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From: Viktor on 21 Jul 2010 05:37

Has anyone here come across this application note for the
ATA8402 (T5754) Atmel 433MHz transmitter?

http://www.atmel.com/dyn/resources/prod_documents/doc9115.pdf

I have very little RF experience and I might be mistaken, but this AN
is very dodgy indeed.
I'm trying to make sense of the impedance-matching capacitor
calculation.

The main problem is that the equations are not accompanied by numeric
examples for the demo board handled in the same AN. Apart from this,
the equations given don't take into account the RF choke, nor the
added Lx,Cx filter in the demo board.

But OK, I don't even understand the matching-capacitor equations as
they are presented.
If I understood correctly, we get Z|| from Eq. 8, then use Eq. 9 to
calculate r, which we later use to get the matching capacitors.
To get r, we need to use the ideal Zload, but this is given as
166+j223 Ohm, i.e. a complex number, while Z|| and r are obviously
real numbers.
So, I'm stuck at Eq. 9 and have no idea how to proceed.
I have asked Atmel support what Zload is and received a short and (for
me) useless response stating that Zload is complex, but giving no hint
as to how the quotient of a real and a complex number should result in
r, a real number.
I asked again and have received no response.

I have since read application notes for competitors' TX chips, some of
which are well written and comprehensible even for an RF beginner like
me, but their IC's do have real output impedances so this problem
doesn't arise.

Thanks for any suggestions.

Viktor
From: markp on 21 Jul 2010 06:13

"Viktor" <vkesler(a)gmail.com> wrote in message
news:6da59961-c57d-4144-8c75-a4b3fe434315(a)j8g2000yqd.googlegroups.com...
>
> Has anyone here come across this application note for the
> ATA8402 (T5754) Atmel 433MHz transmitter?
>
> http://www.atmel.com/dyn/resources/prod_documents/doc9115.pdf
>
> I have very little RF experience and I might be mistaken, but this AN
> is very dodgy indeed.
> I'm trying to make sense of the impedance-matching capacitor
> calculation.
>
> The main problem is that the equations are not accompanied by numeric
> examples for the demo board handled in the same AN. Apart from this,
> the equations given don't take into account the RF choke, nor the
> added Lx,Cx filter in the demo board.
>
> But OK, I don't even understand the matching-capacitor equations as
> they are presented.
> If I understood correctly, we get Z|| from Eq. 8, then use Eq. 9 to
> calculate r, which we later use to get the matching capacitors.
> To get r, we need to use the ideal Zload, but this is given as
> 166+j223 Ohm, i.e. a complex number, while Z|| and r are obviously
> real numbers.
> So, I'm stuck at Eq. 9 and have no idea how to proceed.
> I have asked Atmel support what Zload is and received a short and (for
> me) useless response stating that Zload is complex, but giving no hint
> as to how the quotient of a real and a complex number should result in
> r, a real number.
> I asked again and have received no response.
>
> I have since read application notes for competitors' TX chips, some of
> which are well written and comprehensible even for an RF beginner like
> me, but their IC's do have real output impedances so this problem
> doesn't arise.
>
> Thanks for any suggestions.
>
> Viktor

I haven't used these chips. I decided that, without proper test gear, it
really wasn't worth my while getting involved in creating impedance matching
networks and all the design problems that throws up, so I used an RFM12B
(from www.hoperf.com) instead which is a small surface mountable complete
radio module based on the SiLabs Si4421 chip. These are very popular modules
and lots of application notes and user projects on the 'Net. They are also
very cheap (around $2.20 in volume). I would highly recommend this module, I
have used it very successfully and it has excellent range and sensitivity.

Mark.


