[Elecraft] [K3] SWR - Numerical Indication

[ANDY DURBIN]

"Is this 1.0:1 SWR across the entire 40 meter band curious or remarkable?"

I'd guess that it's improbable and likely the result of measurement error.  The 
reflected voltage will be zero for low or high power if the antenna system is a 
perfect match .  However, the (measured) reflected voltage will also be zero 
for an imperfectly matched antenna system when there is not enough power for 
the reflected voltage to be above the detection threshold on the measurement 
device.The Elecraft SWR meters that I have (KPA500 and KAT500) will 
indicate SWR 1.0:1 with no forward voltage and also with some forward voltage 
and no reflected voltage.   You have to know when to believe the reading and 
that may be only when the reading is not 1.0:1.

Running the sweep with higher power may give quite different results, but 
running high power antenna sweeps may be considered anti-social.An antenna 
analyzer will probably give a much better indication of your antenna system 
characteristics.

Andy, k3wyc

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[Elecraft] [K3] SWR - Numerical Indication

[Dick Dickinson]

Hi Andy,

 

Thanks for sharing your thoughts.

 

Do you find a high degree of correlation between your (assumed) K3 and
KAT500 SWR readings across various levels of SWR?  

 

 

Kindly,

Dick - KA5KKT 

ANDY DURBIN
 a.durbin at
msn.com 
Sun Dec 2 15:13:21 EST 2018 

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"Is this 1.0:1 SWR across the entire 40 meter band curious or remarkable?"

 

I'd guess that it's improbable and likely the result of measurement error.
The reflected voltage will be zero for low or high power if the antenna
system is a perfect match .  However, the (measured) reflected voltage will
also be zero for an imperfectly matched antenna system when there is not
enough power for the reflected voltage to be above the detection threshold
on the measurement device.The Elecraft SWR meters that I have (KPA500
and KAT500) will indicate SWR 1.0:1 with no forward voltage and also with
some forward voltage and no reflected voltage.   You have to know when to
believe the reading and that may be only when the reading is not 1.0:1.

 

Running the sweep with higher power may give quite different results, but
running high power antenna sweeps may be considered anti-social.An
antenna analyzer will probably give a much better indication of your antenna
system characteristics.

 

Andy, k3wyc

 

  _  

 

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[Elecraft] [K3] SWR - Numerical Indication

[Dick Dickinson]

I've noticed that I'm not showing a reading of less than 1.1:1 SWR on my
antennas per K3 SWR Numerical Readout.  K3EZ will record 1.0:1 SWR in band
sweeps.

Can the K3(S) Numerical Display show 1.0:1 SWR?  If so, is there a likely
reason why K3EZ will show 1.0:1 while my K3 will only go as far down as
1.1:1?


Dick -  KA5KKT



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Re: [Elecraft] [K3] SWR - Numerical Indication

[Petr, OK1RP/M0SIS]

Hi Wes,

excellent! 

Many thanks for this post which is nicely explaining what is going on about
the measurement in K3s. 

In fact until now no one talked about the calibrations, uncertainties,
errors, accuracy, reading errors, uncertainties A, B and combined
uncertainties etc. In that case there is several error sources and factors
which need to be calculated in order to get some more precise values ...and
in all cases the uncertainties must be calculated together with measured
value if we would like to talk about scientific or sophisticated
measurement.

Thanks for nice explanation Wes to all.

Best regards.



-
73 - Petr, OK1RP 
"Apple & Elecraft freak" 
B:http://ok1rp.blogspot.com
G+:http://goo.gl/w3u2s9
G+: http://goo.gl/gP99xq
--
Sent from: http://elecraft.365791.n2.nabble.com/
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Re: [Elecraft] [K3] SWR - Numerical Indication

[Don Wilhelm]

Petr and all,

Those digital instruments that show 2, 3, or 4 decimal places have given 
us a false sense of accuracy.
For instance an instrument that is accurate to 5% and has a 4 digit 
display can show us (when measuring a 5 volt source) anywhere between 
4.750 volts and 5.250 volts and still be within the 5% accuracy window 
for the instrument.


Review the specs and calibration for whatever meter you are using and do 
not expect those extra digits to be correct - in other words round the 
numbers displayed.


Many wattmeters are only accurate to 20% of the reading - so if one 
wattmeter at 100 watts shows 120 watts and another shows 80 watts, the 
actual power could be 100 watts.  Take that into consideration.


The Telepost LP-100 when calibrated to NIST standards is accurate to 5% 
(it can be lower, but Larry will not guarantee it).  So any power it 
displays between 95 and 105 watts can actually be 100 watts.


In other words, look at the specified accuracy of whatever meter you are 
using and take that into consideration.  Those extra digits on your 
meter may be meaningless.


73,
Don W3FPR

On 11/30/2018 9:29 AM, Petr, OK1RP/M0SIS wrote:

Hi Wes,

excellent!

Many thanks for this post which is nicely explaining what is going on about
the measurement in K3s.

In fact until now no one talked about the calibrations, uncertainties,
errors, accuracy, reading errors, uncertainties A, B and combined
uncertainties etc. In that case there is several error sources and factors
which need to be calculated in order to get some more precise values ...and
in all cases the uncertainties must be calculated together with measured
value if we would like to talk about scientific or sophisticated
measurement.

Thanks for nice explanation Wes to all.

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Re: [Elecraft] [K3] SWR - Numerical Indication

[W2xj]

I wish I could find the original post that started this discussion. Very 
frustrating when there is no quoted material. 

