|
Hey there knowladge base people,
I’m H4 user. I’ve been tuning some EFHW`s and checking various UHF/VHF aerials for handhelds for a while now. HF’ I’ve build 49:1 un un 20m wire for 7,14,21,28 mhz frequencies. Usually display set 6-29Mhz and calibrate VNA. During the tuning proces I usually make the wire little longer and than shorten it by 15-20cm and than watch the SWR and resonance on freq. I intend to use. Here is the question: Why does the resonant frequency and SWR are not same?
From previous discussions here, I’ve gained awareness that all measurements are more accurate when choosing smaller Span between the stimulus say insted 6-29mhz choosing 6-8mhz (40m band) - 20-22mhz for (15m band). I’ve tried to measure smaller section with similar results those being: when Recall from calibrated memory say 6-8mhz for tuning on morse portion of 7mhz band, the SWR will be say 7.030 yet the resonance displayed on thel left will be @ 6.870
Why is this happening ? Am I missing some technical or physical understanding ?
J. OK4SU 73
|
Hi,
Resonance just indicates that the reactive component (inductive or capacitive) of the impedance is 0.
But since impedance contains both resistance and reactance Z=R±jX in order to acheive an SWR of 1:1 Z must be 50±j0.
So the resistive compnent of the impedance must be 50 ohms whilst the reactive component must be 0 this would produce an SWR of 1:1.
So whilst the reactive component may be 0 it is not a given that the resistive component is 50 ohms.
If it is significantly different from 50 ohms then either side of resonance (X=0) the total complex impedance (R±jX) may come closer to 50 ohms giving a dip in the SWR at other than resonance.
For this reason it is good to overlay the R, X and Z plots on the SWR or return loss graph.
Martin
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On 04/09/2024 1:05 pm, Jakub Sutorý via groups.io wrote: Hey there knowladge base people,
I’m H4 user. I’ve been tuning some EFHW`s and checking various UHF/VHF aerials for handhelds for a while now. HF’ I’ve build 49:1 un un 20m wire for 7,14,21,28 mhz frequencies. Usually display set 6-29Mhz and calibrate VNA. During the tuning proces I usually make the wire little longer and than shorten it by 15-20cm and than watch the SWR and resonance on freq. I intend to use. Here is the question: Why does the resonant frequency and SWR are not same?
From previous discussions here, I’ve gained awareness that all measurements are more accurate when choosing smaller Span between the stimulus say insted 6-29mhz choosing 6-8mhz (40m band) - 20-22mhz for (15m band). I’ve tried to measure smaller section with similar results those being: when Recall from calibrated memory say 6-8mhz for tuning on morse portion of 7mhz band, the SWR will be say 7.030 yet the resonance displayed on thel left will be @ 6.870
Why is this happening ? Am I missing some technical or physical understanding ?
J. OK4SU 73
|
Ok with Martin :)
What is called resonance frequency is a frequency for which the impedance is purely resistive (zero reactive). This frequency is independent of the impedance of the power supply line (50 Ω 600 Ω etc.)
The SWR that you measure with a NanoVNA, depending on the frequency, goes through minima that depend on the normalization impedance of the NanoVNA (50 Ω).
If you want to understand the difference, you have to switch successively from the SWR display to the Smith display.
Always remember to read the impedance expressed in the form A + jB
A is the resistive part in series with the reactive part, both expressed in ohms
--
F1AMM
François
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-----Message d'origine----- De la part de Jakub Sutorý Envoyé : mercredi 4 septembre 2024 11:05
|
How did you connect VNA to antenna?.
I understand you are connecting VNA to 1:7 (49 is squared 7) low impedance side transformer, which is not ideal, so modifies the antenna impedance. Is there a piece of coax to connect VNA-transformer? If yes, did you compensate cable length any way? Have the antenna a counter poise 0,05L? If does not, then the feeder is part of your antenna and it modifies impedance too.
If you load transformer antenna side with 2400R, the VNA will show an impedance curve, smith graph, close to 50R but complex values too. See attached picture.
|
A tip:
To avoid breaking the SMA base on the NanoVNA,
leave the small original SMA cords and place the SMA <-> BNC transition at the end of the cord. With the calibration, this length is neutralized
Making measurements on an antenna fed at the end is not very useful. The measurements have no meaning.
