I have a python program running a loop of two functions "talking" to each other.
Let us call the two functions Function 1 and Function 2, and they are doing similar things as briefly described below.
Function 1 takes care of two Rpi GPIO pins, input pin GPIO In1 is connected (through a 4k7 resistor) to output pin GPIO pin Out2, which is
taken care of by Function 2.
Similarly, GPIO In2 is connected to GPIO Out1.
For each loop Function 1 checks if GPIO pin In1 is low, if yes, Function 1 will make GPIO pin Out1 low, so that Function 2 will
detect this next loop, ...
I googled a bit and found the question is easier than I thought. It is all about PTT and COS pins. Actually the OP is not talking about the ideas, but the PTT and COS pins, as illustrated below.
I found one thing confusing is the the COS pin shares with PL, perhaps that causes confusion.
The python program
Actually I think what the OP needs is the simple program I already briefly described in the question.
Warning to OP
The PTT and COS pins may carry 5V TTL logic signals. Rpi GPIO pins runs on 3V3 logic and are not 5V logic signal level tolerant.
In other words, Rpi might be damaged if the transceiver's PTT/COS pins are directly connected to Rpi GPIO.
On the other hand, 5V Arduino Uno should have no problems, because they are designed to entertain 5V logical level signals. For Rpi the usual get around is to use a logical level converter to step down the ham radio trasnsceiver's possibly 5V signals to 3V3 signals which are now compatible with Rpi. You can google AdaFruit or SparkFun for their very good newbie friendly logical level converter tutorials.
Perhaps I should get a cheapy Motorola M120 from eBay and PTT radio him to clarify! :)
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Amateur Radio Future - Network Radio - Zello PTT Apps? 5,452 views
Amateur Radio Guideto Digital Mobile Radio (DMR)
The most important thing about the hobby of Amateur Radio is to enjoy
learning new technologies, experimentation, meeting new friends,
public service, and to leave the hobby better than when you entered.
The spark gap transmitter gave way to frequency selective transmitters and receivers using CW; CW gave way to AM; AM was largely pushed aside by SSB; FM became the mode of choice for most on the VHF and shorter wavelengths.
The digital ham started at the same humble beginning, CW over spark gap. Over the years, the digital ham’s interests may have included CW, RTTY, then Packet (AX.25), and a whole host of mainstream and experimental digital modes, and even WiFi (802.11). With the advent of faster computer processors and vocoder technology, analog voice moved into the digital age, both on the HF bands and on VHF and higher bands. Vocoder technology merged with packet technology and D-Star took the VHF and UHF bands by storm with the help of a single vendor and the JARL (Japan Amateur Radio League). Yaesu has enter the arena with their proprietary System Fusion.
So What's The COR or COS? - Ric Sohl KK5RIC
The Carrier Operated Switch (COS) used to be called COR.... Short for Carrier Operated Relay.
This is going back to the early days of repeaters in which all the
repeaters had tubes in them, and all circuit switching was done by
relays. Nowadays most of the repeaters are solid state, except for a
few which have tubes in the final amplifier, so now we call it COS or
"Channel Busy" or ...
So you ask how does it work and what's the purpose, and where can I
find this COS on a receiver? The function of the carrier operated
switch is to tell the repeater controller, if the repeater has one,
that the receiver squelch is open, and that there is a signal there.
If the controller is set up for Carrier Squelch (CSQ) it then turns on
and off the repeater transmitter. If the repeater does not have a
controller, the COS simply does the function of turning on and off the
The COS signal can be either a set of relay contacts or a voltage that
swings high or low to give either a + voltage or ground with the
receiver active, (noise or a signal.)
On some receivers the COS uses a relay and that has a dry contact to
ground, and you won't see a swinging voltage, a 5k or so pullup
resistor connected 12 volts, makes the COS voltage swing.
The squelch circuit rectifies the hissing noise, its the noise that we
hear when the squelch is open and no signal is present on the fm
receiver. Sometimes this noise is amplified and is applied to diodes
to converted to a dc voltage, some other times to a voltage doubler to
get a greater level of swinging voltage. That voltage is compared to
the squelch pot and if it's greater the squelch stays closed, if it's
less the squelch opens. There's another way to get a COS voltage from
a receiver, that is with a VOX circuit on the receiver audio output,
it does not work properly on a repeater, (if someone has a full
quieting signal and there is a pause in the speech the VOX closes) so
I won't go in detail with it here.
