For Jim Weir: Transponder Installation

On Mon, 02 Feb 2004 18:24:48 -0800, Jim Weir wrote:

Ron Wanttaja
shared these priceless pearls of wisdom:

-Hey, Jim, I've bought a Microair T2000 to replace the bum transponder in my
-Fly Baby. A couple of questions:
-
-1. The instructions say not to install the antenna within one meter of the
-unit. What's the limiting factor here? I always prefer short cable runs,
-and had a nice spot picked out 15 or so inches away. What problems is a
-near-by antenna introducing?

I'll be darned if I know. The unit is hogged out of a solid aluminum block and
is about as well shielded as anything I've ever seen. Perhaps they are relying
on the loss of the cable to mitigate any reflections from the antenna? I just
don't know. Me? I wouldn't worry about it. Put it where you will and we'll
solve any problems through experimentation.

Right, will do. I'll warm my feet instead of my tushie. Considering this
is just a "regulations require it" installation, I don't anticipate any
problems. If it passes the biannual test, that's all I need.

It is a cute little unit, though. I brought my avionics box home, and my
wife thought the Terra was my new transponder because I'd told her how
small the new one was. I had to take the Microair out of the box to show
her. The Terra was 2 1/4 pounds, the Microair was about a pound less.

-The current antenna location is precisely 4 inches below my heinie, and I'd
-just as soon get it further away, thank'ee.

You mean you are planning on having more kids?

Fewer two-headed ones would be nice... :-)

-2. The Microair uses a DB-25 connector. I haven't soldered onto a
-connector like this for about eighteen years. I'm presuming the best
-approach would be to tin the wires, slide them into their locations, and
-solder them in place? Should I be using shrink tubing on each connection,
-too? (the connector itself has a strain relief).

That's how I did it. Yes, tiny shrink on each one just is belt-and-suspenders
protection.

Well, as of this evening, this is a moot point anyway. I started soldering
the wires from my old transponder cable to the Microair's connector, but
didn't leave enough extra length on the wires...by the time I got to #4, it
had to wrap all the way around the "root ball" and I couldn't get it to
stay in place long enough to solder it. If I'd been just soldering 15 new
wires, it wouldn't have been a problem. But trying to get bundle of old
wires to behave long enough for each solder job was trying, even with a
pair of those aligator-clip hold-em stands.

I bought a new connector, cut the wires off the old one, then decided that
a crimp-on type connector would be a lot easier to install on the existing
cable. And so it proved.

One netter suggested using a premade computer cable with a female DB-25,
and just splice the two cables together. I liked that idea, but could only
find premade cables with 26 gauge wire. Probably good enough for the
encoded altitude, but the Microair installation manual wants 22 gauge wire
(and 18 gauge for the power).

-3. I'm about 99.99999% sure about this, but with $1500 on the line, I'd
-appreciate confirmation: When the installation manual shows the pin
-assignments for the DB-25 connector, the assignments are as if I am looking
-directly at the connector on the transponder...right? In other words, the
-connector itself will be a mirror of this diagram. That seems to be
-confirmed by the teeny teeny numbering on the DB-25 supplied with the unit.

PROBABLY so, but I don't have a copy of the final manual. Microair manuals
leave as whole LOT to be desired. The preliminary manual I have supports your
contention, but ...

The new connector I bought had a LOT more readable set of numbers on it.
BTW, Microair does have the manual online. It gives January 2002 as the
last update to the wiring diagram.

Thanks to Jim and everyone else for their help. I've got the cable
together, and just have to lash up a continuity checker from an old buzzer
and battery to verify the pinouts. Then it's back the airplane to clean up
the current electrical system and stick the avionics box back in place.

Ron Wanttaja

Ron Wanttaja wrote in message . ..
... When the installation manual shows the pin
assignments for the DB-25 connector, the assignments are as if I am looking
directly at the connector on the transponder...right? In other words, the
connector itself will be a mirror of this diagram. That seems to be
confirmed by the teeny teeny numbering on the DB-25 supplied with the unit.


Yes, follow the tiny numbers on the connector. The installation manual
that I got shows connector pinouts from the rear of the
connector. I hooked it up that way and it works fine.

A DB25 solder cup connector is not really difficult.
Try something like high a density DB78 for fun.
-------------------------------------------------------
Paul Lee, SQ2000 canard project: www.abri.com/sq2000