Thursday, February 20, 2014

Linear RF Amp,RM96

The RM96 transmitter is a very successful and re-produceable design. I have used it's different block in various projects. But, never made the tx chain. got the toroids from vu2ptr and started brewing only tx linear part. it is not advisable to make rf ckt on general purpose veroboard. It is good to use the glass epoxy based etched pcb. Manhattan style on copper plane is also a good options. but i dont have those things at my disposals.

A little description of the components shown on board:-(fig.1) 2n2222 a small transistor, then 2n2218 with crown heat sink and lastly bd139 with a bigger aluminium heat sink (found from junk, used parts). will feed it with dsb modulator freq 7058kc, see earlier posts on this blogs for this dsb modulators. Then probably this will drive a single ended linear based on irf830 or any other push pull amp.

Finished the soldering today morning.(25feb) Done little touch-up, visual inspections and then it is time to hot test.
For this test, i did drive this amplifiier with one spare 20 meter (TA7358ap with xtal) based modulator. Linear ckt was powered with 12v. 1 Amp dc supply. 4 watt dummy load also connected as output rf load.
 When the power transistors are touched by finger, it indicates the hot/cool property of temperature. I touched 2n2218 it was hot faithfully. Then, i become happy and touched the BD139. It was as cool as 2n2222. Hmmm,,,,,That means not working/drawing up the dc current. Something fishy. Visual inspection done.  Needs to look for dry connections. Bd139 base shows 0.67 voltds dc. Ok. but collector shows the dc voltage variations 6 to 7 volts. Dry connections and as a rough rf test when touched 2218 it shows increase in the strength of signal in com rx, but when bd139 is touched it does not show any increase that means it is not producing the rf and not radiating to near by com rx.
On voltage test found that when 12v, 1 amp capable power supply was used line voltage dropped to the 11volts. When current increase beyound normal capacity of transformer line voltages becomes low. OK. There was no smoke. Now, it is time to use the real 12v,5amp power supply and it remained at the 12 volt dc..The RF amplifier takes 220 ma constant dc. if bd139 was conducting it should be drawing up more current. say if we consider 50% efficiency then it would require for 550 ma to 1 amp current and peak will be more to produce the 3 to 5 watt rf.
So, work in progress. I had a made two module using the xtal 14318kc dsb once was used in earlier project and this was a spare one. So, far so good. once it is working. it should produce minimum 1watt rf. with it will drive a linear.

I will air test these setup only after more then 10w to 22w external linear is successfully made. I dont want people to look after when it was even not radiating in the locality.

26feb2014:- somehow BD139 was showing some problems, not heating up or producing any rf so removed it. i noticed one thing during experiments, when the 2N2218 stage heats up signal strength meter in the receiver signal stregth goes high up, from 0 to 3. It means, due to heat-up current is increased and so does the rf. a perfect case of thermal run-away. 12.6 volts, 150ma current. also toroid gets heated up as it is not driving anything. Interesting.

evening. I removed the 470ohm and 1n4007 diode network for bias and instead installed a 10k pot. it increased the current and at the 330ma,12vdc it gave me optimum result. please dont forget to put the 10ohm in emiter leg. Also changed the  bd139 with c1162 and it made a good change. Rf has increased but not heating up the 4watt resistors. Only heating up the heatsinks, he he.
Its time to reduce the dc current of 2n2218 stage from 130 ma to about 100ma. and also try to  use irf510 instead of c1162 and see whether it  produces some usefull RF at 12 voltage or not !

in the emiter leg of bd139/c1162 according to the hmy2k8 ckt there is 10 ohms but vu3prx it is 6 ohm and rm96 it is 1 ohm. ohh thats  seems to be my culprit. let me see you.

rm96 linear amplifier stage
rm96 linear amplifier stage
Test set-up for rf and dc
rf amp test for power

From a dsb modulator (ta7358 with xtal ) signal is given to the 2n2222 stage and output is taken from the last transformer T2 on 50 ohm load. RF voltage measured and signal heard on com. rx. 14331kc.

01March2014 ,
this feb is only 28 days. I did rewind the transformer of last bd139 stage, did put the 10 ohm resistor on its base. also put the 1k resistor across 470 ohm in the base of 2n2218. it reduces the current to 80 ma around and there was less heat. but over all power coming out from the c1162 halved that means  it is just putting power in the miliwatts. not even a single full watt. wow ! when the ready made pcb is used those designer / elmers have solved the bugs and made it workable. pity is , somehow we dont  got the transfer  of tech due to the limitation of the bandwidth or space on the magazine or suveniours etc. I hope new homebrewers get the benefit of their techniques  from my quest.

so i  will put one more stage but i  am doubting and want to know first what went wrong. if it does not give me 1 watt how i am going to drive it to other stages ? now i will make one more stage irf510 or 2C2068.... i dont know.

with swamping resistors rf power is reduced but quality improved and self oscillations reduced. it becomes broad band. 
modified bias network
modified bias network

I changed the bias of last stage instead of 470 ohm, 1n4007 network a 10k preset was used. 10 ohm resistor on base of bd139 stage is not used.
 This gives me visual indications. just eye-candy.