Mount your antenna at height, with its onboard transformer. Connect the transformer to your station by a coaxial cable. If possible, ground the station input and take the measurements at this level. You will see the Antenna + transformer + cable effect. In any case, you will be forced to install an impedance adapter at your station.
You can have fun making measurements on a transformer alone but that will not prejudge the real behavior with an antenna because of the antenna reactive that you will not be able to simulate with the transformer alone.
--
F1AMM
François
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-----Message d'origine----- De la part de Juan Pablo EA4CIV Envoyé : mercredi 4 septembre 2024 15:23
|
Here is a non-mathematical explanation of what's going on: http://on5au.be/documents/Standing%20Wave%20and%20SWR.pdfThe standard expression of impedance (impedance explicitly implies the presence of a reactive component) is Z = R ± jX. Resonance is DEFINED where the ± jX term is identically zero. R represents real resistance ONLY. ONLY the R term participates in transmission and reception. The complex term only modifies phase of R. Consider the following Smith Chart plot: [image: image.png] The ONLY position on the chart where resonance occurs is dead center or "bull's eye". I've also drawn a 2:1 SWR circle on the chart (the internal dotted circle). Anything on the circle exhibits a 2:1 SWR. Both the real part and reactive portion of the impedance change as one moves on the circle. But the SWR is ALWAYS 2:1. Further, I've plotted a point on the chart which on first examination, appears miles off a "reasonable" SWR. That point is 890 - j418 ohms. Would you think the resulting SWR would keep the transmitter happy? Well, in spite of the values, it does with an SWR of 1.58:1 - not bad. The qualitative conclusion here is that a "wild" impedance value of 890 - j418 which is far from resonance can and does yield an acceptable SWR. Dave - WØLEV On Wed, Sep 4, 2024 at 9:05 AM Jakub Sutorý via groups.io <j4ku8suti= gmail.com@groups.io> wrote: Hey there knowladge base people,
I’m H4 user. I’ve been tuning some EFHW`s and checking various UHF/VHF
aerials for handhelds for a while now. HF’ I’ve build 49:1 un un 20m wire
for 7,14,21,28 mhz frequencies. Usually display set 6-29Mhz and calibrate
VNA. During the tuning proces I usually make the wire little longer and
than shorten it by 15-20cm and than watch the SWR and resonance on freq. I
intend to use. Here is the question: Why does the resonant frequency and
SWR are not same?
From previous discussions here, I’ve gained awareness that all
measurements are more accurate when choosing smaller Span between the
stimulus say insted 6-29mhz choosing 6-8mhz (40m band) - 20-22mhz for (15m
band). I’ve tried to measure smaller section with similar results those
being: when Recall from calibrated memory say 6-8mhz for tuning on morse
portion of 7mhz band, the SWR will be say 7.030 yet the resonance displayed
on thel left will be @ 6.870
Why is this happening ? Am I missing some technical or physical
understanding ?
