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On Sun, Aug 16, 2020 at 05:38:07PM -0700, Roger Need via groups.io wrote:

The puzzle is this:

if we split the transmission line at one end and bend the split ends to be
180 degrees apart charge acceleration will now occur and we will get EM
radiation.

How does this give us charge acceleration when a 90 degree bend in the
transmission line does not?
Assume the end of the transmission line is open, terminated, or shorted,
whatever works best.

I took an excerpt from a textbook on this subject for you that answers your question. Here is a link...

That's very interesting, thanks!

On 8/17/20 3:36 AM, Stephen Laurence wrote:

Followup from my previous post....
I have just crushed my first female sma on my v2. The connector would not go very far so I took it off, before I started tightening the nut) and looked down the hole.
The leaves of the female socket were bent over but not completely crushed. I got out my Chinese “microscope” and managed to straighten them with the point of a small sewing needle initially, using the eye end for the final nudges. I took pictures of before and after but could not attach them using an Ipad. When I get to a computer, I can post them if anyone is interested.
I looped a short between the two ports and did a scan from 2 to 4ghz and the four traces seemed to be what I would expect, suggesting there was no huge transmission irrregulariy on the repaired connector.
I shall be very careful in future (and throw away all those sma standards that rotate the pin when tightening up). My 4” SAAv2 with n connectors, when it arrives, will have sma adaptors attached and be the main machine. Replacing sma connectors on these devices is not something I want to do very often.
How many of us have had to do this to sma connectors, I wonder.

Connector savers are your friend - I confess, though, that $20 in connector savers (or whatever a M-F thru costs) on a $50 instrument makes me wonder.

Having a $50 VNA changes the whole mindset

On Mon, 17 Aug 2020 at 12:25, Dr. David Kirkby <
drkirkby@...> wrote:

On Mon, 17 Aug 2020 at 01:48, Hugen <hugen@...> wrote:

The load of nanoVNA-H4 is designed according to 6GHz that S11 is better
than -30dB. We can guarantee that S11 is better than -40dB at 1GHz. The 51
ohm resistor is matched in the laboratory, and we need to offset the
parasitic parameters at high frequencies.

How do you measure the return loss?

What I mean is what VNA (NanoVNA?) and what calibration kit?

Dave

On Mon, 17 Aug 2020 at 01:48, Hugen <hugen@...> wrote:

The load of nanoVNA-H4 is designed according to 6GHz that S11 is better
than -30dB. We can guarantee that S11 is better than -40dB at 1GHz. The 51
ohm resistor is matched in the laboratory, and we need to offset the
parasitic parameters at high frequencies.

How do you measure the return loss?

Dave

Followup from my previous post....

I have just crushed my first female sma on my v2. The connector would not go very far so I took it off, before I started tightening the nut) and looked down the hole.

The leaves of the female socket were bent over but not completely crushed. I got out my Chinese “microscope” and managed to straighten them with the point of a small sewing needle initially, using the eye end for the final nudges. I took pictures of before and after but could not attach them using an Ipad. When I get to a computer, I can post them if anyone is interested.

I looped a short between the two ports and did a scan from 2 to 4ghz and the four traces seemed to be what I would expect, suggesting there was no huge transmission irrregulariy on the repaired connector.

I shall be very careful in future (and throw away all those sma standards that rotate the pin when tightening up). My 4” SAAv2 with n connectors, when it arrives, will have sma adaptors attached and be the main machine. Replacing sma connectors on these devices is not something I want to do very often.

How many of us have had to do this to sma connectors, I wonder.

Steve L. G7PSZ

Any one with bad return loss on port 2 (less than 20dB) at 1.5 Ghz ?

On Sun, Aug 16, 2020 at 11:18 PM Peter Ide-Kostic via groups.io
<on7yi.pik973@...> wrote:

Thank you for your reply

1) Please find below the trace between 1.4 and 1.6 ghz, of course there no
change (as expected)

[image: image.png]
2) The cables are fine I am sure, they are quality SS405 cables of 25 cm

3) To make a long story short, it is the owner of the Aliexpress shop
himself who informed me that he could no longer deliver the genuine model
<> that I had initially ordered in the
April time frame as he had switched supplier. I do not want to enter into
details but I was quite lucky with this specific transaction on aliexpress,
I waited a very long time (with at least 3 different shipping attempts) .
When the device finalmly arrived it had been damaged by transport . The
seller then simply offered me to send me the models coming from his new
supplier which I have accepted.

On Sun, Aug 16, 2020 at 10:55 PM CT2FZI <ct2fzi@...> wrote:

Did you calibrate from 1.4GHz to 1.6GHz and tried to measure it again?

Did you tried using another cable?

Why you say it's a clone?