Some AM receivers have COS's also.. not just the FM ones, the major
difference between the two are the FM receivers the COS and squelch
works much better and is harder to be fooled by noise....by the way,
airports with towers use AM receivers with COS. The COS squelch
circuit has been used in repeater receivers for years, long before the
tone squelch came to be very popular. Manufactures paid special
attention to the squelch circuits in their receivers, Motorola even
made a special IC for their MICOR series radios.
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Recommended Rpi GPIO pins to use to interface ham radio transceiver
Some Rpi GPIO pins have alternative functions such as I2c, UART, and
they might have special pull up/down resistors. So it is usually
recommended to use the "pure" GPIO pins without alternative functions,
just to make very sure. The GPIO pins with special alternative
function is illustrated below. For the radio talking program, I would
recommend GPIO GEN_0 to GEN_3.
Ham Radio Setup
Squelch - Wikipedia
In telecommunications, squelch is a circuit function that acts to
suppress the audio (or video) output of a receiver in the absence of a
sufficiently strong desired input signal. Essentially, squelch is a
specialized type of noise gate designed to suppress randomized
signals. Squelch is widely used in two-way radios and radio scanners
to suppress the sound of channel noise when the radio is not receiving
a transmission. Squelch can be opened, which allows all signals
entering the receiver to be heard. This can be useful when trying to
hear distant or otherwise weak signals, for example in DXing.
A carrier squelch or noise squelch is the most simple variant of all.
It operates strictly on the signal strength, such as when a television
mutes the audio or blanks the video on "empty" channels, or when a
walkie-talkie mutes the audio when no signal is present. In some
designs, the squelch threshold is preset. For example, television
squelch settings are usually preset. Receivers in base stations, or
repeaters at remote mountain top sites, are usually not adjustable
remotely from the control point.
In two-way radios (also known as radiotelephones), the received signal
level required to unsquelch (un-mute) the receiver may be fixed or
adjustable with a knob or a sequence of button presses. Typically the
operator will adjust the control until noise is heard, and then adjust
in the opposite direction until the noise is squelched. At this point,
a weak signal will unsquelch the receiver and be heard by the
operator. Further adjustment will increase the level of signal
required to unsquelch the receiver.
A typical FM two-way radio carrier squelch circuit is noise-operated.
To minimize the effects of voice audio on squelch operation, the audio
from the receiver's detector is passed through a high-pass filter,
typically passing 4,000 Hz (4 kHz) and above, leaving only high
frequency noise. The squelch control adjusts the gain of an amplifier
which varies the level of the noise coming out of the filter. This
noise is rectified, producing a DC voltage when noise is present. The
presence of continuous noise on an idle channel creates a DC voltage
which turns the receiver audio off. When a signal with little or no
noise is received, the noise-derived voltage is reduced and the
receiver audio is unmuted. Some applications have the receiver tied to
other equipment that uses the audio muting control voltage, as a
"signal present" indication; for example, in a repeater the act of the
receiver unmuting will switch on the transmitter.
Tone squelch and selective calling
Tone squelch, or another form of selective calling, is sometimes used
to solve interference problems. Where more than one user is on the
same channel (co-channel users), selective calling addresses a subset
of all receivers. Instead of turning on the receiver audio for any
signal, the audio turns on only in the presence of the correct
selective calling code. This is akin to the use of a lock on a door. A
carrier squelch is unlocked and will let any signal in. Selective
calling locks out all signals except ones with the correct key to the
lock (the correct code).
In non-critical uses, selective calling can also be used to hide the
presence of interfering signals such as receiver-produced
intermodulation. Receivers with poor specifications—such as
inexpensive police scanners or low-cost mobile radios—cannot reject
the strong signals present in urban environments. The interference
will still be present, and will still degrade system performance, but
by using selective calling the user will not have to hear the noises
produced by receiving the interference.