J. OK4SU 73
-- *Dave - WØLEV* -- Dave - WØLEV
|
The qualitative conclusion here is that a "wild"
impedance value of 890 - j418 which is far from resonance can and does yield an acceptable
SWR. I guess there might be a mistake If Z=890 + j418 Ω then, relative to 50 Ω ROS=21.7 |S11| = 0.91 S11 = 0.91 -j 0.04 In fact the point you have drawn does indeed produce a ROS < 2 but the impedance it represents is not 890 + j418 Ω or the normalization impedance, which you do not specify, is not 50 Ω -- F1AMM François De la part de W0LEV Envoyé : mercredi 4 septembre 2024 18:55
|
You are so correct. In my many models and in using SimSmith, the "last" was left with an optional Zo of 1050 ohms, NOT 50 OHMS! The 1050 ohms was input into the model to simulate the effect of an ideal 21:1 BB transformer. I didn't notice or remember that when I hit "copy". Thank you for calling out my error! Dave - WØLEV On Wed, Sep 4, 2024 at 5:58 PM François via groups.io <18471= free.fr@groups.io> wrote: The qualitative conclusion here is that a "wild"
impedance value of 890 - j418 which is far from resonance can and does yield an acceptable
SWR. I guess there might be a mistake
If Z=890 + j418 Ω then, relative to 50 Ω
ROS=21.7
|S11| = 0.91
S11 = 0.91 -j 0.04
In fact the point you have drawn does indeed produce a ROS < 2 but the
impedance it represents is not
890 + j418 Ω or the normalization impedance, which you do not specify, is
not 50 Ω
--
F1AMM
François
De la part de W0LEV
Envoyé : mercredi 4 septembre 2024 18:55
-- *Dave - WØLEV* -- Dave - WØLEV
|
Would it be correct to state that for transmit purpose - the SWR is the defining component, not the resonance of the antenna proper ? On Wed, Sep 4, 2024 at 1:03 PM W0LEV via groups.io <davearea51a= gmail.com@groups.io> wrote: You are so correct. In my many models and in using SimSmith, the "last"
was left with an optional Zo of 1050 ohms, NOT 50 OHMS! The 1050 ohms was
input into the model to simulate the effect of an ideal 21:1 BB
transformer. I didn't notice or remember that when I hit "copy".
Thank you for calling out my error!
Dave - WØLEV
On Wed, Sep 4, 2024 at 5:58 PM François via groups.io <18471=
free.fr@groups.io> wrote:
The qualitative conclusion here is that a "wild"
impedance value of 890 - j418 which is far from resonance can and does yield an acceptable
SWR. I guess there might be a mistake
If Z=890 + j418 Ω then, relative to 50 Ω
ROS=21.7
|S11| = 0.91
S11 = 0.91 -j 0.04
In fact the point you have drawn does indeed produce a ROS < 2 but the
impedance it represents is not
890 + j418 Ω or the normalization impedance, which you do not specify, is
not 50 Ω
--
F1AMM
François
De la part de W0LEV
Envoyé : mercredi 4 septembre 2024 18:55
--
*Dave - WØLEV*
--
Dave - WØLEV
|
For an antenna, if it doesn't resonate, it really doesn't radiate!
Ok, Ok, there is some minor leakage from a dummy load.
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On Monday, September 30, 2024 at 12:10:26 PM CDT, Salvatore Terress <salvatoreterress@...> wrote: Would it be correct to state that for transmit purpose - the SWR is the defining component, not the resonance of the antenna proper ? On Wed, Sep 4, 2024 at 1:03 PM W0LEV via groups.io <davearea51a= gmail.com@groups.io> wrote: You are so correct. In my many models and in using SimSmith, the "last"
was left with an optional Zo of 1050 ohms, NOT 50 OHMS! The 1050 ohms was
input into the model to simulate the effect of an ideal 21:1 BB
transformer. I didn't notice or remember that when I hit "copy".
Thank you for calling out my error!
Dave - WØLEV
On Wed, Sep 4, 2024 at 5:58 PM François via groups.io <18471=
free.fr@groups.io> wrote:
The qualitative conclusion here is that a "wild"
impedance value of 890 - j418 which is far from resonance can and does yield an acceptable
SWR. I guess there might be a mistake
If Z=890 + j418 Ω then, relative to 50 Ω
ROS=21.7
|S11| = 0.91
S11 = 0.91 -j 0.04
In fact the point you have drawn does indeed produce a ROS < 2 but the
impedance it represents is not
890 + j418 Ω or the normalization impedance, which you do not specify, is
not 50 Ω
--
F1AMM
François
De la part de W0LEV
Envoyé : mercredi 4 septembre 2024 18:55
--
*Dave - WØLEV*
--
Dave - WØLEV
|
To keep the transmitter happy, yes, a low SWR is the best. For most efficient operation of the antenna/feedline resonance is best. Dave - WØLEV < http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> Virus-free.www.avg.com < http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> On Mon, Sep 30, 2024 at 5:10 PM Salvatore Terress via groups.io <salvatoreterress@...> wrote: Would it be correct to state that for transmit purpose - the SWR is the
defining component, not the resonance of the antenna proper ?