Cheers

A domingo, 16/08/2020, 21:48, Peter Ide-Kostic <on7yi.pik973@...>
escreveu:

Hello,

I bought a nanovna V2 <> on

Aliexpress

a
while ago. When I received it, I realized that it was a clone which I

did

not expect, but ok, I managed (as usual)

I then checked the performance vis a vis of the official nanovna-v2
specifications <> .
Fortunately, on the positive side, there was no problem regarding the

S21

dynamic range and regarding the S11 noise floor that both met the

nanovna

V2 specifications. However I was a bit puzzled to discover that the

return

loss of port 2 of my clone was unfortunately much higher than what is
officially specified....

official return loss specifications for port 2
20dB at 1.5 Ghz, 13 dB at 3 ghz

my measurements after calibration (see picture)
15.7 dB at 1.5 Ghz and 9.5 dB at 3Ghz

I wondering if
- I am doing something wrong the way I did this measurement
- if I am the only owner of a clone with this specific performance

problem

on port 2
- if owners of the genuine nanovna V2 also have the performance issue
- what is the value of the attenuator that you possibly use on port 2
during calibration to compensate for the sub-optimal return loss (I use
between 6 and 12dB depending on the accuracy I need and the dynamic

range I

am willing to sacrifice)

Thanks for sharing your return on experience regarding this issue

[image: image.png]

I see that nanoVNA-H, on its PCB v3.4, has an expansion port. Are there already examples of use of this port? I would like to use it for a bluetooth interface.
Regards
Piero, I0KPT

Dear all,

I have several nanovnas (some lent to friends), a tinysa and a N-connector v2 on its way. I also have a Deepace Kc901s with N-connectors, an ancient (1990’s) home made spectrum analyser to 100mhz with bnc connectors and several lab-standard HP141 and other boatanchors (destined for disposal).

Building up a stock of sma interconnectors, sex changers, pigtails etc was not hugely expensive. My N connected devices will probably have permanent sma adapters attached, BUT, when I want a robust setup to survive being dropped, pulled onto the floor by the heavy cables etc, the N-connectors will survive whereas the sma ones will not.

I do not want another connector type to rear its head, unless it is a screw terminal which I connect a wire or banana plug to it, but generally it is not suitable for rf!

I am happy with what I have got.

When out of the house, the Tinysa is mostly going to be a pocket/ portable device with sniffer/ stub aerial, so sma is ideal.

Steve L, G7PSZ.

@Shirley Dulcey KE1L
I have seen China-made APC7-to-N adapters going for <USD20 online; i.e. about a third of the nanoVna's cost. You will need a minimum of one cable and two adapters to test a two-port DUT. Yes, I do see your point that adopting the APC7 will double or triple the cost of nanoVna ownership, but what other recourse is available for measuring a DUT with same sex connectors (i.e. non-insertable devices)?

@ Jerry Gaffke
Prior to my post, APC7 has never been mentioned in this group. :-) So, there's no APC7 camp, not yet!

Leong, 9W2LC

Roger and Jim.

I looked at Roger's png first, and that does explain why a dipole radiates and a transmission line does not.
Will dig into Jim's antenna book when I have a chance.

Many thanks for the quick answers to a complicated question.

Jim wrote:

You would have problems in other senses, some of which manifest in what you might call efficiency.
The radiation resistance gets very low, so the current, for a given radiated power, gets very high.
So, for a "real antenna" that has ohmic loss, that becomes a big fraction of the "power at the terminals"

A transmission line with an open at the end has zero current and maximum voltage there.
A very short dipole would be a minor step away from that case,
Seems the impedance into such a short dipole should be very high and the antenna current thus very low.
Though Jim used the phrase "for a given radiated power", which complicates things some.

Guess I better read that book.

Jerry, KE7ER

Michael, Please tell this newbee what indicates that the dynamic range is good.
Thanks

The load of nanoVNA-H4 is designed according to 6GHz that S11 is better than -30dB. We can guarantee that S11 is better than -40dB at 1GHz. The 51 ohm resistor is matched in the laboratory, and we need to offset the parasitic parameters at high frequencies.

On Sun, Aug 16, 2020 at 04:47 PM, Jerry Gaffke wrote:

The puzzle is this:

if we split the transmission line at one end and bend the split ends to be
180 degrees apart charge acceleration will now occur and we will get EM
radiation.

How does this give us charge acceleration when a 90 degree bend in the
transmission line does not?
Assume the end of the transmission line is open, terminated, or shorted,
whatever works best.

I took an excerpt from a textbook on this subject for you that answers your question. Here is a link...



Roger

Takes a bit to think of your Yagi antenna as a 50 to 377 Ohm impedance transformer.
And if you are building Stealth aircraft, you want them to look like 377, not 50 Ohm dummy loads!
Kent WA5VJB

On 8/16/20 4:47 PM, Jerry Gaffke via groups.io wrote:

Sounds right mostly.

