17
Section 1: Coupler Tests of FM Systems
5. Use
[
∨
] to adjust the level of the signal to 65 dB SPL.
6. Make a note of the AID OUT on the screen. This is the HEARING AID OUTPUT. See
Figure 1.3.1.
1.3.2 Single frequency output of omni-directional FM mic at 65 dB SPL
1. Set up the FM microphone for testing as described in the FM setup in Section 1.1.3.
The FM receiver should be set to receive FM+ENV.
2. If you followed the steps of Section 1.3.1, the analyzer should be in PURE TONE
MODE with a 65 dB SPL signal at 1000 Hz.
3. Look at the AID OUT on the screen. This is the FM OUTPUT.
4. Adjust the FM receiver volume so that the FM OUTPUT is matched to the HEAR-
ING AID OUTPUT found in Section 1.3.1. This matches the gain of the FM system
and the hearing aid.
1.3.3 Verify increase in signal level
1. Leave the FM system and analyzer set up as described in Section 1.3.2 with the aid
or FM receiver attached to the 2-cc coupler and set to receive FM+ENV.
2. Press
[
∧
] repeatedly to increase the signal level to 80 dB SPL.
3. Look at the AID OUT on the screen. This is the new FM OUTPUT.
4. Compare the HEARING AID OUTPUT found in Section 1.3.1 to this new FM OUT-
PUT, and adjust the FM receiver volume control according to the following:
If the increase is:
• 10 dB, no further adjustments are necessary.
• 15 dB, reduce the FM receiver volume control so that the FM OUTPUT falls by 5 dB.
• 5 dB, increase the FM receiver volume control so that the FM OUTPUT increases
by 7 or 8 dB.
• 0 dB, the FM transmitter must have a very low compression threshold, so
increase the FM receiver volume control so that the FM OUTPUT increases by 5
dB.
1.3.4 Test aid alone with typical input — EHA65
1. Set up the hearing aid for testing as described in Section 1.1.2. The FM transmitter
should be off, and the hearing aid set to receive input from the hearing aid micro-
phone.
2.
Press [RESET] to enter Composite Weighted Gain Mode.
3.
Press [WEIGHT] to enter Composite Weighted Power Mode.
4.
Use [
∨
] to set RMS Source to 65 dB SPL.
