Palstar AT-2K or AT-2KD

[KA2FIR]

Hi,

I understand that the AT-2KD will help you tune your antenna quicker because of the differential 2 knob design but when would one want the 2K over the 2KD?

Tnx,

Mike KA2FIR

[N6GND]

"AT2K: T-network with independently tunable capacitors on independent shafts. Slightly better matching range. More knobs to tune and keep track of... though it should tuneup a wet noodle. No internal balun.

"AT2KD: T-network with tracking tunable capacitors. Slightly narrower matching range with caps tuned by same shaft. No internal balun. Easier to tune... fewer knobs to twiddle, taking much less time to complete the tuning cycle."

I have the KD. Works well for me with a 40-10 nonresonant vertical and an 80-40 dipole with loading coils for 80, both coax fed. Certainly quick to tune. When I change frequencies or bands I peak the noise on receive with the tuner and I'm quite close when I'm ready to transmit. When I used the KD with a nonresonant 90 ft. dipole fed with twinlead, it tuned easily on 80 up to 15 and 10 meters where it could be short on tuning range, depending on feedline length and type of balun (1:1 or 4:1).

[WB6BYU]

With the differential capacitor version you can't have both capacitors at maximum (or
minimum) at the same time.  That may limit your matching range at the low (or high)
ends of the range.  Specifically, for the same maximum capacitance value, the
efficiency will be lower when matching low impedance loads because you can't get
as much capacitance into the circuit, which forces higher circulating currents.  This
is primarily a problem on 80m and 160m.

In my experience, most of the time I can get a match with one or the other
variable capacitor at maximum capacitance.  If so, this will be very close to the
point with the lowest losses.  With one capacitor at maximum, adjusting the other
one and the coil is no more difficult than juggling the coil and differential
capacitor.  (And I put stickers on the face of my tuner to mark the dial settings
for each band, so it doesn't take very long to retune anyway.)

Does it make a big difference?  Probably not if you mostly work 40m through 15m or
so.  You can see for your self using W9CF's handy tuner simulator applet here:

http://fermi.la.asu.edu/w9cf/tuner/tuner.html

You can mimic a differential capacitor by assuming that both capacitors have to
sum to a fixed value, which is the maximum + minimum values.  So, for example,
if your tuner has 250pf capacitors, assume that the two capacitors have to add
up to about 265pf.  Then you can try matching the same load both ways and see
how much difference it makes.