[Elecraft] K3 Tuner

[Alan Bloom]

On Thu, 2008-01-31 at 07:27, G4ILO wrote:
> 
> Brett Howard wrote:
> > 
> > So I was recently reading about the IC756ProIII and noticed that it said
> > its tuner was rated for 3:1?  Does that really mean that you have to 
> > have a 3:1 or better SWR or it can't tune it?
> > 
> Yes it's true, and it's the same for Icom and Kenwood radios too.

If a tuner is specified to match 3:1 at all phase angles, it probably
does much better than that at some phase angles.  For example, the Drake
MN2700 tuner is specified at 5:1.  While it barely meets that spec for
low impedances (around 10 ohms resistive) it does much better than that
for high impedances.  That is, it matches much more than 500 ohms on
most bands.  Very useful for matching end-fed wires.

> Also you
> can't assume the losses in the tuner itself are as low with a big mismatch
> as they are with a good match.

That's very true.  The L-network used in the Elecraft tuners has the
advantage of wide tuning range but, as with most most tuners, the loss
depends on the antenna impedance - generally it gets worse the higher
the SWR.  That's why you won't see an insertion loss specification for
most tuners.

The PI-L network in the Drake tuners has the advantage that the
insertion loss is independent of the antenna impedance (specified at 0.5
dB max in the MN2700).  It also gives reasonably good filtering of
out-of band signals (on both transmit and receive) which is not
generally true with an L-network.

Al N1AL
(designer of the MN-2700 in a previous life)