Sent from my iPad

> On Nov 30, 2018, at 6:29 AM, Petr, OK1RP/M0SIS  wrote:
> 
> Hi Wes,
> 
> excellent! 
> 
> Many thanks for this post which is nicely explaining what is going on about
> the measurement in K3s. 
> 
> In fact until now no one talked about the calibrations, uncertainties,
> errors, accuracy, reading errors, uncertainties A, B and combined
> uncertainties etc. In that case there is several error sources and factors
> which need to be calculated in order to get some more precise values ...and
> in all cases the uncertainties must be calculated together with measured
> value if we would like to talk about scientific or sophisticated
> measurement.
> 
> Thanks for nice explanation Wes to all.
> 
> Best regards.
> 
> 
> 
> -
> 73 - Petr, OK1RP 
> "Apple & Elecraft freak" 
> B:http://ok1rp.blogspot.com
> G+:http://goo.gl/w3u2s9
> G+: http://goo.gl/gP99xq
> --
> Sent from: http://elecraft.365791.n2.nabble.com/
> __
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> This list hosted by: http://www.qsl.net
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> Message delivered to w...@w2xj.net
> 

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Re: [Elecraft] [K3] SWR - Numerical Indication

[Petr Ourednik]

So soryy, my fault...
73 - Petr, OK1RP

> Sent from my iPad
> 
> > On Nov 30, 2018, at 6:29 AM, Petr, OK1RP/M0SIS  wrote:
> > 
> > Hi Wes,
> > 
> > excellent! 
> > 
> > Many thanks for this post which is nicely explaining what is going on about
> > the measurement in K3s. 
> > 
> > In fact until now no one talked about the calibrations, uncertainties,
> > errors, accuracy, reading errors, uncertainties A, B and combined
> > uncertainties etc. In that case there is several error sources and factors
> > which need to be calculated in order to get some more precise values ...and
> > in all cases the uncertainties must be calculated together with measured
> > value if we would like to talk about scientific or sophisticated
> > measurement.
> > 
> > Thanks for nice explanation Wes to all.
> > 
> > Best regards.


In reply to this post by Bob McGraw - K4TAX 

I would be surprised if two garden variety instruments, even placed at the same 
point, would agree. The directional bridges/couplers in most "(V)SWR" meters 
that hams routinely use externally or which are built into our radios are not 
precision instruments.  There are a number of error sources in reflection 
measurements; source match, diode non-linearity, coupler tracking errors and 
often the most significant, directivity error. 

In an ideal coupler, (i.e signal separation device) one port measures the 
forward (incident signal) and another measures the reverse (reflected) signal 
and there is no coupling between ports in the unwanted direction(s).  In other 
words there is no signal at the reverse port due to the forward signal.  In a 
real world coupler there is some leakage signal appearing at the reverse port 
due to the forward signal, absent any reflected signal.  The "goodness" of a 
directional coupler in this instance is called "directivity" and the error 
signal is directivity error. Directivity is usually specified in dB.  Really 
good couplers might have directivities in the 40 dB neighborhood.  Really 
really 
good directional bridges can be 50 dB, but so-so units might be 25-30 dB.  Not 
ready for prime time units are lower than this. 

Now I have no way of knowing what the directivities are of the couplers built 
into K3s, KPA500s, KAT500s, etc. but considering that they have to work over 
about 5 octaves, I'm going out on a limb and saying that 25 to 30 dB is a fair 
estimate.  If I'm wrong, I'm sure I'll hear about it.  For sake of discussion 
I'm going to use 26.5 dB.  What this means is that if I terminate the output 
spigot of one of these radios with a perfect 50+j0 load, I'm going to measure a 
leakage signal (directivity error) that is 26.5 dB below the incident value.  
I'll introduce the concept of return loss here. 

We hams usually speak in terms of SWR.  SWR = (1 + p) / (1 - p) where p is the 
reflection coefficient. Here the p = the voltage measured at the reflected port 
and the constant 1 represents the incident signal.  In reality both of these 
quantities are complex numbers, they have both magnitude and phase but SWR 
measurements are scalar, we throw away the phase (since it's difficult to 
measure) and just use the magnitude. (In fact the symbol "p", which is really 
the Greek letter rho, indicates the magnitude of the reflection coefficient in 
normal usage)  We can also express this ratio as return loss, which is -20 * 
log10(p).  So return loss, SWR and reflection coefficient are just different 
ways to express the same thing; the ratio of incident to reflected signal. 

Let's return to our example; the coupler with 26.5 dB directivity, which 
indicates a return loss (RL) of 26.5 dB even with a perfect termination.  Doing 
the math and converting RL = 26.5 dB to SWR we get 1.1:1.  Our perfect load 
measures 1.1:1 with our imperfect instrument.  And this assumes that there are 
no other errors, which there always are. But it gets worse. 

Let's say that the load we want to measure really is 1.1:1.  We now have two 
(apparent) reflections, 1) the real one and 2) the directivity error and they 
both have the same magnitude.  In our simple detector, they sum together.  Now 
I 
said earlier that we don't measure phase, only magnitude, but just because we 
don't, or can't measure the relative phases doesn't mean they aren't there. We 
will examine two cases to determine the limits of error.  Case 1) both 
reflections are in phase, they add up to p + p or 2p, RL = 20.5 and SWR 
~1.21:1.  Case 2) they are exactly out of phase, they sum to zero.  p = 0, RL 
is 
infinite and SWR = 1:1.  The possible RL error is then -6 to +infinity dB! 