On Wed, Sep 4, 2024 at 1:03 PM W0LEV via groups.io <davearea51a=
gmail.com@groups.io> wrote:
You are so correct. In my many models and in using SimSmith, the "last"
was left with an optional Zo of 1050 ohms, NOT 50 OHMS! The 1050 ohms was
input into the model to simulate the effect of an ideal 21:1 BB
transformer. I didn't notice or remember that when I hit "copy".
Thank you for calling out my error!
Dave - WØLEV
On Wed, Sep 4, 2024 at 5:58 PM François via groups.io <18471=
free.fr@groups.io> wrote:
The qualitative conclusion here is that a "wild"
impedance value of 890 - j418 which is far from resonance can and
does
yield an acceptable
SWR. I guess there might be a mistake
If Z=890 + j418 Ω then, relative to 50 Ω
ROS=21.7
|S11| = 0.91
S11 = 0.91 -j 0.04
In fact the point you have drawn does indeed produce a ROS < 2 but the
impedance it represents is not
890 + j418 Ω or the normalization impedance, which you do not specify,
is
not 50 Ω
--
F1AMM
François
De la part de W0LEV
Envoyé : mercredi 4 septembre 2024 18:55
--
*Dave - WØLEV*
--
Dave - WØLEV
-- *Dave - WØLEV* -- Dave - WØLEV
|
This ends my dream of a non-resonant rhombic... ...poof On 2024-09-30 12:18, KENT BRITAIN wrote: For an antenna, if it doesn't resonate, it really doesn't radiate!
Ok, Ok, there is some minor leakage from a dummy load.
On Monday, September 30, 2024 at 12:10:26 PM CDT, Salvatore Terress <salvatoreterress@...> wrote:
Would it be correct to state that for transmit purpose - the SWR is the
defining component, not the resonance of the antenna proper ?
On Wed, Sep 4, 2024 at 1:03 PM W0LEV via groups.io <davearea51a=
gmail.com@groups.io> wrote:
You are so correct. In my many models and in using SimSmith, the "last"
was left with an optional Zo of 1050 ohms, NOT 50 OHMS! The 1050 ohms was
input into the model to simulate the effect of an ideal 21:1 BB
transformer. I didn't notice or remember that when I hit "copy".
Thank you for calling out my error!
Dave - WØLEV
On Wed, Sep 4, 2024 at 5:58 PM François via groups.io <18471=
free.fr@groups.io> wrote:
The qualitative conclusion here is that a "wild"
impedance value of 890 - j418 which is far from resonance can and does yield an acceptable SWR.
I guess there might be a mistake
If Z=890 + j418 Ω then, relative to 50 Ω
ROS=21.7
|S11| = 0.91
S11 = 0.91 -j 0.04
In fact the point you have drawn does indeed produce a ROS < 2 but the
impedance it represents is not
890 + j418 Ω or the normalization impedance, which you do not specify, is
not 50 Ω
--
F1AMM
François
De la part de W0LEV
Envoyé : mercredi 4 septembre 2024 18:55 -- *Dave - WØLEV* -- Dave - WØLEV
|
Guess you better tell anyone using a Yagi-Uda, or Beverage Antenna that they haven’t really been radiating all these years.
Ed McCann
AG6CX
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On Sep 30, 2024, at 10:19 AM, KENT BRITAIN via groups.io <WA5VJB@...> wrote:
For an antenna, if it doesn't resonate, it really doesn't radiate!
Ok, Ok, there is some minor leakage from a dummy load.
On Monday, September 30, 2024 at 12:10:26 PM CDT, Salvatore Terress <salvatoreterress@...> wrote:
Would it be correct to state that for transmit purpose - the SWR is the
defining component, not the resonance of the antenna proper ?
On Wed, Sep 4, 2024 at 1:03 PM W0LEV via groups.io <davearea51a=
gmail.com@groups.io> wrote:
You are so correct. In my many models and in using SimSmith, the "last"
was left with an optional Zo of 1050 ohms, NOT 50 OHMS! The 1050 ohms was
input into the model to simulate the effect of an ideal 21:1 BB
transformer. I didn't notice or remember that when I hit "copy".
Thank you for calling out my error!
