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We can use the time honored formula of 234/length to get the quarter wave frequency of a piece of wire. But... is there a way to connect that wire (e.g. 14AWG 7 strand insulated) to the NanoVNA and get the near resonant frequency?
Regards
Brian D
KF6BL
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Not really
A 1/4 wave antenna is NON-FUNCTIONAL.
i.e. it does not work ........ by itself.
A 1/4 wave only works as a resonate antenna went mounted on a ground plane about 1/2 by 1/2 wavelengths.
So mount a connector in the middle of the roof of you car, have the NanoVNA on one side and the 1/4 wave element on the other side, and then you can find it's resonate frequency.?
Kent WA5VJB? Antenna Editor CQ Magazine.
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On Sunday, June 19, 2022, 10:01:47 PM CDT, Brian Donaldson <brianb253@...> wrote:
We can use the time honored formula of 234/length to get the quarter wave frequency of a piece of wire. But... is there a way to connect that wire (e.g. 14AWG 7 strand insulated) to the NanoVNA and get the near resonant frequency?
Regards
Brian D
KF6BL
|
Thanks Kent. I wasn't looking at this from a 1/4 wave antenna perspective. I was looking at trying to find what frequencies can be found in a length of wire x feet long. I just happen to use the 234/length formula as an example from the math perspective.
So for another example, say I have a 16 foot length of 14AWG and want to know where the dips and peaks in the return loss are located. But I guess you are saying that in order to do this, I need something for that wire to work against. Would that be a correct thought? Possibly, a VNA of any type would be the wrong tool to use. This is why I am asking.
Regards,
Brian D
KF6BL
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Hi Brian
The basic wavelength calculations would of course be your starting point.Height above ground, nearby objects, are all issues and again you really need a counterpoise to get a good reading.Welcome to the real world!? Kent
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On Sunday, June 19, 2022, 11:16:10 PM CDT, Brian Donaldson <brianb253@...> wrote:
Thanks Kent. I wasn't looking at this from a 1/4 wave antenna perspective. I was looking at trying to find what frequencies can be found in a length of wire x feet long. I just happen to use the 234/length formula as an example from the math perspective.
So for another example, say I have a 16 foot length of 14AWG and want to know where the dips and peaks in the return loss are located. But I guess you are saying that in order to do this, I need something for that wire to work against. Would that be a correct thought? Possibly, a VNA of any type would be the wrong tool to use. This is why I am asking.
Regards,
Brian D
KF6BL
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The "TDR" function works - why shouldn't this?
It's simple enough to test, too!
--
Doug, K8RFT
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Because the TDR is not really a TDR.
Using frequency sweeps it does a TDR like function.But it's just a VNA doing calculations on the peaks and dips of a sweep.
Just a wire by itself is NOT a 50 Ohm transmission line.And the TDR like function only works with 50 Ohm transmission line, and to someextent 72 Ohm lines.? Kent
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On Monday, June 20, 2022, 05:37:46 AM CDT, DougVL <k8rftradio@...> wrote:
The "TDR" function works - why shouldn't this?
It's simple enough to test, too!
--
Doug, K8RFT
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You need to measure against a counter poise. Use 1 or more quarter wavelength radials connected to the ground connector shell of the nanovna. Try to replicate you operating position.
Mike N2MS
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On 06/20/2022 12:38 AM KENT BRITAIN < wa5vjb@... > wrote:
Hi Brian
The basic wavelength calculations would of course be your starting
point.Height above ground, nearby objects, are all issues and again you
really need a counterpoise to get a good reading.Welcome to the real
world!? Kent
On Sunday, June 19, 2022, 11:16:10 PM CDT, Brian Donaldson < brianb253@...
wrote:
Thanks Kent. I wasn't looking at this from a 1/4 wave antenna perspective.
I was looking at trying to find what frequencies can be found in a length
of wire x feet long. I just happen to use the 234/length formula as an
example from the math perspective.
So for another example, say I have a 16 foot length of 14AWG and want to
know where the dips and peaks in the return loss are located. But I guess
you are saying that in order to do this, I need something for that wire to
work against. Would that be a correct thought? Possibly, a VNA of any type
would be the wrong tool to use. This is why I am asking.
Regards,
Brian D
KF6BL
|
Yes, it is, I did it many times and it gives me repeatable results.
