How fast should an ADF point?

My ADF (Narco 841) quit pointing shortly after I got the plane, so
I pulled it and found it was covered in swarf (metal shavings) so I
cleaned it off, cleaned the contacts (card edge connector) and put
it back in. Now it points again. What I'm wondering is: How fast
should it point? Let's say there's nothing on freq 200 (default)
and I tune a nearby NDB/marker on standby and hit swap. How fast
should the needle point? I realize that in flight it doesn't have
much call to move quickly, but until now I was never paying attention.

--
Ben Jackson

http://www.ben.com/

Ben Jackson wrote:

My ADF (Narco 841) quit pointing shortly after I got the plane, so
I pulled it and found it was covered in swarf (metal shavings) so I
cleaned it off, cleaned the contacts (card edge connector) and put
it back in. Now it points again. What I'm wondering is: How fast
should it point? Let's say there's nothing on freq 200 (default)
and I tune a nearby NDB/marker on standby and hit swap. How fast
should the needle point? I realize that in flight it doesn't have
much call to move quickly, but until now I was never paying attention.

I have the Narco ADF 841 in my Warrior. I don't like it nearly as much
as the Bendix-King ADF. When I had the indicator in at the instrument
shop for cleaning and testing, they told me that it uses a funny
mechanism with magnets.

With a strong signal, the needle points fairly quickly; with a weak one,
it takes its sweet time. It both cases, it's slower than others.


All the best,


David

It's a function of distance from the transmitting antenna...you have the
same "radial" spread situation that you have with a VOR in that one degree
spreads out 100 feet per mile from the antenna. The further you are away,
the slower the response. You should also know the class of the facility from
the A/FD...an H beacon is good for 50 miles, HH is good for 75 miles,
LMM/LOM good for 15 miles, MH good for 25 miles. I've had many a pilot try
to pick up an outer marker from 25 miles away and gripe because s/he wasn't
getting a good signal.

Bob Gardner

"Ben Jackson" wrote in message
news:4Iyub.178554$mZ5.1264586@attbi_s54...
My ADF (Narco 841) quit pointing shortly after I got the plane, so
I pulled it and found it was covered in swarf (metal shavings) so I
cleaned it off, cleaned the contacts (card edge connector) and put
it back in. Now it points again. What I'm wondering is: How fast
should it point? Let's say there's nothing on freq 200 (default)
and I tune a nearby NDB/marker on standby and hit swap. How fast
should the needle point? I realize that in flight it doesn't have
much call to move quickly, but until now I was never paying attention.

--
Ben Jackson

http://www.ben.com/

It's signal-to-noise ratio that's the culprit, Bob, not radial spread.
A degree at the ADF antenna on the airplane is always the same size.

Either low signals or high noise will reduce ADF performance.
Everybody knows they get squirrelly around thunderstorms.
---JRC---

"Bob Gardner" wrote in message =
news:0Zyub.182351$9E1.954218@attbi_s52...
It's a function of distance from the transmitting antenna...you have =
the
same "radial" spread situation that you have with a VOR in that one =
degree
spreads out 100 feet per mile from the antenna. The further you are =
away,
the slower the response. You should also know the class of the =
facility from
the A/FD...an H beacon is good for 50 miles, HH is good for 75 miles,
LMM/LOM good for 15 miles, MH good for 25 miles. I've had many a pilot =
try
to pick up an outer marker from 25 miles away and gripe because s/he =
wasn't
getting a good signal.
=20
Bob Gardner
=20
"Ben Jackson" wrote in message
news:4Iyub.178554$mZ5.1264586@attbi_s54...
My ADF (Narco 841) quit pointing shortly after I got the plane, so
I pulled it and found it was covered in swarf (metal shavings) so I
cleaned it off, cleaned the contacts (card edge connector) and put
it back in. Now it points again. What I'm wondering is: How fast
should it point? Let's say there's nothing on freq 200 (default)
and I tune a nearby NDB/marker on standby and hit swap. How fast
should the needle point? I realize that in flight it doesn't have
much call to move quickly, but until now I was never paying =
attention.

--
Ben Jackson

http://www.ben.com/
=20

Yes and no. The rule of 60 still applies, although the s/n ratio certainly
plays a part, given that we are talking about AM.

Bob Gardner

"John R. Copeland" wrote in message
...
It's signal-to-noise ratio that's the culprit, Bob, not radial spread.
A degree at the ADF antenna on the airplane is always the same size.

