开云体育

Hi Jim,


yes, once you got started using SimSmith, you will not want to miss it anymore. It is the perfect companion
of NannVNA and NanoVNA saver or any VNA. You can not only “measure resonance from coax far end”, but so much more.
The best freeware ever programmed – imho – for radio amateur and RF engineering use.




There is, however, one little precaution that needs to be mentioned here, as you said this about SimSmith:

> Like drop in an LC element between two impedances, and it automatically calculates appropriate values to match.

In a sense (when finally matched) that is correct. More generally, (when mismatched) it is not.

I assume you want to get best power transfer (making best use of available power).



SimSmith uses the correct Gamma calculation for T R A N S M IS S I O N L I N E S by using this formula:

Gamma = (Z2 - Z1) / (Z2 + Z1) (a) with Z2 being the load impedance, Z1 the characteristic wave impedance of the line.

This type (a) calculation also is the mapping formula in Smith Charts between the Z (or Y) plane and the Gamma plane.
So far so good, nothing wrong.

But (a) is not generally adequate in your case. Let’s look at this circuit:





Interconnecting two identical impedances, doesn’t lead to maximum power transfer as (a) could make you think.
This is a common mistake resulting from using (a) only and neglecting the difference between

characteristic wave impedance of the line
and
impedance toward the generator (or source).

In your case the impedance toward the source is given. So, instead (a) we need:

Gamma = (ZL - Zs*) / (ZL + Zs) (b) with ZL being impedance toward the load, Zs the impedance toward the source,
and * meaning conjugate complex.

(b) sometimes is called is the "generalized reflection factor". It is valid for any, including imperfectly matched, impedances.
In most publications, this general formula is not mentioned, but often the special case of perfect conjugate match is.

Gamma at resonance does not get real in (a), but only in (b).
Using (a) for arbitrary impedances even could result in negative SWR,
that SimSmith covers up in later versions by saying SWR = |SWR|, thus ironing away the bad looking negative SWR. Why?

Ward Harriman, AE6TY, program Author of SimSmith, belongs to a school that does not accept the difference above.

This school, instead, teaches and believes in a doctrine – that (making me shake my head) even became something like a standard:



(The above I found in a glossary from ATIS or former ANSI.)

The difference of (a) and (b) is marginal near resonance, that is, for well-tuned narrow band antennas.
But it can become important at larger mismatch, i.e. like using a 1.8 MHz resonant antenna at 2.0 MHz,
or when using way out-of-resonance antennas, i.e. an electrically short antenna, with a rig side only tuner.

Having mentioned this little (worth a foot note) precaution, I anyway strongly insist:

SimSmith is absolutely recommended. It's all worth the reasonably small time investment it takes to get started.
I Strongly recommend it. Don’t panic because of the vast number of possibilities SimSmith offers.

Go, find it at

Download it at

and use it with great benefit.

Anyone interested in more detail of (b), is invited to ask me for the derivation of (b).
It takes, however, some basic complex math understanding.

Please don’t try to bother AE6TY with suggesting (b). I did. Save his time. He just doesn’t want it.


73, Hans
DJ7BA










But you wanted to match two impedances by an L/C network (Tuner) made of lumped L and C (but no line) in this example.

Here we have no characteristic wave impedance, but we have two impedances: One, Z2, toward the generator, as above.
But another one, Z1, toward the generator. That one is NOT any characteristic wave impedance of any cable.

As there are no reflections (that would be caused at a mismatched, terminated cable end), but we have a simple
AC serial circuit with the following: Generator (thought as made of a constant voltage source and some Thévenin
internal impedance), and a load impedance (having an resistive part and a reactive part) . That's all. So there is
no reflection (though generally quite often people speak of a reflection factor, as if we had a misterminated line).



The above (a) will do that -in case of perfect conjugate match - a situation we often want, of course.






-----Ursprüngliche Nachricht-----
Von: [email protected] <[email protected]> Im Auftrag von Jim Allyn - N7JA
Gesendet: Freitag, 10. Januar 2020 05:02
An: [email protected]
Betreff: Re: [nanovna-users] Measuring resonance from coax far end.



