload.
Zack W9SZ
On Thu, Aug 10, 2023 at 9:29?PM<greg@...> wrote:
Pardon the basic question. What is the approximate maximum input port RF
voltage before damaging the device? Let's say I hook it up to a tower in a
location with about 100 millivolts per meter of field strength from another
signal. Is this likely to damage the unit? I want to measure reactance and
resistance of a 1/4 wave vertical antenna at approximately 1,000
kilohertz. Thank you.
|
I believe it's 10 dBm (10 mW). Do you really mean 1000 kHz? That's in the
AM broadcast band. That's a vertical of almost 250 feet. That will probably
produce way too much overload.
Zack W9SZ
toggle quoted message
Show quoted text
On Thu, Aug 10, 2023 at 9:29?PM <greg@...> wrote: Pardon the basic question. What is the approximate maximum input port RF
voltage before damaging the device? Let's say I hook it up to a tower in a
location with about 100 millivolts per meter of field strength from another
signal. Is this likely to damage the unit? I want to measure reactance and
resistance of a 1/4 wave vertical antenna at approximately 1,000
kilohertz. Thank you.
|
Re: Best Way to Measure Antenna SWR
Mike,
Tell us more about your antenna.
What length is your EFHW?
Did your EFHW have a reflector stub of some length connected to the shield side or is it fed straight to coax?
Any choke in the line at some point?
I wonder how common mode currents would contribute to the measurement.
73, Bryan, n0lif
|
Re: Best Way to Measure Antenna SWR
You can do both. If you calibrate with the SOLT loads at the cable end you will get the antenna impedance. If you calibrate at the nano-vna end you will get the line plus antenna.
|
Pardon the basic question. What is the approximate maximum input port RF voltage before damaging the device? Let's say I hook it up to a tower in a location with about 100 millivolts per meter of field strength from another signal. Is this likely to damage the unit? I want to measure reactance and resistance of a 1/4 wave vertical antenna at approximately 1,000 kilohertz. Thank you.
|
Re: Basic questions on nanovna-saver and IF filter plots
Thank you Roger, and your math example helps to clarify.
Keith
N3KXZ
|
Re: Basic questions on nanovna-saver and IF filter plots
On Thu, Aug 10, 2023 at 09:51 AM, Keith Ostertag wrote:
1) What exactly is the |S21| plot? I don't know what the vertical axis
represents and its units. Is it the LogMag but with different units?
The |S21| transmission coefficient indicates the insertion loss or gain of your amplifier on a linear scale. It gives you the transmission ratio (output magnitude/input magnitude) in the forward direction. A number smaller than 1 is loss and greater than 1 is gain. S21 Log mag is is a logarithmic dB scale equal to 20 *Log10 |S21|. For example Marker 3 in your plot has a value of |S21| = .575 and 20*log10(0.575) = -4.8 dB which is what is shown as S21 Gain. Roger
|
Re: Basic questions on nanovna-saver and IF filter plots
Thank you Dave and Stan. So would the |S21| linear graph vertical axis have units? Or is it unit-less? (if that is the correct term)
|
Re: Basic questions on nanovna-saver and IF filter plots
I think in you saver graph that the |s21| plot is just the linear
representation of the magnitude of the reflection coefficient (max value
1). The top graph, called logmag s21, is a logarithmic representation of
the same data represented in dB, and is what we normally use for most
purposes.
toggle quoted message
Show quoted text
On Thu, Aug 10, 2023, 11:01 AM W0LEV <davearea51a@...> wrote: No attachment. I'll try attaching the grahic.
Dave - W?LEV
On Thu, Aug 10, 2023 at 5:58?PM W0LEV via groups.io <davearea51a=
[email protected]> wrote:
Here is a graphical - no math - representation of what the S-Parmeters
indicate. It is usually assumed to be in a 50 +/- j0 ohm system.
[image: image.png]
S11: With the output (right side) properly terminated, S11 indicates how
well the input (left side) is matched to a 50 +/- j0 load. As a scalar
measurement, this would be the input SWR.
S12: With the input (left side) properly terminated, S12 represents the
reverse isolation when probed from the output side (right side).
S21: With the input as the energy source and the output probed, S21
represents the forward transfer characteristics of the network. This may
be either gain in the case of an active circuit or a loss in the case of a
passive attenuator, for example.
S22: With the input properly terminated, S22 represents how well the
output is matched to a 50 +/- ohm load. As a scalar measurement, this
would be the SWR of the output port.
Any of these parameters can be expressed in either vector form or
logarithmic form, as in logmag (of the reflection coefficient of the input
or output port).
Dave - W?LEV
On Thu, Aug 10, 2023 at 4:51?PM Keith Ostertag <n3kxz@...> wrote:
Here is a link to a nanovna-saver plot of my current IF filter:
The bandwidth is a bit narrow. How does the ripple look?
A few basic questions:
1) What exactly is the |S21| plot? I don't know what the vertical axis
represents and its units. Is it the LogMag but with different units?
2) When I run the "Analysis" it says "Insufficient data for analysis.
Increase segment count." But increasing the segment count does not clear
that statement. Perhaps I am misunderstanding what it wants?
