THE major difference between the KX-155/165 and KX-155A/165A is this:

http://www.faa.gov/certification/air...st/8400-11.doc

3. Harmonic interference (12th and 13th harmonic) from VHF
transmissions on 121.150, 121.175, 121.200, 131.250, 131.275, and 131.300
MHz has been observed to adversely affect reception of the GPS signal. Low
pass or notch filters (with an insertion loss of 2 Db or less or the
aircraft VHF COM radio must be re-certified) installed at the output of the
VHF transmitter to attenuate the undesired harmonic signal, or modification
of the VHF transmitter to improve internal harmonic attenuation, may be
required. Shorted stubs, of appropriate lengths, could also possibly
provide effective filtering and antenna matching."



The straight 155/165 was designed long before GPS was ever envisioned, and
are very noisy in 12th and 13th harmonics. Most IFR installations with these
radios were made without regard to the interference, with the certifying
pilot either ignorant or lying about the interference.



The "A" model was designed to be free of these interferences.



Other nice features are much better feeling rotary switches, with smoother,
shorter and more precise clicks. Also, the 165A is available with 8.33 MHz
spacing. The US may or may not go to 8.33 spacing, but since Europe already
has the US will probably tow the line, like they did with METARS/TAF. Which
brings up a funny point. I fly all over Europe regularly. IT is very
uncommon to see a proper METAR/TAF report sequence. They report as they damn
well please with any sequence that comes to mind at the moment. To get a
proper sequence you need to fly in the US.



So much for the vaulted "commonality" that was forced down our throats!



Karl





"Mike Rapoport" wrote in message
ink.net...
The KX155 in my "new" airplane (Helio Courier) seems to have bitten the
dust. It looks like an old POS and I am trying to figure out what to do.
What are the functional differences between the KX155, KX165 and the
KX155A
and KX165A? The airplane has a Garmin 300XL as #1 and a switching relay
to
allow the 300XL or the KX155 to drive the HSI. I am trying to decide what
to do.

My options a

A:
#1 Garmin 430
#2 KX155
Get rid of the "GPS/NAV" switch/annunciator box

B:
Same as A but with 530. Pricey, but I could just buy the tray and
connectors and shuttle the 530 in my MU-2 back and forth until Garmin has
WAAS and then buy a 530A for the MU-2. This has the advantage of
presumably
saving the cost of the WAAS upgrade thereby reducing the 530 premium
somewhat.

C:
#1 Currently installed 300XL.
#2 KX 155 or 165 I would prefer the 165 since I can get rid of the
converter
box that drives the HSI.
Keep the GPS/NAV switch/annunciator box

The advantage of going with a 430 or 530 is that I have flown them for
800+
hrs and am comfortable with the operating logic. I can't say the same
about
the 300X:L.

Cost is an issue. This is a second airplane and I anticipate using it 95%
VFR. I would rather spend the money on floats or skis :-). Since the
airplane may be left unattended in the backcountry for days at a time, I
would also like avionics that are not very attractive to a thief.

What do you think?

Mike
MU-2