In other words, an actual SWR of 1.1:1 can be measured anywhere between 1.0:1 
and 1.2:1.  Is it any wonder that we often read about concerns that one device 
measures one thing, while another located at the same, or close location 
measures something different.  Of course all of this is predicated on a 
directional coupler with 26.5 dB directivity and no other error sources.  It's 
entire

Re: [Elecraft] [K3] SWR - Numerical Indication

[Charlie T]

Yep,  ur right Don.  A freebie Harbor Freight digital voltmeter appears to
have a helluva lot better accuracy than reality.
Digital calculators on the other hand, ARE accurate.
This changes our mind-set, simply because we see all those digits past the
decimal point on a dVOM.

it was better when we only had slide-rules to calculate things.
Accuracy to more than three places was at best, a guess.
Besides, what good does it do to arrive at a required by-pass capacitor's
value of 0.0110987 µF ?

73, Charlie k3ICH




-Original Message-
From: elecraft-boun...@mailman.qth.net  On
Behalf Of Don Wilhelm
Sent: Friday, November 30, 2018 9:56 AM
To: elecraft@mailman.qth.net
Subject: Re: [Elecraft] [K3] SWR - Numerical Indication

Petr and all,

Those digital instruments that show 2, 3, or 4 decimal places have given us
a false sense of accuracy.
For instance an instrument that is accurate to 5% and has a 4 digit display
can show us (when measuring a 5 volt source) anywhere between
4.750 volts and 5.250 volts and still be within the 5% accuracy window for
the instrument.

Review the specs and calibration for whatever meter you are using and do not
expect those extra digits to be correct - in other words round the numbers
displayed.

Many wattmeters are only accurate to 20% of the reading - so if one
wattmeter at 100 watts shows 120 watts and another shows 80 watts, the
actual power could be 100 watts.  Take that into consideration.

The Telepost LP-100 when calibrated to NIST standards is accurate to 5% (it
can be lower, but Larry will not guarantee it).  So any power it displays
between 95 and 105 watts can actually be 100 watts.

In other words, look at the specified accuracy of whatever meter you are
using and take that into consideration.  Those extra digits on your meter
may be meaningless.

73,
Don W3FPR


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Re: [Elecraft] [K3] SWR - Numerical Indication

[Don Wilhelm]

All,

There is a big difference between accuracy and precision.
Precision can be accomplished by adding the extra digits, but the 
accuracy of the instrument will tell you how many of those extra digits 
are to be considered.


Most digital voltmeters, even the cheap or free ones from Harbor Freight 
and others are surprisingly accurate (5% or so is common), but typical 
voltage readings of 3 significant digits are reasonable but any digits 
more than that are extraneous unless the instrument is of lab quality.


73,
Don W3FPR

On 11/30/2018 11:12 AM, Charlie T wrote:

Yep,  ur right Don.  A freebie Harbor Freight digital voltmeter appears to
have a helluva lot better accuracy than reality.
Digital calculators on the other hand, ARE accurate.
This changes our mind-set, simply because we see all those digits past the
decimal point on a dVOM.

it was better when we only had slide-rules to calculate things.
Accuracy to more than three places was at best, a guess.
Besides, what good does it do to arrive at a required by-pass capacitor's
value of 0.0110987 µF ?

73, Charlie k3ICH




-Original Message-
From: elecraft-boun...@mailman.qth.net  On
Behalf Of Don Wilhelm
Sent: Friday, November 30, 2018 9:56 AM
To: elecraft@mailman.qth.net
Subject: Re: [Elecraft] [K3] SWR - Numerical Indication

Petr and all,

Those digital instruments that show 2, 3, or 4 decimal places have given us
a false sense of accuracy.
For instance an instrument that is accurate to 5% and has a 4 digit display
can show us (when measuring a 5 volt source) anywhere between
4.750 volts and 5.250 volts and still be within the 5% accuracy window for
the instrument.

Review the specs and calibration for whatever meter you are using and do not
expect those extra digits to be correct - in other words round the numbers
displayed.

Many wattmeters are only accurate to 20% of the reading - so if one
wattmeter at 100 watts shows 120 watts and another shows 80 watts, the
actual power could be 100 watts.  Take that into consideration.

The Telepost LP-100 when calibrated to NIST standards is accurate to 5% (it
can be lower, but Larry will not guarantee it).  So any power it displays
between 95 and 105 watts can actually be 100 watts.

In other words, look at the specified accuracy of whatever meter you are
using and take that into consideration.  Those extra digits on your meter
may be meaningless.

73,
Don W3FPR


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Re: [Elecraft] [K3] SWR - Numerical Indication

[Phil Kane]

On 11/30/2018 8:12 AM, Charlie T wrote:

> it was better when we only had slide-rules to calculate things.

And we had to have "situational awareness" of the order of magnitude of
the result.
"What is the relationship between a megaphone and a microphone?"  Answer
- 10^12

Back on topic - what is the "advertised accuracy" of the KAT100 SWR bridge?

73 de K2ASP - Phil Kane
Elecraft K2/100   s/n 5402

>From a Clearing in the Silicon Forest
Beaverton (Washington County) Oregon
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Re: [Elecraft] [K3] SWR - Numerical Indication

[Dave Hachadorian]

This discussion reminds me of a lesson in engineering class (55 
years ago) about the difference between precision and accuracy. 
The professor used the example of bullet holes in a target.


If the holes were closely spaced, but far from the bulls-eye, the 
shooter was inaccurate but precise.


If the holes were widely spaced, but the average was near the 
bulls-eye the shooter was accurate but imprecise.


Closely spaced on the bulls-eye precise and accurate

Widely spaced, and the average not near the bulls-eye, imprecise 
and inaccurate.


Easy to remember.

Some other memorable nuggets from that class:
Evaporation is a cooling process.
High octane gasoline is slow-burning gasoline.
The electric company bills you for kilowatt-hours, so they are 
not a power company, they are an energy company.



