| |
G8MNY > TECH 29.11.20 10:30l 175 Lines 7981 Bytes #999 (0) @ WW
BID : 14250_GB7CIP
Read: GUEST
Subj: CTCSS add on Project
Path: IZ3LSV<I0OJJ<N6RME<CX2SA<N3HYM<WW1R<N9PMO<JE7YGF<GB7CIP
Sent: 201129/0923Z @:GB7CIP.#32.GBR.EURO #:14250 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Nov 16)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
This is from a talk by Andy G4WGZ on his implementation of Weyer VK2KUR's idea.
FREQUENCIES
There are 41 Continuous Tone Coded Squelch System tones in this USA designed
PMR squelch system, only 9 (A-J) of the less noticeable lowest ones (not 100Hz)
are used in the UK repeater network.
67.0 71.9 74.4 77.0 79.7 82.5 85.4 88.5 91.5 94.8 97.4 100.0 103.5
A B C D E F G
107.2 110.9 114.9 118.8 123.0 127.3 131.8 136.8 141.3 146.2 151.4 156.7 162.2
H J
167.9 173.8 179.9 186.2 192.8 203.5 206.5 210.7 218.1 225.7 229.7 233.6 241.8
250.3 256.3 All in Hz
Each CTCSS tone channel is only 3% wide, & with guard bands this means your
frequency needs to be better than ñ1% accurate for the system to work.
In the UK CTCSS tones can be used for repeaters access instead of the normal
1750Hz access tone burst, to give a selective call. (The UK recommendation from
the RSGB is that repeaters should be equipped for both systems, not just one!)
Note that only about half the VHF/UHF radio in use have CTCSS!
The frequencies are allocated regionally & a Morse letter is often sent with
the repeater ID, to say which is in use on that repeater (A-J not I).
In practice only a few are needed from any one location, unless you want to
work the Dx repeaters. If set up properly CTCSS tones should be able to keep a
repeater open at a higher noise level (weaker signal) than a normal squelch
circuit can.
TEST KIT NEEDED
An AF frequency Counter, with 10 second gate (to 0.1Hz), or period timer mode.
An AF oscilloscope is useful, A sound card scope/counter will do.
CTCSS RX TONE FILTER
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄ>Pin 4 LEVEL
1M NPN ³ 4k7<ÄÄ¿+ ³ -LOUD-COMMS-AF-
u1 ³ ³/ pot ===100u ³12dB .-ÄÄÄ-.
>Ä´ÃÄÁÄ18kÂÄ18kÂÄ´ ³ _³_ 16V ³ /O.' \
From ³ ³ ³\e ³/e TO ³ ú' -CTCSS--\ 18dB/Octave cut
Rx ³ u1 ³ ÃÄÄ´ PNP NE567 ³' BAND \
Disc ÃÄ´ÃÄ)ÄÄÄ´ ³\ u1 ³ \
_³_ === 10k ÃÄÄÂÄÄÄ´ÃÄÄ>Pin 3 ÀÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂ Hz
\_/ ³33n³ 1k ===u22 20 40 100 200 400 800 1k6 3k2
ÄÄÄÄÄÄÄÄÄÄ)ÄÄÄÄÁÄÄÄÁÄÄÄÄÁÄÄÁÄÄÄÄÄÄÄ>Pin 7 Frequency
ÀÄ<PTT Kill Rx on Tx
The Rx audio (from before Rx squelch) must be cut off on Tx (normally done by
your rig's Rx circuit, but a diode kill option shown here if needed), or it
will affect the stability of the Tx CTCSS tone frequency.
The NPN makes a low pass Butterworth filter & the PNP makes a variable gain amp
also with top cut, to give an overall 18dB/octave cut, to reduce the amount of
comms audio sent into the PLL tone IC, for better CTCSS tone detection.
The 1M bias may need selecting depending on the gain of your transistor to get
about 5V on the NPN's emitter.
The preset pot sets the gain of the PNP stage (1/5 to 100x) & hence the CTCSS
tone detection sensitivity.
