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 Loop and ferrite directional antennas 
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Post Loop and ferrite directional antennas
I have wound a lot of wire onto a frame to make an 80m loop for DF work. Trouble is it isnt very directional and there's not much of a null. I have tried various capacitors but cant really find a resonant freq anywhere near 80m!


Second thing is that I am about to wind a ferrite rod antenna - should I bridge the wire tails with a capacitor? What would be a good ball park figure?


Dimbo Dave

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Thu Oct 15, 2015 11:24 am
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 Loop and ferrite directional antennas 
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Post Re: Loop and ferrite directional antennas
You need to give us more information:

How many turns on the frame?
What's the size of the frame?
How many turns on the ferrite rod?
What material is the ferrite?
What's the size of the ferrite?

Steve G3TXQ


Thu Oct 15, 2015 11:43 am
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 Loop and ferrite directional antennas 
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Post Re: Loop and ferrite directional antennas
I used to use a shielded loop and it is very directional, I built it for 80 and 160 out of two turns of UR67 and the diameter was just over 2 feet. I've still got it in the loft, I can probably get the exact dimensions when I get home from work this afternoon. It is an active loop, so it has got a small amplifier on the ends of the loop.

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Thu Oct 15, 2015 12:11 pm
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 Loop and ferrite directional antennas 
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Post Re: Loop and ferrite directional antennas
Steve
Sorry. Sixty turns on a foot square.

Ferrite is,Erm, ferrite. That's all I know. About 6 in long, 8mm diameter.

D.

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Thu Oct 15, 2015 1:44 pm
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 Loop and ferrite directional antennas 
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Post Re: Loop and ferrite directional antennas
Paul that sounds good to me. It's a club huffduff project I'm putting together.

D

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Thu Oct 15, 2015 1:45 pm
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 Loop and ferrite directional antennas 
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Post Re: Loop and ferrite directional antennas
G4YVM wrote:
Sixty turns on a foot square.

That explains why you can't tune it with a capacitor - 80m is way above its self-resonant frequency. Its inductance will be several mH !!!

Why did you use so many turns?

Steve G3TXQ


Thu Oct 15, 2015 1:55 pm
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 Loop and ferrite directional antennas 
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Post Re: Loop and ferrite directional antennas
:blush: I thought more wire = longer wire = lower freq.

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Thu Oct 15, 2015 1:57 pm
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 Loop and ferrite directional antennas 
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Post Re: Loop and ferrite directional antennas
G4YVM wrote:
:blush: I thought more wire = longer wire = lower freq.


Correct - I reckon it'll be resonant at the bottom end of the medium wave-band with no external capacitor :shock:

Steve G3TXQ


Thu Oct 15, 2015 2:01 pm
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 Loop and ferrite directional antennas 
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Post Re: Loop and ferrite directional antennas
Ok.

How many turns do you think I ought to have? (before I start unwinding )

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Thu Oct 15, 2015 2:04 pm
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 Loop and ferrite directional antennas 
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Post Re: Loop and ferrite directional antennas
fifteen turns seems to do it Steve

D

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Thu Oct 15, 2015 2:50 pm
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 Loop and ferrite directional antennas 
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Post Re: Loop and ferrite directional antennas
I've just checked my loop and it's a 12 foot length of UR67 coiled 3 times, so the diameter it 16 inches with it's little differential amplifier on the ends. If you are still interested I'll post some photo's and if I can find it the circuit of the differential amplifier.

If you are going with what you've got there I won't bother.

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Thu Oct 15, 2015 3:48 pm
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 Loop and ferrite directional antennas 
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Post Re: Loop and ferrite directional antennas
Paul, Id be really interested please. Yours sounds a better club project!

D

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Thu Oct 15, 2015 4:39 pm
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 Loop and ferrite directional antennas 
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Post Re: Loop and ferrite directional antennas
You might also like to look through this earlier thread on loops:

viewtopic.php?f=43&t=39964

Steve G3TXQ


Thu Oct 15, 2015 4:48 pm
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 Loop and ferrite directional antennas 
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Post Re: Loop and ferrite directional antennas
Paul I cant PM you but any joy?

D

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Fri Oct 16, 2015 9:58 pm
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 Loop and ferrite directional antennas 
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Post Re: Loop and ferrite directional antennas
Morning David,

Sorry I've disabled the PM's because some members don't seemed to know how to use it, they PM me instead of posting on the forum.

This is a picture of the loop, excuse the background, but it was taken in the loft.

The length of the loop the 12 feet with a split in the coax in the middle. It is coiled in 3 turns so the diameter is about 16 inches.

Image

This is the ends of the loop.

Image

This is another picture of the differential amplifier.

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Unfortunately I've lost the circuit diagram of the differential amplifier, if you need that I will have to dismantle the box and remove the PCB and trace the circuit out. The amplifier uses a pair of FET's because the ends of the loop are a very high impedance.

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Sat Oct 17, 2015 8:09 am
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