I'm wanting to build this active antenna, but can't find the core to
wind the output coupling transformer.

http://www.elecdesign.com/Articles/I...ArticleID=6244

This is the authors description of the transformer.

"The toroidal transformer’s primary is 36 turns of No.24 enameled wire
wound on a core from a Sony 1-421-302 line choke. Its secondary is
nine turns of No.24 telephone wire."

And this is his decsription of the performance of the amplifier.

The frequency response at low gain is very flat (±0.2 dB) from 200 kHz
to 35 MHz, and is only 0.4 dB down at 60 MHz. At standard high gain,
the response is very flat to 25 MHz and -3 dB at 50 MHz. The maximum
output level in all gain configurations is over 500 mV rms into a
75ohm load.

Does anyone have any idea what type of core that would work as well?

Thanks
Mike

The frequency response at low gain is very flat (±0.2 dB) from 200 kHz
to 35 MHz, and is only 0.4 dB down at 60 MHz. At standard high gain,
the response is very flat to 25 MHz and -3 dB at 50 MHz. The maximum
output level in all gain configurations is over 500 mV rms into a
75ohm load.

Does anyone have any idea what type of core that would work as well?
================================
Assuming the freq range intended is 1 - 30 MHz an Iron powder core made of
Mix No 2 material (permeability 10) ,colour code : RED , would be suitable.

Size T50 has outer diameter 0.5 inch and inner diameter 0.30 inch
hence T50-2
Size T68 has outer diameter 0.69 inch and inner diameter 0.37 inch
hence T68-2
Size T80 has outer diameter 0.795 inch and inner diameter 0.495 inch hence
T80-2

If the frequency range is to be from 0.02 - 30 MHz the above type of Iron
core can be combined with a same size core of Mix no 3 material ,colour
code : GREY eg the 2 types of ring glued together and wound together.

There is also a ferrite type core which covers the frequency range
0.02 -30MHz made from Mix No 61 material ( permeability 125) ;colour code
: GREY ; designations FT50-61 ; FT68-61 ; FT80-61.

Frank GM0CSZ / KN6WH

Mike wrote:
I'm wanting to build this active antenna, but can't find the core to
wind the output coupling transformer.

http://www.elecdesign.com/Articles/I...ArticleID=6244

This is the authors description of the transformer.

"The toroidal transformer's primary is 36 turns of No.24 enameled wire
wound on a core from a Sony 1-421-302 line choke. Its secondary is
nine turns of No.24 telephone wire."

And this is his decsription of the performance of the amplifier.

The frequency response at low gain is very flat (±0.2 dB) from 200 kHz
to 35 MHz, and is only 0.4 dB down at 60 MHz. At standard high gain,
the response is very flat to 25 MHz and -3 dB at 50 MHz. The maximum
output level in all gain configurations is over 500 mV rms into a
75ohm load.

Does anyone have any idea what type of core that would work as well?

It sounds like a conventional broadband transformer. The ARRL Handbook
has some guidelines on how to design the things, it's quite simple, if
you select a suitable ferrite core.

Mike wrote:
I'm wanting to build this active antenna, but can't find the core to
wind the output coupling transformer.

http://www.elecdesign.com/Articles/I...ArticleID=6244

This is the authors description of the transformer.

"The toroidal transformer’s primary is 36 turns of No.24 enameled wire
wound on a core from a Sony 1-421-302 line choke. Its secondary is
nine turns of No.24 telephone wire."

With that turns ratio, I would use a smaller wire for the primary,
probably No. 30 silver plates Kynar insulated wire wrap wire.

And this is his decsription of the performance of the amplifier.

The frequency response at low gain is very flat (±0.2 dB) from 200 kHz
to 35 MHz, and is only 0.4 dB down at 60 MHz. At standard high gain,
the response is very flat to 25 MHz and -3 dB at 50 MHz. The maximum
output level in all gain configurations is over 500 mV rms into a
75ohm load.

Does anyone have any idea what type of core that would work as well?

I would try a core ordinarily used as a medium frequency noise
suppression core, with enough window area to allow non overlapped
turns around the hole. Perhaps a Steward 28B0870-000, 22mm OD, 13.7mm
ID, 6.4mm thick. This is made of 850u material, flat permeability out
to about 2 MHz, and then rolling off with increasing loss as frequency
rises.
http://www.steward.com/web_part_no.a...rt=28B0870-000
There is also one twice as thick, if you want to lower the turns count
a bit. 28B0870-100.

But if the goal is to have optimum response at the low frequency end,
and to absorb the higher frequency end, a core made of the 5000u
material would be even better. Type 35 (Steward's low frequency bead
material) has flat permeability to only 300kHz. A usable example
might be LFB220140-000, 22mm OD, 14mm ID, 12.7mm thick.
http://www.steward.com/web_part_no.a...=LFB220140-000
This one could probably work with fewer turns, but the same ratio.