THE TONE IC
_____
10-16V>ÄÂÄ´75L08ÃÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄ>+8v ÚÄ<PTT offset
===ÀÄÄÂÄÄÙ 680 4³ === 10u ³
u1ÀÄÄÄÄ´ _³_ ÚÄÄÄÄÄÁÄÄÄÄ¿6 _³_ 4M7
_³_ =\_/ 3³ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄ¿ Triangle wave
RX CTCSS LED³ in>Ä´ ³ 12x Presets ÃÄ> to buffer
__ o______ ³ ³ SE567 ³ ÚÄ10kÄÄÄÄo ³
To \o ³ \³ ³ out ³ NE567 ³ ÀÄÄÄÄÄÄ¿ <ÄÄ82kÄ´
LS ³ _³_ ÃÄ10kÄÁÄÄÄÄÄÄ´ ³5 ÚÄ10kÄÄÁÄo CTCSS³
Relay³ /_\ e/³ 8³ ÃÄ¿ ÀÄÄÄÄÄÄ¿ FREQ ³
³ ³ ³ ÀÄÂÄÄÂÄÄÄÂÄÙ ÃÄÄÄÄ10kÄÄÁÄo ³
³ ³ ³ 7³ 2³ 1³ oTP1 u47 ===
³ ³ ³ ³ === === Square wave ³
ÄÄÄÁÄÄÁÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄ
4u7 33u
12 10k multiturn preset are all in series (any number could be uses), & mounted
around a switch, they set each CTCSS frequency. Although this arrangement is
comblesome to calibrate, it gives the most fine adjustment needed for these
close together frequencies.
The timing capacitor 0.47u & the 82k with 1st preset, set the highest frequency
you need, & must be a very stable types! (Try a hot-cold thermal test!)
The 4u7 & 33u set the PLL bandwidth & lock detector time.
PTT offset is needed between Rx & Tx as the PLL is most sensitive when it is
about 1Hz LF of the desired frequency, the 4M7 to PTT line provides this free
running QSY shift.
The 12V relay (not shown) just disconnects the LS line, as this was an outboard
design, but other muting solutions inside rigs are possible.
A 2 pole CTCSS ON/OFF switch disconnects the Tx output & squelch relay so
allowing the Rig to be used normally, while still checking on what CTCSS tones
are in use via the LED.
CTCSS TX TONE FILTER
ÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄ<+8V
10k ³
Pot<ÄÄ¿ Clip ³
³e ³ level ³/
Triangle ³/ ³ ÚÄÄÂÄ18kÄÂÄ´ NPN
Wave >ÄÄÄ´ PNP ³ ³ ³ ³ ³\e
³\ 1k TP2 18k ÀÄ´ÃÄÄ)ÄÄÄ´ Tx
³ ³ o ³ u1 ³ ³ u1 CTCSS
³ ÃÄÄÄÄÄÁÄÄÄÄÄ´ ³ 10k<ÄÄ´ÃÄÄo\oÄÄÄÄÄ> to rig
³ ÀÄ´<ÃÄÂÄ´>ÃÄÙ 33n=== pot on/off mic stages
³ === 100u ³ ³
ÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÁÄÄÄÄÄÄ
/\ /\ __ __ .-.
/ \ / \ / \ / \ / \ /
/ \/ \ / \__/ \ '-'
Triangle Wave TP2 Very Pure Sinewave
The triangle wave is buffered with the PNP & then the tips are clipped with the
2 silicon diodes to make it more like a sine wave. It is then filtered in
another low pass 12dB/O Butterworth filter, to remove ALL the higher harmonic
frequencies that would otherwise be audible in the comms AF channel.
The Tx output level from the Tx, (Rig input may be much higher if there is LF
loss!) should be set to about -20dB (10%) of peak level, so that the tone (HUM)
is not too audible! e.g. ONLY around ñ250Hz deviation on a 12.5kHz system.
CALIBRATION
Frequencies: These are measured on square wave test point TP1 using a 1/10
scope probe, into a counter with 10 seconds gate time, or by using a counter
in period mode & calculating the "1/f time" in mS for 1 cycle. e.g. 100Hz =
10.00mS (note the period is the time between 2 crests & not the ON time!)
As the pots are all in series, calibration MUST start at the highest
frequency (min resistance) first & with the Tx operated use a dummy load so
there is no RFI. As it is easy to adjust the wrong preset, mark them with the
frequency.
Clipper: Scope the diode test point TP2 & adjust the clipper drive level pot to
give the best near sine wave. Scoping after the filter should look like a
VERY pure sine wave (<0.1% distortion).
Deviation: Rx the Tx audio on a 2nd Rx (with good LF responce) & with a scope
adjust the CTCSS mic tone level to be 1/10 the height of the peak audio, this
is all that is needed! Check the deviation is about right on all CTCSS
frequencies.
Sensitivity: Adjust the 4k7 preset so that on just noise the CTCSS does not
quite open. Check the setting on all CTCSS frequencies you have used.
IN USE
Identifying a brief CTCSS tone of a repeater is difficult as you have to be
quick scanning with the switch. But other than that the unit works as expected.
CTCSS Squelch Delay is very short about 1/5 second.
You should now hear only the one repeater & no "not in use repeater IDs" (IF
THE REPEATER IS CORRECTLY SET UP!).
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
Read previous mail | Read next mail
| |