Dave Hachadorian, K6LL
Yuma, AZ


-Original Message- 
From: Don Wilhelm

Sent: Friday, November 30, 2018 7:55 AM
To: elecraft@mailman.qth.net
Subject: Re: [Elecraft] [K3] SWR - Numerical Indication

Petr and all,

Those digital instruments that show 2, 3, or 4 decimal places 
have given

us a false sense of accuracy.
For instance an instrument that is accurate to 5% and has a 4 
digit
display can show us (when measuring a 5 volt source) anywhere 
between
4.750 volts and 5.250 volts and still be within the 5% accuracy 
window

for the instrument.

Review the specs and calibration for whatever meter you are using 
and do
not expect those extra digits to be correct - in other words 
round the

numbers displayed.

Many wattmeters are only accurate to 20% of the reading - so if 
one
wattmeter at 100 watts shows 120 watts and another shows 80 
watts, the

actual power could be 100 watts.  Take that into consideration.

The Telepost LP-100 when calibrated to NIST standards is accurate 
to 5%
(it can be lower, but Larry will not guarantee it).  So any power 
it

displays between 95 and 105 watts can actually be 100 watts.

In other words, look at the specified accuracy of whatever meter 
you are
using and take that into consideration.  Those extra digits on 
your

meter may be meaningless.

73,
Don W3FPR

On 11/30/2018 9:29 AM, Petr, OK1RP/M0SIS wrote:

Hi Wes,

excellent!

Many thanks for this post which is nicely explaining what is 
going on about

the measurement in K3s.

In fact until now no one talked about the calibrations, 
uncertainties,
errors, accuracy, reading errors, uncertainties A, B and 
combined
uncertainties etc. In that case there is several error sources 
and factors
which need to be calculated in order to get some more precise 
values ...and
in all cases the uncertainties must be calculated together with 
measured
value if we would like to talk about scientific or 
sophisticated

measurement.

Thanks for nice explanation Wes to all.

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Re: [Elecraft] [K3] SWR - Numerical Indication

[John Oppenheimer]

Hi Dick,

Some numbers: using the K3 Schematic, "K3S RF Board" Sheet 2, Section
B1. The power meter uses a series Schottky diode detector. The low
reasonable resolution is about 0.3 VDC, or 0.3 * .707 = 0.21 Vrms out of
the directional coupler.

The Power for 0.21 Vrms is:
0.21^2 / 50 = .88 mW
Assuming a 20 dB coupler 1:10 turns ratio, 0.88mW * 100 = 0.88W
reflected power.

Assuming forward power of 100 watts and 0.88 watt reflected power the
return loss is:
10 * log(100 / 0.88) = 20.6 dB

Using the calculator:
https://www.allaboutcircuits.com/tools/vswr-return-loss-calculator/
20.6 dB Return Loss computes to VSWR = 1.222

Therefore, the best lowest estimated K3 VSWR, assuming a 20 dB coupler,
is about 1.2.

Check my numbers.

John KN5L


On 7/27/18 9:58 AM, Dick Dickinson wrote:
> I've noticed that I'm not showing a reading of less than 1.1:1 SWR on my
> antennas per K3 SWR Numerical Readout.  K3EZ will record 1.0:1 SWR in band
> sweeps.
> 
> Can the K3(S) Numerical Display show 1.0:1 SWR?  If so, is there a likely
> reason why K3EZ will show 1.0:1 while my K3 will only go as far down as
> 1.1:1?
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Re: [Elecraft] [K3] SWR - Numerical Indication

[Dick Dickinson]

Thanks for the explanation,  John.

 

I’m not an electronically educated fellow, merely just seeking the
practical.  

 

A resolution to my post was provided in the suggestion that the apparent
1.1:1 SWR might be the result of common mode current.  Sure enough when I
installed a 1:1 current balun at the feed point of the antennas (2
perpendicular Inverted Vees with a switchable common feed point), the value
went from 1.1:1 to 1.0:1 and the bottom of the SWR curves which also
broadened out.

 

Still that doesn’t explain why the K3 was showing 1.1:1 while passing 1.0:1
information to K3EZ, or so it seems.  I don’t think that the K3EZ is
‘measuring SWR’ rather merely posting information it is getting from the
K3…no different measuring device or location.  Perhaps it is a sort of
‘rounding error.’  By the way, for those who haven’t come across it, K3EZ
has the great feature of being able to step the K3 across a frequency range,
momentarily key it, step again, etc. and plot in text an SWR chart…a handy
feature for working with an antenna installation.

 

Following is a situation that perhaps you have the theoretical background to
explain…

 

I have a full-size monoband vertical for 40 meters.  Simple architectural
aluminum tapering from 1 ¼” (?) in 6’ telescoping sections.  The radial
field is designed to provide a 50 ohm match at the feed point…12 – 13’+
radials.  It is fed directly…no matching device with RG-213 from the remote
antenna switch about 50’ away at my tower.  The coax from the rig to the
remote antenna switch is estimated to be ~ 50’ in length.  A lot of the time
running K3EZ to sweep the band (typically 20 watts), it will indicate a
1.0:1 SWR from 7.0 MHz to 7.3 MHz in 20 kHz steps.  Occasional deviation
from one K3EZ run to another might be due to variations in moisture content
of the ground or less than perfect connection to the vertical…an uncommon
situation.  The K3 shows the same readings.

 

Is this 1.0:1 SWR across the entire 40 meter band curious or remarkable?

