Hey group,

Got a few questions concerning the fabrication of an antenna tuner.

I am using Arnie Coro of DX Unlimited's instructions for a simple PI
network tuner.

http://www.radiohc.org/Distributions.../pi-tuner1.htm

Instead of a 10 position switch I am using a 2 pole 6 position switch
then fliping a toggle to use the other 6 positions for a total of 12
inductance settings. But thats not my question.

My question is:

Given the small size of the box this all is going to fit into, I would
like to use a torroidal core instead of an air core.

1) Does Radio Shack sell torroidial cores?

2) Would I wind it similarly to the air core in that each winding is
separated by one wire width and tapped every 3rd turn?

If I understand the concept correctly, it's seems the PI network tuner
tunes both ends of the equation. This would be good as I am using a
Sony ICF-SW7600GR and dont have a clue what the input impedance might
be.

3) Is that how it really works? Tuning both the antenna and the line
out to the receiver?

Arnie says this tuner will work down to 5kHz. And given my research of
this tuner type, I would need to switch in extra capacitance to get
down low for say the AM band. I am considering adding in a few more
toggles to achieve this. My variables are 365pf.

4)How much extra capacitance would be needed? And would this be
practical or should I switch in another inductor creating a PI-L?


Thanks in advance,

Mike

Behold, mike signalled from keyed 4-1000A filament:


1) Does Radio Shack sell torroidial cores?

No. Go to http://www.amidoncorp.com

2) Would I wind it similarly to the air core in that each winding is
separated by one wire width and tapped every 3rd turn?

No. Your winding will be determined by the mu and Al value of the core.
Amidon supplies those values and the math.

If I understand the concept correctly, it's seems the PI network tuner
tunes both ends of the equation. This would be good as I am using a Sony
ICF-SW7600GR and dont have a clue what the input impedance might be.

PI network is great if both the source and load impedances are unknown.

3) Is that how it really works? Tuning both the antenna and the line out
to the receiver?

It' an impedance changer with low pass filter effect as well. Nothing
more, nothing less.

Arnie says this tuner will work down to 5kHz.

Not unless your inductance in in the hundreds of mH and you have uF of
capacitance.

And given my research of
this tuner type, I would need to switch in extra capacitance to get down
low for say the AM band. I am considering adding in a few more toggles
to achieve this. My variables are 365pf.

AM band is easy to reach. Wind your coil for the lowest frequency you
expect to receive.

4)How much extra capacitance would be needed? And would this be
practical or should I switch in another inductor creating a PI-L?

PI-L has a useless advantage for receiving, only good for transmitting.

I suggest you go to your library and read an older (mid 80's) ARRL Radio
Amateur's Handbook. They have a lot of vanluable information on this
tiopic, with the related math, even charts for Amidon toroids.

--
Gregg
*It's probably useful, even if it can't be SPICE'd*
http://geek.scorpiorising.ca

Take a look at this for some ideas on using toroids for your tuner:

http://www.alg.demon.co.uk/radio/qrp/port_atu.htm

.... and it most certainly WILL help in receiving.

jw
wb9uai

Sorry, that was a lousy link, this one is better:

http://users.hcis.net/kr8l/fptuner.htm

jw
wb9uai

On Fri, 19 Sep 2003 16:16:36 GMT, Gregg wrote:


. Your winding will be determined by the mu and Al value of the core.
Amidon supplies those values and the math.

Thanks, after playing with a toroid I pulled from a power supply I
gave up after realizing it had a Al of 79 - way too much to be useful.

To get 3uH with that I would need about 1.5 turns...he,he.
Not easy to get six taps on that.

PI network is great if both the source and load impedances are unknown.

Yes, its pretty cool how it balances my Sony input very nicely.


Arnie says this tuner will work down to 5kHz.

Not unless your inductance in in the hundreds of mH and you have uF of
capacitance.

After a few trial and error sessions I used a suite of calculators I
found he http://eweb.chemeng.ed.ac.uk/jack/radio/projsoft.html

The result of my labor is a 6 inch piece of PVC pipe wraped for 4
inches with 15 turns of 12 guage speaker wire. My thoughts are its
pretty darn close to 3uH given it resonates down to 4800kHz. It
suprised me.

AM band is easy to reach. Wind your coil for the lowest frequency you
expect to receive.

I probably will order 2 toroids and wind one for AM and the other for
SW then connect them to a toggle with the other end connecting to my 6
position tap switch. That should bring my random wire to life.

I suggest you go to your library and read an older (mid 80's) ARRL Radio
Amateur's Handbook. They have a lot of vanluable information on this
tiopic, with the related math, even charts for Amidon toroids.

I guess with the advance of the internet and satellite, homebrew is
not so common anymore. However, I find them complemtory with the
plethera of info thats online. I found the charts you mentioned online
which helped me realize my torroid was useless.

If I had shopped around for better prices I could have assembled my PI
tuner for 35 bucks or less using the air form coil. Given nothing at
Radio Shack is cheap, my total is about 50 bucks.

It works great.

Thanks for your help,

Mike

Hey thanks, thats a great link!

mike




On 20 Sep 2003 21:35:27 GMT, (J999w) wrote:

Sorry, that was a lousy link, this one is better:

http://users.hcis.net/kr8l/fptuner.htm

jw
wb9uai