"Fred McKenzie" wrote in message
...

In article ,
"Wayne" wrote:

I was looking at a MFJ remote antenna tuner, and it is specified as being
able to match 12 to 1600 ohms.

What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600
ohms a SWR of about 32:1.

If one started from 1600 ohms around a Smith chart, the circle would
intersect at the other side at about 0.64 ohms.

Likewise starting at 12 ohms and going halfway around the chart would end
up
at 210 ohms, not 1600.

How does one use the specs if the antenna to be matched has a complex
impedance? Look at the internal tuner component ranges?

Your Smith Chart is normalized to 50 Ohms, but the tuner may not have a
"characteristic impedance". So to use the Smith Chart approach, assume
that it does. In that case, Z divided by 12 is equal to 1600 divided by
Z. Therefore Z squared is equal to the product of 12 and 1600, or Z =
138.6 Ohms.

You can normalize a Smith Chart to that value. Now see if the tuner
will work with all values within the circle!

I suppose that would help a bit. Thanks.

"John S" wrote in message ...

On 8/9/2015 12:23 PM, Wayne wrote:
I was looking at a MFJ remote antenna tuner, and it is specified as
being able to match 12 to 1600 ohms.

What does that mean? At 12 ohms the SWR would be about 4.2:1 and at
1600 ohms a SWR of about 32:1.

If one started from 1600 ohms around a Smith chart, the circle would
intersect at the other side at about 0.64 ohms.

Likewise starting at 12 ohms and going halfway around the chart would
end up at 210 ohms, not 1600.

How does one use the specs if the antenna to be matched has a complex
impedance? Look at the internal tuner component ranges?

# What antenna are you thinking to match?

My yard is very difficult for getting antennas up. I currently use a
vertical on 20-10 that is mounted on top of a rather large metal patio
cover.
The cover does have AC voltage available for patio lights/fans/bird bath
pump and such. So I could power a remote tuner separate from the coax if
required.

The current antenna for 20-10 is a 14.5 foot vertical, fed with a short run
of good coax and tuned at the rig end of the coax.

IIRC, the swr is about 6:1 on 20 meters, dips around 18 MHz and rises to
about 20:1 on 10 meters.
For 20:1 the charts say I will lose not more than 3 db with the short run of
coax, which is acceptable.

In practice, the antenna is performing well enough for me to leave it alone.
.....but you know how hams are.....

wrote in message
...
bilou wrote:

wrote in message
...
Wayne wrote:
Those ranges of impedances are basically worthless.
I don't agree :-)
If I had to test such a tuner the first thing I would do
is put a pure resistor of those values and try to
match them accross the frequency and power range announced.
Measuring the insertion loss would be nice too.
Of course it is not the complete story but a good start.

Which basically tells you nothing about the ability to match a complex
load.
Hello
You are absolutely right in fact a perfect ferrite transformer would be
better.
But an aerial must have a real impedance part to be of any use :-)
Specifications must be easy to verify.
Here it is the case.
How do you check the 0.1dB noise figure advocated by many LNB's ?
:-)

bilou wrote:

wrote in message
...
bilou wrote:

wrote in message
...
Wayne wrote:
Those ranges of impedances are basically worthless.
I don't agree :-)
If I had to test such a tuner the first thing I would do
is put a pure resistor of those values and try to
match them accross the frequency and power range announced.
Measuring the insertion loss would be nice too.
Of course it is not the complete story but a good start.

Which basically tells you nothing about the ability to match a complex
load.
Hello
You are absolutely right in fact a perfect ferrite transformer would be
better.

It is rather difficult for a ferrite transformer to convert a random
complex impedance to approximately 50 Ohm resistive, which is what
an autotuner does.

But an aerial must have a real impedance part to be of any use :-)

Which is why one uses an autotuner to convert the random complex impedance
to approximately 50 Ohm resistive.

Specifications must be easy to verify.

And life must be fair...

Here it is the case.
How do you check the 0.1dB noise figure advocated by many LNB's ?

With test equipment.


--
Jim Pennino

On 8/9/2015 4:24 PM, Wayne wrote:


"John S" wrote in message ...