 

 

Dick – KA5KKT

 

 


--

 

Hi Dick,

 

Some numbers: using the K3 Schematic, "K3S RF Board" Sheet 2, Section

B1. The power meter uses a series Schottky diode detector. The low

reasonable resolution is about 0.3 VDC, or 0.3 * .707 = 0.21 Vrms out of

the directional coupler.

 

The Power for 0.21 Vrms is:

0.21^2 / 50 = .88 mW

Assuming a 20 dB coupler 1:10 turns ratio, 0.88mW * 100 = 0.88W

reflected power.

 

Assuming forward power of 100 watts and 0.88 watt reflected power the

return loss is:

10 * log(100 / 0.88) = 20.6 dB

 

Using the calculator:

https://www.allaboutcircuits.com/tools/vswr-return-loss-calculator/

20.6 dB Return Loss computes to VSWR = 1.222

 

Therefore, the best lowest estimated K3 VSWR, assuming a 20 dB coupler,

is about 1.2.

 

Check my numbers.

 

John KN5L

 

 

On 7/27/18 9:58 AM, Dick Dickinson wrote:

> I've noticed that I'm not showing a reading of less than 1.1:1 SWR on my

> antennas per K3 SWR Numerical Readout.  K3EZ will record 1.0:1 SWR in band

> sweeps.

> 

> Can the K3(S) Numerical Display show 1.0:1 SWR?  If so, is there a likely

> reason why K3EZ will show 1.0:1 while my K3 will only go as far down as

> 1.1:1?

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Re: [Elecraft] [K3] SWR - Numerical Indication

[John Oppenheimer]

Hi Dick,

An EZNEC and SimSmith model of the on ground 1/4 wave vertical:
https://www.kn5l.net/images/SS-KA5KKT-vertical.png

SimSmith R1 represents ground loss, the value set to establish a 50 ohm
load at the transmitter, G in SimSmith.

According to the models, the 7 to 7.3 MHz SWR is a little below 1.3.

A flat measurement using the K3 SWR meter seams reasonable. My
suggestion is to use a Antenna Analyzer to measure the antenna and system.

John KN5L

On 12/2/18 12:16 AM, Dick Dickinson wrote:
> I have a full-size monoband vertical for 40 meters.  Simple architectural
> aluminum tapering from 1 ¼” (?) in 6’ telescoping sections.  The radial
> field is designed to provide a 50 ohm match at the feed point…12 – 13’+
> radials.  It is fed directly…no matching device with RG-213 from the remote
> antenna switch about 50’ away at my tower.  The coax from the rig to the
> remote antenna switch is estimated to be ~ 50’ in length.  A lot of the time
> running K3EZ to sweep the band (typically 20 watts), it will indicate a
> 1.0:1 SWR from 7.0 MHz to 7.3 MHz in 20 kHz steps.  Occasional deviation
> from one K3EZ run to another might be due to variations in moisture content
> of the ground or less than perfect connection to the vertical…an uncommon
> situation.  The K3 shows the same readings.
> 
> Is this 1.0:1 SWR across the entire 40 meter band curious or remarkable?
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Re: [Elecraft] [K3] SWR - Numerical Indication

[John Oppenheimer]

Hi Dick,

An EZNEC and SimSmith model of the on ground 1/4 wave vertical:
https://www.kn5l.net/images/SS-KA5KKT-vertical.png

SimSmith R1 represents ground loss, the value set to establish a 50 ohm
load at the transmitter, G in SimSmith.

According to the models, the 7 to 7.3 MHz SWR is a little below 1.3.

A flat measurement using the K3 SWR meter seams reasonable. My
suggestion is to use a VNA to measure the antenna and system.

John KN5L

On 12/2/18 12:16 AM, Dick Dickinson wrote:
> Thanks for the explanation,  John.
> 
> I’m not an electronically educated fellow, merely just seeking the
> practical.  
> 
> A resolution to my post was provided in the suggestion that the apparent
> 1.1:1 SWR might be the result of common mode current.  Sure enough when I
> installed a 1:1 current balun at the feed point of the antennas (2
> perpendicular Inverted Vees with a switchable common feed point), the value
> went from 1.1:1 to 1.0:1 and the bottom of the SWR curves which also
> broadened out.
> 
> Still that doesn’t explain why the K3 was showing 1.1:1 while passing 1.0:1
> information to K3EZ, or so it seems.  I don’t think that the K3EZ is
> ‘measuring SWR’ rather merely posting information it is getting from the
> K3…no different measuring device or location.  Perhaps it is a sort of
> ‘rounding error.’  By the way, for those who haven’t come across it, K3EZ
> has the great feature of being able to step the K3 across a frequency range,
> momentarily key it, step again, etc. and plot in text an SWR chart…a handy
> feature for working with an antenna installation.
> 
> Following is a situation that perhaps you have the theoretical background to
> explain…
> 
> I have a full-size monoband vertical for 40 meters.  Simple architectural
> aluminum tapering from 1 ¼” (?) in 6’ telescoping sections.  The radial
> field is designed to provide a 50 ohm match at the feed point…12 – 13’+
> radials.  It is fed directly…no matching device with RG-213 from the remote
> antenna switch about 50’ away at my tower.  The coax from the rig to the
> remote antenna switch is estimated to be ~ 50’ in length.  A lot of the time
> running K3EZ to sweep the band (typically 20 watts), it will indicate a
> 1.0:1 SWR from 7.0 MHz to 7.3 MHz in 20 kHz steps.  Occasional deviation
> from one K3EZ run to another might be due to variations in moisture content
> of the ground or less than perfect connection to the vertical…an uncommon
> situation.  The K3 shows the same readings.
> 
> Is this 1.0:1 SWR across the entire 40 meter band curious or remarkable?
> 
> Dick – KA5KKT
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Re: [Elecraft] [K3] SWR - Numerical Indication

[Bob McGraw K4TAX]

What is VSWR? There are many misconceptions and myths about VSWR. To try to 
overcome some of these misconceptions and to try to provide an easy and 
understandable summary, Electronics Notes has developed a page describing what 
VSWR is and this is accompanied by an embedded video.