These cores go for less than a dollar each from Digikey.

The material curves are in the toroid manual:
http://www.steward.com/pdfs/ToroidCatalog-rev11-C.pdf

Highland Ham wrote:

================================
Assuming the freq range intended is 1 - 30 MHz an Iron powder core made of
Mix No 2 material (permeability 10) ,colour code : RED , would be suitable.

Size T50 has outer diameter 0.5 inch and inner diameter 0.30 inch
hence T50-2
Size T68 has outer diameter 0.69 inch and inner diameter 0.37 inch
hence T68-2
Size T80 has outer diameter 0.795 inch and inner diameter 0.495 inch hence
T80-2

If the frequency range is to be from 0.02 - 30 MHz the above type of Iron
core can be combined with a same size core of Mix no 3 material ,colour
code : GREY eg the 2 types of ring glued together and wound together.

There is also a ferrite type core which covers the frequency range
0.02 -30MHz made from Mix No 61 material ( permeability 125) ;colour code
: GREY ; designations FT50-61 ; FT68-61 ; FT80-61.

Frank GM0CSZ / KN6WH

I disagree with this advice. It would be appropriate for a narrowband,
tuned transformer, but that's not what the schematic indicates. It's a
broadband transformer which has different requirements for a core. What
you need is high winding impedance, not the high Q and relatively low
impedance provided by the cores Frank is recommending. An appropriate
core is a "low frequency" ferrite such as Fair-Rite (and Amidon) type
70-series (72, 73, 77, etc), or type 43 which is very widely used for
EMI filtering applications. You can easily identify "low frequency"
ferrites because they're the only ones which give you any continuity
(although the R might be high) when probed at two points with an
ohmmeter. Type 43 can't be identified this way -- they'll show an open
circuit. As for core size, the number of turns specified on the diagram
will provide enough impedance with any core of size half inch diameter
or so, or larger, and with normal geometry. You could probably get by
with a core smaller than that if necessary.

High frequeny ferrites (which aren't suitable) like 61 are relatively
rare, so if you have any ferrite cores in your junk box, they're likely
to be ok. Powdered iron cores won't give you enough winding impedance.

Roy Lewallen, W7EL

On Tue, 31 Jan 2006 12:44:28 -0800, Roy Lewallen
wrote:

Highland Ham wrote:

================================
Assuming the freq range intended is 1 - 30 MHz an Iron powder core made of
Mix No 2 material (permeability 10) ,colour code : RED , would be suitable.

Size T50 has outer diameter 0.5 inch and inner diameter 0.30 inch
hence T50-2
Size T68 has outer diameter 0.69 inch and inner diameter 0.37 inch
hence T68-2
Size T80 has outer diameter 0.795 inch and inner diameter 0.495 inch hence
T80-2

If the frequency range is to be from 0.02 - 30 MHz the above type of Iron
core can be combined with a same size core of Mix no 3 material ,colour
code : GREY eg the 2 types of ring glued together and wound together.

There is also a ferrite type core which covers the frequency range
0.02 -30MHz made from Mix No 61 material ( permeability 125) ;colour code
: GREY ; designations FT50-61 ; FT68-61 ; FT80-61.

Frank GM0CSZ / KN6WH

I disagree with this advice. It would be appropriate for a narrowband,
tuned transformer, but that's not what the schematic indicates. It's a
broadband transformer which has different requirements for a core. What
you need is high winding impedance, not the high Q and relatively low
impedance provided by the cores Frank is recommending. An appropriate
core is a "low frequency" ferrite such as Fair-Rite (and Amidon) type
70-series (72, 73, 77, etc), or type 43 which is very widely used for
EMI filtering applications. You can easily identify "low frequency"
ferrites because they're the only ones which give you any continuity
(although the R might be high) when probed at two points with an
ohmmeter. Type 43 can't be identified this way -- they'll show an open
circuit. As for core size, the number of turns specified on the diagram
will provide enough impedance with any core of size half inch diameter
or so, or larger, and with normal geometry. You could probably get by
with a core smaller than that if necessary.

High frequeny ferrites (which aren't suitable) like 61 are relatively
rare, so if you have any ferrite cores in your junk box, they're likely
to be ok. Powdered iron cores won't give you enough winding impedance.

Roy Lewallen, W7EL

Well, It appears that I'm not the only one confused about core types.
I do have some FT50-43 cores, so I think I'll try that first and see
what happens.

Thanks to all for the suggestions.

Mike

Mike wrote:

Well, It appears that I'm not the only one confused about core types.
I do have some FT50-43 cores, so I think I'll try that first and see
what happens.

Thanks to all for the suggestions.

Those are type 43 ferrite (Fair-Rite designation), the most common kind.
Your cores will be just fine for this and similar applications.

You're definitely not the only one confused about core types. Very few
people seem to understand what the requirements are for cores used in
various applications and therefore what cores are suitable for a given
application.

Roy Lewallen, W7EL