What is big deal, you flip the switch and from transmit you are on receive mode and vice versa. True for the SSB or FM transmitter. The PTT switch do it very simply, but here in
the CW transmitter lots of things has to be switched on and off for
receiver to transmit in various stages .
Any new home-brewer for him/her the QSK is a biggest hurdles. as they do not know exactly what is going on between receiver to transmitter handover. Lets understand what is happening. Jump to conundrom portions.
You may first listen my bablings please. As my transmitter were built as a stand -alone unit thus they were not compatible with the receiver sections. I used them as a stand alone devices and was not testing their air worthiness so did not bother to do anything or make them compatible. I enjoyed making things for myself. Time passed on. Lots of things changed. The fuckers bitx failed and i am back into the cw dsb game plan. Now all those small QRP transmitters needs to be put on air. So the re-inventing the wheel of qsk.
Have a look at these ckts. a single transistors is used as switch. It is simply keying a tx stage. general purpose transistor BC547 keys around 100ma ,good for single oscillator and pre-driver stage or for driving a relay. This served me well. Like it. If you need more current then 100ma use BD139 etc heavey duty, heat sinkable transistors.
Now, I tried to make transceiver from tx and rx modules. I have observed that, when you are putting rx tx modules in a single cabinet box, the Rx Stages comes near the heavy TX RF fields. This will create the havoc on receivers. So, you got to put the tx modules and receiver module in their respective small metal enclosures , well shielded from each others. Use the plenty of metal separations sheets wherever possible. Use shielded cables for interconnections. This will help, cope up with each other. Putting RF ckt in small small closed environment / boxes makes it neat and clean. in long run the dust does not accumulate on it.
There is a qsk ckt given in the ARRL Hand Book 1978 ,gifted by Guru DEV, vu2dev(sk).
Design element
Important thing to SEE is R-C time constant (the time delay ) how much the relay is hold before it gives the controls back to the receiver. In cw there is spaces between the each charactes and dot dashes so the ckt should remain in the tx mode even if the key is not down for space time. This varies with operators speed. Hence a variable pot is used to manage the delay.
when is key is pressed the Vcc line is enabled to the electrolytic capacitor, which is connected at base of relay driving transistor. The transistor immediately switches on. Relay is switched on. The capacitor retains the charges and slowly discharges through B-E path and the variable resistor. To switch on a silicon ransistor 0.7 volts is needed. So this capacitor due to its charge reservoire keeps the transistor in on stage. when capacitor is discharged it switches off the transistor. This creates the time delay.
Here is LIBRA80 ckt Have a look at this website https://www.qsl.net/sp5ddj/Libra.htm. You may find plenty of functional home-brew projects there. I will try to imitate his QSK which is similar to ARRL handbook. I keep all the ckt in blog as this becomes my handy resources to look and compare things for design.
In this conun-drum there are few issues.
a) CW transmitter = keying. oscillator /driver PA. antenna change over.
b) RX = Antenna change-over, protecting the RF input stage from desensitizing, audio chain muting, side-tones generating, shifting of VXO/BFO frequency for 600hz shift / RIT.
c) Tune provisions, indipendant of QSK ckt for matching Tx and Rx frequencies.
Any Simple well designed switch over circuit can over ride all these problems. what should be characteristics ? There should be time-delay for matching up the CW speed . on keying TX should fire up and receiver should immediately go into protect mode. If you do not do it fast the RF inputs goes to RX front end and destroys and desensitize it. when morce key is up for space at this time rx should not be enabled because there will be another possible key push coming after the space time. So, it should be protected otherwise the quick relay change over will make very hard and annoying to listen to. If on qrp rig ear-fones are used see that there is no loud-thumping due to change over audio blasting. If there is any agc-line you have to make provisions for it. In ill-designed circuit the relay chattering takes places and that harms a lots of things.wear and tear of relay happens.
Solutions are-
There are many ways to do RX-TX handover.
First is - Simple manual switch, this will change-over the all the modules Vcc. one connection of (relay )for antenna, hand over to rx and tx pa side. Another line for the tx/rx Vcc. thats it. 6 pole switch or 6 pole relay does the job. Many homebrew xtal controlled transceivers use this method. simple effective. you need to provide for sidetones otherwize its good one.VK3YE has done it and you can see his vedio of 30 watt cw transmitter.
Second is:- Full qsk everything is selected with proper care, very complex circuit board is needed. Many commercial transceiver does have these plan.
Third is :- Semi-automatic qsk, here muting ckts, tx-rx antenna switching with relays, Vcc etc is done
Fourth is- for QRP only a diode switch over, rit and audio mute is done. no electro-mechanical devices used for antenna change over. antenna is always connected. good for qrp power only.
Fifth is:- if you are using the microcontrollers , all problems solutions can be implemented in the software. here cw keyer, automatic cw calling etc can also be implemented. using little bit of silicon brain makes our simple transmitter at par with big guns.
too much blah blah, lets do it.(to be continued ...)
11 april 2020. Given below is link to vedio. I have used manual mechanical switch as qsk. very very rudimentary and usage is deprecated, but at least it enabled me to finish up the "bleeding long" project into a logical quietus. Due to lock-down the Relay is not available. So from my junk-boxes found a working DPDT switch from a long forgotten board, dusted it, cleaned it and tested . Now cw tx is working but very clumsy and inconvenient to switch on and off.
