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