The page and video describe how a perfect match means that all the power is 
absorbed by the load, and it then goes on to show what happens when there is a 
mismatch. The case of the open and short circuits are used to show the extreme 
situations and then these are developed to show what happens with loads that 
are less than or greater then the characteristic impedance of the feeder.

Understanding how the reflected power gives rise to voltage and current 
standing waves is the key to understanding what happens when there is a high 
VSWR.

Read all about VSWR:
https://www.electronics-notes.com/articles/antennas-propagation/vswr-return-loss/what-is-vswr.php

Watch the video:
https://youtu.be/BSa051lWB.c om 





73
Bob, K4TAX


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Re: [Elecraft] [K3] SWR - Numerical Indication

[Dick Dickinson]

Hi John,

 

Per your suggestion, I ran a sweep of my 40 meter vertical with the K3 /
K3EZ software.

I then measured at ~20 kHz steps with my MFJ-259B.

Both sets of measurements were taken from the PL-259 that plugs into the rig
or 259B.

 

Conditions were ~60 degrees F, ground nearly saturated.

 

Attached is an image of the results.

 

 

Kindly,

Dick - KA5KKT


---

Hi Dick,

 

An EZNEC and SimSmith model of the on ground 1/4 wave vertical:

https://www.kn5l.net/images/SS-KA5KKT-vertical.png

 

SimSmith R1 represents ground loss, the value set to establish a 50 ohm load
at the transmitter, G in SimSmith.

 

According to the models, the 7 to 7.3 MHz SWR is a little below 1.3.

 

A flat measurement using the K3 SWR meter seams reasonable. My suggestion is
to use a Antenna Analyzer to measure the antenna and system.

 

John KN5L

 

On 12/2/18 12:16 AM, Dick Dickinson wrote:

> I have a full-size monoband vertical for 40 meters.  Simple 

> architectural aluminum tapering from 1 ¼” (?) in 6’ telescoping 

> sections.  The radial field is designed to provide a 50 ohm match at 

> the feed point…12 – 13’+ radials.  It is fed directly…no matching 

> device with RG-213 from the remote antenna switch about 50’ away at my 

> tower.  The coax from the rig to the remote antenna switch is 

> estimated to be ~ 50’ in length.  A lot of the time running K3EZ to 

> sweep the band (typically 20 watts), it will indicate a

> 1.0:1 SWR from 7.0 MHz to 7.3 MHz in 20 kHz steps.  Occasional 

> deviation from one K3EZ run to another might be due to variations in 

> moisture content of the ground or less than perfect connection to the 

> vertical…an uncommon situation.  The K3 shows the same readings.

> 

> Is this 1.0:1 SWR across the entire 40 meter band curious or remarkable?

 

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Re: [Elecraft] [K3] SWR - Numerical Indication

[John Oppenheimer]

Hi Dick,

The Elecraft list does not accept attachments. Send to me directly.

John KN5L

On 12/2/18 4:14 PM, Dick Dickinson wrote:
> Hi John,
> 
> Per your suggestion, I ran a sweep of my 40 meter vertical with the K3 /
> K3EZ software.
> 
> I then measured at ~20 kHz steps with my MFJ-259B.
> Both sets of measurements were taken from the PL-259 that plugs into the rig
> or 259B.
> 
> Conditions were ~60 degrees F, ground nearly saturated.
> 
> Attached is an image of the results.
> 
> Kindly,
> Dick - KA5KKT
> 
> 
> ---
> 
> Hi Dick,
> 
> An EZNEC and SimSmith model of the on ground 1/4 wave vertical:
> https://www.kn5l.net/images/SS-KA5KKT-vertical.png
> 
> SimSmith R1 represents ground loss, the value set to establish a 50 ohm load
> at the transmitter, G in SimSmith.
> 
> According to the models, the 7 to 7.3 MHz SWR is a little below 1.3.
> 
> A flat measurement using the K3 SWR meter seams reasonable. My suggestion is
> to use a Antenna Analyzer to measure the antenna and system.
> 
> John KN5L
> 
> On 12/2/18 12:16 AM, Dick Dickinson wrote:
>> I have a full-size monoband vertical for 40 meters.  Simple 
>> architectural aluminum tapering from 1 �� (?) in 6� telescoping 
>> sections.  The radial field is designed to provide a 50 ohm match at 
>> the feed point�12 � 13�+ radials.  It is fed directly�no matching 
>> device with RG-213 from the remote antenna switch about 50� away at my 
>> tower.  The coax from the rig to the remote antenna switch is 
>> estimated to be ~ 50� in length.  A lot of the time running K3EZ to 
>> sweep the band (typically 20 watts), it will indicate a
>> 1.0:1 SWR from 7.0 MHz to 7.3 MHz in 20 kHz steps.  Occasional 
>> deviation from one K3EZ run to another might be due to variations in 
>> moisture content of the ground or less than perfect connection to the 
>> vertical�an uncommon situation.  The K3 shows the same readings.
>>
>> Is this 1.0:1 SWR across the entire 40 meter band curious or remarkable?

