Minicircuits 10% discount in December
Hi
On Nov 27, 2014, at 5:59 PM, Jim Lux jimlux@earthlink.net wrote:
On 11/27/14, 3:10 PM, Gerhard Hoffmann wrote:
Am 27.11.2014 um 23:30 schrieb Bob Camp:
Hi
Finding the RF transformer parts is still a bit of a challenge.
No. These work quite good for me:
CX2074 4:1 CT
CX2147 1:1 CT
<
http://www.digikey.de/product-search/de/rf-if-and-rfid/balun/3539019?k=cx2074
The 1:1 is optimum for the NIST doubler at the sources, btw.
The 4:1 as an autotransformer 9:1 at the drains. (2*BF862).
Gives you 13 dBm @ 2f for 13 dBm in at 1f upto 40 MHz in.
Still searching a good balun xformer for 800 MHz in.--> 1600 out.
Analog Devices seems to use these for their various application circuits
Up to 3 GHz is the Mini-Circuits TC1-1-13.
From 3 GHz to 4 GHz is the Johanson Technology
3600BL14M050.
From 4.9 GHz to 6 GHz is the Johanson Technology
5400BL15B050.
For pre-wound parts, there are a number of outfits that will sell you sub $1 transformers. How well they work .. who knows.
One example:
http://www.digikey.com/product-detail/en/MABA-007159-000000/1465-1302-2-ND/4429718
There are other parts in the same series at similar prices. Don’t want to go for the 2K pc minimum order? Price roughly doubles.
Bob
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Here are a couple of links to some Fair-Rite documentation that can help you
determine which cores will work for broadband transformers
Use of Ferrites in Broadband Transformers
http://www.fair-rite.com/newfair/pdf/Broadband.pdf
And the current Fair-Rite product catalog
http://www.fair-rite.com/newfair/pdf/Fair-Rite_Catalog_17th_Edition.pdf
HTH,
Dave M
Bob Camp wrote:
Hi
On Nov 27, 2014, at 5:10 PM, Gerhard Hoffmann dk4xp@arcor.de wrote:
Am 27.11.2014 um 23:30 schrieb Bob Camp:
Hi
Finding the RF transformer parts is still a bit of a challenge.
No. These work quite good for me:
CX2074 4:1 CT
CX2147 1:1 CT
To get back to the original post:
Which Fair-Rite cores listed on Mouser can be used for making
transformers?
There are a variety of people making pre-wound parts.
Bob
The 1:1 is optimum for the NIST doubler at the sources, btw.
The 4:1 as an autotransformer 9:1 at the drains. (2*BF862).
Gives you 13 dBm @ 2f for 13 dBm in at 1f upto 40 MHz in.
Still searching a good balun xformer for 800 MHz in.--> 1600 out.
regards, Gerhard
Hi
Those are the sort of parts I was looking for. There are about 10 of them listed at Mouser, all with rational prices. That’s a reasonable selection for starters. It’s still (unfortunately) a small selection compared to the full range of product.
Bob
On Nov 27, 2014, at 6:17 PM, Tim Shoppa tshoppa@gmail.com wrote:
43 binocular core: 2843002402, 14 cents qty 1 at Mouser.
77 binocular core: 2873000202, 59 cents qty 1 at Newark.
43 material toroid: 5943000201, 12 cents qty 1 at Mouser.
Clifton Labs has good examples and measurements on transformers wound on
these and other cores.
On Thu, Nov 27, 2014 at 6:54 PM, Bob Camp kb8tq@n1k.org wrote:
To get back to the original post:
Which Fair-Rite cores listed on Mouser can be used for making transformers?
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Hi
I’ve been using their products (and their competitors) to make transformers for at least 40 years. It’s amazingly easy to do. The problem has always been finding the raw cores without buying a ton of them at a time.
