ADF Problem

tony roberts wrote:

To respond to the questions that were in some responses,
if a fly a 360 the needle tracks the NDB if I am near it, but not if I
am several miles away.

I had some similar problems with the Narco ADF 841. It wouldn't lock onto
anything more than a few miles away until the radio had been on for an hour
or so. I sent it in for repair, the shop tested it and replaced two
capacitors, and now it works perfectly.

A one-hour bench-test of your ADF at a good avionics shop is probably the
cheapest place to start -- just yank it out yourself and mail or drive it
in. You're right that the problem could be the antenna or connections, but
it will take longer to test those (and most shops don't even have proper
equipment for ramp-testing an ADF antenna and cables the way they can
ramp-test a VOR antenna and cables), so you might as well rule out the radio
first: besides, you won't have to ground your plane while the radio's being
tested, unless you need it for a specific IFR approach.


All the best,


David

On Tue, 11 May 2004 02:37:46 GMT, tony roberts
wrote:

Thanks very much for all the advice.
It looks as though loop antenna is most likely, with radio interference
as the second most likely. I'll fly it with everything shut off to see
if the problem persists, to help narrow it further.

To respond to the questions that were in some responses,
if a fly a 360 the needle tracks the NDB if I am near it, but not if I
am several miles away.

Nospam asked if my crab angle was 30 degrees. No. If the NDB were ahead
of the nose the needle pointed at 330, regardless of whether the NDB was
at 300 degrees or 40 degrees.

Thanks again for all the advice - I'll post the solution when I have it

Tony

As has alrady been suggested it may be interference, since it works
close to the NDB.

You say ' the needle tracks the NDB if I am near' so have you listened
to the audio out of the ADF receiver? Maybe you can identify some
interference.

Sounds like a similar problem, we had, which was due to alternator
noise (a whining noise which varies with engine RPM). In our case an
alternator decoupling capacitor had not been fitted with the
replacement alternator which did not have an inbuilt suppressor.




E-mail (Remove Space after pilot): pilot

writes:
[snip]
As has alrady been suggested it may be interference, since it works
close to the NDB.

You say ' the needle tracks the NDB if I am near' so have you listened
to the audio out of the ADF receiver? Maybe you can identify some
interference.

Sounds like a similar problem, we had, which was due to alternator
noise (a whining noise which varies with engine RPM). In our case an
alternator decoupling capacitor had not been fitted with the
replacement alternator which did not have an inbuilt suppressor.

Onboard interference source sounds very likely. The ADF
may even be giving a clue as to the general direction of
the interference source from the antennas and may help
isolate it. [Note the "may" in the statement.]