Dave - WØLEV
On Wed, Sep 4, 2024 at 5:58 PM François via groups.io <18471=
free.fr@groups.io> wrote:
The qualitative conclusion here is that a "wild"
impedance value of 890 - j418 which is far from resonance can and does yield an acceptable
SWR. I guess there might be a mistake
If Z=890 + j418 Ω then, relative to 50 Ω
ROS=21.7
|S11| = 0.91
S11 = 0.91 -j 0.04
In fact the point you have drawn does indeed produce a ROS < 2 but the
impedance it represents is not
890 + j418 Ω or the normalization impedance, which you do not specify, is
not 50 Ω
--
F1AMM
François
De la part de W0LEV
Envoyé : mercredi 4 septembre 2024 18:55
--
*Dave - WØLEV*
--
Dave - WØLEV
|
But it ain't a fraction of a wavelength element!
Vivaldi antennas would fall into that family of antennas as well.
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On Monday, September 30, 2024 at 12:31:46 PM CDT, John <radio@...> wrote: This ends my dream of a non-resonant rhombic... ...poof On 2024-09-30 12:18, KENT BRITAIN wrote: For an antenna, if it doesn't resonate, it really doesn't radiate!
Ok, Ok, there is some minor leakage from a dummy load.
On Monday, September 30, 2024 at 12:10:26 PM CDT, Salvatore Terress
<salvatoreterress@...> wrote:
Would it be correct to state that for transmit purpose - the SWR is
the
defining component, not the resonance of the antenna proper ?
On Wed, Sep 4, 2024 at 1:03 PM W0LEV via groups.io <davearea51a=
gmail.com@groups.io> wrote:
You are so correct. In my many models and in using SimSmith, the
"last"
was left with an optional Zo of 1050 ohms, NOT 50 OHMS! The 1050 ohms
was
input into the model to simulate the effect of an ideal 21:1 BB
transformer. I didn't notice or remember that when I hit "copy".
Thank you for calling out my error!
Dave - WØLEV
On Wed, Sep 4, 2024 at 5:58 PM François via groups.io <18471=
free.fr@groups.io> wrote:
The qualitative conclusion here is that a "wild"
impedance value of 890 - j418 which is far from resonance can and does
yield an acceptable SWR.
I guess there might be a mistake
If Z=890 + j418 Ω then, relative to 50 Ω
ROS=21.7
|S11| = 0.91
S11 = 0.91 -j 0.04
In fact the point you have drawn does indeed produce a ROS < 2 but the
impedance it represents is not
890 + j418 Ω or the normalization impedance, which you do not specify,
is
not 50 Ω
--
F1AMM
François
De la part de W0LEV
Envoyé : mercredi 4 septembre 2024 18:55 -- *Dave - WØLEV* -- Dave - WØLEV
|
Yagi's are very resonate.
Now a beverage has more in common with a directional coupler than an antenna.
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On Monday, September 30, 2024 at 12:41:19 PM CDT, AG6CX <edwmccann@...> wrote: Guess you better tell anyone using a Yagi-Uda, or Beverage Antenna that they haven’t really been radiating all these years. Ed McCann AG6CX On Sep 30, 2024, at 10:19 AM, KENT BRITAIN via groups.io <WA5VJB@...> wrote:
For an antenna, if it doesn't resonate, it really doesn't radiate!
Ok, Ok, there is some minor leakage from a dummy load.
On Monday, September 30, 2024 at 12:10:26 PM CDT, Salvatore Terress <salvatoreterress@...> wrote:
Would it be correct to state that for transmit purpose - the SWR is the
defining component, not the resonance of the antenna proper ?
On Wed, Sep 4, 2024 at 1:03 PM W0LEV via groups.io <davearea51a=
gmail.com@groups.io> wrote:
You are so correct. In my many models and in using SimSmith, the "last"
was left with an optional Zo of 1050 ohms, NOT 50 OHMS! The 1050 ohms was
input into the model to simulate the effect of an ideal 21:1 BB
transformer. I didn't notice or remember that when I hit "copy".
Thank you for calling out my error!
