[Lowfer] TX looping

[Bill Ashlock]

Archie,

>Made the coupling transformer today two turns secondary and 8 primary wi=
th taps each turn.
>Archie K9VQR  185.306.

That doesn't work out on paper if your Vcc is 24v (which I highly recomme=
nd).  If you have an Rac for the loop of 1 ohm, for example, and 24vdc at=
 the final the power equals VRMS squared/R =3D 1W. Where R =3D the value =
of Rac reflected back through the transformer. Therefore VRMS sq =3D  R. =
The VRMS would be about 8, so 8 squared is 64 ohms. The transformer imped=
ance ratio would be 64 to 1, so you need an 8 to 1 ratio. Recommend a #77=
 core rather than a #43 so you will have enough inductance on the primary=
 side not give up any power. With a #43 core you can double the turns, go=
ing 16 to 2, but that gets a bit messy. As you improve the loop conductor=
, IE: lower the Rac, the turns ratio increases to as much as 13 to 1. =20

Be sure you drive the transistors into full saturation, but not excessive=
ly so. Either way they will run hot, wasting precious power. They should =
actually be cold to the touch if you use my base current limiting circuit=
 that I describe in my follow-up article. A scope has been proven to be a=
 necessity, here, because there are many ways to go wrong including ringi=
ng on the drive from the shack and unbalance of the transistors.  Install=
ing the loop and resonating it to 185.3 is the easy part. Right Mike? <G>

Have fun....and we'll be waiting to see you on a screen not so near to yo=
u!

BillGet more from the Web.  FREE MSN Explorer download : http://explorer.=
msn.com


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