From: pimpom on 21 Jul 2010 11:02
markp wrote:
> "Viktor" <vkesler(a)gmail.com> wrote in message
> news:6da59961-c57d-4144-8c75-a4b3fe434315(a)j8g2000yqd.googlegroups.com...
>>
>> Has anyone here come across this application note for the
>> ATA8402 (T5754) Atmel 433MHz transmitter?
>>
>> http://www.atmel.com/dyn/resources/prod_documents/doc9115.pdf
>>
>> I have very little RF experience and I might be mistaken, but
>> this AN
>> is very dodgy indeed.
>> I'm trying to make sense of the impedance-matching capacitor
>> calculation.
>>
>> The main problem is that the equations are not accompanied by
>> numeric
>> examples for the demo board handled in the same AN. Apart from
>> this,
>> the equations given don't take into account the RF choke, nor
>> the
>> added Lx,Cx filter in the demo board.
>>
>> But OK, I don't even understand the matching-capacitor
>> equations as
>> they are presented.
>> If I understood correctly, we get Z|| from Eq. 8, then use Eq.
>> 9 to
>> calculate r, which we later use to get the matching
>> capacitors.
>> To get r, we need to use the ideal Zload, but this is given as
>> 166+j223 Ohm, i.e. a complex number, while Z|| and r are
>> obviously
>> real numbers.
>> So, I'm stuck at Eq. 9 and have no idea how to proceed.
>> I have asked Atmel support what Zload is and received a short
>> and
>> (for me) useless response stating that Zload is complex, but
>> giving
>> no hint as to how the quotient of a real and a complex number
>> should
>> result in r, a real number.
>> I asked again and have received no response.
>>
>> I have since read application notes for competitors' TX chips,
>> some
>> of which are well written and comprehensible even for an RF
>> beginner
>> like me, but their IC's do have real output impedances so this
>> problem doesn't arise.
>>
>> Thanks for any suggestions.
>>
>> Viktor
>
> I haven't used these chips. I decided that, without proper test
> gear,
> it really wasn't worth my while getting involved in creating
> impedance matching networks and all the design problems that
> throws
> up, so I used an RFM12B (from www.hoperf.com) instead which is
> a
> small surface mountable complete radio module based on the
> SiLabs
> Si4421 chip. These are very popular modules and lots of
> application
> notes and user projects on the 'Net. They are also very cheap
> (around
> $2.20 in volume). I would highly recommend this module, I have
> used
> it very successfully and it has excellent range and
> sensitivity.

I have not used the RFM12B but the OP's post immediately made me
think of it as I've been considering it for a project. It seems
to be all you claim for it, and is stated to have automatic
impedance matching of the antenna.


From: markp on 21 Jul 2010 11:38

"pimpom" <pimpom(a)invalid.invalid> wrote in message
news:i27273$lgp$1(a)news.albasani.net...
> markp wrote:
>> "Viktor" <vkesler(a)gmail.com> wrote in message
>> news:6da59961-c57d-4144-8c75-a4b3fe434315(a)j8g2000yqd.googlegroups.com...
>>>
>>> Has anyone here come across this application note for the
>>> ATA8402 (T5754) Atmel 433MHz transmitter?
>>>
>>> http://www.atmel.com/dyn/resources/prod_documents/doc9115.pdf
>>>
>>> I have very little RF experience and I might be mistaken, but this AN
>>> is very dodgy indeed.
>>> I'm trying to make sense of the impedance-matching capacitor
>>> calculation.
>>>
>>> The main problem is that the equations are not accompanied by numeric
>>> examples for the demo board handled in the same AN. Apart from this,
>>> the equations given don't take into account the RF choke, nor the
>>> added Lx,Cx filter in the demo board.
>>>
>>> But OK, I don't even understand the matching-capacitor equations as
>>> they are presented.
>>> If I understood correctly, we get Z|| from Eq. 8, then use Eq. 9 to
>>> calculate r, which we later use to get the matching capacitors.
>>> To get r, we need to use the ideal Zload, but this is given as
>>> 166+j223 Ohm, i.e. a complex number, while Z|| and r are obviously
>>> real numbers.
>>> So, I'm stuck at Eq. 9 and have no idea how to proceed.
>>> I have asked Atmel support what Zload is and received a short and
>>> (for me) useless response stating that Zload is complex, but giving
>>> no hint as to how the quotient of a real and a complex number should
>>> result in r, a real number.
>>> I asked again and have received no response.
>>>
>>> I have since read application notes for competitors' TX chips, some
>>> of which are well written and comprehensible even for an RF beginner
>>> like me, but their IC's do have real output impedances so this
>>> problem doesn't arise.
>>>
>>> Thanks for any suggestions.
>>>
>>> Viktor
>>
>> I haven't used these chips. I decided that, without proper test gear,
>> it really wasn't worth my while getting involved in creating
>> impedance matching networks and all the design problems that throws
>> up, so I used an RFM12B (from www.hoperf.com) instead which is a
>> small surface mountable complete radio module based on the SiLabs
>> Si4421 chip. These are very popular modules and lots of application
>> notes and user projects on the 'Net. They are also very cheap (around
>> $2.20 in volume). I would highly recommend this module, I have used
>> it very successfully and it has excellent range and sensitivity.
>
> I have not used the RFM12B but the OP's post immediately made me think of
> it as I've been considering it for a project. It seems to be all you claim
> for it, and is stated to have automatic impedance matching of the antenna.
>

Yes, it really is a nice module (the Si4421 is a great little chip). It even
has a wakeup timer which is very low current, 1.5uA if I remember, and that
was even lower than my micro, plus the resolution of that timer can be
programmable to much finer resolution than my micro. I used that to achieve
pseudo-random wakeup times. It runs from 3.8V down to 2.2V too which is
ideal for 2 alkaline cells.


