[Elecraft] Question about forthcoming KAT500

[Alan Bloom]

On Sat, 2011-12-31 at 17:14 -0800, Rick Bates wrote:
> Alan,
> 
> Isn't that true of most tuners, that higher impedance is tolerated (matched)
> better than low impedance?  

That tends to be true, but it really depends on the particular circuit.
For an L-network, like in the Electaft tuners, matching a low impedance
requires a large variable capacitor, which tends to be physically large
and expensive.  However, the Elecraft designs use relay-switched fixed
capacitors so that might not be such a big issue.

The Drake tuners used a pi-L network.  The bandswitched input pi section
transforms 50 ohms up to a high impedance and the L section (using two
variable capacitors) brings it back down again as needed for the
particular antenna.  For that reason, it naturally tends to match high
impedances easily, at least on the higher bands.  The bandswitched pi-L
topology has the advantage of better filtering and it is easier to tune
manually, at the expense of a smaller tuning range.

Alan N1AL


> If so, that easily explains why a 4:1 (or worse, a 9:1) balun is a bad
> choice on a multiband antenna.  Such devices might lower the impedance too
> much on any given band.  It might also explain why they're more lossy.
> 
> 73 es HNY,
> Rick WA6NHC
> 
> -----Original Message-----
> From: Alan Bloom
> 
> On some bands it barely
> made 10 ohms at the low end but it would typically do much better than
> that at other phase angles.  For example, it would match much greater
> than 250 ohms resistive on most bands.
> 
>