cw transceivers

Problems:- 

I enjoy home brewing. When project  takes too much time in development , board is finished but i do not have other necessary technologies, to wrap up the things i box them up as it is. later on, when time comes ripe, i use these boxed-device after lots of changes. I am rejuvenating one of that transceiver project. That was made few years back. That was never tried on air nor their air worthiness checked.

Our ham station must have some air worthy transceiver.

On impulse of coming to air, few months back tried to make the 21168kc xtal based cwtx-dcrx transceiver but the xtal was 3rd harmonic one. It was not usable on 15 meter and did not liked to use it on the 7056, So i tried the 21096 in the same platform. RX was good sensitive but the irf 510 is not producing enough umphhhh.  Need to redesign the cw tx chain with 2n3866, 2n2078 etc a big work. not doing. abandoned the 15meter for now.

Then i remember in last to last lamington road electronic market, mumbai visit i had bought the 10 number of 3686 kc xtal.  I placed this 3686kc xtal in this modules and there  was RF ,light in the lamp load. WOW.  It might be producing more than 2 watt RF power. workable. This RF power can drive external linear. good. or it should be usable for local com. hope so.

I am becoming old without any contact. Story can be depicted " unused old stock but brand new in package". he he. Why we should re-invent new new platforms for each receiver and transceiver. I am really tired of making separate seperate receiver, transmitter, transceiver for different different bands. A thought was puzzling me, can't we make something that is workable, usable , reproduce-able and worth every cent of that dollar spent ? This  trx making is costly, time consuming, tedious task.

We need one unit with 3-4 bands, even if it is xtal based, DC receiver and CW / DSB transmitter. We must have at-least 2 to 5 watt. this can be put in small box ( samilar as MTR3-B ) and an external 20 watt linear for reliable communications.

Solutions:-

There must be some solutions. Then i searched my xtal storages boxes. i found this 6 xtal sets. All these are in ham-band. and does not fall into any popular crowded net.

meter band =  tx freq crystal = poliakov rx freq crystal
80 meter band = 3686kc = 1843kc
40 meter band  =7159kc= 3579kc
20 meter band= 14318kc=7159kc

So with one cw tx board, band switching and using the poliakov dc receiver using sub-harmonics oscillators i can make three band portable transceiver.

Good idea.When you are making new device, Plan it right as time is finite. Make airworthy, use whatever you have, operate on cw ,then modify for DSB fone. RX front end should have good band-pass filter. there should be wide/narrow AF filter. there must be RIT. Easy tx-rx change over. There should be RF-indicators. And VSWR antenna tuning. side-tones makes it perfect. just have a look at vk3ye.com and youtube for his work and idea in cw qrp.

So work is in progress when its finished will reveal here with a different write-up. 

And yes, i will be QRT with twitter, facebook social media . also not recharged the mobile-fones internet as no work no money due to corona epidemic.

Straight keying morse is a very tiring work so, i will make arduino automatic cq caller. cq cq cq de vu3inj vu3inj k. Please scan the band. you might catch me on 14315kc, 3686 kc calling cw. Send the SWL report and i will reply with handmade QSL card. i will reply very very short "ur rst 5nn bk hw cpy ? "
73
vu3inj
indrajit.
click here to see " 3686kc transceiver " on youtube.

how to do cw qso ?

here is a image i got from net.cw4u.org

have a look. and also visit at cw4u.org.
Enjoy 73
cu on 14.315 Mhz cw, 3686kc

QSK

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. 
 

DC receiver march 2020

The corona blockade has forced to me to do something worthwhile. If we are able to do even then do not fulfilling our dreams  is not a good thing. I wanted a receiver for my 14.318 mhz xtal Transmitter. I have one good  single frequency superhet receivers based on RM-96 derivatives but it needs to be aligned and fixed and nothing ready made.

I looked into the junk box ? what i have. few unfinished junked DC receivers and one un-finished superhet receivers ? any worthy candidate. first and foremost criteria  a working tested modules. because i did not have time and patients for new RAnD.

Here comes my rescue an old "superhet receiver module " where mixing stage somehow did not worked or may be i did not make the good filter or first IF amplifier was too much bad. I used feed back and all short of gimmics (farhans copy) but fucker did not work for me. Finally dismantled that RF amplifier. Removed the 10 mhz xtal filters. Removed VXO crystals. You can look at that module some pages back.

I had removed the audio amplifier, so found another working the ic LM386. I was heating up the ic oscillating up etc. removed it , put the good air, cleaned up and low behold no motor boating and no noise. Then put the separations shields. These are gimmicks/witch crafts but it works. After putting these copper separating shields everything remains in their boundary ? he he.

vu3inj receiver.

Then finally after two - three days soldering and using the good smoothing calming words. the boards is ready with their damsels. Size is very small. See the ball-pen. The women are beautiful. Once our late rev. guru dev ji (vu2dev-sk) had remarked me about my putting the ckt with damsels. I smiled back.

There should be no oscillations, motor boating. There should be good filtering of audio and RF. there should be frequency stability.  Everything should be tight coupled and nothing should be loose. Put it in the good mechanical sturdy box.

RX has golden finger test. When you do not connect to the signal source, all gain AF at their maximum and there should be no big noise. There should be mild hissing when you listen very near to the loudspeakers. Now, go away from loudspeakers. Touch the Finger to the input jack or small 1 foot wire antenna and it should start roaring and there should be high noise. Then you have good noise and good gain in your receiver chain.  This concept of using a xtal filter for a single frequency receiver is boon for early stages of RanD and point to point communication with dedicated group of friends.

As of 4 april 2020- fixed up the QSK but it seems, it reduce the gain. May be attenuating and increasing the noise floor of the receiver . disliking it. lets see that can be improvised later on. needs to be boxed. found out the noise issue, input 100pf removed to 0.1mfd and signal level increased, it over rode the noise floor. hmm.

If i can use the 7812 internally then i may use the 35 volt power supply itself. This tx chain dose not need more power. just 2 watt. means 300 ma at max. tomorrows deadline, no use of internet but just use the time to fix up relays trx and put the beeps. enough is enough. power supply is still a problem. with peak 35 volts dc input 78024 ,7812/7805 will NOT be able to handle. I needs to go for the transitor for a first drop and then regulator will think of it.

On 05-april-2020. fixed up everything called up a friend vu2exp. due to lock down the qth setup is locked up and living at another qth. ok ok. so thought of checking whether rx is working and can cope up with the tx power.  have a look at my 1 minutes YOUTUBE vedio  20 mb test set up is working click here.

As i am fixing up RX in the original tx box which was only for the CWTX chain. little bit of cramped space.  As this is copper plane its rock-solid. Ohh i have to tune it also.

spart 152, M0DGQ

Now, it needs to be boxed and fixed in the cw transmitter box with all RF change over , side tone controls. wait for it.
Thats it falk, here i am re-re-re-inventing the wheels.