TopBand: beverage transformers

Tom Rauch
Sat, 27 Feb 1999 18:53:41 -0500

Hi Rick,

> With the recent discussion of beverage matching transformers, I am
> curious about why everyone builds their own matching transformers.
> On my 600 ft beverage, I am using a little RF Prime/Mini-Circuits
> 9:1 impedance transformer bought off the shelf.  Seems to work fine.
> Do I really need to wind up one of my 2 1/2 inch 43 toroids to do
> this job?  Am I missing something here?

While both work, a 73 core takes 1/3 the number of turns as 43 
material for the same core style, offering better bandwidth and 
easier construction. In either case the transformer certainly doesn't 
need be very large at all, and you have freedom to wind any 
impedance ratio you need (an exact match is not required however, 
unless you are constructing a reflection transformer).

Minicircuit's transformers, while very convenient, do not handle dc 
or low frequency currents, nor do they handle more than a few 
hundred milliwatts of RF, without core saturation and generation of 

As little as 20 mA of current starts to saturate the very high ui core 
they use. In many cases they work, but in some situations odd 
problems like superimposed hum or signals mixing occurs. 

I remember building a high performance push-pull preamp using 
their transformers, and the weakest link in IMD performance was 
the Minicircuit transformer. 
73, Tom W8JI

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