as long as it for receive only, I think the best way will be to use a
toroid with a rather high AL value. About 30 years ago I had to design an rx
input balun transformer for a military receiver for the frequency range 10 kHz
to 3o MHz and have used SIEMENS N30 without any problems, employing the rule
that the XL of the coils should be about 3-4 times the impedance to be
transformed at the lowest frequency. In this application the balun has been
wound with triple twisted enamelled wire on a SIEMENS B62152-A0007-X030 core.
73 Ha-Jo, DJ1ZB
Alberto di Bene schrieb:
I need some words of wisdom and a bit of help about the
construction of a small toroid transformer.
First the antefact : I swapped recently my TS-850 for a TS-950SDX,
a very fine radio, but much less sensitive on the LF band than the TS-850.
Looking at the schematics, and doing some filter simulation with
Electronic Workbench, I think to have found the culprit, i.e. L3, a small
toroidal transfomer, with ratio 1:4, which is inserted in the signal path,
after the input attenuator, and before the filters bank. With all probability,
its response at 136kHz leaves much to be desired. The TS-850 doesn't
have any such transformer, the signal goes straight to the filters.
So I have decided to replace it. Looking in the MiniCircuits catalog, I have
found what seems to be the ideal replacement, the T4-6T-KK81 model, which
has a -3dB response from 10kHz to 100MHz. Problem is that this transformer
is not carried in stock by the Italian distributor, and both they and the
MiniCircuits sales office have a minimum quantity amount for an order.
At this point the only choice is to build it myself. And this is were your
come in my rescue. I need to know what your experiences are in building
such a wideband kind of transformers. What is the best type of material,
caveats to not forget, optimal number of turns, you name it.
TNX for any help,
73 Alberto I2PHD