Simply connect the single wire into the S11 input (a cable with a PL239 socket here), I also ground the nanovna at the socket (the results are similar without the ground, it depends).
I do evaluate the |Z| then in the nanovna-saver.
Attached a picture from a real EFHW antenna measurement - the wire only.
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Can¡¯t you just put it up as you intend to use it and find the low points in the SWR chart, or am I forgetting something? That way it would work against the counterpoise/ground plane that you intend to use.
--
Steve M0NMA
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Years ago I needed to do some tests with a real TDR, so I put one together using some CMOS chips. It worked quite well despite its simplicity. It didn't care what the impedance of the transmission line was. Now I have a real TDR - a Tek 1502. Zack W9SZ On Mon, Jun 20, 2022 at 7:16 AM KENT BRITAIN <WA5VJB@...> wrote: Because the TDR is not really a TDR.
Using frequency sweeps it does a TDR like function.But it's just a VNA
doing calculations on the peaks and dips of a sweep.
Just a wire by itself is NOT a 50 Ohm transmission line.And the TDR like
function only works with 50 Ohm transmission line, and to someextent 72 Ohm
lines. Kent
On Monday, June 20, 2022, 05:37:46 AM CDT, DougVL <
k8rftradio@...> wrote:
The "TDR" function works - why shouldn't this?
It's simple enough to test, too!
--
Doug, K8RFT
<> Virus-free. www.avast.com <> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
|
Good morning Mikki from Atlanta Ga.
I have a question for you regarding the length of this wire. I have this
full wave 80m loop up in the air and would like to measure it and see where
the resonant points are located. would this work?
Fred - N4CLA
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On Mon, Jun 20, 2022 at 9:05 AM Zack Widup <w9sz.zack@...> wrote: Years ago I needed to do some tests with a real TDR, so I put one together
using some CMOS chips. It worked quite well despite its simplicity. It
didn't care what the impedance of the transmission line was. Now I have a
real TDR - a Tek 1502.
Zack W9SZ
On Mon, Jun 20, 2022 at 7:16 AM KENT BRITAIN <WA5VJB@...> wrote:
Because the TDR is not really a TDR.
Using frequency sweeps it does a TDR like function.But it's just a VNA
doing calculations on the peaks and dips of a sweep.
Just a wire by itself is NOT a 50 Ohm transmission line.And the TDR like
function only works with 50 Ohm transmission line, and to someextent 72 Ohm
lines. Kent
On Monday, June 20, 2022, 05:37:46 AM CDT, DougVL <
k8rftradio@...> wrote:
The "TDR" function works - why shouldn't this?
It's simple enough to test, too!
--
Doug, K8RFT
<
Virus-free.
www.avast.com
<
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
|
Brian,
to measure the resonances of that single wire, you need to extend it straight in clear air, far from any objects, connect it to the center pin of the NanoVNA's port, and connect the shell to an "infinite ground". That is a magical device that can take any current, at any frequency, without causing any voltage drop. That is, it's a zero-impedance sink.
When you only need to measure over a narrow frequency range, such an infinite ground is reasonably well approximated by several radial wires that are a quarter wave long each, and are out in the free air. But if you want to take a wire of random length, and measure its quarter wave length, this isn't good enough, because any little shift away from the resonant frequency of those radials will cause a change in the reading, and you can't separate the effect of the radial wires from that of the the random wire being measured.
A better approach to an infinite ground is a flat metal sheet that is several times larger than the quarter wavelength at the lowest frequency you will measure. Sometimes the sheet metal roof of a barn might be usable, but it's not very comfortable to climb up there to do measurements... And for UHF a car roof might suffice, but not really on VHF, let alone on lower frequencies.
Any imperfection of the ground you use will cause an error in your measurement, shifting the resonant frequencies you measure for the wire.
So my suggestion is this: Simple use two identical pieces of wire, and configure them as a dipole. Hang this dipole out in the clear, far away from any other objects, specially any conductive objects of significant size. Let the battery-powered NanoVNA dangle freely from that dipole. If the wires you are measuring are very much longer than the NanoVNA, then having the NanoVNA dangling there will cause very little error. But if the wires are short, then you need to isolate the instrument from the dipole, and that requires a good balun. Any imperfection of the balun, that introduces significant inductance or capacitance, will again cause an error in the measurement, and the presence of the NanoVNA near the wires will also change their resonant frequency. So better don't even try to measure short wires.