Dave - WØLEV
On Wed, Sep 4, 2024 at 5:58 PM François via groups.io <18471=
free.fr@groups.io> wrote:
The qualitative conclusion here is that a "wild"
impedance value of 890 - j418 which is far from resonance can and does yield an acceptable
SWR. I guess there might be a mistake
If Z=890 + j418 Ω then, relative to 50 Ω
ROS=21.7
|S11| = 0.91
S11 = 0.91 -j 0.04
In fact the point you have drawn does indeed produce a ROS < 2 but the
impedance it represents is not
890 + j418 Ω or the normalization impedance, which you do not specify, is
not 50 Ω
--
F1AMM
François
De la part de W0LEV
Envoyé : mercredi 4 septembre 2024 18:55
--
*Dave - WØLEV*
--
Dave - WØLEV
|
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On Sep 30, 2024, at 10:47 AM, KENT BRITAIN via groups.io
<WA5VJB@...> wrote:
Yagi's are very resonate.
Now a beverage has more in common with a directional coupler than an
antenna.
On Monday, September 30, 2024 at 12:41:19 PM CDT, AG6CX
<edwmccann@...> wrote:
Guess you better tell anyone using a Yagi-Uda, or Beverage Antenna that
they haven’t really been radiating all these years.
Ed McCann
AG6CX
On Sep 30, 2024, at 10:19 AM, KENT BRITAIN via groups.io
<WA5VJB@...> wrote:
For an antenna, if it doesn't resonate, it really doesn't radiate!
Ok, Ok, there is some minor leakage from a dummy load.
On Monday, September 30, 2024 at 12:10:26 PM CDT, Salvatore Terress
<salvatoreterress@...> wrote:
Would it be correct to state that for transmit purpose - the SWR is the
defining component, not the resonance of the antenna proper ?
On Wed, Sep 4, 2024 at 1:03 PM W0LEV via groups.io <davearea51a=
gmail.com@groups.io> wrote:
You are so correct. In my many models and in using SimSmith, the "last"
was left with an optional Zo of 1050 ohms, NOT 50 OHMS! The 1050 ohms was
input into the model to simulate the effect of an ideal 21:1 BB
transformer. I didn't notice or remember that when I hit "copy".
Thank you for calling out my error!
Dave - WØLEV
On Wed, Sep 4, 2024 at 5:58 PM François via groups.io <18471=
free.fr@groups.io> wrote:
The qualitative conclusion here is that a "wild"
impedance value of 890 - j418 which is far from resonance can and does
yield an acceptable
SWR.
I guess there might be a mistake
If Z=890 + j418 Ω then, relative to 50 Ω
ROS=21.7
|S11| = 0.91
S11 = 0.91 -j 0.04
In fact the point you have drawn does indeed produce a ROS < 2 but the
impedance it represents is not
890 + j418 Ω or the normalization impedance, which you do not specify, is
not 50 Ω
--
F1AMM
François
De la part de W0LEV
Envoyé : mercredi 4 septembre 2024 18:55
--
*Dave - WØLEV*
--
Dave - WØLEV
|
Well, you do need just the right phase delay between elements to
get the clean forward lobe.
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On Monday, September 30, 2024 at 01:08:12 PM CDT, AG6CX <edwmccann@...> wrote: True that the Yagi is resonant, but it radiates as traveling wave, doesn’ it? Like the V, the rhombic, etc. 5wFenuUq5MiLpT756 ( https://search.app/5wFenuUq5MiLpT756 ) PDF Document · 787 KB ( https://search.app/5wFenuUq5MiLpT756 ) ( https://search.app/5wFenuUq5MiLpT756 ) Ed McCann AG6CX
On Sep 30, 2024, at 10:47 AM, KENT BRITAIN via groups.io
<WA5VJB@...> wrote:
Yagi's are very resonate.
Now a beverage has more in common with a directional coupler than an
antenna.
On Monday, September 30, 2024 at 12:41:19 PM CDT, AG6CX
<edwmccann@...> wrote:
Guess you better tell anyone using a Yagi-Uda, or Beverage Antenna that
they haven’t really been radiating all these years.
Ed McCann
AG6CX
On Sep 30, 2024, at 10:19 AM, KENT BRITAIN via groups.io
<WA5VJB@...> wrote:
For an antenna, if it doesn't resonate, it really doesn't radiate!