Bob
On Nov 27, 2014, at 6:34 PM, Dave M dgminala@mediacombb.net wrote:
Here are a couple of links to some Fair-Rite documentation that can help you determine which cores will work for broadband transformers
Use of Ferrites in Broadband Transformers
http://www.fair-rite.com/newfair/pdf/Broadband.pdf
And the current Fair-Rite product catalog
http://www.fair-rite.com/newfair/pdf/Fair-Rite_Catalog_17th_Edition.pdf
HTH,
Dave M
Bob Camp wrote:
Hi
On Nov 27, 2014, at 5:10 PM, Gerhard Hoffmann dk4xp@arcor.de wrote:
Am 27.11.2014 um 23:30 schrieb Bob Camp:
Hi
Finding the RF transformer parts is still a bit of a challenge.
No. These work quite good for me:
CX2074 4:1 CT
CX2147 1:1 CT
To get back to the original post:
Which Fair-Rite cores listed on Mouser can be used for making
transformers?
There are a variety of people making pre-wound parts.
Bob
The 1:1 is optimum for the NIST doubler at the sources, btw.
The 4:1 as an autotransformer 9:1 at the drains. (2*BF862).
Gives you 13 dBm @ 2f for 13 dBm in at 1f upto 40 MHz in.
Still searching a good balun xformer for 800 MHz in.--> 1600 out.
regards, Gerhard
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and follow the instructions there.
Rick,
Thanks for the brief review of MiniCircuits stuff (I'm not connected with
them in any way except as a customer).
Since you've characterized some of their parts, perhaps you could help
answer a question that someone else posted, and one that I would like to
have answered as well.
Have you measured the effects of DC current in the windings of an RF
transformer, such as is seen if the transformer is in the collector circuit
of an amplifier? If so, could you provide a generalization of the effects,
such as changes in frequency response, losses, etc.?
Many Thanks!,
Dave M
Richard (Rick) Karlquist wrote:
On 11/27/2014 7:07 AM, Tim Shoppa wrote:
For a hobbyist doing things a few at a time, what advantage is there
to buying RF transformers made by Mini-circuits etc., vs winding
them using commonly available ferrite cores/binocular cores?
If I needed to do a production run of 1000+ boards with tiny SMT
transformers, sure, no problem buying them from mini-circuits or a
distributor etc. But for hobbyist stuff seems far more flexible to
wind them onesy-twosy using not so tiny cores and windings selected
for the particular application.
Tim N3QE
You need the tiny cores to get the performance of the MiniCircuits
transformers. You just can't get the same bandwidth using macro sized
"binocular" cores. Now, if you don't need a lot of bandwidth, then
what you are saying could make sense. Another issue is stray
capacitance. Considerably lower with a tiny core.
I have spent many hours characterizing MiniCircuits transformers
beyond the data sheet specs, and dissecting them to learn how they
do it. They really do have a lot of rocket science in them. In
terms of the engineering I am buying (especially in a one-off
application) they are ridiculously cheap. And I say that as a fairly
knowledgeable transformer designer in my own right.
I do keep binocular cores around for higher power transformers, and
for "emergencies" when I need a transformer "yesterday".
Rick Karlquist N6RK
On 11/28/2014 10:08 AM, Dave M wrote:
Rick,
Thanks for the brief review of MiniCircuits stuff (I'm not connected
with them in any way except as a customer).
Since you've characterized some of their parts, perhaps you could help
answer a question that someone else posted, and one that I would like to
have answered as well.
Have you measured the effects of DC current in the windings of an RF
transformer, such as is seen if the transformer is in the collector
circuit of an amplifier? If so, could you provide a generalization of
the effects, such as changes in frequency response, losses, etc.?
Many Thanks!,
Dave M
The very tiny cores on MiniCircuits transformers will start to saturate
at hundreds of mA. The effect is that the magnetizing inductance drops,
which matters more at low frequencies than high frequencies. I try
to avoid feeding DC to an amplifier through a transformer winding.
Instead I use a separate RF choke for that. However, it would probably
work OK for, say, up to 25 mADC for a small signal transistor, but
why take a chance.