It turns out that an accurate measurement of a wire's real, own resonant frequency (or electrical length) is quite hard to do! And in practical applications, like antenna building, it's irrelevant to, because what you need to get right is the real resonance of the antenna, with all effects from nearby objects and of stuff connected to the antenna, like feedlines, balun, real (imperfect) ground, etc. In short, the real world, mentioned by Kent.
Manfred
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Real world. Interesting. If Hertz and Marconi stayed in the real world, would we have what we have now?
So, if the tool we have won't work, fine. I understand that. I have seen where random lengths of wires were bundled together and the return loss on various frequencies were charted. But I am not sure what tool was used or how the individual performed the test. That is why I am curious to know if the NanoVNA might be able to do this.
It is all good. Thanks guys for the reply.
Brian D
KF6BL
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They put an amp meter between the transmitter and the antenna.
Adjusted for MAX AMPS!
The output circuit has lots of taps and variable caps.Could be adjusted over a wide impedance range.50 Ohms was many years later.? ? ?Kent WA5VJB
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On Monday, June 20, 2022, 02:00:41 PM CDT, Brian Donaldson <brianb253@...> wrote:
Real world. Interesting. If Hertz and Marconi stayed in the real world, would we have what we have now?
So, if the tool we have won't work, fine. I understand that. I have seen where random lengths of wires were bundled together and the return loss on various frequencies were charted. But I am not sure what tool was used or how the individual performed the test. That is why I am curious to know if the NanoVNA might be able to do this.
It is all good. Thanks guys for the reply.
Brian D
KF6BL
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Their antennas were NOT resonant! But they kept trying different things until they got their signals heard where they wanted. They learned as they went along. Just like my first lousy 80 meter dipole¡.. way off but the pi network and the 6146 worked well enough to make contacts.
Dave K8WPE.
David J. Wilcox¡¯s iPad
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On Jun 20, 2022, at 3:12 PM, KENT BRITAIN <WA5VJB@...> wrote:
? They put an amp meter between the transmitter and the antenna.
Adjusted for MAX AMPS!
The output circuit has lots of taps and variable caps.Could be adjusted over a wide impedance range.50 Ohms was many years later. Kent WA5VJB
On Monday, June 20, 2022, 02:00:41 PM CDT, Brian Donaldson <brianb253@...> wrote:
Real world. Interesting. If Hertz and Marconi stayed in the real world, would we have what we have now?
So, if the tool we have won't work, fine. I understand that. I have seen where random lengths of wires were bundled together and the return loss on various frequencies were charted. But I am not sure what tool was used or how the individual performed the test. That is why I am curious to know if the NanoVNA might be able to do this.
It is all good. Thanks guys for the reply.
Brian D
KF6BL
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Hi Fred
How do you feed that 80m loop??
1:1?
1:2?
1:4?
Or monoband with a quarterwave 75ohm line and a 1:1 balun or current choke??
So.. I fact you can measure your loop... If you messure on a coax cable..
Dg9bfc sigi
Am 20.06.2022 21:13 schrieb KENT BRITAIN <WA5VJB@...>:
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They put an amp meter between the transmitter and the antenna.
Adjusted for MAX AMPS!
The output circuit has lots of taps and variable caps.Could be adjusted
over a wide impedance range.50 Ohms was many years later.? ? ?Kent WA5VJB
On Monday, June 20, 2022, 02:00:41 PM CDT, Brian Donaldson
<brianb253@...> wrote:
Real world. Interesting. If Hertz and Marconi stayed in the real world,
would we have what we have now?
So, if the tool we have won't work, fine. I understand that. I have seen
where random lengths of wires were bundled together and the return loss on
various frequencies were charted. But I am not sure what tool was used or
how the individual performed the test. That is why I am curious to know if
the NanoVNA might be able to do this.
It is all good. Thanks guys for the reply.
Brian D
KF6BL
|
Sure they were!? Those big taped coils in the transmitter outputs became antenna loading coils.
You could say the antenna by itself wasn't resonate, but the transmitter-antenna system was.
(Well, might be if the operator actually owned an amp meter!)
FYI, I have a spark gap system I build several years ago, and contend that it is ham legal!? ?You won't find it's design in any old copies of QST.