Ok, Ok, there is some minor leakage from a dummy load.
On Monday, September 30, 2024 at 12:10:26 PM CDT, Salvatore Terress
<salvatoreterress@...> wrote:
Would it be correct to state that for transmit purpose - the SWR is the
defining component, not the resonance of the antenna proper ?
On Wed, Sep 4, 2024 at 1:03 PM W0LEV via groups.io <davearea51a=
gmail.com@groups.io> wrote:
You are so correct. In my many models and in using SimSmith, the "last"
was left with an optional Zo of 1050 ohms, NOT 50 OHMS! The 1050 ohms was
input into the model to simulate the effect of an ideal 21:1 BB
transformer. I didn't notice or remember that when I hit "copy".
Thank you for calling out my error!
Dave - WØLEV
On Wed, Sep 4, 2024 at 5:58 PM François via groups.io <18471=
free.fr@groups.io> wrote:
The qualitative conclusion here is that a "wild"
impedance value of 890 - j418 which is far from resonance can and does
yield an acceptable
SWR.
I guess there might be a mistake
If Z=890 + j418 Ω then, relative to 50 Ω
ROS=21.7
|S11| = 0.91
S11 = 0.91 -j 0.04
In fact the point you have drawn does indeed produce a ROS < 2 but the
impedance it represents is not
890 + j418 Ω or the normalization impedance, which you do not specify, is
not 50 Ω
--
F1AMM
François
De la part de W0LEV
Envoyé : mercredi 4 septembre 2024 18:55
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*Dave - WØLEV*
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Dave - WØLEV
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You can tell that there are some very strong opinions on this subject.
I will try to be objective.
1) Non-resonant antennas can be very effective, and many hams use them all the time. But when you use them, you normally need to use a tuner to keep the SWR low so the transmitter is happy.
2) Resonant antennas are in general more effective than non-resonant ones, so they are often preferred. And you can often build a resonant antenna that has a native low SWR, i.e. a resonant dipole properly constructed will have an SWR of 1.5:1 or less. But not always, many resonant antennas don't have a feedpoint impedance near 50 ohms, so they need a transformer or other matching element.
3) SWR, however, is not an indicator of how well the antenna is radiating. And it can fool you into believing you have a great antenna when you don't, if there is significant loss in the feedline or matching circuits (more than a couple of dB) - because such loss makes SWR at the transmitter better, when it is causing your antenna to have less radiation.
So there is most often a trade-off between SWR and Resonance. The resonant point is often not at the lowest SWR point - for example, if an antenna is resonant, say, at an SWR of 1.5:1, you will likely get better overall performance by using it at the resonant point than tuning off resonance for the lowest 1.1:1 SWR.
For the QxX series of radios, SWR must be controlled (since they have no internal protection) - so that makes SWR most important, at least to get it below about 2:1, so you don't damage your radio. But you also have to make sure your antenna is radiating well, either from being near resonance, or having suitable low-loss matching.
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By adding Inductance and Capacitance to that coat hanger, you have made the coat hanger
into a resonate system.
You have me thinking of many VLF antenna systems where 1 or 2% efficiency is considered great! Usually resistance losses due to the high currents from the resonance.
The Nano's are great little portable VNA's. Lot easier to haul around than my HP 8510
and well over a hundred lbs lighter. But it's #1 Calibration issue (At least on my three) is that 50 Ohm load they supply It look pretty bad above 100 MHz on a professional VNA.
Option 1 Get a better 50 Ohm load.Option 2 Got any SMA attenuators? Put a 10 to 20 dB in series with the load. Most SMA attenuators will clean up the load's reactance.
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On Monday, September 30, 2024 at 02:27:09 PM CDT, Stan Dye <standye@...> wrote:
You can tell that there are some very strong opinions on this subject.
I will try to be objective.
1) Non-resonant antennas can be very effective, and many hams use them all the time. But when you use them, you normally need to use a tuner to keep the SWR low so the transmitter is happy.
2) Resonant antennas are in general more effective than non-resonant ones, so they are often preferred. And you can often build a resonant antenna that has a native low SWR, i.e. a resonant dipole properly constructed will have an SWR of 1.5:1 or less. But not always, many resonant antennas don't have a feedpoint impedance near 50 ohms, so they need a transformer or other matching element.