Here's a link to the analysis:
Thanks,
Keith
N3KXZ
--
*Dave - W?LEV*
--
Dave - W?LEV
--
*Dave - W?LEV*
--
Dave - W?LEV
|
Re: Basic questions on nanovna-saver and IF filter plots
No attachment. I'll try attaching the grahic. Dave - W?LEV On Thu, Aug 10, 2023 at 5:58?PM W0LEV via groups.io <davearea51a= [email protected]> wrote: Here is a graphical - no math - representation of what the S-Parmeters
indicate. It is usually assumed to be in a 50 +/- j0 ohm system.
[image: image.png]
S11: With the output (right side) properly terminated, S11 indicates how
well the input (left side) is matched to a 50 +/- j0 load. As a scalar
measurement, this would be the input SWR.
S12: With the input (left side) properly terminated, S12 represents the
reverse isolation when probed from the output side (right side).
S21: With the input as the energy source and the output probed, S21
represents the forward transfer characteristics of the network. This may
be either gain in the case of an active circuit or a loss in the case of a
passive attenuator, for example.
S22: With the input properly terminated, S22 represents how well the
output is matched to a 50 +/- ohm load. As a scalar measurement, this
would be the SWR of the output port.
Any of these parameters can be expressed in either vector form or
logarithmic form, as in logmag (of the reflection coefficient of the input
or output port).
Dave - W?LEV
On Thu, Aug 10, 2023 at 4:51?PM Keith Ostertag <n3kxz@...> wrote:
Here is a link to a nanovna-saver plot of my current IF filter:
The bandwidth is a bit narrow. How does the ripple look?
A few basic questions:
1) What exactly is the |S21| plot? I don't know what the vertical axis
represents and its units. Is it the LogMag but with different units?
2) When I run the "Analysis" it says "Insufficient data for analysis.
Increase segment count." But increasing the segment count does not clear
that statement. Perhaps I am misunderstanding what it wants?
Here's a link to the analysis:
Thanks,
Keith
N3KXZ
--
*Dave - W?LEV*
--
Dave - W?LEV
-- *Dave - W?LEV* -- Dave - W?LEV
|
Re: Basic questions on nanovna-saver and IF filter plots
Here is a graphical - no math - representation of what the S-Parmeters
indicate. It is usually assumed to be in a 50 +/- j0 ohm system.
[image: image.png]
S11: With the output (right side) properly terminated, S11 indicates how
well the input (left side) is matched to a 50 +/- j0 load. As a scalar
measurement, this would be the input SWR.
S12: With the input (left side) properly terminated, S12 represents the
reverse isolation when probed from the output side (right side).
S21: With the input as the energy source and the output probed, S21
represents the forward transfer characteristics of the network. This may
be either gain in the case of an active circuit or a loss in the case of a
passive attenuator, for example.
S22: With the input properly terminated, S22 represents how well the
output is matched to a 50 +/- ohm load. As a scalar measurement, this
would be the SWR of the output port.
Any of these parameters can be expressed in either vector form or
logarithmic form, as in logmag (of the reflection coefficient of the input
or output port).
Dave - W?LEV
toggle quoted message
Show quoted text
On Thu, Aug 10, 2023 at 4:51?PM Keith Ostertag <n3kxz@...> wrote: Here is a link to a nanovna-saver plot of my current IF filter:
The bandwidth is a bit narrow. How does the ripple look?
A few basic questions:
1) What exactly is the |S21| plot? I don't know what the vertical axis
represents and its units. Is it the LogMag but with different units?
2) When I run the "Analysis" it says "Insufficient data for analysis.
Increase segment count." But increasing the segment count does not clear
that statement. Perhaps I am misunderstanding what it wants?
Here's a link to the analysis:
Thanks,
Keith
N3KXZ
-- *Dave - W?LEV*
--
Dave - W?LEV
|
Basic questions on nanovna-saver and IF filter plots
Here is a link to a nanovna-saver plot of my current IF filter:
The bandwidth is a bit narrow. How does the ripple look?
A few basic questions:
1) What exactly is the |S21| plot? I don't know what the vertical axis represents and its units. Is it the LogMag but with different units?
2) When I run the "Analysis" it says "Insufficient data for analysis. Increase segment count." But increasing the segment count does not clear that statement. Perhaps I am misunderstanding what it wants?
Here's a link to the analysis:
Thanks,
Keith
N3KXZ
|
Re: Best Way to Measure Antenna SWR
The minimums are almost the same. . . thanks for the measurement.
Vy 73, Roger DL2YDP
|
Re: Best Way to Measure Antenna SWR
Second time lucky ...
--
Mike G8GYW
|
Re: Best Way to Measure Antenna SWR
Here's an EFHW I measured at the antenna and in the shack.
First I calibrated the NanoVNA at the far end of the feeder (18 metres long and about 0.5dB loss) and measured the VSWR there. Then I calibrated again on a short cable and measured inside the shack.
Here's the result.
--
Mike G8GYW
|
Barry K3EUI
F4WCV
Roger Need
Roger DL2YDP
