Re: Poor Quality 50 Ohm Load - Where to get accurate ones?
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
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Re: We started selling SAA2 with N-type RF connector and 4-inch display
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
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Re: Performance of my nanovna V2 clone - return loss of port 2 seems much too high ?
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
|
Re: We started selling SAA2 with N-type RF connector and 4-inch display
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.
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Re: We started selling SAA2 with N-type RF connector and 4-inch display
@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
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Re: O S L on antenna side of a balun / choke with stud terminals?
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
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Re: Bad V2 clones incoming
Michael, Please tell this newbee what indicates that the dynamic range is good.
Thanks
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Re: Poor Quality 50 Ohm Load - Where to get accurate ones?
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.
|
Re: O S L on antenna side of a balun / choke with stud terminals?
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
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Re: O S L on antenna side of a balun / choke with stud terminals?
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
toggle quoted message
Show quoted text
On Sunday, August 16, 2020, 6:16:32 PM CDT, Jerry Gaffke via groups.io <jgaffke@...> wrote: 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 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?
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Re: O S L on antenna side of a balun / choke with stud terminals?
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
|
Re: O S L on antenna side of a balun / choke with stud terminals?
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
|
Re: Poor Quality 50 Ohm Load - Where to get accurate ones?
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.
toggle quoted message
Show quoted text
On 8/16/20 8:17 AM, Dr. David Kirkby, Kirkby Microwave Ltd wrote: On Fri, 14 Aug 2020 at 02:34, Jim Lux <jimlux@...> wrote:
On 8/13/20 5:52 PM, Glen Jenkins WB4KTF wrote:
The 50 OHM load (SMA-Male) that came with my nanoVNA-H4 measures 51.13+ ohms. Not a good start for calibration. Where is a good source for GOOD
loads that are accurate?
that's a VSWR of 1.023:1 and a S11 of -39dB
That¡¯s true only if the reactance is zero.
How much are you willing to pay?
Pasternack has a SMA Male load (PE6002) for $38 Many RF engineers call them Pastercrap. I tested 10 Pastercrap loads and
not one met the specification.
For $1900 they'll sell you a 3.5mm load for a cal kit
up to 4GHz they claim S11 mag <-40dB
A Keysight load, with a better specification, would cost less, and would
actually meet its specification.
That's about the same as the load you have.
The chart in the data sheet actually shows better than -50dB at 1 GHz
That¡¯s ¡°typical¡±, but I don¡¯t believe much from Pastercrap.
My company could supply decent loads, but I would need to charge nearly
twice what a NanoVNA would cost.
<>
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Re: O S L on antenna side of a balun / choke with stud terminals?
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
|
Re: O S L on antenna side of a balun / choke with stud terminals?
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
toggle quoted message
Show quoted text
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?
|
Re: O S L on antenna side of a balun / choke with stud terminals?
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?
|
Re: O S L on antenna side of a balun / choke with stud terminals?
First, design the best antenna you can with your accepted compromises
(4NEC2 or EZNEC, and a few others).
Then, and only then, measure whatever impedance that structure presents,
and accomplish the match to whatever as a *circuit problem*. That does not
include shortening/legthening elements and/or adjusting spacing. You've
already designed the best antenna structure. Don't play with these
parameters which will only compromise your design. Treat the matching
exercise as a circuit problem,only!
Dave - WW?LEV
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Show quoted text
On Sun, Aug 16, 2020 at 6:44 PM Chris Wilson <chris@...> wrote: Hello David,
Sunday, August 16, 2020
How many attempt it is pretty irrelevant ;) The fact is, some antennas
allow this and one of the main purposes people on here will probably
buy a
nanoVNA is to check and hopefully improve their antenna efficiency
by whatever means its design makes available to them. Transformation
of impedance is surely more efficient at the antenna, rather than in
the radio room, feedline efficiency aside. LDF4-50 is pretty
efficient at HF, but that doesn't negate the fact that matching where
possible at the antenna end will be the most effective and efficient.
This particular antenna is a monoband two element cubical quad.
Element spacing has a marked effect on the driven element's
impedance, (as well as other factors), so I want to measure this at
the antenna, to decide the best compromises.
Best regards,
Chris mailto:chris@...