3) SWR, however, is not an indicator of how well the antenna is radiating. And it can fool you into believing you have a great antenna when you don't, if there is significant loss in the feedline or matching circuits (more than a couple of dB) - because such loss makes SWR at the transmitter better, when it is causing your antenna to have less radiation.
So there is most often a trade-off between SWR and Resonance. The resonant point is often not at the lowest SWR point - for example, if an antenna is resonant, say, at an SWR of 1.5:1, you will likely get better overall performance by using it at the resonant point than tuning off resonance for the lowest 1.1:1 SWR.
For the QxX series of radios, SWR must be controlled (since they have no internal protection) - so that makes SWR most important, at least to get it below about 2:1, so you don't damage your radio. But you also have to make sure your antenna is radiating well, either from being near resonance, or having suitable low-loss matching.
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A Yagi is not a traveling wave antenna. Most familiar to the amateur community would be the beverage which is a traveling wave antenna. Above ground power grid conductors are also traveling wave antennas and, therefore, gather lots of energy from any HAB (High Altitude [nuclear] Burst). Dave - WØLEV < http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> Virus-free.www.avg.com < http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> On Mon, Sep 30, 2024 at 7:05 PM KENT BRITAIN via groups.io <WA5VJB= FLASH.NET@groups.io> wrote: Well, you do need just the right phase delay between elements to
get the clean forward lobe.
On Monday, September 30, 2024 at 01:08:12 PM CDT, AG6CX <
edwmccann@...> wrote:
True that the Yagi is resonant, but it radiates as traveling wave, doesn’
it?
Like the V, the rhombic, etc.
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Ed McCann
AG6CX
On Sep 30, 2024, at 10:47 AM, KENT BRITAIN via groups.io
<WA5VJB@...> wrote:
Yagi's are very resonate.
Now a beverage has more in common with a directional coupler than an
antenna.
On Monday, September 30, 2024 at 12:41:19 PM CDT, AG6CX
<edwmccann@...> wrote:
Guess you better tell anyone using a Yagi-Uda, or Beverage Antenna that
they haven’t really been radiating all these years.
Ed McCann
AG6CX
On Sep 30, 2024, at 10:19 AM, KENT BRITAIN via groups.io
<WA5VJB@...> wrote:
For an antenna, if it doesn't resonate, it really doesn't radiate!
Ok, Ok, there is some minor leakage from a dummy load.
On Monday, September 30, 2024 at 12:10:26 PM CDT, Salvatore Terress
<salvatoreterress@...> wrote:
Would it be correct to state that for transmit purpose - the SWR is the
defining component, not the resonance of the antenna proper ?
On Wed, Sep 4, 2024 at 1:03 PM W0LEV via groups.io <davearea51a=
gmail.com@groups.io> wrote:
You are so correct. In my many models and in using SimSmith, the
"last"
was left with an optional Zo of 1050 ohms, NOT 50 OHMS! The 1050 ohms
was
input into the model to simulate the effect of an ideal 21:1 BB
transformer. I didn't notice or remember that when I hit "copy".
Thank you for calling out my error!
Dave - WØLEV
On Wed, Sep 4, 2024 at 5:58 PM François via groups.io <18471=
free.fr@groups.io> wrote:
The qualitative conclusion here is that a "wild"
impedance value of 890 - j418 which is far from resonance can and
does
yield an acceptable
SWR.
I guess there might be a mistake
If Z=890 + j418 Ω then, relative to 50 Ω
ROS=21.7
|S11| = 0.91
S11 = 0.91 -j 0.04
In fact the point you have drawn does indeed produce a ROS < 2 but the
impedance it represents is not
890 + j418 Ω or the normalization impedance, which you do not
specify, is
not 50 Ω
--
F1AMM
François
De la part de W0LEV
Envoyé : mercredi 4 septembre 2024 18:55
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*Dave - WØLEV*
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Dave - WØLEV
-- *Dave - WØLEV* -- Dave - WØLEV
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Juan Pablo EA4CIV
