Magnetic loop antenna ( again )
Adrian Scripca YO8SSW
I started a topic regarding magloop antennas few weeks ago asking about
ways to replace the ferite coupling method. Some hams, to whom I deeply
thank, have replied to the topic and provided some valuable insights on
the matter.
Since then I managed to "build" an acceptable antenna. The only problem
with it is that it doesn't work. yet, that is. HI!
Here's what happens : the moment I plug it into the FT100 ( both wires,
not only the central conductor ) I get silent background ( low level
noise ) as if it had no antenna at all. An uneducated guess of mine
would be that maybe the feeder shorts *before* the coupling loop.
Here's a link to a page describing the way I did it which contains a
small picture gallery of various parts. http://benny.kappa.ro/antenna/
Perhaps someone could enlighten me by providing any debugging tips and
tricks. The downside is that I don't really have any specialised
testing rig. I only own a multimeter, the ft100, the mfj in the picture
and a soldering iron :]
Thank you for your time,
73 de YO8SSW
Richard Harrison
"The only problem with it is that it doesn`t work yet---"
Does the main loop tune over the desired range using your tuning
caoacitor, without the coupling loop, as seen with a dip meter?
Best regards, Richard Harrison, KB5WZI
Richard Clark
<beni...@gmail.com> wrote:
>Since then I managed to "build" an acceptable antenna. The only problem
>with it is that it doesn't work. yet, that is. HI!
>
>Here's what happens : the moment I plug it into the FT100 ( both wires,
>not only the central conductor ) I get silent background ( low level
>noise ) as if it had no antenna at all. An uneducated guess of mine
>would be that maybe the feeder shorts *before* the coupling loop.
Hi Adrian,
Your pictures are quite good. However, with 25M of feeder how do you
tune up?
73's
Richard Clark, KB7QHC
Adrian Scripca YO8SSW
as I stated before I don't have any testing rig besides what I
described above so no, I didn't get a chance to run a dipmeter on it
Adrian Scripca YO8SSW
Forgive my lameness, but does the size of the feeder have such a big
impact upon the antenna's performance especially when it's shielded
coax cable ?
Richard Clark
<beni...@gmail.com> wrote:
>Forgive my lameness, but does the size of the feeder have such a big
>impact upon the antenna's performance especially when it's shielded
>coax cable ?
Hi Adrian,
Only when your antenna's adjustment is more than your arm's length
from the transmitter during tune-up. It looked like your antenna was
outside, and your transmitter inside. When you transmit, what do you
do to adjust SWR?
Have you tried applying power to the antenna?
Reg Edwards
much noise.
Complain only when you don't hear any signals.
To hear any signals both the receiver and antenna must be tuned
exactly to the same frequency.
How do you ensure that both are tuned to the same frequency?
By the way, the 1/5th diameter coupling loop is much more likely to be
working correctly than the ferrite ring method. There's no way for the
coupling loop to go wrong. It is more efficient too.
There's no need at all for the coupling loop to be made of coax. Just
a length of self-supporting wire is perfectly adequate. Best if there
is no direct connection to the main loop.
----
Reg, G4FGQ
==================================
"Adrian Scripca YO8SSW" <beni...@gmail.com> wrote in message
news:1118928345.3...@g47g2000cwa.googlegroups.com...
Adrian Scripca YO8SSW
I changed the coupling loop to a length of self suporting wire as you
suggested, I turned the trcv on and surprise : it was alive. Tweaked it
for a maximum noise on receive.
SWR was/is high so I had to add an antenna tuner. nevertheless, on
14Mhz, cw portion I heard G, ON, LY, LZ, SV, UA, RV, RW, UR, EA, JA,
JS.
I even managed to work about all of them. I got kind of weak reports
but it's a start. If only I could tweak it so that I get SWR down
without the tuner.
> How do you ensure that both are tuned to the same frequency?
I don't. I have no rig for that. I go for the max noise on receive.
73 de YO8SSW
Reg Edwards
===================================
Hi Adrian,
Pleased to hear you are now working OK
The correct way to reduce SWR is to adjust the diameter of the
coupling loop.
There's no way to tell which way to adjust the loop except to try it.