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On Monday, June 20, 2022, 04:04:35 PM CDT, David Wilcox K8WPE via groups.io <djwilcox01@...> wrote: Their antennas were NOT resonant!? But they kept trying different things until they got their signals heard where they wanted.? They learned as they went along.? Just like my first lousy 80 meter dipole¡.. way off but the pi network and the 6146 worked well enough to make contacts. Dave K8WPE. David J. Wilcox¡¯s iPad On Jun 20, 2022, at 3:12 PM, KENT BRITAIN <WA5VJB@...> wrote:
? They put an amp meter between the transmitter and the antenna.
Adjusted for MAX AMPS!
The output circuit has lots of taps and variable caps.Could be adjusted over a wide impedance range.50 Ohms was many years later.? ? Kent WA5VJB
? ? On Monday, June 20, 2022, 02:00:41 PM CDT, Brian Donaldson <brianb253@...> wrote:?
Real world. Interesting. If Hertz and Marconi stayed in the real world, would we have what we have now?
So, if the tool we have won't work, fine. I understand that. I have seen where random lengths of wires were bundled together and the return loss on various frequencies were charted. But I am not sure what tool was used or how the individual performed the test. That is why I am curious to know if the NanoVNA might be able to do this.
It is all good. Thanks guys for the reply.
Brian D
KF6BL
|
Yes, the NANOVNAs are capable of making these measurements. HOWEVER, and
that's a huge "however", the chassis of the NANOVNA needs to supply the
other portion of the wire. An end fed is only half the antenna. The other
half must be supplied by a long set of wires with a good connection to
earth (far more than a single earth rod) This is to provide a good
conductor against which the end fed whatever can work against.
Example: Ask yourself which of the following will radiate and why / why
not:
[image: image.png]
The top illustration is like connecting only one lead to a battery (if this
were DC). No current can flow as there is no return. Therefore, the top
will not radiate as there is no counterpoise, or, in more "accepted"
language among the amateur community, "ground".
The bottom will, indeed, radiate (a simple 1/2-wavelength dipole) as there
is a return for the current. This is analogous to connecting both
terminals of a battery (if this were DC).
Ideally the return for the chassis of the NANOVNA should be lossy to
prevent it from entering the measured resonant behavior of the EFW (end fed
wire).
Dave - W?LEV
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On Mon, Jun 20, 2022 at 7:00 PM Brian Donaldson <brianb253@...> wrote: Real world. Interesting. If Hertz and Marconi stayed in the real world,
would we have what we have now?
So, if the tool we have won't work, fine. I understand that. I have seen
where random lengths of wires were bundled together and the return loss on
various frequencies were charted. But I am not sure what tool was used or
how the individual performed the test. That is why I am curious to know if
the NanoVNA might be able to do this.
It is all good. Thanks guys for the reply.
Brian D
KF6BL
-- *Dave - W?LEV* *Just Let Darwin Work*
--
Dave - W?LEV
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On Mon, Jun 20, 2022 at 05:50 PM, W0LEV wrote: The top illustration is like connecting only one lead to a battery (if this
were DC). No current can flow as there is no return. Therefore, the top
will not radiate as there is no counterpoise, or, in more "accepted"
language among the amateur community, "ground".
Or, more to the point, it _may_ radiate in some manner, because any end-fed wire will find _something_ to act as the image antenna, whether that something is intentional or not. Whether or not the thing it finds also happens to be a "good" source for the image antenna is also an unknown variable. It could be somethibng useful, or it could be your feedline. We provide "ground" (whether a true earth or a capacitively coupled ground plane) or "counterpoises" to make the system more measurable and consistent. Thus, the point of all this measuring and whatnot is so we can somehow find a way to have reality and theory of our radiating systems correspond in some manner. Otherwise, don't even use a VNA. Just hang any old length of wire out the window and hope for the best. This has worked well for decades for many hams, but it is not something that is either repeatable or consistent.
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I'm not building an antenna. All I want to know is if the NanoVNA can show me return loss peaks with a single length of stranded wire. Nothing more. I have an antenna and it works just fine. Don't need an antenna.
If the NanoVNA cannot do a single wire return loss reading, then fine.
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Steve marsh (M0NMA)
David Wilcox K8WPE
