Odd Experience with ANR Headset

I have a Flightcom Denali ANR headset that does a fairly good job of
cutting down the noise level. However, with an open-cockpit airplane,
there's a limit. When making a long flight, I generally use a pair of foam
earplugs to cut down on the noise energy my ears are exposed to. This
*almost* works; I can pretty much make out the traffic calls if I really
pay attention. Biggest drawback is that the sidetone is totally
eliminated...usually catches me off guard, the first time I transmit.

I usually leave the ANR turned off when I have the plugs in my ears...no
need to waste the battery (which doesn't last long in an open-cockpit
environment, anyway). When I get close to my destination, I turn on the
ANR and dig the plugs out of my ears.

Anyway, I flew to the Arlington Fly-In yesterday. They've got an ATIS
frequency, so I tuned to it when I was still about 50 miles out. As I got
closer (ANR off and foam plugs in my ears), it started getting just loud
enough to understand.

When I got about fifteen miles out, I turned on the ANR. The volume level
jumped nicely...but the volume of the static jumped at the same time, and
just about totally swamped the signal. I was in a situation where I had a
clearer signal with ANR off.

I eventually removed the plugs, and the ANR did its usual fine job. No
problems understanding either the ATIS or the tower.

I like my Denalis, but this is the first time I've ever had better
operation with them turned off. I expect the amplification included with
the ANR circuitry was just naturally boosting the background noise
(RF-related, not audio) as much as the received signal. The Denalis were
cutting down the background audio noise, while boosting the static noise on
the frequency.

Ron Wanttaja