Hi all,=20
Seems my info wasn't clear, I'll try to explain.
> > I made a transformer using a 4229 pot core of 3F3 material.
4229 is the size of the pot core, 3F3 is the type of ferrite material.
> I put 13 turns on the bobbin for the primary, insulated it and then =
>wrapped a brass shield around the winding with out allowing the >ends =
to touch. A tab was brought out for connection,this is an >electrostatic =
shield to limit capacitive coupling between windings.
Early on in the discussions about transformers there was a lot of talk =
about limiting the capacitive coupling between the primary and the =
secondary winding. Putting the brass shield between windings=20
and grounding it prevents much of the capacitive coupling.
>>I cut a Styrofoam clam shells to fit around the shield,=20
I cut a donut shape out of Styrofoam, split it and put it over the brass =
shield. This was to put more distance between the primary and secondary =
to help limit capacitive coupling. This step might be overkill, but it =
was not difficult to do.
>>I wrapped 3 turns around the Styrofoam as the secondary.=20
I used a 13 turn to 3 turn ratio because it is close to the=20
SQRT of 900ohms/50ohms.
>>I gapped the core very slightly to have 200 ohms impedance at >>550 =
Khz.=20
I wanted the transformer to work down to 550khz, so I put a very small =
gap between the two halves of the pot core to adjust the=20
A sub L of the core so that the 3 turns measured 200 ohms at 550khz. =
This is the recommended 4 times the 50 ohm load.
I probably could have left it ungapped but was concerned about
self resonance of the 13 turns.
>>I soldered a box together using PCB material, mounted a UHF =
>>connector and brass screws for the antenna connections. The >>brass =
shield has a separate wire that runs back to the mast and >>is connected =
to ground.
I made a box using PC board, mounted the appropriate connectors. I =
brought out a connection for the brass shield to run to ground.=20
I do have some question regarding how effective the brass shield can be =
when the grounding wire is 14ft of horizontal wire and 19ft of vertical =
wire coonected to a ground rod.
Any feedback appreciated.
Mike
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