This basic dipole will radiate even if the radiating elements are quite short compared to the 30M wavelength

Though I'd guess not very efficiently.

Just as efficiently in one sense - an infinitesimal dipole still radiates.

You would have problems in other senses, some of which manifest in what you might call efficiency. The radiation resistance gets very low, so the current, for a given radiated power, gets very high. So, for a "real antenna" that has ohmic loss, that becomes a big fraction of the "power at the terminals"

Also, if you have a 50 ohm source, you either have a big mismatch (making it hard to push power into the 1 ohm antenna) or you have a matching network to transform it, which will have loss.

There are lots of interesting designs where the power amplifier is integrated as part of the antenna which aren't in the "must have 50 ohms" bucket. For instance, transistor amplifiers have a "natural" output impedance that is very low, so they could efficiently couple to a low resistance feed. (you still have the ohmic loss in the antenna issue).

The puzzle is this:

if we split the transmission line at one end and bend the split ends to be 180 degrees apart charge acceleration will now occur and we will get EM radiation.

How does this give us charge acceleration when a 90 degree bend in the transmission line does not?
Assume the end of the transmission line is open, terminated, or shorted, whatever works best.
Again, your answer sounds right.
And I suspect a full explanation of the basic physics would take some doing.
Just wondering if there is a simple answer.

There's a very nice development of this in Kraus's Antennas text book where he discusses the transformation from propagating wave in free space to propagating wave in a two wire transmission line of arbitrary impedance. (Chapter 2 in the 1988 2nd edition, you can find it as a pdf online - it's probably the same in all editions - My father's older edition has the same exposition). In later chapters, the theory is developed.

After all, you can make a low loss impedance transformer with a tapered transmission line.

And a horn antenna is literally an aperture in free space transforming to a waveguide, which can then transform to a balanced transmission line. The longer the horn and the more gradual the transition, the better it works.

Jerry, KE7ER
On Sun, Aug 16, 2020 at 04:25 PM, Roger Need wrote:

On Sun, Aug 16, 2020 at 02:33 PM, <namerati@...> wrote:

If all that is true, what actually causes an antenna (or any structure)
to resonate? Are they merely transformers matching the input line to the
impedance of free space? Why not just then wind a 50 to 376 ohm matching
transformer and leave the secondary open?

Antennas are actually a type of "transducer" which is a device that converts
energy from one form to another. In the case of an antenna they convert RF
electric current to electromagnetic (EM) waves that are radiated into space.
How do we create an EM wave? Whenever charges are accelerated an
electromagnetic field is created. This acceleration occurs whenever a charge
changes direction or velocity.

For example take the case of some twin lead with a signal generator set for 10
MHz. at one end and open at the other with everything sitting in free space.
No radiation will take place. However if we split the transmission line at one
end and bend the split ends to be 180 degrees apart charge acceleration will
now occur and we will get EM radiation. This simple dipole antenna and
transmission line form a simple antenna system. This basic dipole will radiate
even if the radiating elements are quite short compared to the 30M wavelength
of the RF signal generator source. This can be seen in this animation graphic
link ....



So far I have not said anything about resonance. If we increase the length of
the dipole arms until they are 1/4 wavelength each (1/2 wavelength end-to-end)
we will be at the resonant frequency of the dipole. Under these conditions the
current and voltage are exactly in phase at the feed point and the antenna
feedpoint impedance is purely resistive, with zero reactive component. If we
are greater or less than 1/2 wavelength there will be a resistive and a
reactive component.

In summary charge acceleration causes EM radiation and resonance is not
required to radiate. In fact non-resonant antennas can be quite efficient
radiators especially if matching networks are used at the antenna feedpoint to
offset the reactance.

Roger

Sounds right mostly.

This basic dipole will radiate even if the radiating elements are quite short compared to the 30M wavelength

Though I'd guess not very efficiently.


The puzzle is this:

if we split the transmission line at one end and bend the split ends to be 180 degrees apart charge acceleration will now occur and we will get EM radiation.

How does this give us charge acceleration when a 90 degree bend in the transmission line does not?
Assume the end of the transmission line is open, terminated, or shorted, whatever works best.

Again, your answer sounds right.
And I suspect a full explanation of the basic physics would take some doing.
Just wondering if there is a simple answer.

Jerry, KE7ER



On Sun, Aug 16, 2020 at 04:25 PM, Roger Need wrote:

On Sun, Aug 16, 2020 at 02:33 PM, <namerati@...> wrote:

If all that is true, what actually causes an antenna (or any structure)
to resonate? Are they merely transformers matching the input line to the
impedance of free space? Why not just then wind a 50 to 376 ohm matching
transformer and leave the secondary open?

