[ARC5] Why an UNUN?

[Mike Hanz]

On 10/25/2012 8:06 AM, Neil wrote:
> > Pick a number...any number...between 0.1 and 13. <huge grin>  If you'll
> > go to http://aafradio.org/docs/Aircraft_Antenna_Design.html you'll see
> > why it's difficult to specify a lower limit for a transmitter designed
> > to go in a number of aircraft, from small fighters to large bombers.
> > Their example is a 47 foot antenna resonant at 5MHz, operating at 3MHz -
> > the radiation resistance is 1.9 ohms. The graph at the bottom is perhaps
> > more useful in visualizing the problem.
>
> >> The 13 seems a bit high. Is there a lower limit given also? I don't 
> have
> >> that manual to hand.
> > I've seen a figure of 5 ohms, but I can't recall where.
> > Most likely on this very forum.
> I didn't express myself as clearly as I should have, and meant that
> somewhere I've seen 5 ohms as the impedance that the transmitter
> is designed to work into.

That seems as good a design center as anything, Neil.  My only point was 
that it had to tune a range around that point, so it's hard to say 
precisely what center point the ARC engineers chose.  I seem to recall a 
5 ohm figure as well, but I couldn't find it during a lineup of the 
usual suspects.
  - Mike