Thanks for this info Bob. I would like to get a L network
tuner... I remember back I think in the 60s and 70s and
wished I had the Johnson Matchbox!!
Paul Gates, KD3JF
--- Bob McGraw - K4TAX <RMcGraw@Blomand.net> wrote:
> And using a bridge such as one of the MFJ's or Autec's
> will tell more about
> the bandwidth and Q of the network and serve to keep QRM
> off of the air and
> make transistors in the PA last a lot longer.
> I much prefer the L type network over the Pi or T for the
> network. The L
> will have typically only one place that the match is good
> and that place it
> the lowest loss configuration.
> Then too the old Johnson Matchbox is the daddy of
> matching devices for
> balanced feed systems.
> Bob, K4TAX
> >> CATFISHTWO@aol.com wrote:
> >> > but when you use a
> >> > random dipole and a tuner, you are leaving some of
> your power in the
> >> > tuner,
> > The power you loose in the tuner can depend on the
> impedance ratio
> > between the feed line and the desired Z for the
> transmitter, the tuner
> > circuit, and the losses in the tuner components. When
> the load is highly
> > reactive and the impedance a long ways away from 50
> ohms, the T, PI, or
> > L match sometimes requires running at a high loaded Q
> and that makes the
> > circulating currents higher. And its those high
> circulating currents
> > that lead to greater losses in the unbalanced tuner.
> Tuning through a
> > balun is often fraught with great difficulty, more
> times than I care to
> > have tried I've found a tuning position that presented
> a match to the
> > transmitter, but that match didn't change with the
> antenna disconnected.
> > All the power was going into the ferrite cored balun
> and the coil in the
> > tuner. The DX-40 would tune and load up to full power
> with no antenna on
> > its Pi network. I suppose all the RF power was being
> used to heat the
> > coil.
> > For a balanced load, its hard to beat a link coupled
> parallel or series
> > tuned tuner. Series tuned for low impedance, parallel
> tuned for high.
> > And its highly practical to tap the feed line down from
> the ends of the
> > parallel tuned link coupled tuner. Its been around for
> 3/4 century and
> > still works fine.
> > As for tuner sizes, a compact tuner is the enemy of
> efficiency. Small
> > coils are always more lossy than large coils. Air
> spaced capacitors are
> > really pretty good unless made of steel and not silver
> plated. Silver
> > plated copper are best and losses can be reduced a bit
> more for the old
> > capacitor by adding a braid or strap connection for the
> rotor, getting
> > away from friction and a dirty sliding contact.
> > If there are two or more tuner settings that will match
> the antenna, the
> > one with the greater bandwidth should be the one with
> lower loss because
> > greater bandwidth says lower loaded Q and so smaller
> > currents in the tuner circuits.
> > --
> > 73, Jerry, K0CQ,
> > All content copyright Dr. Gerald N. Johnson, electrical
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