Can you measure and post your DTMF Twist?
 

Twist = 20*log(FMhi/FMlo) where FMhi is the FM deviation of the DTMF high
tone (1209, 1336, 1477 or 1633 Hz) and FMlo is the FM deviation of the DTMF
low tone (697, 770, 852 or 941 Hz). FMtotal = FMlo + FMhi. Typically,
FMtotal is adjusted on amateur HTs to be 3.0 to 3.5 kHz. Twist should be
about 2 dB. For example, pressing and holding the "1" key should result in
a 697 Hz tone with 1550 Hz FM deviation and a 1209 Hz tone with 1950 Hz FM
deviation. (FMtotal = 1550 + 1950 = 3500 Hz, twist = 20*log(1950/1550) =
2.0 dB.)

If you have access to test equipment that can measure FMlo and FMhi of your
FM transmitter, could you please post the results? I have access to such
test equipment and my Kenwood TH-G71A looks like this:

(Hz) (Hz) (Hz) (dB)
Sym FM Low FM Hi FM Twist
=== ====== ===== ===== ======
1 2223 1862 = 4085 -1.542
5 2202 1750 = 3952 -1.996
9 2173 1640 = 3812 -2.446
D 2108 1502 = 3610 -2.941

The 3.6 to 4.1 kHz FMtotal looks reasonable, but the twist values should be
around +2 dB, not -1.5 to -2.9 dB.

A friend's Icom IC-W2A produces a "1" symbol with FMtotal = 2.6 kHz (a
little low) and Twist = 6.5 dB (4 dB higher than expected). I would like to
find out if we both have misadjusted transmitters, or all Icoms and Kenwoods
show the same error, or perhaps that twist is just a neglected spec and all
radios vary widely.

Rick
WA6NDR
Liberty Lake, WA



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