On 1/9/20 3:55 PM, WB2UAQ wrote:

I bet SimSmith will make it even easier but right now I don't have the

patience to sit still and figure out how to run it:)

You won't need any patience, it's amazingly simple. Like drop in an LC element between two impedances, and it automatically calculates appropriate values to match. Tell it you want a high pass instead of a low pass, and it automatically recalculates.

Sorry, after having rearranged my text, some not meant to send text had remained below

73, Hans
DJ7BA

Sorry, please ignore this remainder.



Von: DJ7BA <dj7ba@...>
Gesendet: Freitag, 10. Januar 2020 22:33
An: '[email protected]' <[email protected]>
Betreff: AW: [nanovna-users] SimSmith - great, not only for Measuring resonance from coax far end.



Hi Jim,


yes, once you got started using SimSmith, you will not want to miss it anymore. It is the perfect companion
of NannVNA and NanoVNA saver or any VNA. You can not only “measure resonance from coax far end”, but so much more.
The best freeware ever programmed – imho – for radio amateur and RF engineering use.



There is, however, one little precaution that needs to be mentioned here, as you said this about SimSmith:

> Like drop in an LC element between two impedances, and it automatically calculates appropriate values to match.

In a sense (when finally matched) that is correct. More generally, (when mismatched) it is not.

I assume you want to get best power transfer (making best use of available power).



SimSmith uses the correct Gamma calculation for T R A N S M IS S I O N L I N E S by using this formula:

Gamma = (Z2 - Z1) / (Z2 + Z1) (a) with Z2 being the load impedance, Z1 the characteristic wave impedance of the line.

This type (a) calculation also is the mapping formula in Smith Charts between the Z (or Y) plane and the Gamma plane.
So far so good, nothing wrong.

But (a) is not generally adequate in your case. Let’s look at this circuit:



Interconnecting two identical impedances, doesn’t lead to maximum power transfer as (a) could make you think.
This is a common mistake resulting from using (a) only and neglecting the difference between

characteristic wave impedance of the line
and
impedance toward the generator (or source).

In your case the impedance toward the source is given. So, instead (a) we need:

Gamma = (ZL - Zs*) / (ZL + Zs) (b) with ZL being impedance toward the load, Zs the impedance toward the source,
and * meaning conjugate complex.

(b) sometimes is called is the "generalized reflection factor". It is valid for any, including imperfectly matched, impedances.
In most publications, this general formula is not mentioned, but often the special case of perfect conjugate match is.

Gamma at resonance does not get real in (a), but only in (b).
Using (a) for arbitrary impedances even could result in negative SWR,
that SimSmith covers up in later versions by saying SWR = |SWR|, thus ironing away the bad looking negative SWR. Why?

Ward Harriman, AE6TY, program Author of SimSmith, belongs to a school that does not accept the difference above.

This school, instead, teaches and believes in a doctrine – that (making me shake my head) even became something like a standard:



(The above I found in a glossary from ATIS or former ANSI.)

The difference of (a) and (b) is marginal near resonance, that is, for well-tuned narrow band antennas.
But it can become important at larger mismatch, i.e. like using a 1.8 MHz resonant antenna at 2.0 MHz,
or when using way out-of-resonance antennas, i.e. an electrically short antenna, with a rig side only tuner.

Having mentioned this little (worth a foot note) precaution, I anyway strongly insist:

SimSmith is absolutely recommended. It's all worth the reasonably small time investment it takes to get started.
I Strongly recommend it. Don’t panic because of the vast number of possibilities SimSmith offers.

Go, find it at

Download it at

and use it with great benefit.

Anyone interested in more detail of (b), is invited to ask me for the derivation of (b).
It takes, however, some basic complex math understanding.

Please don’t try to bother AE6TY with suggesting (b). I did. Save his time. He just doesn’t want it.


73, Hans
DJ7BA










But you wanted to match two impedances by an L/C network (Tuner) made of lumped L and C (but no line) in this example.

