3813Re: Tranmitting Loop for 6m & 10m
- Jul 31, 2007At 7:40 am ((PDT)) Mon Jul 30, 2007, in Digest 881, Richards wrote:
>[snip] For my experiment, I tuned weak and moderate signalsYou do not say what the winding pitch is: my bet is that
>in the 31 m short wave band (around 9.4 MHz).
>What seemed to work as well as anything, was a mere 16 seat of wire
>looped twice around a 2 foot by 2 foot square PVC pipe frame I built for
>another purpose. Using coax cable feed line, it did not seem to matter
>whether I connected just one end of the wire loop, or both ends - one
>end to the coax cable center conductor, and the other to the shield.
>I don't know why it did not matter how I connected it, but it
>seemed to work the same either way.
your loop is close wound, in which case the loop's self-
resonance will be at around 2Mhz. (It depends somewhat
on wire diameter, which you also didn't care to tell us.)
You would benefit from RJELOOP3.EXE by Reg Edwards.
This is designed for square receiving loops and will tell you
the inductance, approximate self-resonance frequency,
capacitor for resonance (if used) and other interesting
By using RJELOOP3 you will discover that you need to
increase the winding pitch to 2 wire diameters or more
in order to raise the self-resonance above your frequency
If you are planning to tune the loop I would suggest a bigger
spacing, since self-capacitance is worse for Q than a good-
quality external C and will also limit the tuning range attainable.
>[snip]Not practical: the loop is already capacitive above its
>I wonder whether tuning capacitor would help adjust the wire to various
>or below its resonant frequency?Yes, but first you need to raise its self-resonance above
your frequency of interest.
>I wonder whether I could locate the tuning capacitor inYes, if you don't mind adding the resistance and capacitance
>the shack, rather than out at the loop in the backyard?
of your feeder to the loop resonant circuit (which you should).
>I am, based on the discussion here, presuming that myHow does
>16 foot long wire in a
>figure-8 double looprelate to
>(i.e. going twice around my 2 feet per side pvc frame)?
Or are you trying to tell us at this late stage in the discussion
that you wound it with figure-8 zip cord?
>is approximately 1/10 wavelength for the 31 m (9.5 MHz)300m/9.5Mhz = 104ft approx.; 16ft = 0.154 wavelength;
a >50% error over 1/10 wavelength but, since you have
coiled it, you have brought the low-current ends back to
overlap the maximum-current centre, so the spacial
distribution of current will be more uniform than a single
turn of this wire length would have been and I'm guessing
that means it will give you good "small loop" performance.
>I also presume that I would have to select a differentAny loop of wire below its self-resonant frequency behaves
>length of wire, perhaps, or a different band in the spectrum. Or is
>this mistaken, would any short loop work? Would any short length work,
>but with a tuner?
just as you should expect a loop of wire to behave: it has an
area which determines how it interacts with the spatial RF field
and an inductance and capacitance which determines how
you can couple it to the rest of your circuit.
When the length is greater the spatial arrangement and
possible self-resonant modes take over, and you will need
either experiment or an antenna-modelling package to
discover what its impedance and radiation pattern are,
which is one reason for sticking with published designs
so you can benefit from someone else's experience.
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