Hi

What time (note the tie in to be on topic for the list :) will their retail location open on Thanksgiving?

Spending quality time on the auction sites can yield some pretty substantial discounts on RF transformers. The search process is not simple due to the crazy range of part numbers.

Once you have the transformer you get to decide how to handle coax grounds. In most cases the solution either creates a bunch of problems or it eliminates any benefit of transformer isolation.

Bob

Sent from my iPhone

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

On Thu, Nov 27, 2014 at 9:58 AM, Bob Camp kb8tq@n1k.org wrote:

Hi

I believe I made that point earlier. The main complaint is the difficulty of getting the correct cores. I seem to have a few dozen bags of cores. I still go shopping for more as projects come up

Bob

Sent from my iPhone

On 11/27/14, 7:07 AM, Tim Shoppa wrote:

Probably depends on the frequency ranges and such.  The commercial
transformers are very small, and probably have more consistent properties.

Sure.. it's a trade time for money situation.

OTOH, most hobby tinkerers are not going to fabricate semiconductor
devices like MMICs (although I'm sure there's a [semi-fab-nuts] list out
there for folks who have a 3" wafer line in their garage).

On Thu, Nov 27, 2014 at 10:28 AM, Bob Camp kb8tq@n1k.org wrote:

The mainline distributors (Allied, Newark, Mouser, etc.)  have excellent
selection of Fair-Rite and other cores. Admittedly to a neophyte the
equivalence of Fair-Rite or Laird part numbers to an Amidon-style number
may not be evident.

Clifton labs has excellent webpages of examples and is also a good way to
find the cores sizes and materials commonly stocked at the mainline
distributors using the manufacturer's part number (often with cross-ref to
Amidon style number as a strong hint!)

Recently some here expressed concern that the mini-circuits part may
saturate with medium DC currents. Of course if you are doing a SMT
production run you don't want to use bigger cores than necessary and most
of the mini-circuits parts tend to be physically very tiny to meet this
market. But if you wind your own on bigger cores this is a non-issue.

Tim N3QE

Hi

At least last time I looked, the “easy to find” distributors had great selections of parts used for switching power supplies and EMI suppression. When you started to dig for the specialized parts for RF transformers and tuned filters, the stock was pretty thin to nonexistent. If you move from ferrite to powdered iron, the search process alway has been more difficult...

Bob

Again I refer you to Clifton Labs website and cross-references there to the
Fair-Rite part numbers/mixes. Although the marketing largely emphasizes EMI
suppression, all the mainline distributors now offer several mixes and core
styles that are perfect for RF transformers.

Powdered iron, yeah, those are not so easily found at mainline
distributors, I end up getting them from kitsandparts.com or Amidon.

And to Jim's point... "build your own" MMIC from discrete RF transistors
(often different generations of CATV-oriented transistors - you get the
advantage that you get tune bias currents etc. for individual need) is
quite easy using parts stocked at Mouser etc. They also have these
impressive super-beefy broadband CATV distribution/isolation amplifiers.

Tim N3QE

On Thu, Nov 27, 2014 at 12:49 PM, Bob Camp kb8tq@n1k.org wrote:

On 11/27/2014 7:07 AM, Tim Shoppa wrote:

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 11/27/2014 9:09 AM, Tim Shoppa wrote:

I recently needed some binocular cores for a transformer for a client.
After checking all the distributors, I had to buy 500 of them.  Minimum
quantity.  So much for one-off hobbyist projects.  The reason why I
did not use a MiniCircuits transformer for this client is that the
impedance was much less than 50 ohms.  This is one area that
MiniCircuits really does not address.

Rick Karlquist N6RK

Another reason is reproducibility. If you or someone else wants to reproduce your design, using a well defined and available commercial part makes it much easier to achieve the same performance, particularly for RF components.

Didier KO4BB

On November 27, 2014 12:41:34 PM CST, "Richard (Rick) Karlquist" richard@karlquist.com wrote:

--
Sent from my Motorola Droid Razr HD 4G LTE wireless tracker while I do other things.

YES!
That's exactly why I go to Mini-Circuits.
Jim

On 11/27/2014 2:03 PM, Didier Juges wrote:

This email has been checked for viruses by Avast antivirus software.
http://www.avast.com

On 11/27/2014 11:03 AM, Didier Juges wrote:

to reproduce your design, using a well defined and available

commercial part makes it much easier to achieve the same

performance, particularly for RF components.

Exactly right.

I wrote an article on receiving loops and showed a design
with a 50:5 (turns ratio) transformer wound on a toroid.
Again, this is not available from MiniCircuits.  I have
wasted time dealing with numerous dumb questions about
"can I use XXX core that I have laying around the lab?"
or can I use a different gauge wire to wind it, etc.
So many people complained about the shipping cost to
buy one core that I stocked the cores and included them
with PC boards I was already selling to reduce the shipping
cost to "zero".

BTW, 73 material would NOT work in this application.
I was asked about that multiple times even though the
article specifically said it would not work and explained
why.

Rick Karlquist N6RK

As the things I want to do become more complex, and time gets more precious, I have adopted the mantra “buy the biggest piece you can. . .”
Don

Mouser carries a selection from Fair-Rite. They don't make it easy to
find a specific part number, however.

http://www.mouser.com/Fair-Rite/Passive-Components/EMI-RFI-Components/EMI-RFI-Suppressors-Ferrites/Ferrite-Toroids-Ferrite-Rings/_/N-bw7t9?P=1z13m3cZ1yxh9di

Joe Gray
W5JG

On Thu, Nov 27, 2014 at 11:34 AM, Tim Shoppa tshoppa@gmail.com wrote:

Hi

Finding the RF transformer parts is still a bit of a challenge.

Bob

Am 27.11.2014 um 23:30 schrieb Bob Camp:

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.

regards, Gerhard

Hi

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

On 11/27/14, 3:10 PM, Gerhard Hoffmann wrote:

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.

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:

Hi

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

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

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

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

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 11/28/2014 10:08 AM, Dave M wrote:

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

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

On 11/28/2014 1:04 PM, Bob Camp wrote:

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

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:

Try that:  < http://lmgtfy.com/?q=T1-1-KK81.pdf  >

The first anwer looks like a hit.

regards, Gerhard