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[K3] SWR - Numerical Indication

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Dick Dickinson

[K3] SWR - Numerical Indication

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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ab2tc

Re: [K3] SWR - Numerical Indication

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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ab2tc

Re: [K3] SWR - Numerical Indication

In reply to this post by Dick Dickinson

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

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Bob McGraw - K4TAX

Re: [K3] SWR - Numerical Indication

In reply to this post by Dick Dickinson

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
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home:http://mailman.qth.net/mailman/listinfo/elecraft
> Help:http://mailman.qth.net/mmfaq.htm
> Post:mailto:[hidden email]
>
> This list hosted by:http://www.qsl.net
> Please help support this email list:http://www.qsl.net/donate.html
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>

Elecraft mailing list

Re: [K3] SWR - Numerical Indication

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 <[hidden email]>
To: [hidden email]
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:

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Wes Stewart-2

Re: [K3] SWR - Numerical Indication

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
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.testmart.com/webdata/appnote/763.PDF

On 7/27/2018 1:08 PM, Bob McGraw K4TAX wrote:

> 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

Petr, OK1RP/M0SIS

Re: [K3] SWR - Numerical Indication

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
--
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73 - Petr, OK1RP
"Apple & Elecraft freak"
B:http://ok1rp.blogspot.com
MeWe: https://bit.ly/2HGPoDx
MeWe: https://bit.ly/2FmwvDt

Don Wilhelm

Re: [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.

W2xj

Re: [K3] SWR - Numerical Indication

In reply to this post by Petr, OK1RP/M0SIS

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 <[hidden email]> 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/
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

Petr, OK1RP/M0SIS

Re: [K3] SWR - Numerical Indication

This post was updated on .

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

> Sent from my iPad
>
> > On Nov 30, 2018, at 6:29 AM, Petr, OK1RP/M0SIS <indians@xsmail.com> 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
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.testmart.com/webdata/appnote/763.PDF

On 7/27/2018 1:08 PM, Bob McGraw K4TAX wrote:

> 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

... [show rest of quote]

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Post: mailto:[hidden email]

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On Fri, Nov 30, 2018, at 4:47 PM, W2xj wrote:
> 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 <indians@xsmail.com> 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/
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:Elecraft@mailman.qth.net
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> > Message delivered to w2xj@w2xj.net
> >
>

--
73 - Petr, OK1RP
--
B: http://goo.gl/Fd2JhJ
G+: http://goo.gl/w3u2s9
G+: http://goo.gl/gP99xq
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73 - Petr, OK1RP
"Apple & Elecraft freak"
B:http://ok1rp.blogspot.com
MeWe: https://bit.ly/2HGPoDx
MeWe: https://bit.ly/2FmwvDt

Charlie T, K3ICH

Re: [K3] SWR - Numerical Indication

In reply to this post by Don Wilhelm

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: [hidden email] <[hidden email]> On
Behalf Of Don Wilhelm
Sent: Friday, November 30, 2018 9:56 AM
To: [hidden email]
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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Don Wilhelm

Re: [K3] SWR - Numerical Indication

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: [hidden email] <[hidden email]> On
> Behalf Of Don Wilhelm
> Sent: Friday, November 30, 2018 9:56 AM
> To: [hidden email]
> 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
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

Phil Kane-2

Re: [K3] SWR - Numerical Indication

In reply to this post by Charlie T, K3ICH

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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Dave Hachadorian-2

Re: [K3] SWR - Numerical Indication

In reply to this post by Don Wilhelm

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: [hidden email]
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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John Oppenheimer

Re: [K3] SWR - Numerical Indication

In reply to this post by Dick Dickinson

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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Dick Dickinson

Re: [K3] SWR - Numerical Indication

In reply to this post by Dick Dickinson

Thanks for the explanation, John.

Im 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 doesnt explain why the K3 was showing 1.1:1 while passing 1.0:1
information to K3EZ, or so it seems. I dont think that the K3EZ is
measuring SWR rather merely posting information it is getting from the
K3no different measuring device or location. Perhaps it is a sort of
rounding error. By the way, for those who havent 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 charta 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 point12 13+
radials. It is fed directlyno 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 verticalan 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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John Oppenheimer

Re: [K3] SWR - Numerical Indication

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

John Oppenheimer

Re: [K3] SWR - Numerical Indication

In reply to this post by Dick Dickinson

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?

Bob McGraw - K4TAX

Re: [K3] SWR - Numerical Indication

In reply to this post by Dick Dickinson

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 <https://youtu.be/BSa051lWB.com>om
<https://youtu.be/BSa051lWB.com>

73
Bob, K4TAX

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ANDY DURBIN

[K3] SWR - Numerical Indication

In reply to this post by Dick Dickinson

"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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