Antenna is up and working. Took me and daughter's boyfriend about 3
hours to build and install into attic. It ended up being almost 40
feet long with about 13" spreaders. This works out to be about 8mc. I
think.

For the Balun I wound 4 turns for the coax end and 8 turns for the
antenna end. I put them on a pair of Amidon FT114-67 cores I had.

Al = 5mH/1000t so 25nH/t
1.6uh for 8 turns
90 ohms at 9mc

oops, I think 3.2uH cause I stacked two cores. This works out to
about 180 ohms at around 9mc. I suppose a few more turns would be ok
since antanna impedance is 300 ohms. I think the rule of thumb is to
keep transformer reactance a few times the circuit impedance. I'm not
exactly sure how the number of turns effects the signal. For transmit
I know I would use enough turns or stack lots of cores to keep
magnetizing flux low to keep cores from overheating.

Anyway, TWISTED terminated folded dipole seems to be working nicely.
It is quieter than my verticle or dipoles. Good call.

regards,
Bob
N9NEO

In article . com,
N9NEO wrote:
Antenna is up and working. Took me and daughter's boyfriend about 3
hours to build and install into attic. It ended up being almost 40
feet long with about 13" spreaders. This works out to be about 8mc. I
think.

For the Balun I wound 4 turns for the coax end and 8 turns for the
antenna end. I put them on a pair of Amidon FT114-67 cores I had.

Al = 5mH/1000t so 25nH/t

Inductance goes as Turns SQUARED. Half the turns, 1/4th the
inductance.

500t = 1.25 mH, etc.

Mark Zenier
Googleproofaddress(account:mzenier provider:eskimo domain:com)

TWISTEDHED IS MY HERO!!!!

"N9NEO" wrote in message
ups.com...
Antenna is up and working. Took me and daughter's boyfriend about 3
hours to build and install into attic. It ended up being almost 40
feet long with about 13" spreaders. This works out to be about 8mc. I
think.

For the Balun I wound 4 turns for the coax end and 8 turns for the
antenna end. I put them on a pair of Amidon FT114-67 cores I had.

Al = 5mH/1000t so 25nH/t
1.6uh for 8 turns
90 ohms at 9mc

oops, I think 3.2uH cause I stacked two cores. This works out to
about 180 ohms at around 9mc. I suppose a few more turns would be ok
since antanna impedance is 300 ohms. I think the rule of thumb is to
keep transformer reactance a few times the circuit impedance. I'm not
exactly sure how the number of turns effects the signal. For transmit
I know I would use enough turns or stack lots of cores to keep
magnetizing flux low to keep cores from overheating.

Anyway, TWISTED terminated folded dipole seems to be working nicely.
It is quieter than my verticle or dipoles. Good call.

regards,
Bob
N9NEO

Yes, you are right Mark. Thanks for pointing this out. Not really
sure where my math error is. I've become way too dependant on mathcad
to do all my thinking for me. Looks like just a brainfart - only had
to move the decimal over 6 places.

Not sure where the 25nH came from, should have just been 5nH/t
5mH *(1/1000) * (1/1000)

So that 8 turns should have been 5*8*8 or 320nH. Two cores stacked
makes 640nH.

Maybe just j36 ohms at 9mc then.

In either case I think it's getting to be time for a balun tweak.
Ladder is up near attic hatch so don't have to climb two floors I got
nice big #43 cores at work that my boss gave me. I can probably set it
up to run ok on 20m.

In article .com,
"N9NEO" wrote:

Yes, you are right Mark. Thanks for pointing this out. Not really
sure where my math error is. I've become way too dependant on mathcad
to do all my thinking for me. Looks like just a brainfart - only had
to move the decimal over 6 places.

Not sure where the 25nH came from, should have just been 5nH/t
5mH *(1/1000) * (1/1000)

So that 8 turns should have been 5*8*8 or 320nH. Two cores stacked
makes 640nH.

Maybe just j36 ohms at 9mc then.

In either case I think it's getting to be time for a balun tweak.
Ladder is up near attic hatch so don't have to climb two floors I got
nice big #43 cores at work that my boss gave me. I can probably set it
up to run ok on 20m.

I think the impedance of that antenna is depended on the centered
termination resistor at 600 ohms. There is also a 1/4 wave transformer
section. This is from memory I didn't look it up. Since this being used
fro receiving and not transmitting where you are trying to use the
antenna fro a load I would not bother with the termination resistor or
impedance transformation section of the antenna design and just use it
as a basic loop antenna. The impedance of the loop will be somewhere in
the 50 to 100 ohm range so you don't need a transformer.

--
Telamon
Ventura, California