Have a look at this finished setup CW Transmitter 1 minute vedio is here, click this link.
Any new home-brewer for him/her the QSK is a biggest hurdles. as they do not know exactly what is going on between receiver to transmitter handover. Lets understand what is happening. Jump to conundrom portions.
You may first listen my bablings please. As my transmitter were built as a stand -alone unit thus they were not compatible with the receiver sections. I used them as a stand alone devices and was not testing their air worthiness so did not bother to do anything or make them compatible. I enjoyed making things for myself. Time passed on. Lots of things changed. The fuckers bitx failed and i am back into the cw dsb game plan. Now all those small QRP transmitters needs to be put on air. So the re-inventing the wheel of qsk.
Have a look at these ckts. a single transistors is used as switch. It is simply keying a tx stage. general purpose transistor BC547 keys around 100ma ,good for single oscillator and pre-driver stage or for driving a relay. This served me well. Like it. If you need more current then 100ma use BD139 etc heavey duty, heat sinkable transistors.
Now, I tried to make transceiver from tx and rx modules. I have observed that, when you are putting rx tx modules in a single cabinet box, the Rx Stages comes near the heavy TX RF fields. This will create the havoc on receivers. So, you got to put the tx modules and receiver module in their respective small metal enclosures , well shielded from each others. Use the plenty of metal separations sheets wherever possible. Use shielded cables for interconnections. This will help, cope up with each other. Putting RF ckt in small small closed environment / boxes makes it neat and clean. in long run the dust does not accumulate on it.
There is a qsk ckt given in the ARRL Hand Book 1978 ,gifted by Guru DEV, vu2dev(sk).
Design element
Important thing to SEE is R-C time constant (the time delay ) how much the relay is hold before it gives the controls back to the receiver. In cw there is spaces between the each charactes and dot dashes so the ckt should remain in the tx mode even if the key is not down for space time. This varies with operators speed. Hence a variable pot is used to manage the delay.
when is key is pressed the Vcc line is enabled to the electrolytic capacitor, which is connected at base of relay driving transistor. The transistor immediately switches on. Relay is switched on. The capacitor retains the charges and slowly discharges through B-E path and the variable resistor. To switch on a silicon ransistor 0.7 volts is needed. So this capacitor due to its charge reservoire keeps the transistor in on stage. when capacitor is discharged it switches off the transistor. This creates the time delay.
Here is LIBRA80 ckt Have a look at this website https://www.qsl.net/sp5ddj/Libra.htm. You may find plenty of functional home-brew projects there. I will try to imitate his QSK which is similar to ARRL handbook. I keep all the ckt in blog as this becomes my handy resources to look and compare things for design.
a) CW transmitter = keying. oscillator /driver PA. antenna change over.
b) RX = Antenna change-over, protecting the RF input stage from desensitizing, audio chain muting, side-tones generating, shifting of VXO/BFO frequency for 600hz shift / RIT.
c) Tune provisions, indipendant of QSK ckt for matching Tx and Rx frequencies.
Any Simple well designed switch over circuit can over ride all these problems. what should be characteristics ? There should be time-delay for matching up the CW speed . on keying TX should fire up and receiver should immediately go into protect mode. If you do not do it fast the RF inputs goes to RX front end and destroys and desensitize it. when morce key is up for space at this time rx should not be enabled because there will be another possible key push coming after the space time. So, it should be protected otherwise the quick relay change over will make very hard and annoying to listen to. If on qrp rig ear-fones are used see that there is no loud-thumping due to change over audio blasting. If there is any agc-line you have to make provisions for it. In ill-designed circuit the relay chattering takes places and that harms a lots of things.wear and tear of relay happens.
Solutions are-
There are many ways to do RX-TX handover.
First is - Simple manual switch, this will change-over the all the modules Vcc. one connection of (relay )for antenna, hand over to rx and tx pa side. Another line for the tx/rx Vcc. thats it. 6 pole switch or 6 pole relay does the job. Many homebrew xtal controlled transceivers use this method. simple effective. you need to provide for sidetones otherwize its good one.VK3YE has done it and you can see his vedio of 30 watt cw transmitter.
Second is:- Full qsk everything is selected with proper care, very complex circuit board is needed. Many commercial transceiver does have these plan.
Third is :- Semi-automatic qsk, here muting ckts, tx-rx antenna switching with relays, Vcc etc is done
Fourth is- for QRP only a diode switch over, rit and audio mute is done. no electro-mechanical devices used for antenna change over. antenna is always connected. good for qrp power only.
Fifth is:- if you are using the microcontrollers , all problems solutions can be implemented in the software. here cw keyer, automatic cw calling etc can also be implemented. using little bit of silicon brain makes our simple transmitter at par with big guns.
too much blah blah, lets do it.(to be continued ...)
11 april 2020. Given below is link to vedio. I have used manual mechanical switch as qsk. very very rudimentary and usage is deprecated, but at least it enabled me to finish up the "bleeding long" project into a logical quietus. Due to lock-down the Relay is not available. So from my junk-boxes found a working DPDT switch from a long forgotten board, dusted it, cleaned it and tested . Now cw tx is working but very clumsy and inconvenient to switch on and off.
Have a look at this finished setup CW Transmitter 1 minute vedio is here, click this link.
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