Four different techniques are commonly used. Selective calling can be
regarded as a form of in-band signaling.
CTCSS (Continuous Tone-Coded Squelch System) continuously superimposes
any one of about 50 low-pitch audio tones on the transmitted signal,
ranging from 67 to 254 Hz. The original tone set was 10, then 32
tones, and has been expanded even further over the years.
CTCSS is often called PL tone (for Private Line, a trademark of
Motorola), or simply tone squelch. General Electric's implementation
of CTCSS is called Channel Guard (or CG). RCA Corporation used the
name Quiet Channel, or QC. There are many other company-specific names
used by radio vendors to describe compatible options. Any CTCSS system
that has compatible tones is interchangeable. Old and new radios with
CTCSS and radios across manufacturers are compatible.
Selcall (Selective Calling) transmits a burst of up to five in-band
audio tones at the beginning of each transmission. This feature
(sometimes called "tone burst") is common in European systems. Early
systems used one tone (commonly called "Tone Burst"). Several tones
were used, the most common being 1,750Hz, which is still used in
European amateur radio repeater systems. The addressing scheme
provided by one tone was not enough, so a two-tone system was
devised—one tone followed by a second tone (sometimes called a "1+1"
system). Motorola later marketed a system called "Quik-Call" that used
two simultaneous tones followed by two more simultaneous tones
(sometimes called a "2+2" system) that was heavily used by fire
department dispatch systems in the USA. Later selective call systems
used paging system technology that made use of a burst of five
DCS (Digital-Coded Squelch), generically known as CDCSS (Continuous
Digital-Coded Squelch System), was designed as the digital replacement
for CTCSS. In the same way that a single CTCSS tone would be used on
an entire group of radios, the same DCS code is used in a group of
radios. DCS is also referred to as Digital Private Line (or DPL),
another trademark of Motorola, and likewise, General Electric's
implementation of DCS is referred to as Digital Channel Guard (or
DCG). DCS is also called DTCS (Digital Tone Code Squelch) by Icom, and
other names by other manufacturers. Radios with DCS options are
generally compatible, provided the radio's encoder-decoder will use
the same code as radios in the existing system.
DCS adds a 134.4 bps (sub-audible) bitstream to the transmitted audio.
The code word is a 23-bit Golay (23,12) code which has the ability to
detect and correct errors of 3 or fewer bits. The word consists of 12
data bits followed by 11 check bits. The last 3 data bits are a fixed
'001', this leaves 9 code bits (512 possibilities) which are
conventionally represented as a 3-digit octal number. Note that the
first bit transmitted is the LSB, so the code is "backwards" from the
transmitted bit order. Only 84 of the 512 possible codes are
available, to prevent falsing due to alignment collisions.
XTCSS is the newest signalling technique, and provides 99 codes with
the added advantage of "silent operation". XTCSS-fitted radios are
purposed to enjoy more privacy and flexibility of operation. XTCSS is
implemented as a combination of CTCSS and in-band signalling.
Squelch was invented first and is still in wide use in two-way radio,
especially in the amateur radio world. Squelch of any kind is used to
indicate loss of signal, which is used to keep commercial and amateur
radio repeaters from continually transmitting. Since a carrier squelch
receiver cannot tell a valid carrier from a spurious signal (noise,
etc.), CTCSS is often used as well, as it avoids false keyups. Use of
CTCSS is especially helpful on congested frequencies or on frequency
bands prone to skip and during band openings.
It is a bad idea to use any coded squelch system to hide interference
issues in systems with life-safety or public-safety uses such as
police, fire, search and rescue or ambulance company dispatching.
Adding tone or digital squelch to a radio system does not solve
interference issues, it just covers them up. The presence of
interfering signals should be corrected rather than masked.
Interfering signals masked by tone squelch will produce apparently
random missed messages. The intermittent nature of interfering signals
will make the problem difficult to reproduce and troubleshoot. Users
will not understand why they cannot hear a call, and will lose
confidence in their radio system.
Professional wireless microphones use squelch to avoid reproducing
noise when the receiver does not receive enough signal from the
microphone. Most professional models have adjustable squelch, usually
set with a screwdriver adjustment or front-panel control on the
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