DE> How many hams actually match *at the feedpoint* to a 50-ohm coaxial
line?
DE> I'll bet very few. At VHF and UHF, yes, at the antenna match is
practical
DE> and usually accomplished, but not at HF.
DE> That's why I use open wire feeders where SWR losses are *far* less
than in
DE> coaxial cable and the feedline is not stressed even with SWR at full
DE> power. And......I use a single set of wires for 630 through 6-meters
with
DE> that system with home brew matching network.
DE> Antennas do not require being resonant to do a good job of radiating.
My
DE> system is not resonant (¡À jX = 0.00, the definition of resonance) in
any of
DE> the HF ham bands, but it does very well, both in practice and in the
4NEC2
DE> model. It's lowest 1/2-wavelength resonant frequency is 950 kHz, the
lower
DE> 1/3 of the AM BC band. I seriously doubt I'd do any better with
resonant
DE> dipoles for all the individual bands.
DE> Dave - W?LEV
DE> On Sun, Aug 16, 2020 at 6:07 PM Chris Wilson <chris@...>
wrote:
Hello David,
Sunday, August 16, 2020
Without knowing what impedance the antenna itself presents, how do I
know the best way to match it to the coax impedance?
Best regards,
Chris mailto:chris@...
DE> What's important is the load the antenna plus feedline present to
our
DE> modern transceivers. So, why the concern for 'at the antenna'
DE> measurements? Sure, its nice to know, but the coax contributes it's
own
DE> impedance transforming properties. If you must, make the
measurement
at
DE> the shack end of the feedline, and use a tool such as SimSmith to
take
out
DE> the impact of the coaxial line.
DE> Again, what is important is the load presented to the transmitter,
not
DE> necessarily what the antenna impedance is at the feedpoint. One
must
STILL
DE> consider the transmission line between the transmitter and the
antenna
DE> feedpoint to obtain this result.
DE> Dave - W?LEV
DE> On Sun, Aug 16, 2020 at 5:31 PM Jerry Gaffke via groups.io
<jgaffke=
[email protected]>> wrote:
Roger wrote:
You can clearly see that the two plots are nearly identical. What kind of coax?
I bet it isn't RG174.
I have seen significant differences when checking out an HF antenna
over
100 feet of RG8X.
I have a 20M dipole with a current balun attached to it which for
this
test I consider to be the "feedpoint" of the antenna.
Not totally clear which side of the balun you consider to be the
feedpoint
of the antenna
I assume this means you leave the balun attached to the antenna, and
only
calibrate out the coax.
Jerry, KE7ER
On Sun, Aug 16, 2020 at 09:47 AM, Roger Need wrote:
I have a 20M dipole with a current balun attached to it which for
this
test I
consider to be the "feedpoint" of the antenna. 55 feet of coax runs
back
to
the shack. First measurement with NanoVNA Saver was made at the feedpoint and
stored as an s1p file. The coax was then "calibrated out" and a
second
Saver
measurement made back in the shack. The first s1p file was then
loaded
and a
comparison was made. You can clearly see that the two plots are
nearly
identical.
Roger
--
*Dave - W?LEV*
*Just Let Darwin Work*
|
Re: O S L on antenna side of a balun / choke with stud terminals?
Sorry. You are in error. A conducting structure need not be resonant at
the operating frequency to be an efficient radiator. The function of an
'antenna tuner' is ONLY to establish a 50 ¡Àj0 ohm match at the input to the
transmitter from whatever the antenna / transmission line at the shack end
presents to the input of the matching network. It does, *N O T*....N O T
(!!!) 'tune' the antenna!!! It is just an impedance transforming network
consisting of adjustable reactive circuit elements. Become a bit familiar
with the Smith Chart and you will better understand.
I can adjust my matching network (a.k.a., antenna "tuner"), for example, to
produce a 50 ¡À j0.0 match on 7.2 MHz with the feedline connected to the
input of my matching network (a.k.a., antenna "tuner"). The measured
impedance at 7.200 MHz of my HF doublet is 10 - j80 ohms. The function
of the matching network (a.k.a., antenna "tuner") is to transform in a
passive manner that 10 - j80 ohms to 50 ¡À j 0.0 ohms. It in no way 'tunes'
the antenna. However, adjustment of the matching network in NO WAY, alters
the basic resonant structure of my doublet. The matching network does NOT
effect the antenna structure, itself. It only establishes a match of
whatever the doublet at the end of my parallel conductor transmission line
at the shack end presents to the input of the matching network. The
resonant structure of the antenna does not change with the adjustment of
the matching network! ! ! ! ! Even after transforming the measured 10 -
j80 ohms to 50 ¡À j0 ohms, the lowest 1/2-wavelength resonant frequency of
the doublet still remains at 950 kHz.