Either low signals or high noise will reduce ADF performance.
Everybody knows they get squirrelly around thunderstorms.
---JRC---

"Bob Gardner" wrote in message
news:0Zyub.182351$9E1.954218@attbi_s52...
It's a function of distance from the transmitting antenna...you have the
same "radial" spread situation that you have with a VOR in that one degree
spreads out 100 feet per mile from the antenna. The further you are away,
the slower the response. You should also know the class of the facility
from
the A/FD...an H beacon is good for 50 miles, HH is good for 75 miles,
LMM/LOM good for 15 miles, MH good for 25 miles. I've had many a pilot try
to pick up an outer marker from 25 miles away and gripe because s/he
wasn't
getting a good signal.

Bob Gardner

"Ben Jackson" wrote in message
news:4Iyub.178554$mZ5.1264586@attbi_s54...
My ADF (Narco 841) quit pointing shortly after I got the plane, so
I pulled it and found it was covered in swarf (metal shavings) so I
cleaned it off, cleaned the contacts (card edge connector) and put
it back in. Now it points again. What I'm wondering is: How fast
should it point? Let's say there's nothing on freq 200 (default)
and I tune a nearby NDB/marker on standby and hit swap. How fast
should the needle point? I realize that in flight it doesn't have
much call to move quickly, but until now I was never paying attention.

--
Ben Jackson

http://www.ben.com/

Pointing accuracy, measured in degrees by your ADF,
does not depend upon your distance to the beacon,
except insofar as signal-to-noise ratio is affected.
The goniometer sensor of the ADF antenna simply measures
angle of arrival for its received signal.

VOR signals, by contrast, carry the azimuth angle *from the VOR*
which is the information decoded in your VOR receiver.
VOR reception has the "radial spread" phenomenon because of that.
i.e., at great distances from a VOR station, you can move a substantial
tangential distance without much change in your VOR azimuth.

I'm unsure we're talking about the same things here, Bob.
Am I misinterpreting something you said?
I'm sure you must know these basics as well as I.

But back to the original poster's question of response speed...
If the ADF needle is truly more sluggish than it used to be,
the amplitudes of the signals at the nulling circuitry may be unequal.
A good *old-fashioned* ADF technician who still understands the
old technology will be able to re-balance the signals.

Understand, though, that the ADF designer made a conscious
trade-off between needle slew rate and pointer stability.
A tune-up won't make the needle any more responsive than
the manufacturer originally intended it to be.
I have no access to specifications for Ben's Narco 841 ADF,
so I have no idea what slew rate he should expect.
I hope some 841 owner will make the test Ben asked about.
---JRC---

"Bob Gardner" wrote in message =
news:FkEub.184768$275.617118@attbi_s53...
Yes and no. The rule of 60 still applies, although the s/n ratio =
certainly
plays a part, given that we are talking about AM.
=20
Bob Gardner
=20
"John R. Copeland" wrote in message
...
It's signal-to-noise ratio that's the culprit, Bob, not radial spread.
A degree at the ADF antenna on the airplane is always the same size.
=20
Either low signals or high noise will reduce ADF performance.
Everybody knows they get squirrelly around thunderstorms.
---JRC---
=20
"Bob Gardner" wrote in message
news:0Zyub.182351$9E1.954218@attbi_s52...
It's a function of distance from the transmitting antenna...you have =
the
same "radial" spread situation that you have with a VOR in that one =
degree
spreads out 100 feet per mile from the antenna. The further you are =
away,
the slower the response. You should also know the class of the =
facility
from
the A/FD...an H beacon is good for 50 miles, HH is good for 75 =
miles,
LMM/LOM good for 15 miles, MH good for 25 miles. I've had many a =
pilot try
to pick up an outer marker from 25 miles away and gripe because s/he
wasn't
getting a good signal.

Bob Gardner

"Ben Jackson" wrote in message
news:4Iyub.178554$mZ5.1264586@attbi_s54...
My ADF (Narco 841) quit pointing shortly after I got the plane, so
I pulled it and found it was covered in swarf (metal shavings) so =
I
cleaned it off, cleaned the contacts (card edge connector) and put
it back in. Now it points again. What I'm wondering is: How =
fast
should it point? Let's say there's nothing on freq 200 (default)
and I tune a nearby NDB/marker on standby and hit swap. How fast
should the needle point? I realize that in flight it doesn't have
much call to move quickly, but until now I was never paying =
attention.

--
Ben Jackson

http://www.ben.com/

"John R. Copeland" wrote in message
...

Understand, though, that the ADF designer made a conscious
trade-off between needle slew rate and pointer stability.
A tune-up won't make the needle any more responsive than
the manufacturer originally intended it to be.
I have no access to specifications for Ben's Narco 841 ADF,
so I have no idea what slew rate he should expect.
I hope some 841 owner will make the test Ben asked about.
---JRC---

Have 841 and service manual. Yes, there's a lag in response following
tuning to a station, and more so than I recall in using a KR-86 and
ADF-31. The manual does not say directly how this lag is accomplished
nor what's normal, and I'll guess it's in the programming of the
microprocessor.

Fred F.