It may not be the best setting for ALL bands.
But it IS better to do without the tuner if you can manage it.
Adjust the loop diameter for minimum SWR on your favourite band and it
will also be fairly close on the other bands.
It will be easier to change the diameter of the coupling loop now that
it is just a simple length of wire.
Now that you can hear some noise, the correct way to set the loop and
receiver both to the same frequency is to VERY SLOWLY, vary the loop
tuning capacitor for maximum noise in the receiver.
----
73, Reg, G4FGQ
Dick
Thanks for the confirming information. I will be making a trip to the
attic soon. I presently have the 20m loop fed with a Gamma feed which is
not too critical but de-mystifying the "plain" loop coupling seems to be
the way to go with more variables in geometry. Hams like lots of things
to twiddle.
Dick N3HKN
Reg Edwards wrote:
> There must be at least two variable components on every antenna tuner.
> This is because every impedance has two components, R and jX.
>
> With a magloop one variable is the loop tuning capacitor. The other
> variable is the diameter of the small coupling loop.
>
> It so happens that the setting of the coupling loop diameter does not
> change very much from one band to another. Users who never have to
> touch it don't realise how lucky they are compared with other types of
> tuner which have at least two knobs.
>
> The main loop and coupling loop are like the primary and secondary
> windings on an impedance matching transformer. The turns ratio cannot
> be changed but the diameter of the coupling loop can be. The greater
> its diameter the greater the coupling.
>
> It so happens that for loops of typical dimensions the ratio of the
> two loop diameters is approximately 5-to-1. Optimum setting does
> change a little from one band to another as can be seen using program
> MAGLOOP4 from website below.
>
> The coupling loop is often screened inside a short length of coax line
> because the designer saw it done that way in a magazine. Or he just
> copied somebody else's without having any reason.
>
> If there's any noise to be picked up it will be 25 times stronger on
> the main loop and nobody bothers to screen THAT. What might be picked
> up on the very small coupling loop is quite insignificant in
> comparison.
>
> And it's much easier to adjust the coupling between the two loops if
> one of them is just a self-supporting length of wire no thicker in
> principle than the diameter of the coaxial inner conductor.
>
> Instead of reducing its diameter it can be rotated a little or bent
> out of the plane of the main loop to have a similar effect. Or
> squashed flatter to reduce the area enclosed.
> ----
> ............................................................
> Regards from Reg, G4FGQ
> For Free Radio Design Software go to
> http://www.btinternet.com/~g4fgq.regp
> ............................................................
>
>
Dick
Sorry to butt in but I have a loop question.
Presently I have a loop for 20M made from 1/2 inch copper pipe in the
attic. I use a large 4500v variable capacitor turned by a small motor.
It works very well and is better than my GAP Challenger vertical (31ft)
in favored directions. Noise is higher in the attic but I can bring that
down with a Timewave ANC-4 noise canceling (by phasing) unit.
My question is about the coupling loop. Everything I had ever seen on
the coupling loop was that it had to be an odd construction of coax,
i.e. some sort of Faraday shield?? I noticed your comment to Adrian
about a simple stiff wire coupling loop.
Is this loop simply shield to one side and center conductor to the other?
Is there a size/diameter ratio of the coupling loop to the main loop?
Is the antenna now more likely to have increased noise due to an
"unshielded" coupling loop?
Thanks & regards,
Dick N3HKN
> ===================================
> Hi Adrian,
>
> Pleased to hear you are now working OK
>
> The correct way to reduce SWR is to adjust the diameter of the
> coupling loop.
> There's no way to tell which way to adjust the loop except to try it.
> It may not be the best setting for ALL bands.
> But it IS better to do without the tuner if you can manage it.
> Adjust the loop diameter for minimum SWR on your favourite band and it
> will also be fairly close on the other bands.
>
> It will be easier to change the diameter of the coupling loop now that
> it is just a simple length of wire.
>
> Now that you can hear some noise, the correct way to set the loop and
> receiver both to the same frequency is to VERY SLOWLY, vary the loop
> tuning capacitor for maximum noise in the receiver.
> ----
> 73, Reg, G4FGQ
>
>
> From - Wed