Here we have no characteristic wave impedance, but we have two impedances: One, Z2, toward the generator, as above.
But another one, Z1, toward the generator. That one is NOT any characteristic wave impedance of any cable.

As there are no reflections (that would be caused at a mismatched, terminated cable end), but we have a simple
AC serial circuit with the following: Generator (thought as made of a constant voltage source and some Thévenin
internal impedance), and a load impedance (having an resistive part and a reactive part) . That's all. So there is
no reflection (though generally quite often people speak of a reflection factor, as if we had a misterminated line).



The above (a) will do that -in case of perfect conjugate match - a situation we often want, of course.





-----Ursprüngliche Nachricht-----
Von: [email protected] <mailto:[email protected]> <[email protected] <mailto:[email protected]> > Im Auftrag von Jim Allyn - N7JA
Gesendet: Freitag, 10. Januar 2020 05:02
An: [email protected] <mailto:[email protected]>
Betreff: Re: [nanovna-users] Measuring resonance from coax far end.



On 1/9/20 3:55 PM, WB2UAQ wrote:

I bet SimSmith will make it even easier but right now I don't have the

patience to sit still and figure out how to run it:)

You won't need any patience, it's amazingly simple. Like drop in an LC element between two impedances, and it automatically calculates appropriate values to match. Tell it you want a high pass instead of a low pass, and it automatically recalculates.

Hans, DJ7BA wrote: Anyone interested in more detail of (b), is invited to ask me for the derivation of (b).

Hans, because of real world losses, in a system with only one matching network, instead of a lossless system-wide conjugate match we can only have a conjugate match at a single reference plane. In most amateur systems, the matching plane is located at the Z0-match at the tuner input. My question is: Given that maximum power transfer occurs at the conjugate match reference plane, in a typical amateur radio system, where should that matching plane be located? (1) At the tuner input, (2) At the antenna feedpoint, (3) Somewhere else

Dig further back into the matching system. In our modern transceivers, the
match begins at the collector / drain of the output devices (the PA).
There is typically no attempt to do conjugation at that point, just bring
the impedance from the (generally) far left of the Smith Chart to something
significantly closer to the center of the chart. This must be accomplished
in a broadband manner.

Dave - W?LEV

--

*Dave - W?LEV*
*Just Let Darwin Work*
*Just Think*

Hi Dave,

Yes, you are right: There are good examples when we don't want or need perfect conjugate match by
design (or whatever other) reasons.

No matter, if we need it, can use it, or want it or not, (b) still generally describes physics of power
transfer, while (a) doesn't - except for the quite common special case: No generator reactance.
In this special case the general formula (a) flaw (wrong reactance compensation) is zero, as Z1 = Z1*.
In an almost tuned situation, the fault is marginal only and in practice often hardly matters. So the (a)
or (b) question often is no big issue. For electrically short antennas it may, however, be significant.

We are talking about a connection of two impedances, be they made of lumped serial elements, or be
they the Thévenin impedance at some point (=equivalent impedance toward the generator), connected
to the load impedance (=equivalent impedance toward the load).

And we are talking about physically correct power transfer description, which mostly is what we want,
unless the aim is echo suppression, maybe for an old time analog TV ghost suppression, stealth radar
applications, or whistle suppression on long phone lines. In these cases the reflection suppressionn is
most important, and there we correctly must use (a) instead of (b).

Reflection at a line termination, correctly described by (a), is not the same physical phenomenon as the
role of impedances in a serial circuit, that only is generally correctly described by (b). (Any parallel circuit
could be recalculated to be a serial equivalent, so "serial" will do.)

Contrary to echo suppression, however, most DXers want to get through in a pileup. Maximum possible
signal received by the rare DX station is achieved by max. real power transferred to our transmitting antenna.
I never heard of echo suppression in that context.


Thanks, Dave for suggesting your nice application of a modern very low internal resistance PA.

These units have a limit: That usually is max. PA heat dissipation. That's why the specs allow a certain max. SWR,
or else the TX protection circuit will reduce RF power or even switch off. In most 1.8 ... 30 MHz low internal resistance
PAs we have filters for different frequency ranges. These are necessary to suppress possible oscillations at certain
frequencies. Because of these filters we don't have a purely resistive internal impedance at the antenna socket.


