K1TTT Technical Reference

Subj:   Rotor box bypass - details
Date:   95-03-12 13:02:10 EST
From:   hwardsil@seattleu.edu
To:     cq-contest@tgv.com

From: hwardsil@seattleu.edu (H. Ward Silver)
Sender: owner-cq-contest@tgv.com
Reply-to: hwardsil@seattleu.edu (H. Ward Silver)
To: cq-contest@tgv.com

Well, this seems to be of general interest, so...

The procedure is probably more than everyone needs, but it's exactly how I
did all three of my rotor boxes (T2X, HAM-IV, and HD-73).  The T2X is the
only one I suspect of causing problems because the other two have been in
service for some time without trouble.  However, I didn't want to do only
one then find out I had to do the others...

My ground system is unspectacular.  Two 6' lengths of 1/2" copper pipe
with 1/8" holes every six inches or so.  I fill the open pipe with salt
water every month. (It's under a deck, so nothing grows there, anyway.) 
The pipes are soldered to a piece of 1" copper strap which runs up about
6' and goes under the window to the radio desk.  The strap bends
90-degrees and extends about 2' with RG-58 braid soldered to it as
grounding straps.  Every piece of gear in the RF system is tied to a strap.

Re: ferrite on the control leads.  That will work for the higher
frequencies, but not very well at AM-BC.  Put the bypassing on the OUTSIDE
of the control box - once it's inside, the RF will get into the rectifiers
some way.  

If you put a bead on the control cable wires, install it so that it is on
the *rotor cable* side of the bypass capacitor.  Otherwise the bead and
cap will make a parallel resonant circuit at some frequency - probably the
run station frequency.  With the bead outside the cap, they make a series
resonant circuit which is just fine with me. 

Oh well, more than you ever wanted to hear about rotor boxes.  I don't
think anything has to be done at the rotor end as there usually aren't any
diodes in the rotors themselves.  Bypassing the direction pot might not be
a bad idea, but I haven't had trouble there...yet.

Have fun and get rid of those annoying noises...

Materials - 

0.001 to 0.1uF monolithic ceramic or disc ceramic caps, 100V rating or
better, one for each control cable lead
        (do NOT use the film-type caps, too inductive)

8" of bare (non-enamelled) copper wire (#16 - #18) stiff enough to hold
its shape under mild mechanical insult

1 ea. #6 or #8 pan-head sheet metal screw and two flat washers


four-letter lubricant as required after patience runs out ;-)

1 ea. cold 807 (Mackenna stout recommended)

Procedure -

1) Install the screw immediately adjacent to the control cable terminal
strip.  If it's the all-in-line terminal strip, then put the screw at one
end.  If it's the four-over-four terminal strip, put the sheet metal screw
next to the dividing line of the strip at one end. 

2) Assuming you have the four-over-four terminal strip.  Form the wire
into a "U" which is wide enough to clear the terminal strips by about
1/4".  Make a small loop at the bottom of the U to mount to the screw. 
The following desperately inept character-based drawing should give the
general idea.  The in-line strip is a little easier.  Don't put the wire
on the screw just yet.

        |  1   2   3   4    terminal strip positions
 screw  O
        |  5   6   7   8

3) Leave the cable attached - you DO have crimp lugs on the cable don't
you?  If not - the remainder of this task is impossible.  Put the lugs on
first.  If you have the lugs on, loosen each terminal enough for a
capacitor lead to slip under the screw.

4) Trim and bend the capacitor lead so that you can hook it under the
terminal screw.  Leave the other end long for the moment, it makes a good
handle.  Tighten the terminal screw.  Repeat for all 6 or 8 terminals. 
You now have a little forest of leads sticking up and down.  They should
all line up and space about equally.

5) Put the wire U on the screw.  Bend it to press against the capacitor
leads.  Hook the cap leads farthest from the sheet metal screw over the
wire to hold everything in place.

6) Solder each cap lead to the wire.  No need to hook all the cap leads
over the wire, just solder 'em.  Trim the excess lead.

7) Add the station ground wire to the sheet metal screw.  Check to be sure
nothing is shorting.  Bend to taste.

8) Done.  Consume final assembly item.