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Re: [Elecraft] [K3] SWR - Numerical Indication

[ANDY DURBIN]

"Do you find a high degree of correlation between your (assumed) K3 and KAT500 
SWR readings across various levels of SWR? "

I don't have a K3.  I do have loads of recorded data that would allow 
comparison of KPA500 SWR and LP-100A SWR and a more limited set of data that 
would allow comparison of KAT500 SWR with LP-100A SWR.  I have not performed 
either comparison but, as a general observation, it's obvious that the LP-100A 
is far more useful at low power levels or for mismatches that would give low 
reflected power.  At high power levels there is quite good agreement between 
the LP-100A and the KPA500 for power and SWR.  Since I know that, I look mainly 
at the LP-100A data.

I did a quick test on 20 m.  For an antenna system load that my LP-100A reports 
as SWR 1.09 with  Z of 52.7 ohm at 4.3 deg it took about 70 W output power for 
my KAT500 to change from 1.00 to 1.11 SWR.

To look at this another way - until the meter moves off the peg it isn't 
telling you much about the signal being measured.  All it's telling you is that 
you need a better meter.

I'm not saying there is anything wrong with the KPA500 or KAT500 SWR metering.  
You just need to know how it behaves and what it is useful for.  I expect the 
same applies to the K3 SWR meter.

Andy, k3wyc

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Re: [Elecraft] [K3] SWR - Numerical Indication

[ab2tc]

Hi,

Get a good dummy load and you will get the indication "1.0 - 1". I have both
the K3 (souped up to near K3S) and the K3S and they both do it. You are not
confusing this with with 1.1, are you?

AB2TC - Knut





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Re: [Elecraft] [K3] SWR - Numerical Indication

[ab2tc]

Hi again,

Oops I accidentally sent the message without the context quote.

Get a good dummy load and you will get the indication "1.0 - 1". I have both
the K3 (souped up to near K3S) and the K3S and they both do it. You are not
confusing this with with 1.1, are you? 

AB2TC - Knut 


Dick Dickinson wrote
> I've noticed that I'm not showing a reading of less than 1.1:1 SWR on my
> antennas per K3 SWR Numerical Readout.  K3EZ will record 1.0:1 SWR in band
> sweeps.
> 
> Can the K3(S) Numerical Display show 1.0:1 SWR?  If so, is there a likely
> reason why K3EZ will show 1.0:1 while my K3 will only go as far down as
> 1.1:1?
> 
> 
> Dick -  KA5KKT
> 
> 





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Re: [Elecraft] [K3] SWR - Numerical Indication

[Bob McGraw K4TAX]

Yes, the K3S SWR display can show a 1.0:1 value.  But in my case,  it 
does not exactly agree with another instrument in the feed line system. 
    As to why you are showing two different values, as minute as they 
are I might add, you are measuring 2 different places in the feed line. 
  In my thinking, it is physically impossible to put two  SWR bridges 
in the same place electrically.


In theory the SWR on a given line should be the same at all places, but 
maybe not since there is loss of some minute value in the line.      
Since you are measuring on antennas, common mode current, may be the 
contributing cause.  Difference in measurement calibration, may be a 
factor as well.


VSWR bridges are calibrated with some specific value of load. Ideally, 
it is 50 ohm non-reactive, but it could be 49 ohms or 51 ohms or some 
other value.   Just because a load says "50 ohms" on the label is no 
real indication that is actually fact.    To that end, I have 3 dummy 
loads which are "50 ohm" loads according to the label but none are not 
true 50 ohm loads.    I do have a Celwave load that says 50.5 ohms on 
the label and measures 50.5 ohms per my General Radio bridge.    The 
others are +/- something, but good enough to evaluate a ham transmitter 
or amplifier.


Frankly, a difference between 1.1:1 and 1.0:1 won't make any realistic 
difference in any form or fashion other than to appease the operator.


73

Bob, K4TAX



On 7/27/2018 9:58 AM, Dick Dickinson wrote:

I've noticed that I'm not showing a reading of less than 1.1:1 SWR on my
antennas per K3 SWR Numerical Readout.  K3EZ will record 1.0:1 SWR in band
sweeps.

Can the K3(S) Numerical Display show 1.0:1 SWR?  If so, is there a likely
reason why K3EZ will show 1.0:1 while my K3 will only go as far down as
1.1:1?


Dick -  KA5KKT



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Re: [Elecraft] [K3] SWR - Numerical Indication

[Mel Farrer via Elecraft]

Dick, 
While Bob is correct, the bottom line is not SWR but the R and j numbers.  
There are numerous values that will give you a 1.1:1, but only 50+j0 will be 
the true match of 1.0:1.  So,unless you do not have the equipment to measure 
the polar values, be thankful you have 1.1:1.  
Mel, K6KBE

  From: Bob McGraw K4TAX 
 To: elecraft@mailman.qth.net 
 Sent: Friday, July 27, 2018 1:10 PM
 Subject: Re: [Elecraft] [K3] SWR - Numerical Indication
   
Yes, the K3S SWR display can show a 1.0:1 value.  But in my case,  it 
does not exactly agree with another instrument in the feed line system. 
     As to why you are showing two different values, as minute as they 
are I might add, you are measuring 2 different places in the feed line. 
   In my thinking, it is physically impossible to put two  SWR bridges 
in the same place electrically.

In theory the SWR on a given line should be the same at all places, but 
maybe not since there is loss of some minute value in the line.      
Since you are measuring on antennas, common mode current, may be the 
contributing cause.  Difference in measurement calibration, may be a 
factor as well.