A look at the PA specs:

Let's arbitrarily assume your modern PA has an internal generator impedance of 8 +j 2 Ohms at a frequency of interest.
Let's further assume, the PA's max. permitted SWR is 2.0 with 50 + j 0 Ohms reference.

This indeed means, we cannot make full use of perfect conjugate match anyway, be it using (a) or (b). For some,
the discussion here ends. That's ok. But let's have a closer look:

If we had no reactive parts in the generator, max power could be sent to the antenna, if the load was 25 + j 0 Ohms:
But we have a reactive part of + j2 Ohms, that (b) will compensate, while (a) would not compensate, but double it.

Resulting from (a) is a blind current that does not increase the radiated real power, only unnecessarily increases the current
through the generator's 8 Ohm resistive part, causing more heat in it and sooner action of the protection circuit, triggered
by the somewhat worse SWR due to the (doubled) reactive component.

On the bottom line:

I cannot see why your modern PA application could causes (a) to be any better than (b) - as both are limited by other reasons.
(a) is even limited a bit earlier.

Nothing speaks against (b) when trying to generally make best power match in so many applications.

Having said this: SimSmith (though not in the manual, but elsewhere: W0QE, who made many videos on SimSmith) sais:

You should us Z1* instead of Z1.
That is only correct for perfect match. Otherwise it would
result in:

Gamma = (Z1 - Z1*) / (Z2 + Z1*) (c).
But sorry: That also does not generally compensate the reactive parts either, except at perfect conjugate match. Only (b) does.

So (c) also does not correctly describe power transfer for poorly matched situations, that in practice easily do occur, as antenna
heights and resonance as well as ground conditions often cannot be changed to what would be the perfect ideal 50 + j0 Ohm
feedpoint impedance.


But - in spite of all above: I cannot stress it often enough:

I have not seen any better free software for the earnest radio amateur than SimSmith.
The missing of (b) can never be a good enough reason to not use SimSmith.

Go, get it, if you havn't yet.

If you know (b), you can calculate with it in SimSmith. Just use the plots feature. It accepts complex math formula.

So the value of mentioning (b), though the theory is correct, imho is worth not much more than a necessary footnote.
Many only know (a) and it serves them, too. Though scarcely known, others use (b), but SimSmith doesn't.

73, Hans
DJ7BA

-----Ursprüngliche Nachricht-----
Von: [email protected] <[email protected]> Im Auftrag von David Eckhardt
Gesendet: Samstag, 11. Januar 2020 17:13
An: NANO VNA <[email protected]>
Betreff: Re: [nanovna-users] SimSmith - great, not only for Measuring resonance from coax far end.

Dig further back into the matching system. In our modern transceivers, the match begins at the collector / drain of the output devices (the PA).
There is typically no attempt to do conjugation at that point, just bring the impedance from the (generally) far left of the Smith Chart to something significantly closer to the center of the chart. This must be accomplished in a broadband manner.

Dave - W?LEV

--

*Dave - W?LEV*
*Just Let Darwin Work*
*Just Think*

Right, W5DXP,

for lossless transmission lines and tuners the maximum power transfer theorem holds and
the location of the tuner would not matter.

But your question becomes a very important one, if lossy non 50 Ohm feed lines are involved,
where bad SWR matters much.


I just had started to study that issue by comparison: I have done two 3.51 MHz Double Zepp SimSmith
simulations, one with a single rig side tuner, the other one with two tuners. (In order to not clutter
results with tuner losses, I assumed ideal tuners.) These two simulations nicely illustrate your question.

I do hope you have SimSmith.

You can see, that by far the single best tuner plane is, where without a tuner the mismatch would be largest.
That in this case (as almost always) is at the antenna.

The results are convincing: Though you have a nice SWR = 1:1 at the TX end, the rig side tuner matched system
lets very little RF power get across the antenna feedpoint. Most power is lost in the lossy, high SWR feedline.

If the mismatch at the antenna feedpoint side is tuned away, too, we almost can transfer all of our available
power into that otherwise same antenna with same feedline.