But, a very useful visual aid for rf strength indications, if the stage is self oscillating presence of rf also can be seen.
Best test for oscillations is done on comm.rx or oscilloscope and spectrum analyzers.

I feel that:-
There should be one more stage of amplifications & filtering ahead of the 2N2222 stage. As, all these amplifiers are "class-A" stages ,more the input signal more will be output at T2 secondary.  Ok, then, i can put the swamping resistors back and enjoy. Efficiency will be very low, say typical 25% for class-A.

Also can try another stage of class-AB amplifier after  the c1162/bd139 to reach the elusive 5 watt level.

You must get the proper toroids, without them project will fail. I will put another page link (here )for showing the voltage charts , references, toroids windings , rf power meter etc.

So, thats it. now will tweak it little to box it. End of write-up. There will be no further editing etc (2march2014)

wheel has been not re-invented fully, but still you can use it as it is.....

toroid transformers

RM96 second part is written here. (3march2014).

 Toroid transformer winding

I was making the linear of rm96. wanted to see the toroids. Put query on facebook then searched the web, i was surprized that in google search my web page was showing the rm96 of vu3kod, it was clear in one aspect.
that how to wind the primary.
Rule of thumbs are:-
One turn is one pass from core.
idealy 30  %  of core should be free i.e to spread the wire equally on rest of the portion.

Secondary should be wound over the primary. not spread like primary.
where to put the secondary - in middle. Now, which one is hot /inphase of secondary? (still to know i feel that the same directions starting points are in phase. Inphase means the sinusoidal signal cycle is sympathetic to input . Out of phase means -it is opposite of input cycle). Secondary winding starts from the arrow shown and the same way and direction as the primary.

T1 (L11 of rm96 )an T2 (L12 of rm96 ) turns details are.

L11- 30 turns primary, 4 turns-secondary, 28 swg, on t-05 hfa.
L12- 6 turns primary, 4 turns-secondary,28 swg, Looped through an 1/2" balun core.

To put in the paper and actually see the thing is both a different type of experience, intelligence. I still want to see others rm96 boards which used different type of toroids. Over the years we have made lots of rm96 , ats-1,hmy2k8 etc etc but no one has put the internal picture of the ckt.  Its okey. Once you know one, then you know all.

Indicators i rely

These are not proper instruments with accuracy. But, they gives the tale tale sign and as a rough estimate useful for quick test. here are they.

(1) a simple diode with 10k resistor to test whether the dc supply is present or not.

(2) it is a simple diodes (as a rectifier)  which drives a small led to indicate the rough presence of rf. I put it with dummy load to see the presence of rf. it does not measure anything.

(3) same as first but two LEDs back to back. connect one end to ground and other to test the vcc.

(4) Another not shown here is a rf sniffer. It just indicates the presence of rf with led light. ckt is same as 2 but a two direct coupled transistors are put as amplifiers to drive the LED. this can even work as a very crude fsm.

(Please note these probes should not be used with ac line voltages , it will give you plenty of electric shock ! )

RF Power calculations:- 

dummy load & rf power calculations
In the age of microprocessor and digital age who wants to measure the power in old fashioned analogue way. No need to have those latest fency equipments, if you dont want accuracy and exact quantity.

A time proven method can work for you.

All the theories and practice see in the picuture. Resistive load is designed for qrp. i could  only find 100 ohm ,2 watt  in carbon but high powers resistors were all wire wound. So, be careful what resistors are you using as a load. For RF load t should be carbon variety. If high wattage resitors are are not available ,then you can use smaller values carbon resitors, whose parallel value is roundabout 50 ohm.

For measuring , use the dc range of voltmeter. for a 1 watt ,5 watt a 20 volt range will be okey. calculate the power as given in the formuas. You can make a little cheat shit. showing the power read on the meter and rf watts. Thats it.

Further notes on Linear rf amp, RM96 ( to be conitnue... voltage charts as given by vu3prx and a little writeup by vu2hmy ) and then will finish this topic here.

Thank you all from whom i liberally took ckts, notes and other details to put as a study to make a working transmitter. Hope, my quest will help the new hams. If anything is amiss please do tell me, it will be corrected.

Tuesday, February 18, 2014

power supply, 36 volts

power supply
For a 40 meter linear rf amplifier based on irf840 a suitable dc power source was needed.
Transformer is capable to provide 5amp current,  for 24 volt ac. It has 24-0-24  secondary and also 12 volt secondary , so this 12 can be used for the control as well as other receiver chains.

I used the big diodes - 3 amp current capable i.e 1N5408. smoothing capacitor is 4700mfd,50v dc working voltage. Put the fuse of 3 amp and switch.

