Transponder Praise

While not a really close call, I had my eyes opened last week, too.
Our airport is located between PHL and ACY (Class C) and Maguire AFB.
The heavies are rarely a problem but there is also an airway that
runs adjacent to the field and I try to keep extra vigilant when near
it. (I don't have a transponder). I was thermalling near the airway at
about 4000' when I saw four dots under a line at my altitude and they
appeared to be heading right at me. I moved away and watched a 747 go
by at a distance close enough to see that, while painted, it had no
logos showing anywhere. He wasn't heading toward PHL or ACY and didn't
appear to be climbing or descending and wasn't on the airway. He
wasn't flying in the "normal" places and I doubt he saw me. A few more
turns in the thermal w/o seeing him would have made things very
interesting. I think its time to invest in some electronic
insurance.

Mike

P3, learning where the "big boys" are is something I've just gotten
involved with. I persuaded a FedEx pilot to educate me about approach
charts, and using that information I've modified my SUA file to mark
VORs and PHL approach fixes in and near the lower part of the southern
Governor's Cup route. I'll contact you off line - I'd be glad to share
and would like to learn from you the 3 or 4 places you would never
want to be on the GC route.

-John

On Jul 7, 1:29 pm, Papa3 wrote:
What I particularly like about John's post is that it's a "total
package" approach. No one item is enough, and even all of them
combined aren't foolproof.

As an aside, any of us who fly on the perimeter of busy class B
airspace need to take the time to understand the standard terminal
arrival routes. Spend some time learning where the "big boys" are
and make a conscious decision not to go there. For instance, there
are 3 or 4 places in our local contest area (Governor's Cup) where I
would never want to be even if the best thermal in the world is
sitting right there.

As a second aside, I came as close as I've ever come to being skewered
by a Dash-8 a couple of weeks ago at 5,000 feet in a spot that's not
on anyone's "standard" anything. Who knows if the guy was being
vectored for spacing or whatever, but it was REAL close. "Get the
transponder installed" has been on the to-do list for the winter. I
think it's going to make it to the "must do" list for the next month
or so.

P3

Eric, I wasn't too impressed with the antenna extenders that Zaon
offers. They use RG-174 cable, and while it's OK for short runs it
would markedly decrease the signal strength running from my tail cone
to my instrument panel. I've found several places on line that offer 6
meter male to female RP SMA cables made from LMR 200 for less than
$15. The attenuation with LMR 200 at 1 GHz is 10 dB per 100 feet,
rather than the 22 dB per 100 feet with RG-174.

I guess there's a possibility that high interrogation rates could mess
up the Zaon range estimate, but even here in the PHL NY area the
transponder's transmitting triangle only flashes about once a second.
Could be that there are many, many transmissions per flash, but I've
noticed that generally if the Zaon says the range is within 3 miles of
me it is pretty accurate (to my "calibrated" eye, that is).

-John

On Jul 7, 2:39 pm, Eric Greenwell wrote:
Shadowing is certainly a possibility. I've also wondered if the amount
of radar interrogations can cause the same thing; e.g., where I fly in
SE Washington state, my transponder is triggered only 5-10 times a minute.

Rather than just relocating the antenna, you can get Zaon's dual antenna
option. That puts antennas top and bottom on the aircraft, essentially
eliminating all shadowing. It might be easier than moving one antenna to
the tail, but it's pricey at $280 for the option, plus two blade antennas.

--
Eric Greenwell - Washington State, USA

jcarlyle wrote:
Eric, I wasn't too impressed with the antenna extenders that Zaon
offers. They use RG-174 cable, and while it's OK for short runs it
would markedly decrease the signal strength running from my tail cone
to my instrument panel. I've found several places on line that offer 6
meter male to female RP SMA cables made from LMR 200 for less than
$15. The attenuation with LMR 200 at 1 GHz is 10 dB per 100 feet,
rather than the 22 dB per 100 feet with RG-174.

The PCAS MRX Dual Antenna Harness isn't really an "extender", but a way
of improving coverage to eliminate blind spots. I believe the antennas
used with the extender could be mounted close to the cockpit: e.g., one
on top of the glare shield, and one below it on the outside of the
glider (you couldn't do that on a glider that uses a CG hook to tow
with, of course).

Those locations would allow very short cables, if you wanted to;
however, the fact that two antennas are used probably makes up for
losses in the cable. If my math is right, the 15 foot cables they supply
do cut the signal from each antenna by one half, so that suggests they
intend the total signal (both antennas) to be the same as the one
antenna mounted directly on the unit. In any case, the dual antenna
package and the PCAS MRX Single Antenna Harness include "gain adapters",
so perhaps concerns about signal loss are irrelevant.

I suggest calling tech support at Zaon about the cable to use for a
remote mounting. Proper operation might require these losses, which
could be accounted for by the gain adapter.


I guess there's a possibility that high interrogation rates could mess
up the Zaon range estimate, but even here in the PHL NY area the
transponder's transmitting triangle only flashes about once a second.
Could be that there are many, many transmissions per flash, but I've
noticed that generally if the Zaon says the range is within 3 miles of
me it is pretty accurate (to my "calibrated" eye, that is).

Actually, I was thinking infrequent interrogations might be the problem,
but it was just a guess.

--
Eric Greenwell - Washington State, USA
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You're absolutely correct on the heights! Since most of my close calls
have come from IFR traffic, though, I tend to become more antsy at
multiples of 1000. Doesn't mean I let down my guard at other
altitudes...

-John

On Jul 7, 11:31 pm, Clark wrote:
Keeping a sharp eye out around VOR's is good. Avoiding VOR's is probably
better. Still a lot of traffic without GPS out there.

Assuming you're in the USA: IFR traffic will be on the 1000's, VFR will be on
the 500's. Within 3000 AGL all bets are off.