The comparison shows:

In the two tuner system the question (a) or (b) doesn't matter, as SWR is low and thus (a) and (b) are similar.
At both places we tune to a real only generator side impedance. (b) makes no difference, as Z1 = Z1*.
But in the rig side only tuner system, the feedpoint mismatch is extreme and causes really bad losses.

Here is your point: The tuning location can matter very much. Seen that way, the Gamma or SWR at the feedpoint is
of high importance here. This is, why we imho do need (b). As SimSmith originally doesn't have (b), I calculated
it using plots. Not a problem, it just takes an extra calculation.

I think, much can be learned from this simulation. I still have some doubts concerning the powers shown in SimSmith,
as these are not consistent with what must be expected from the SWR 12.8959 as calculated by (b). At present I must leave
it still open, what causes the difference, but I dare to gueth, that (b) is correct and the 14.4 Watts at the feedpoint are not.
I will have to further study that. But I don't want to jump to conclusions prematurely. You may want to find out, too.

Excuse me for a non-finished answer. It's after midnight in Germany.

73, Hans
DJ7BA




-----Ursprüngliche Nachricht-----
Von: [email protected] <[email protected]> Im Auftrag von W5DXP
Gesendet: Samstag, 11. Januar 2020 15:05
An: [email protected]
Betreff: Re: [nanovna-users] SimSmith - great, not only for Measuring resonance from coax far end.

Hans, DJ7BA wrote: Anyone interested in more detail of (b), is invited to ask me for the derivation of (b).

Hans, because of real world losses, in a system with only one matching network, instead of a lossless system-wide conjugate match we can only have a conjugate match at a single reference plane. In most amateur systems, the matching plane is located at the Z0-match at the tuner input. My question is: Given that maximum power transfer occurs at the conjugate match reference plane, in a typical amateur radio system, where should that matching plane be located? (1) At the tuner input, (2) At the antenna feedpoint, (3) Somewhere else

Hans, DJ7BA, wrote:

I do hope you have SimSmith. Excuse me for a non-finished answer. It's after midnight in Germany.

I do have SimSmith and your experience and mine coincide, Hans. Ideally, we want the maximum available power transfer to occur at the antenna feedpoint. However, in a very low-loss system, we may have a system-wide *near-conjugate match* such that given a standard S-unit is 6 dB, the difference may be undetectable by the human ear.

I agree. It takes extreme cases like that short Double Zepp , to show that in an otherwise tuned system the feedpoint SWR
really makes that much difference. In this case some 8 dB are hidden behind the nice looking rig side 1:1 seen at the SWR meter.
That is the order of magnitude saving you a 700 Watt PA behind your 100 Watt transceiver. SimSmith shows the real powers,
and that also indicates the loss. Similarly in RX direction, the 8 dB could let your DX signal go beneath the noise blanket.


A not so nice side effect of the issue is:

If someone uses a complex Zo impedance (which I think is normally not necessary) , because of (a) he might get some negative
SWR shown in a passive lumped element setup.

Or, the Gamma and SWR indicated below the generator block can be inconsistent with the powers indicated, if you compare
|Gamma| calculated from available and transferred powers with |Gamma| calculated from the two impedances using (a).

This shouldn't happen, as users unnecessarily may think they did something wrong.


73, Hans
DJ7BA


-----Ursprüngliche Nachricht-----
Von: [email protected] <[email protected]> Im Auftrag von W5DXP
Gesendet: Sonntag, 12. Januar 2020 16:46
An: [email protected]
Betreff: Re: [nanovna-users] SimSmith - great, not only for Measuring resonance from coax far end.

Hans, DJ7BA, wrote:

I do hope you have SimSmith. Excuse me for a non-finished answer. It's after midnight in Germany.

I do have SimSmith and your experience and mine coincide, Hans. Ideally, we want the maximum available power transfer to occur at the antenna feedpoint. However, in a very low-loss system, we may have a system-wide *near-conjugate match* such that given a standard S-unit is 6 dB, the difference may be undetectable by the human ear.