From: Viktor on 21 Jul 2010 16:05
On Jul 21, 5:38 pm, "markp" <map.nos...(a)f2s.com> wrote:
> "pimpom" <pim...(a)invalid.invalid> wrote in message
>
> news:i27273$lgp$1(a)news.albasani.net...
>
>
>
> > markp wrote:
> >> "Viktor" <vkes...(a)gmail.com> wrote in message
> >>news:6da59961-c57d-4144-8c75-a4b3fe434315(a)j8g2000yqd.googlegroups.com....
>
> >>> Has anyone here come across this application note for the
> >>> ATA8402 (T5754) Atmel 433MHz transmitter?
>
> >>>http://www.atmel.com/dyn/resources/prod_documents/doc9115.pdf
>
> >>> I have very little RF experience and I might be mistaken, but this AN
> >>> is very dodgy indeed.
> >>> I'm trying to make sense of the impedance-matching capacitor
> >>> calculation.
>
> >>> The main problem is that the equations are not accompanied by numeric
> >>> examples for the demo board handled in the same AN. Apart from this,
> >>> the equations given don't take into account the RF choke, nor the
> >>> added Lx,Cx filter in the demo board.
>
> >>> But OK, I don't even understand the matching-capacitor equations as
> >>> they are presented.
> >>> If I understood correctly, we get Z|| from Eq. 8, then use Eq. 9 to
> >>> calculate r, which we later use to get the matching capacitors.
> >>> To get r, we need to use the ideal Zload, but this is given as
> >>> 166+j223 Ohm, i.e. a complex number, while Z|| and r are obviously
> >>> real numbers.
> >>> So, I'm stuck at Eq. 9 and have no idea how to proceed.
> >>> I have asked Atmel support what Zload is and received a short and
> >>> (for me) useless response stating that Zload is complex, but giving
> >>> no hint as to how the quotient of a real and a complex number should
> >>> result in r, a real number.
> >>> I asked again and have received no response.
>
> >>> I have since read application notes for competitors' TX chips, some
> >>> of which are well written and comprehensible even for an RF beginner
> >>> like me, but their IC's do have real output impedances so this
> >>> problem doesn't arise.
>
> >>> Thanks for any suggestions.
>
> >>> Viktor
>
> >> I haven't used these chips. I decided that, without proper test gear,
> >> it really wasn't worth my while getting involved in creating
> >> impedance matching networks and all the design problems that throws
> >> up, so I used an RFM12B (fromwww.hoperf.com) instead which is a
> >> small surface mountable complete radio module based on the SiLabs
> >> Si4421 chip. These are very popular modules and lots of application
> >> notes and user projects on the 'Net. They are also very cheap (around
> >> $2.20 in volume). I would highly recommend this module, I have used
> >> it very successfully and it has excellent range and sensitivity.
>
> > I have not used the RFM12B but the OP's post immediately made me think of
> > it as I've been considering it for a project. It seems to be all you claim
> > for it, and is stated to have automatic impedance matching of the antenna.
>
> Yes, it really is a nice module (the Si4421 is a great little chip). It even
> has a wakeup timer which is very low current, 1.5uA if I remember, and that
> was even lower than my micro, plus the resolution of that timer can be
> programmable to much finer resolution than my micro. I used that to achieve
> pseudo-random wakeup times. It runs from 3.8V down to 2.2V too which is
> ideal for 2 alkaline cells.

Thanks for the pointer about the Silabs range of RF IC's.
I don't think the modules actually solve the antenna matching problem
since they don't have the antennas on them and I suspect the IC's RF
pins are just connected to the module header.
(Correct me if I'm wrong here.)

What kind of antenna do you use and how did you match the impedance?

There's some vague reference to an auto-tuning circuit in the IC
datasheet, but the optimum load impedance is also given as 52+j152
Ohms for 433MHz, so it seems you have to achieve that for optimum
power output.
I looked at Silabs AN369 and saw that they took a different approach
with the PCB loop antenna matching problem. They used an EM modelling
software to tweak a rather complicated loop antenna to have just the
right impedance for the IC's PA output.
This approach seems to me in the
million_monkeys_eventually_writing_Shakespeare category.

Anyway, I'm stuck with Atmel's chips for now. Both the receiver and
transmitter are past the prototype stage. I'll just have to tweak the
caps by trial and error or settle for less than maximum attainable
range.

Thanks again,

Viktor

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