Dave - W?LEV
toggle quoted message
Show quoted text
On Sun, Aug 16, 2020 at 6:39 PM KENT BRITAIN <WA5VJB@...> wrote: The wire may be non-resonate without your home brew matching network,but
with the network it has to be. To be an efficient radiator, you haveto
resonate. Kent WA5VJB
On Sunday, August 16, 2020, 1:34:08 PM CDT, David Eckhardt <
davearea51a@...> wrote:
How many hams actually match *at the feedpoint* to a 50-ohm coaxial line?
I'll bet very few. At VHF and UHF, yes, at the antenna match is practical
and usually accomplished, but not at HF.
That's why I use open wire feeders where SWR losses are *far* less than in
coaxial cable and the feedline is not stressed even with SWR at full
power. And......I use a single set of wires for 630 through 6-meters with
that system with home brew matching network.
Antennas do not require being resonant to do a good job of radiating. My
system is not resonant (¡À jX = 0.00, the definition of resonance) in any of
the HF ham bands, but it does very well, both in practice and in the 4NEC2
model. It's lowest 1/2-wavelength resonant frequency is 950 kHz, the lower
1/3 of the AM BC band. I seriously doubt I'd do any better with resonant
dipoles for all the individual bands.
Dave - W?LEV
On Sun, Aug 16, 2020 at 6:07 PM Chris Wilson <chris@...> wrote:
Hello David,
Sunday, August 16, 2020
Without knowing what impedance the antenna itself presents, how do I
know the best way to match it to the coax impedance?
Best regards,
Chris mailto:chris@...
DE> What's important is the load the antenna plus feedline present to our
DE> modern transceivers. So, why the concern for 'at the antenna'
DE> measurements? Sure, its nice to know, but the coax contributes it's
own
DE> impedance transforming properties. If you must, make the measurement
at
DE> the shack end of the feedline, and use a tool such as SimSmith to take
out
DE> the impact of the coaxial line.
DE> Again, what is important is the load presented to the transmitter, not
DE> necessarily what the antenna impedance is at the feedpoint. One must
STILL
DE> consider the transmission line between the transmitter and the antenna
DE> feedpoint to obtain this result.
DE> Dave - W?LEV
DE> On Sun, Aug 16, 2020 at 5:31 PM Jerry Gaffke via groups.io <jgaffke=
[email protected]>> wrote:
Roger wrote:
You can clearly see that the two plots are nearly identical. What kind of coax?
I bet it isn't RG174.
I have seen significant differences when checking out an HF antenna
over
100 feet of RG8X.
I have a 20M dipole with a current balun attached to it which for
this
test I consider to be the "feedpoint" of the antenna.
Not totally clear which side of the balun you consider to be the
feedpoint
of the antenna
I assume this means you leave the balun attached to the antenna, and
only
calibrate out the coax.
Jerry, KE7ER
On Sun, Aug 16, 2020 at 09:47 AM, Roger Need wrote:
I have a 20M dipole with a current balun attached to it which for
this
test I
consider to be the "feedpoint" of the antenna. 55 feet of coax runs
back
to
the shack. First measurement with NanoVNA Saver was made at the feedpoint and
stored as an s1p file. The coax was then "calibrated out" and a
second
Saver
measurement made back in the shack. The first s1p file was then
loaded
and a
comparison was made. You can clearly see that the two plots are
nearly
identical.
Roger
--
*Dave - W?LEV*
*Just Let Darwin Work*
--
*Dave - W?LEV*
*Just Let Darwin Work*
|
Re: Performance of my nanovna V2 clone - return loss of port 2 seems much too high ?
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.
toggle quoted message
Show quoted text
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]
|
Dr. David Kirkby, Kirkby Microwave Ltd
Roger Need