See, the second foto graph, i have assembled it  in hurry to check whether transformer is working or not. it will need some big cabinets and all the essential ckt i.e voltage regulators, current limiters,  ameter (yes sir ameter ) and also 1n4007 diode bride with capacitor for regulated 12 v dc.etc

But, with this , i can start powering / testing the new homebrew rf amplifers. Beware , 4700mfd is not enough it will require more filtering i.e 4 or 5 more big capacitors and bleeder resistor to discharge these capacitors.
(as of 27jan2015)
Later on I put the transformer on the thick metal plate for heat sink purpose. Used LM7812 for 12vdc and drive a fan to cool the transformer without it was getting very hot. Also put fuse and extra switches. 

When the RF amplifier loaded the supply with 1.6amp current the power rail becomes about 25volts. VU2ORO said its okey. 1.2 is the voltage of secondary... Now a days transformers are not putting that much power like old timers as we are compromising on the laminates now...

Sunday, February 9, 2014


This is part-2

5volts and 3.6 volt power supply for ebay module
all diodes are 1N4007, C1 and C2 are 100mfd,25volt electolytic capacitor. voltage regulator is LM7805.
 diode matrix there are 32 plus 1 diodes. one end of dip switch is connect and goes to the counter ic. please note that on the resistor where diode joins it is indicated by dots.
resistors are 68k, all diodes are 1n4148
four dip switch. DIP switch has 8 on/off individual switch in miniature.
I have soldered the 16pin ic pad and on that mounted the dip switch.
All the diodes are connected with dip switch as shown on the w4 . For the clarities sake i have not drawn the other diodes.

low fequency oscillator and counter for driving the diode matrix and putting the word into the dds vfo ad9850.

74hc04 is gate. 74hc4017 is a counter ic.

Interconnections of this modules.

work is in progess and there is still some glitches. i am little strained at present and hope to redo this module in future.( what i mean by glitch, setting of freq is not perfect, low freq osc is wobbling changing its own freq and thus effecting the modules output freq.....)
please note:-  
It is tiresome to work on simple vero board, if you want to try please make a proper pcb.

it has the limitations also,
its a fixed frequency type.
you have to tweak a little to run it on your exact desired frequency.
buffer after the ebay module is needed.
some sort of shielding for rf is needed.

but, with this ckt you will be able to test your bunch of ebay modules.... so, it does not replace any pic, processor based ckt but it complements and where beacon is to be run or only wants to be on afixed freq  this is a good and cheap options,


AS OF 06 MARCH 2014 .

Anyone wants to try please let me known your outcome, so i also change my ckt accordingly and thank you.

This is second part the PREVIOUS ARTICLE IS

Friday, February 7, 2014


For a homebrew linear , more than 3amp power supply was needed. Bought 24-0-24, 5amp transformer, at this stage a current meter was highly needed. Searched in local shops. They have 500v ac voltmeter and 20 ampere meter used in the water pumpsets. Now a days, electronic spare parts shops are not providing the 5 amp range ameter. In the local science shop there is 5 amp meter but i doubt its quality -they were meant for study experiments i.e for few minutes use only. If the thing is used in some commercial product they are presumed to work round the clock and manufactured accordingly. I had the old 5amp meter lying somewhere , with intention to repair it i opened and also fotographed hope this will give insight to all of us who want to know the inside of the meter (be it a voltmeter , ameter or galvanometer !).

In standard 8th i leared this in techincal shcool as i had opted the technical subjects instead of regular subjects. In the whole gujarat state there were only 3 or 4 technical shcool.

Meter principle in a very simple terms :- current passing through coil produces the electromagnetic fields and according to it the magnet moves- mechanical arrangemetn is done so that the end result is shown as the deflection on the pointer dial.This meter is a very practical subject.

Hope to upload few more theory regarding converting the range and ameter, voltmeter making. but, now enjoy the foto as it will be found nowhere. by the way my meter is not going to work as litte ring is broken but still it gave me satisfactory decko.



ameter frong view

look closely to pivot ring its half broken

Times of India, Ahmedabad edition date 6feb2014. beautiful looking lady has no connection with meter.she is Maria Sharapova, a tennis player from russia. Just eye candy nothing more.

Sunday, February 2, 2014

drill bit

drill bit making
A component ( diode 1n5408 ) was not going into the veroboard's drilled holes, as it was slightly thicker than its low current variety (diode 1n4007) . Looked into the box, don't have any smaller drillbits ! To go out means burning more petrol than drill bits cost.

So, remembered making a quick and dirty but effective drill bit for small work.

You will need hammer, chissel, benchpress, file and nails. Yes, also the drill. Please note this will not work for electric drills. It works only for handdrill used manually and for smaller bits.

Take a nail. Remove its head by cutting with the hammer and chissel. If you flatten the head, it will create the problems in the drill chuck. 

Now, flatten the Sharp pointed edge by carefully hammering, so that it becomes evenly flat on both side and becomes pointed like a flank. But, beware you dont have to make it thin. Let, it remain thick. 

Put it on a bench press and file carefully. Now, see the fig.4 and 5. Round circular arrow shows the direction of the drill. Straights, arrow shows the direction of the file movement. The Edge has to be sharp. End result will be 6.

Use it, but as it is not thermally treated, metal will wear down. It will be useful for pcb, wood and small thick plastic but no metal please !

Thats it folk , we have re-invented a small wheel. Enjoy the ride.