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Old July 8th 04, 02:03 PM
vandmand
 
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Default MFJ 1786 magnetic loop

I have just started to use my new MFJ 1876 located om my balcony.
Before the antenna went into operartion the motor unit has to be replaced.
:-(
However, my problem is that the antenna will not tune in the frequency area
10.1 - 18 MHz.
On higher band there is no problem.
I known that the loaction on my balcony is not ideal but i donĀ“t think thats
the problem or?
Any ideas??
Best regards
OZ1JZV - John



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Old July 9th 04, 12:47 PM
vandmand
 
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"John Passaneau" skrev i en meddelelse
...
Hi:
Do you have the loop horizontal or vertical? Horizontal mounting requires

it
to be 20 feet (sorry can't do meter in my head) above ground. Your balcony
most likely has steel structure holding it up and that is always ground.

Try
mounting it vertical if you have not already done so.


--


Hi

Thanks for you mail.

The loop is mounted vertically.

Yes, your are right. There is a lot of steel and aluminium in the structure
of my balcony.

I have tried to replace the loop but it still "refuse" to tune below 21 MHz.

I can se a small dip on the meter but are not able tuned it manually.

From 21 MHz and above I get a very low SWR.

In the instruction manual it is mentioned if there is a high SWR due to
placement of the loop, the feed loop in the antenna can be tuned to get a
lower SWR.

I have not tried this solution yet due to the good SWR on higher band, but
perhaps I should.



Regards
OZ1JZV - John


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Old July 9th 04, 05:22 PM
aunwin
 
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I think I would try adding a capacitor first
Art

"vandmand" wrote in message
. ..

"John Passaneau" skrev i en meddelelse
...
Hi:
Do you have the loop horizontal or vertical? Horizontal mounting

requires
it
to be 20 feet (sorry can't do meter in my head) above ground. Your

balcony
most likely has steel structure holding it up and that is always ground.

Try
mounting it vertical if you have not already done so.


--


Hi

Thanks for you mail.

The loop is mounted vertically.

Yes, your are right. There is a lot of steel and aluminium in the

structure
of my balcony.

I have tried to replace the loop but it still "refuse" to tune below 21

MHz.

I can se a small dip on the meter but are not able tuned it manually.

From 21 MHz and above I get a very low SWR.

In the instruction manual it is mentioned if there is a high SWR due to
placement of the loop, the feed loop in the antenna can be tuned to get a
lower SWR.

I have not tried this solution yet due to the good SWR on higher band, but
perhaps I should.



Regards
OZ1JZV - John




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Old July 9th 04, 05:37 PM
Richard Clark
 
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Default

On Fri, 09 Jul 2004 16:22:01 GMT, "aunwin"
wrote:
I think I would try adding a capacitor first

It has a capacitor.
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Old July 9th 04, 05:50 PM
Richard Clark
 
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Default

On Fri, 9 Jul 2004 12:47:53 +0100, "vandmand"
wrote:
In the instruction manual it is mentioned if there is a high SWR due to
placement of the loop, the feed loop in the antenna can be tuned to get a
lower SWR.

I have not tried this solution yet due to the good SWR on higher band, but
perhaps I should.


Hi John,

Yes, the manual suggests this, but it seems strange advice. Move your
antenna inside to a room that has less metal nearby (away from railing
and major building components) and confirm you "can" adjust for low
SWR at your problem frequencies.

73's
Richard Clark, KB7QHC


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Old July 9th 04, 05:59 PM
Reg Edwards
 
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I think I would try adding a capacitor first.


It has a capacitor.


What is to prevent him adding another. The more pF the merrier.


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Old July 9th 04, 06:39 PM
Richard Clark
 
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On Fri, 9 Jul 2004 16:59:33 +0000 (UTC), "Reg Edwards"
wrote:
I think I would try adding a capacitor first.

It has a capacitor.

What is to prevent him adding another. The more pF the merrier.

This is like charging the battery to fix a flat tire.
  #8   Report Post  
Old July 9th 04, 10:50 PM
aunwin
 
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Default

Since it normally requires more capacitance at that end of the band it was
my intent to make the capacitance larger. But it would appear that I am in
error and should be scolded , tho I hardly believe that it is inductance
should be added for it to present a purely resistive load, It will be
interesting to find out why.
Apologies for the incorrect suggestion
Art

"aunwin" wrote in message
news:JCzHc.49499$%[email protected]_s01...
I think I would try adding a capacitor first
Art

"vandmand" wrote in message
. ..

"John Passaneau" skrev i en meddelelse
...
Hi:
Do you have the loop horizontal or vertical? Horizontal mounting

requires
it
to be 20 feet (sorry can't do meter in my head) above ground. Your

balcony
most likely has steel structure holding it up and that is always

ground.
Try
mounting it vertical if you have not already done so.


--


Hi

Thanks for you mail.

The loop is mounted vertically.

Yes, your are right. There is a lot of steel and aluminium in the

structure
of my balcony.

I have tried to replace the loop but it still "refuse" to tune below 21

MHz.

I can se a small dip on the meter but are not able tuned it manually.

From 21 MHz and above I get a very low SWR.

In the instruction manual it is mentioned if there is a high SWR due to
placement of the loop, the feed loop in the antenna can be tuned to get

a
lower SWR.

I have not tried this solution yet due to the good SWR on higher band,

but
perhaps I should.



Regards
OZ1JZV - John






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Old July 10th 04, 03:00 AM
Tom Ring
 
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Default

Unless what he wants to do is lower the frequency. It is, after all,
just a very leaky tank circuit with "no load". (That was "tongue in
cheek" for those of you that normally fail to recognize it)

tom
K0TAR

Richard Clark wrote:

On Fri, 9 Jul 2004 16:59:33 +0000 (UTC), "Reg Edwards"
wrote:

I think I would try adding a capacitor first.

It has a capacitor.


What is to prevent him adding another. The more pF the merrier.


This is like charging the battery to fix a flat tire.

  #10   Report Post  
Old July 10th 04, 05:54 AM
Richard Clark
 
Posts: n/a
Default

On Fri, 09 Jul 2004 21:00:25 -0500, Tom Ring
wrote:
Unless what he wants to do is lower the frequency.


Hi Tom,

But that is NOT what he is trying to do. He simply wants it to work
"as advertised." Everyone is re-inventing it to do what it was
already designed to do. It already resonates at these frequencies, to
add capacitance is very poor advice for any of several reasons.

What John needs is to determine if it is broke, or if it is
environment that is getting in the way. He is not asking for the
antenna to tune outside of its characteristic range.

The advice in the handbook suggests he open up the case and squash the
feed loop to compensate for nearby interfering, metallic structures.
This may solve the problem, but it is a ****-poor solution. If it
were a general, preferrable condition, they would sell them all this
way.

73's
Richard Clark, KB7QHC


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