On 8/9/2015 12:23 PM, Wayne wrote:
I was looking at a MFJ remote antenna tuner, and it is specified as
being able to match 12 to 1600 ohms.

What does that mean? At 12 ohms the SWR would be about 4.2:1 and at
1600 ohms a SWR of about 32:1.

The 12 to 1600 ohms is the RANGE that the tuner is capable of
matching. Forget SWR because it has no meaning at this point.

That's a bit of what I was getting at. I have another tuner rated for
4:1 SWR, and I assume that means it will match all the way around the 4
circle.

I don't know what to do with a 12 to 1600 ohm spec.



If one started from 1600 ohms around a Smith chart, the circle would
intersect at the other side at about 0.64 ohms.

You are not analyzing this correctly. If you are really comfortable
with a Smith chart, put a capacitor across the 1600 ohms and then put
an inductor in series with the results. By adjusting the values, you
can achieve a 50 ohm output.

Likewise starting at 12 ohms and going halfway around the chart would
end up at 210 ohms, not 1600.

This is similar to the above, but now you want a series impedance and
a shunt impedance following it.

I was just showing that the 12 and 1600 are not on the same circle.



How does one use the specs if the antenna to be matched has a complex
impedance? Look at the internal tuner component ranges?

That is a good question. Do you want to buy the tuner and tear it down
to explore the component ranges, or would it be better to ask the
designers? You should ask them to define the type (complex impedance)
of the load to which their specs apply.

I suspect the designers have a gag order from the marketing guys.

I found the following on the MFJ site for the MFJ-998RT. See page 2 at
this link:

http://www.mfjenterprises.com/Downlo...df&company=mfj

•Impedance matching range: 12 to 1600 ohms
•SWR matching range: up to 4:1 for 50 ohms and upto 32:1 for 50 ohms
•Minimum power for tuning: 5 watts
•Maximum power while tuning: 100 watts with foldback, 20 watts without
foldback
•RF power limit: 1500 watts SSB/CW
•Frequency range: 1.8 to 30 MHz continuous coverage
•Frequency counter accuracy: ±1 kHz across HF bands

•Capacitance range: 0 to 3926 pF nominal (256 values) on input side 0 to
976 pF nominal (64 values) on output side

•Inductance range: 0 to 24.28 µH nominal (256 values)

On 8/11/2015 6:18 PM, John S wrote:
On 8/9/2015 4:24 PM, Wayne wrote:


"John S" wrote in message ...

On 8/9/2015 12:23 PM, Wayne wrote:
I was looking at a MFJ remote antenna tuner, and it is specified as
being able to match 12 to 1600 ohms.

What does that mean? At 12 ohms the SWR would be about 4.2:1 and at
1600 ohms a SWR of about 32:1.

The 12 to 1600 ohms is the RANGE that the tuner is capable of
matching. Forget SWR because it has no meaning at this point.

That's a bit of what I was getting at. I have another tuner rated for
4:1 SWR, and I assume that means it will match all the way around the 4
circle.

I don't know what to do with a 12 to 1600 ohm spec.



If one started from 1600 ohms around a Smith chart, the circle would
intersect at the other side at about 0.64 ohms.

You are not analyzing this correctly. If you are really comfortable
with a Smith chart, put a capacitor across the 1600 ohms and then put
an inductor in series with the results. By adjusting the values, you
can achieve a 50 ohm output.

Likewise starting at 12 ohms and going halfway around the chart would
end up at 210 ohms, not 1600.

This is similar to the above, but now you want a series impedance and
a shunt impedance following it.

I was just showing that the 12 and 1600 are not on the same circle.



How does one use the specs if the antenna to be matched has a complex
impedance? Look at the internal tuner component ranges?

That is a good question. Do you want to buy the tuner and tear it down
to explore the component ranges, or would it be better to ask the
designers? You should ask them to define the type (complex impedance)
of the load to which their specs apply.

I suspect the designers have a gag order from the marketing guys.

