[CQ-Contest] Stub Switching

[Fred Hopengarten]

	As a result of N6TR's Dayton talk  on single operator, multiple
transmitter operations, I resumed thinking about interstation
interference here at K1VR (where such interference is not yet down to
zero).

	I am but a humble  JD/MBA (sorry, I just came back from a
convention -- the Annual Meeting of the American Psychiatric Association
-- where everyone seemed to wear all of his or her advanced degrees on
his or her chest). As a result, I don't have answers, but perhaps I can
pose some questions (with commentary).

Background

	At my station, and I am sure that others with tribanders face the
same problem, one must switch stubs without switching antennas.  By
contrast, on 40 and 80, I just leave the stubs in the line to those
antennas, respectively, at all times.  But with tribanders,  interstation
interference is even worse because the antenna is resonant on the band
which should be rejected.

Hardware

	The Top Ten Devices controller, through the use of a diode
matrix, can be "programmed" to do anything you like.  Mine is already
programmed to select the same antenna (the tribander stack, or the single
tribander on a separate tower) no matter whether 10, 15, or 20 is the
transmit band.  The question  is:  For switching stubs in and out, who
makes the best (or the most readily modified) switching box?  Candidates
would seem to be:  DuneStar, Top  Ten, and other remote control boxes. 
As I use products from both companies and find them to be well
engineered, I spoke to representatives of both companies, plus friends
N4KG, AA1AA and AA1K.

Chosing a Stub

	Should the box for Station A, which is (let us posit) on 20,  be
switching IN a 20 meter bandpass stub?  In this case, the bandpass stub
would be selected by Station A's selector.  Or should the box for Station
A be switching IN 10 and 15 meter band reject stubs (the "cross-control"
strategy)?  If the latter, then wouldn't Station A's switch be controlled
by Station B's controller?

Grounding

	With several stubs (at laest one per band, but we'll get to the
number in a minute) hanging off the same switchbox, should the grounds
all be tied together or should they float when not in the circuit?  I ask
because it would seem to complicate the cutting of the stubs if they
interact with one another, making the process iterative to the point of
distraction..

Stub Creation

	Would you cut one or two stubs per band?  Why?

	Would you make them out of hardline? Or what would you make them
out of? 

	If making two stubs per band, for higher Q, what coax would you
use for the quarter-wave link between the two stubs?  More hardline, or a
coil of RG-213?

	Would you make the shorted end or open end versions? (I would
think that open end versions are faster to cut and try.)

	Would you use the AEA, Autek  or MFJ box (which model?) for stub
cutting?	

First Steps

	While in Dayton, I put these questions to N3RD of Top Ten Devices
(who said:  "Could you mail these questions to W2VJN?")  and WX0B of
DuneStar (who said: "Let me think about that.").

	Now I've put these questions to the reflector.  What say, OM's?	

		 
Fred Hopengarten  K1VR                                           
617/259-0088
Six Willarch Road
Lincoln, MA 01773-5105
permanent e-mail address:  fhopengarten at mba1972.hbs.edu


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