If you are using a DC feed through a transformer winding, be careful
not to accidently short circuit it, causing the full available current
from the power supply to flow through the transformer. This can
actually magnetize the core and permanently damage it. Saturation
via DC is much more deleterious than saturation via AC.
It is easy to calculate the flux density using Ampere's law, which
is one of the four Maxwell's equations. H = I/(2piR). Since R
(radius) is in the denominator, cores saturate from the inside
first before the whole core is saturated. Multiply H by mu,
(as any time nut knows) to get B. If R is 1 mm, and I is 628 mA,
then H = 10 ampere turns per meter. If mu-relative is 1000, then
B = 4piX10^-7 X 1000 X 10 = 125 mT. That is a hefty 1250 Gauss.
Some materials may be affected at 1/10 this flux density.
Now a days, a lot of RF is differential, in which case you are
free to feed DC through the output transformer without worrying
about this issue.
I worked for several companies where those 6 hole cylindrical chokes
were ubiquitous. I specifically characterized those and established
a maximum current rating of only 100 mA. Of course, many production
designs exceeded this limit and "worked" anyway. I actually observed
someone try to put 20A through one of these. The tantalum capacitors
on the "cold" side of the bead actually exploded due to RF current.
Rick Karlquist N6RK
Hi
On Nov 28, 2014, at 2:27 PM, Richard (Rick) Karlquist richard@karlquist.com wrote:
On 11/28/2014 10:08 AM, Dave M wrote:
Rick,
Thanks for the brief review of MiniCircuits stuff (I'm not connected
with them in any way except as a customer).
Since you've characterized some of their parts, perhaps you could help
answer a question that someone else posted, and one that I would like to
have answered as well.
Have you measured the effects of DC current in the windings of an RF
transformer, such as is seen if the transformer is in the collector
circuit of an amplifier? If so, could you provide a generalization of
the effects, such as changes in frequency response, losses, etc.?
Many Thanks!,
Dave M
The very tiny cores on MiniCircuits transformers will start to saturate
at hundreds of mA. The effect is that the magnetizing inductance drops,
which matters more at low frequencies than high frequencies. I try
to avoid feeding DC to an amplifier through a transformer winding.
Instead I use a separate RF choke for that. However, it would probably
work OK for, say, up to 25 mADC for a small signal transistor, but
why take a chance.
If you are using a DC feed through a transformer winding, be careful
not to accidently short circuit it, causing the full available current
from the power supply to flow through the transformer. This can
actually magnetize the core and permanently damage it. Saturation
via DC is much more deleterious than saturation via AC.
It is easy to calculate the flux density using Ampere's law, which
is one of the four Maxwell's equations. H = I/(2piR). Since R
(radius) is in the denominator, cores saturate from the inside
first before the whole core is saturated. Multiply H by mu,
(as any time nut knows) to get B. If R is 1 mm, and I is 628 mA,
then H = 10 ampere turns per meter. If mu-relative is 1000, then
B = 4piX10^-7 X 1000 X 10 = 125 mT. That is a hefty 1250 Gauss.
Some materials may be affected at 1/10 this flux density.
Now a days, a lot of RF is differential, in which case you are
free to feed DC through the output transformer without worrying
about this issue.
I worked for several companies where those 6 hole cylindrical chokes
were ubiquitous. I specifically characterized those and established
a maximum current rating of only 100 mA. Of course, many production
designs exceeded this limit and "worked" anyway. I actually observed
someone try to put 20A through one of these. The tantalum capacitors
on the "cold" side of the bead actually exploded due to RF current.
If you do need to run substantial current through a choke core, the larger binocular cores with a half turn through them are a better choice.
Still useless for 20A (or even 2A) though …
Bob
Rick Karlquist N6RK
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On 11/28/2014 1:04 PM, Bob Camp wrote:
If you do need to run substantial current through a choke core, the larger binocular cores with a half turn through them are a better choice.