I found the following on the MFJ site for the MFJ-998RT. See page 2 at
this link:

http://www.mfjenterprises.com/Downlo...df&company=mfj


•Impedance matching range: 12 to 1600 ohms
•SWR matching range: up to 4:1 for 50 ohms and upto 32:1 for 50 ohms
•Minimum power for tuning: 5 watts
•Maximum power while tuning: 100 watts with foldback, 20 watts without
foldback
•RF power limit: 1500 watts SSB/CW
•Frequency range: 1.8 to 30 MHz continuous coverage
•Frequency counter accuracy: ±1 kHz across HF bands

•Capacitance range: 0 to 3926 pF nominal (256 values) on input side 0 to
976 pF nominal (64 values) on output side

•Inductance range: 0 to 24.28 µH nominal (256 values)

I think their minimums are not realistic. I would not know how to
achieve 0pF with a 3926pF variable cap, for example. Also, why 3926
rather than 3900 or even 3920? It isn't all that easy to measure 6pF out
of 3920pF. I'm thinking that somebody just threw some numbers at the
spec sheet.

BUT! It is better than nothing and may help to make some reasonable
judgements.

On 8/10/2015 8:30 PM, Wayne wrote:


"John S" wrote in message ...

On 8/9/2015 12:23 PM, Wayne wrote:
I was looking at a MFJ remote antenna tuner, and it is specified as
being able to match 12 to 1600 ohms.

What does that mean? At 12 ohms the SWR would be about 4.2:1 and at
1600 ohms a SWR of about 32:1.

If one started from 1600 ohms around a Smith chart, the circle would
intersect at the other side at about 0.64 ohms.

Likewise starting at 12 ohms and going halfway around the chart would
end up at 210 ohms, not 1600.

How does one use the specs if the antenna to be matched has a complex
impedance? Look at the internal tuner component ranges?

# What antenna are you thinking to match?

My yard is very difficult for getting antennas up. I currently use a
vertical on 20-10 that is mounted on top of a rather large metal patio
cover.
The cover does have AC voltage available for patio lights/fans/bird bath
pump and such. So I could power a remote tuner separate from the coax
if required.

The current antenna for 20-10 is a 14.5 foot vertical, fed with a short
run of good coax and tuned at the rig end of the coax.

IIRC, the swr is about 6:1 on 20 meters, dips around 18 MHz and rises to
about 20:1 on 10 meters.
For 20:1 the charts say I will lose not more than 3 db with the short
run of coax, which is acceptable.

In practice, the antenna is performing well enough for me to leave it
alone. ....but you know how hams are.....

I remember now. I even made an EZNEC model (including your metal patio)
and got results for all the ham bands. Using the specs for the
MFJ-998RT, it seems that it may match all but the 1.8MHz band IF the
specs can be relied upon.

I don't want to encourage you to spend a lot of money based on my input.
I just had fun doing the modelling.

In article , John S wrote:

I think their minimums are not realistic. I would not know how to
achieve 0pF with a 3926pF variable cap, for example. Also, why 3926
rather than 3900 or even 3920? It isn't all that easy to measure 6pF out
of 3920pF. I'm thinking that somebody just threw some numbers at the
spec sheet.

BUT! It is better than nothing and may help to make some reasonable
judgements.

Typically, these tuners use banks of capacitors, switched in and out
(parallel for caps, series for inductors) using relays. The
components are often in a 1:2:4:8:... power series. "256 values"
implies 8 components, and 8 relays, giving you anywhere from 0 to 255
times the "fundamental" value.

I expect that "0" means "all caps open, or all inductors shorted",
and "3926" is the sum of the nominal values of the caps in the bank.
If their starting value is around 15 pF, 255 times that would be
3825; add in a few pF of stray capacitance per relay and you'd be
in the neighborhood of 3926.

(Having figures like that, in the face of component variations and
strays and measurement errors, reminds me a bit of some dialog from
Harry Harrison's "Star Smashers of the Galaxy Rangers."

"[certain ancient events] took place approximately 14 billion years
ago."

"That figure is exact?"

"Of course."
)

John S wrote:
On 8/11/2015 6:18 PM, John S wrote:
On 8/9/2015 4:24 PM, Wayne wrote:


"John S" wrote in message ...

On 8/9/2015 12:23 PM, Wayne wrote:
I was looking at a MFJ remote antenna tuner, and it is specified as
being able to match 12 to 1600 ohms.

