Re: correct position of coupling loop
- --- In firstname.lastname@example.org, "qrpbear" <qrpbear@...> wrote:
>This is one of those ideas I keep meaning to try. But then I keep thinking about the massive electrical field around the capacitor, and I just can't bring myself to place the loop controls, cables, and mounting structure near the capacitor where they risk upsetting the loop balance.
> There is another way to couple into a loop antenna which is done at the tuning capacitor. It's known as the "army loop method tuner" since it was originally designed for use by the US Army. You can see it here...
> Might be worth a try.
Here is a posting describing one user's problems with common mode currents when using the MFJ loop tuner, which is essentially the same as the army loop tuner linked above.
Note how WB6BYU states "such circuits are inherently unbalanced." So you can probably get the army loop tuner to work, but you may have to deal with common mode currents.
- Thanks for the info about 4NEC2, I was able to run the file saved according to your directions.
A very informative page on voltages and current, electric and magnetic fields near a small loop can be read here:
--- In email@example.com, "qrp.gaijin" <qrp.gaijin@...> wrote:
> --- In firstname.lastname@example.org, "JK De Marco" <py2wm@> wrote:
> > > The loop voltage is highest near the capacitor. For example, in the following image I calculated the electric field around the capacitor for a 2 meter by 2 meter loop antenna resonant at 7 MHz:
> > >
> > > http://postimg.org/image/n091ogqbl/
> > Very nice and informative image! What software did you use to produce it? Thanks.
> 4nec2 (available free of charge). It's available here: http://www.qsl.net/4nec2/
> For the near field, it can calculate and display in 3D the near E-field and near H-field. Note that in the above image, the horizontal purple line (very high voltage), extending far outside of the loop boundaries along the axis of the top side of the loop, may be some numeric calculation error, maybe due to the geometry or position of the loop. It doesn't make sense that the E-field would extend so far beyond the loop boundaries. (Maybe I should ask on the 4nec2 forum about this anomaly.) Apart from that, the results seem reasonable.
> Here is the input file, if you want to experiment with the model. Save the following text to "something.nec" and load it into 4nec2. Note that the field separator, between items on a single line, is the tab character. The loop is resonant at 7.003 MHz, but has not been matched to 50 ohms.
> SY C=6.6e-11
> GW 1 20 -1 0 0.5 -1 0 2.5 .0127
> GW 2 20 -1 0 2.5 1 0 2.5 .0127
> GW 3 20 1 0 2.5 1 0 0.5 .0127
> GW 4 20 1 0 0.5 -1 0 0.5 .0127
> GE 1
> LD 0 2 10 10 0.2 0 C
> LD 5 1 1 20 58000000
> LD 5 2 1 20 58000000
> LD 5 3 1 20 58000000
> LD 5 4 1 20 58000000
> GN 2 0 0 0 5 0.001
> EX 6 4 10 0 1 0 0
> FR 0 0 0 0 7.003 0
- Interesting read. Thanks!
On 5/05/2013, at 2:29 PM, JK De Marco wrote:
> A very informative page on voltages and current, electric and magnetic fields near a small loop can be read here: