Silence.txt
#define Sil1Val 0x0D9F8
#define Sil2Val 0x0D9FA


Signal at SilVal
Line 1 In 700 Hz square wave
-40 dBm 04DAH
-30 dBm 1063H F50H (-28 dBm)
-20 dBm 1D05H 18F0H
-10 dBm 2C00H 2700H
0 dBm 3C00H 30D6H (-3.5 dBm)
+6 dBm 45A0H


-30 7427 7437 7442 7437 7447 7437
-29 7849 7839 7843 7846 7831 7844
-28 8229 8227 8233 8225 8207 8230
-27 8574 8609 8567 8574 8575 8560
-26 8974 8922 8942 8935 8942 8946
-25 9341 9303 9309 9311 9326 9289
-24 9671 9662 9677 9674 9658 9679
-23 10055 10045 10086 10102 10090 10062
-22 10498 10476 10499 10495 10524 10496
-21 10900 10848 10876 10869 10879 10875
-20 11256 11252 11246 11234 11228 11224
-19 11639 11637 11648 11684 11623 11617
-18 12058 12002 12006 11978 12067 12017
-17 12446 12467 12461 12443 12445 12433
-16 12884 12868 12842 12841 12878 12861
-15 13303 13271 13303 13322 13273 13313
-14 13673 13701 13720 13689 13734 13684
-13 14072 14155 14128 14055 14058 14045
-12 14506 14468 14535 14472 14464 14495
-11 14911 14900 14904 14929 14903 14924
-10 15376 15347 15332 15373 15365 15340
- 9 15802 15771 15755 15749 15749 15778
- 8 16171 16145 16151 16156 16176 16118
- 7 16588 16557 16641 16573 16535 16582
- 6 16985 16935 16939 16987 16981 16923
- 5 17401 17387 17385 17396 17403 17399
- 4 17872 17831 17860 17848 17845 17877 clip just barely
- 3 18105 18158 18183 18189 18176 18115
- 2 18422 18437 18433 18436 18395 18424
- 1 18652 18650 18664 18570 18633 18623
0 18880 18851 18896 18876 18900 18854
1 19048 19033 18960 19023 18997 18986
2 19147 19257 19212 19229 19241 19199


Computed by program LarkSilenceTest 700
Frequency 700
dBm square sine ami
-50: 960 924 0
-49: 1120 1028 0
-48: 1280 1152 0
-47: 1440 1304 0
-46: 1600 1456 0
-45: 1760 1620 0
-44: 2080 1792 0
-43: 2240 1952 0
-42: 2560 2116 0
-41: 2720 2280 0
-40: 2880 2476 0
-39: 3040 2680 0
-38: 3200 2880 0
-37: 3520 3129 0
-36: 3840 3396 0
-35: 4160 3680 0
-34: 4480 3940 0
-33: 4800 4173 0
-32: 5120 4444 0
-31: 5440 4736 0
-30: 5760 5032 0
-29: 5920 5364 0
-28: 6400 5724 0
-27: 6720 6036 0
-26: 7200 6348 0
-25: 7680 6668 0
-24: 7840 7000 0
-23: 8160 7360 0
-22: 8640 7748 0
-21: 8960 8110 0
-20: 9440 8480 0
-19: 9920 8824 254
-18: 10240 9209 0
-17: 10560 9588 254
-16: 10880 9972 254
-15: 11360 10404 254
-14: 11840 10792 254
-13: 12320 11136 254
-12: 12800 11504 508
-11: 13120 11916 508
-10: 13440 12352 508
-9: 13760 12796 762
-8: 14240 13168 762
-7: 14720 13528 1016
-6: 15360 13928 1016
-5: 15520 14364 1524
-4: 16000 14756 2032
-3: 16320 15240 2540
-2: 16800 15660 3048
-1: 17280 16076 3810
0: 17760 16364 4826
1: 18080 16863 6096
2: 18400 17284 7874
3: 18880 17721 9906
4: 19360 18080 12446
5: 19840 18316 15494
6: 20320 18620 19558
7: 20320 18772 20320
8: 20320 18864 20320
9: 20320 19160 20320
10: 20320 19300 20320

Subject: Lark Reference Levels

To: VoiceProject^.pa

Cc: Stewart

Here are some figures referenced to the "0 dBm" level inside the Lark. This reference level is 3.17 dB below the codec clipping level, per CCITT.

A 0 dBm signal from the codec generates a 1.025 Vrms voltage accross tip and ring of the back door. This is +2.43 dBm in 600 ohms.

A -6.93 dBm signal (0.349 Vrms) at Line In generates 0 dBm digital.

A 0 dBm signal from the codec generates a -7.4 dBm signal at Line out (0.325 Vrms)

Touch tones from TeleSet source generate -12.1 dBm at line out (or -4.7 digital)
The same phone generates 0.715 Vrms accross tip and ring (0.7 dBm) or equivalent -3.13 dBm digital.

Called up 9-494-0020 (test tone).

With the telephone reverted, there was a .478 Vrms (-4.2 dBm) signal accross tip and ring and a .121 Vrms (-16.1 dBm) signal accross the receiver, for a loss of 11.9 dB.

With the telephone unreverted, using the Lark to field the call, there was a .334 Vrms (-7.3 dBm) signal accross tip and ring and a .104 Vrms (-17.4 dBm) signal accross the receiver, for a loss of 10.1 dB.

The test tone produces 0.348 Vrms (-6.95 dBm) at Line out, or 0.446 dBm equivalent digital.

The following levels are all equivalent:

0 dBm digital
-6.93 at Line In
-7.4 dBm at Line Out
2.43 dBm at TeleWall Out
-7.75 dBm at TeleWall In
-9 dBm at TeleSet Out (earpiece)
5.3 dBm at TeleSet In (mouthpiece)

These figures take into account the way the telephone set behaves when connected to the Lark instead of the phone line. A signal that would have been -7.75 dBm at the teleset when reverted will only be -9 dBm when using the electronic phone. A signal from the teleset that would have been 5.3 dBm when reverted will only be 2.43 dBm using the electronic phone.

Thus:

The Lark presents a 3.1 dB heavier load to the phone line. A given signal from the CO is 3.1 dB quieter when driving the Lark instead of a phone instrument.

The electronic phone is a transmit level to the CO 2.9 dB softer than the reverted phone.

The electronic phone has a receive level 1.25 dB softer than the reverted phone.

The telephone transmits DTMF on the wires to the CO at +0.7 dBm for a pair of tones, or -2.7 dBm per tone. The digital DTMF signals should be roughly -6 dBm per tone to achieve about the same voltage.

To limit voice power on the phone lines to -9 dBm average, the digital limiting will have to be
at -11.4 dB.

 -Larry