Sunday, April 6, 2014

20 meter transmitter
The QRP transmitter.

 I was seeing through my old copy of the EFY. Found this. In year 96-y2k, Pradeep.G,   D.Prabhakaran,    vu3nsh etc had published very good work.

I have not made this. But made two tx on 80 meter using little different design and they had worked. All parts are easily available and can be substituted with others. It is a very straight forward transmitter.

If transistor SL100 is not available try 2n2219. Use crown heatsink.

Instead of BD139 try C1162 transistors with heatsink. Any metal slab with 5 cm by 5cm and 2 to 5mm thickness should work. Or try any heatsink you have. You can also try to use the cabinet chasis as heatsink but do care to use the mica washer (but dont use this last option). If you are feeling that transistor is making too much heat try a small fan, computer fan. Now a days computer fans cost very less !. Put it above the heatsink directly throwing air on it. fasten the fan tightly so it dont wobble the chasis or the ckt. Do, power the fan seperately as it requires 210ma ,12v dc.

Seperation of PA and other stage is not marked by dotten line, but i suggest to make the PA in different board, if using the general purpose pcb . Please also enclose the oscillator stage in a small aluminium box for xtra stabilty.

Minimum component and QRP does not mean we dont give it a big box. Of course ! cost will increase, but the metal box enhances the quality of your projects. In the end you will like the result.

May be we can switch the oscillator and buffer stage by a transistor switch. Try SK100, BD140 OR 2n3054 (?)  or a relay if its chattering is not annoying to you.

I see one further developement that we can modulelate the pa stage to make AM Transmitter for local use. It is worth a try.

JF01 ? getting old so forgetting his name also made three transistor 40 meter transmitter. Xtal is important. We will find this 14.318 xtal for some more years. its very cheap 10/-rs per piece. Dont try to port it for other band, you will end up frustrated. Use it as it is.

If i make then, will be sure to upload with my own version. But one last tip. Try one stage at a time. First make oscillator, then make the second stage use it. tweak it. box it. now make the cabinet put everything, fan etc and make the thrid stage. Some sort of atu and relay to switch ON off and QSK is needed. If some seniour hams with antenna analyzer makes some antenna then it will be our standard rig for lots of hams. By, the way 14.318kc xtal freq is very less populated so THE QRP ham can survive there. thanks enjoy de vu3inj

please search the jf10zl.html and you will get lots of information regarding homebrew project using simple transistors and they work nice.

14318kc cw transmitter
 This is my hand drawing.
 This is how i put fan on the box , above the power transistor.

For the AM Modifications please search the pirate radio transmitter, they have excellent modulations method i.e heising modulations. Here a choke is used. Now a days there is no audio choke available, best ways is to wind yourself or order speciallly to local transformer manufecturer. You have to provide the data.

Another method is to use 12-0-12, 1Amp power transformers secondary. It work. There you will also need an audio amplifier.

I hope to make this one for  am local use .

In this project please look the blog from time to time. I will not disappoint you FRIENDS.....

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