What does that mean? At 12 ohms the SWR would be about 4.2:1 and at
1600 ohms a SWR of about 32:1.

The 12 to 1600 ohms is the RANGE that the tuner is capable of
matching. Forget SWR because it has no meaning at this point.

That's a bit of what I was getting at. I have another tuner rated for
4:1 SWR, and I assume that means it will match all the way around the 4
circle.

I don't know what to do with a 12 to 1600 ohm spec.



If one started from 1600 ohms around a Smith chart, the circle would
intersect at the other side at about 0.64 ohms.

You are not analyzing this correctly. If you are really comfortable
with a Smith chart, put a capacitor across the 1600 ohms and then put
an inductor in series with the results. By adjusting the values, you
can achieve a 50 ohm output.

Likewise starting at 12 ohms and going halfway around the chart would
end up at 210 ohms, not 1600.

This is similar to the above, but now you want a series impedance and
a shunt impedance following it.

I was just showing that the 12 and 1600 are not on the same circle.



How does one use the specs if the antenna to be matched has a complex
impedance? Look at the internal tuner component ranges?

That is a good question. Do you want to buy the tuner and tear it down
to explore the component ranges, or would it be better to ask the
designers? You should ask them to define the type (complex impedance)
of the load to which their specs apply.

I suspect the designers have a gag order from the marketing guys.

I found the following on the MFJ site for the MFJ-998RT. See page 2 at
this link:

http://www.mfjenterprises.com/Downlo...df&company=mfj


?Impedance matching range: 12 to 1600 ohms
?SWR matching range: up to 4:1 for 50 ohms and upto 32:1 for 50 ohms
?Minimum power for tuning: 5 watts
?Maximum power while tuning: 100 watts with foldback, 20 watts without
foldback
?RF power limit: 1500 watts SSB/CW
?Frequency range: 1.8 to 30 MHz continuous coverage
?Frequency counter accuracy: ?1 kHz across HF bands

?Capacitance range: 0 to 3926 pF nominal (256 values) on input side 0 to
976 pF nominal (64 values) on output side

?Inductance range: 0 to 24.28 ?H nominal (256 values)

I think their minimums are not realistic. I would not know how to
achieve 0pF with a 3926pF variable cap, for example. Also, why 3926
rather than 3900 or even 3920? It isn't all that easy to measure 6pF out
of 3920pF. I'm thinking that somebody just threw some numbers at the
spec sheet.

BUT! It is better than nothing and may help to make some reasonable
judgements.

The parts in a modern autotuner are not variable, they are a bunch of
fixed components switched in and out by relays.

The 3926 pF is the value of ALL the capacitors in parallel and 0 pF
would be a straight connection.



--
Jim Pennino

On 8/11/2015 7:17 PM, Dave Platt wrote:
In article , John S wrote:

I think their minimums are not realistic. I would not know how to
achieve 0pF with a 3926pF variable cap, for example. Also, why 3926
rather than 3900 or even 3920? It isn't all that easy to measure 6pF out
of 3920pF. I'm thinking that somebody just threw some numbers at the
spec sheet.

BUT! It is better than nothing and may help to make some reasonable
judgements.

Typically, these tuners use banks of capacitors, switched in and out
(parallel for caps, series for inductors) using relays. The
components are often in a 1:2:4:8:... power series. "256 values"
implies 8 components, and 8 relays, giving you anywhere from 0 to 255
times the "fundamental" value.

I expect that "0" means "all caps open, or all inductors shorted",
and "3926" is the sum of the nominal values of the caps in the bank.
If their starting value is around 15 pF, 255 times that would be
3825; add in a few pF of stray capacitance per relay and you'd be
in the neighborhood of 3926.

(Having figures like that, in the face of component variations and
strays and measurement errors, reminds me a bit of some dialog from
Harry Harrison's "Star Smashers of the Galaxy Rangers."

"[certain ancient events] took place approximately 14 billion years
ago."

"That figure is exact?"

"Of course."

Haw!

Very good, Dave. It seems that I am a fossil. The world changed while I
slept.

Thanks for the education.