Still useless for 20A (or even 2A) though …
Bob
The binocular cores come in several hole sizes.
All other things being equal, current handling
capacity is directly proportional to hole size.
One thing to watch out for with putting DC thru
binocular cores happens in push pull RF power amplifiers.
The output transformer is usually a binocular
core on steroids, or its equivalent constructed
with beads or sleeves, etc, threaded over a single
"turn" made from brass tubes connected together
at the end away from the transistors.
In cheap (illegal) CB amplifiers, you will frequently see
+13.6 VDC connected to the junction of the brass
tubes, as if it were a center tap. It actually isn't
a center tap in terms of core saturation, and the DC
currents to the transistors are unmitigated in terms of
magnetizing the core. Although the cores are larger,
so are the currents, and these amplifiers just live with
the degradation including the magnetization. This
occurs because each core sees only a half-turn. If
you replace the tubes with a 2 turn wire primary, then
the problem goes away, but of course then the amplifier
would never work as high as 27 MHz, which is does normally
only by resonating stray PC board trace inductance with
peaking capacitors on the transformer. This forms a
two stage step up structure. If you "improve" the layout
to get rid of the trace inductance, the amplifier no longer
works! See Motorola AN-762.
Rick Karlquist N6RK
The very tiny cores on MiniCircuits transformers will start to
saturate at hundreds of mA. The effect is that the magnetizing inductance
drops, which matters more at low frequencies than high frequencies. I try
to avoid feeding DC to an amplifier through a transformer winding.
Instead I use a separate RF choke for that. However, it would
probably work OK for, say, up to 25 mADC for a small signal transistor,
but
why take a chance.
If you are using a DC feed through a transformer winding, be careful
not to accidently short circuit it, causing the full available current
from the power supply to flow through the transformer. This can
actually magnetize the core and permanently damage it. Saturation
via DC is much more deleterious than saturation via AC.
It is easy to calculate the flux density using Ampere's law, which
is one of the four Maxwell's equations. H = I/(2piR). Since R
(radius) is in the denominator, cores saturate from the inside
first before the whole core is saturated. Multiply H by mu,
(as any time nut knows) to get B. If R is 1 mm, and I is 628 mA,
then H = 10 ampere turns per meter. If mu-relative is 1000, then
B = 4piX10^-7 X 1000 X 10 = 125 mT. That is a hefty 1250 Gauss.
Some materials may be affected at 1/10 this flux density.
Now a days, a lot of RF is differential, in which case you are
free to feed DC through the output transformer without worrying
about this issue.
I worked for several companies where those 6 hole cylindrical chokes
were ubiquitous. I specifically characterized those and established
a maximum current rating of only 100 mA. Of course, many production
designs exceeded this limit and "worked" anyway. I actually observed
someone try to put 20A through one of these. The tantalum capacitors
on the "cold" side of the bead actually exploded due to RF current.
Rick Karlquist N6RK
Thanks for the insight, Rick. You confirmed many of my own assumptions
about RF transformers and cores. I hadn't thought about permanently
magnetizing a core with excessive DC current, but it makes sense. Same
theory applies to line frequency power transformers and inductors; if the
core saturates, inductance takes a nose-dive and current goes wild.
A couple weeks ago, I sent an email to the Minicircuits technical support
folks in hopes of getting this, or similar, info about a couple of their
transformer models (specifically, T1-1 and T4-1-KK81), but so far, I'm still
waiting. Guess I should give them a call.. got great technical advice from
them when I called for help some time ago.
Cheers,
Dave M
Am 28.11.2014 um 23:42 schrieb Dave M:
A couple weeks ago, I sent an email to the Minicircuits technical
support folks in hopes of getting this, or similar, info about a
couple of their transformer models (specifically, T1-1 and T4-1-KK81),
but so far, I'm still waiting. Guess I should give them a call.. got
great technical advice from them when I called for help some time ago.