VSWR bridges are calibrated with some specific value of load. Ideally, 
it is 50 ohm non-reactive, but it could be 49 ohms or 51 ohms or some 
other value.   Just because a load says "50 ohms" on the label is no 
real indication that is actually fact.    To that end, I have 3 dummy 
loads which are "50 ohm" loads according to the label but none are not 
true 50 ohm loads.    I do have a Celwave load that says 50.5 ohms on 
the label and measures 50.5 ohms per my General Radio bridge.    The 
others are +/- something, but good enough to evaluate a ham transmitter 
or amplifier.

Frankly, a difference between 1.1:1 and 1.0:1 won't make any realistic 
difference in any form or fashion other than to appease the operator.

73

Bob, K4TAX



On 7/27/2018 9:58 AM, Dick Dickinson wrote:
> I've noticed that I'm not showing a reading of less than 1.1:1 SWR on my
> antennas per K3 SWR Numerical Readout.  K3EZ will record 1.0:1 SWR in band
> sweeps.
>
> Can the K3(S) Numerical Display show 1.0:1 SWR?  If so, is there a likely
> reason why K3EZ will show 1.0:1 while my K3 will only go as far down as
> 1.1:1?
>
>
> Dick -  KA5KKT
>
>
>
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Re: [Elecraft] [K3] SWR - Numerical Indication

[Wes Stewart]

I would be surprised if two garden variety instruments, even placed at the same 
point, would agree. The directional bridges/couplers in most "(V)SWR" meters 
that hams routinely use externally or which are built into our radios are not 
precision instruments.  There are a number of error sources in reflection 
measurements; source match, diode non-linearity, coupler tracking errors and 
often the most significant, directivity error.


In an ideal coupler, (i.e signal separation device) one port measures the 
forward (incident signal) and another measures the reverse (reflected) signal 
and there is no coupling between ports in the unwanted direction(s).  In other 
words there is no signal at the reverse port due to the forward signal.  In a 
real world coupler there is some leakage signal appearing at the reverse port 
due to the forward signal, absent any reflected signal.  The "goodness" of a 
directional coupler in this instance is called "directivity" and the error 
signal is directivity error. Directivity is usually specified in dB.  Really 
good couplers might have directivities in the 40 dB neighborhood.  Really really 
good directional bridges can be 50 dB, but so-so units might be 25-30 dB.  Not 
ready for prime time units are lower than this.


Now I have no way of knowing what the directivities are of the couplers built 
into K3s, KPA500s, KAT500s, etc. but considering that they have to work over 
about 5 octaves, I'm going out on a limb and saying that 25 to 30 dB is a fair 
estimate.  If I'm wrong, I'm sure I'll hear about it.  For sake of discussion 
I'm going to use 26.5 dB.  What this means is that if I terminate the output 
spigot of one of these radios with a perfect 50+j0 load, I'm going to measure a 
leakage signal (directivity error) that is 26.5 dB below the incident value.  
I'll introduce the concept of return loss here.


We hams usually speak in terms of SWR.  SWR = (1 + p) / (1 - p) where p is the 
reflection coefficient. Here the p = the voltage measured at the reflected port 
and the constant 1 represents the incident signal.  In reality both of these 
quantities are complex numbers, they have both magnitude and phase but SWR 
measurements are scalar, we throw away the phase (since it's difficult to 
measure) and just use the magnitude. (In fact the symbol "p", which is really 
the Greek letter rho, indicates the magnitude of the reflection coefficient in 
normal usage)  We can also express this ratio as return loss, which is -20 * 
log10(p).  So return loss, SWR and reflection coefficient are just different 
ways to express the same thing; the ratio of incident to reflected signal.


Let's return to our example; the coupler with 26.5 dB directivity, which 
indicates a return loss (RL) of 26.5 dB even with a perfect termination.  Doing 
the math and converting RL = 26.5 dB to SWR we get 1.1:1.  Our perfect load 
measures 1.1:1 with our imperfect instrument.  And this assumes that there are 
no other errors, which there always are. But it gets worse.


Let's say that the load we want to measure really is 1.1:1.  We now have two 
(apparent) reflections, 1) the real one and 2) the directivity error and they 
both have the same magnitude.  In our simple detector, they sum together.  Now I 
said earlier that we don't measure phase, only magnitude, but just because we 
don't, or can't measure the relative phases doesn't mean they aren't there. We 
will examine two cases to determine the limits of error.  Case 1) both 
reflections are in phase, they add up to p + p or 2p, RL = 20.5 and SWR 
~1.21:1.  Case 2) they are exactly out of phase, they sum to zero.  p = 0, RL is 
infinite and SWR = 1:1.  The possible RL error is then -6 to +infinity dB!


In other words, an actual SWR of 1.1:1 can be measured anywhere between 1.0:1 
and 1.2:1.  Is it any wonder that we often read about concerns that one device 
measures one thing, while another located at the same, or close location 
measures something different.  Of course all of this is predicated on a 
directional coupler with 26.5 dB directivity and no other error sources.  It's 
entirely possible that the Elecraft couplers are better than this.  They are 
certainly no better than 40 dB since the internal reference resistors are 51 
instead of 50 ohm.  Plus the "Tandem Match" configuration is in itself not a 
great match to the transmitter output.(1)  Furthermore, the coupler, at least in 
a K3 is driven by a LPF, which isn't a great 50 ohm source. Plus the coupler 
output port isn't connected directly to the coax connector. and so on and so 
forth (2).  All of this creates "uncertainty."


In a metrology lab heroic efforts are made to reduce uncertainty but do we, or 
should we, really care in this situation?  In my opinion, no, but everyone is 
free to differ.


Wes  N7WS

(1)  See "An HF In-Line Return Loss And Power Meter" by Paul Kiciak, N2PK.  
http://n2pk.com/#TP3


(2)  See "Gauge the Accuracy of SNA Measurements" 
http://www.