Antennas are actually a type of "transducer" which is a device that converts
energy from one form to another. In the case of an antenna they convert RF
electric current to electromagnetic (EM) waves that are radiated into space.
How do we create an EM wave? Whenever charges are accelerated an
electromagnetic field is created. This acceleration occurs whenever a charge
changes direction or velocity.

For example take the case of some twin lead with a signal generator set for 10
MHz. at one end and open at the other with everything sitting in free space.
No radiation will take place. However if we split the transmission line at one
end and bend the split ends to be 180 degrees apart charge acceleration will
now occur and we will get EM radiation. This simple dipole antenna and
transmission line form a simple antenna system. This basic dipole will radiate
even if the radiating elements are quite short compared to the 30M wavelength
of the RF signal generator source. This can be seen in this animation graphic
link ....



So far I have not said anything about resonance. If we increase the length of
the dipole arms until they are 1/4 wavelength each (1/2 wavelength end-to-end)
we will be at the resonant frequency of the dipole. Under these conditions the
current and voltage are exactly in phase at the feed point and the antenna
feedpoint impedance is purely resistive, with zero reactive component. If we
are greater or less than 1/2 wavelength there will be a resistive and a
reactive component.

In summary charge acceleration causes EM radiation and resonance is not
required to radiate. In fact non-resonant antennas can be quite efficient
radiators especially if matching networks are used at the antenna feedpoint to
offset the reactance.

Roger

I used Pasternack as an example of what's available at a variety of retail price points. Not as a recommendation of what to buy.

It was too much trouble to hunt through Keysight's website to look for loads, calkits, etc., but yes, they have them, and I think I'd trust them more than Pasternack.

On Sun, Aug 16, 2020 at 02:33 PM, <namerati@...> wrote:

If all that is true, what actually causes an antenna (or any structure)
to resonate? Are they merely transformers matching the input line to the
impedance of free space? Why not just then wind a 50 to 376 ohm matching
transformer and leave the secondary open?

Antennas are actually a type of "transducer" which is a device that converts energy from one form to another. In the case of an antenna they convert RF electric current to electromagnetic (EM) waves that are radiated into space. How do we create an EM wave? Whenever charges are accelerated an electromagnetic field is created. This acceleration occurs whenever a charge changes direction or velocity.

For example take the case of some twin lead with a signal generator set for 10 MHz. at one end and open at the other with everything sitting in free space. No radiation will take place. However if we split the transmission line at one end and bend the split ends to be 180 degrees apart charge acceleration will now occur and we will get EM radiation. This simple dipole antenna and transmission line form a simple antenna system. This basic dipole will radiate even if the radiating elements are quite short compared to the 30M wavelength of the RF signal generator source. This can be seen in this animation graphic link ....



So far I have not said anything about resonance. If we increase the length of the dipole arms until they are 1/4 wavelength each (1/2 wavelength end-to-end) we will be at the resonant frequency of the dipole. Under these conditions the current and voltage are exactly in phase at the feed point and the antenna feedpoint impedance is purely resistive, with zero reactive component. If we are greater or less than 1/2 wavelength there will be a resistive and a reactive component.

In summary charge acceleration causes EM radiation and resonance is not required to radiate. In fact non-resonant antennas can be quite efficient radiators especially if matching networks are used at the antenna feedpoint to offset the reactance.

Roger

I think the question comes down to what makes the antenna structure radiate efficiently.
This usually involves getting some conductors up that are a significant fraction of the wavelength.
And at least some of us are curious in what direction it radiates.

Resonant is not so much an issue.
We can match the impedance of almost anything with the appropriate antenna tuner.

That "impedance of free space" thing is a new concept for me, rather cool.
Seems to be an integral part of how a radio wave propagates through space,
but not so much with how we launch it into said space.


Jerry, KE7ER

On Sun, Aug 16, 2020 at 01:07:50PM -0700, Roger Need via groups.io wrote:

On Sun, Aug 16, 2020 at 11:39 AM, KENT BRITAIN wrote:

? To be an efficient radiator, you have to
resonate.???? Kent WA5VJB

This is not true. Many types of antenna systems are "efficient radiators" off their resonant frequency. Rather than go into a long discussion here I will refer to this post by Owen Duffy because he has detailed examples.

From his article

"It is often that one hears in QSO, one OM to another, describing their antenna and stressing the importance of >>resonance, almost as qualification that if the antenna is resonant, then it performs well, and that by implication a
non- resonant antenna has poor performance.

Whilst the importance of resonance is often parroted on the bands, reputable texts do not seem to echo the sentiment."

If all that is true, what actually causes an antenna (or any structure) to resonate? Are they merely transformers matching the input line to the impedance of free space? Why not just then wind a 50 to 376 ohm matching transformer and leave the secondary open?