Wednesday, April 23, 2014

Dummy Load

To give a standard Lamp-test of the  VWN 40meter a lamp was needed. This vwn tx uses  the premixed 7059kc (11059-4000 kc xtals) as reference oscillator.

First Tried the kcommon electric lamp. It did not work. Then went for the torch light lamp.

Searched, in the general stores, paanwalahs and all sort of peoples who used to sell the torch lights and electronics related goods. No way. One gave me a fused lamp for rs10/-. then i was watching the autor rixa repair job in the station area, wow its tail has the good old lamp. i asked repair man and he said two types of the lamp are used. one is 12volts, 35 watt as head light and other is the 12 volt, 5 watt as tail lamp. Oh my god, i searched the entire city and they were found near my qth and this 5 watt lamp is cheap also. Just rs.5/- per pices. It will be available for some more time. So, this is a standard and cheap thing.

When i used the 5 watt electric light lamp, i could not get it lighted up in the transmitter. so was worrying whats wrong! is it the transmitter not pumping out the oscillations ? whats up mate !

Now, found the solutions in the form of ohm low. here is little maths to muse.

for auto tail lamp:- it takes 12 volts dck at 350 mili ampere. which turns out the about 33 ohm. near about the real dummy load of 50 ohm.

for the electric lamp:- by this ohms law resistance becomes very high and not in the viscinity of the 50 ohm. thats the reason for qrp  i could not get this lamp lighted.

v= i * r, v-volts, i, currents, r - resistance,
w=i *v

Thursday, April 17, 2014

RA3AAE detector


I had tried serveral projects of ra3aae detectors PA2OHH and KE3IJ . Well before these projects, i had never worked or heard of it. Both hams have good projects on their website. worth to see it.


My experience of these humble diodes have been nice, diodes always provided me a reproduceable results.

During brewing of the  first 40 meter receiver and then second  48 mhz rx , i found that some peculiar problems. i.e noise, antenna mismatch, microfonics, sudden breaking of audio oscillations etc arises, i tried all my tricks to get something which others can use.. but i did not work. so left it.

( (6meter tx and rx (ra3aae) experiments. & RA3AAE detector )
(Please visit my earlier two posts to get reference of things i am stating here.)

RA3AAE detector has the reputation of "works on first trial". so little puzled  and after some rest and new lights, once again tried to tame it. here is the results.
hello cq cq can you hear me !

fsm meter , what a simpicity








































For starting the test,

i put these modules in the workbench once again.  gave cw tone okey. it works but it did not give the performance i wanted. Audio is little odd.

I said why not make another ckt to understand this ckt.

Then it was time to make my third detector from the scratch i started with audio amplifier first. hmmm, BC547B based af pre-amplifier stage, LM386 based audio amplifier. Ok.
 
Made a dedicated amplifer for the detector and then i tried to reduce the gain of lm386 presto ! sound is crystal clear.


Now ? let me first test it with existing detector. so, tested and within half hours understood what was the problem with earlier ckts - high gain audio amplifier.

LM386 problem and solutions.

10mfd placed between 1 and 8 pin is not needed. No need of high gain. How much high gain 200 times. Without 10mfd only gain of 20 times.

In AF pre-amp stage feed back of 100pf improves audio quality and reduces noice .

From 12Volt dc, 1amp capable power supply, whole radio circuit takes 40 to 140 ma. When i connected with 9volt pp3 batery it took 19.1 to 29.1 ma but on high volume it breaked into uncontrolled oscillations. may be with high impedance source i.e low current capcity-source. cure is to place 470mfd to 1000mfd capacitor across the power rails then af amplifier works better.
(kindly read handwritten notes will write it down shortly. Please.)
Antennas:-

a small piece of 1 feet wire was connected to the high impedance side of tank i.e top of it and signal came rouring. Night time BCB, other hams signals to be observed. In subsequent night observed. It is okey. there is slight BCB.But not too heavy. You can safely put headfone.

I want to connect the dipole and reduce the qrm so two tuned ckt will be employed in the front..( aantenna work is in progress, )
ra3aae detector problem solved

design on paper

af pre amp stages

conclusion too much gain in the audio stage is not needed as we are providing the bc547 based rf and af pre amps.


Failure of my ta7358 ( see earlier post)  might have the same problem, excessive gains. ???
(when i tested this theory later on ta7358ap has started behaving good )





Impedances:-

Here,ckt has been taken from pa2ohh. we are using the 470 ohm and another 1k pot with diodes so the impedances are high. Not just 50 ohms. Keep this in mind. So, when i tried the CB af preamp stage of KE3IJ it did not work with this designs. KE3IJ has intentionally made this cb amplifier to adapt the 50 ohm dipole antenna. wow.

Logic behind the designs.

when we adapt two stage from different design we should also take cognizance of the impedance they are looking and many of the time failure of the ckt is due to the mismatch in the impedances other wise individually they are working fine.

so, we have to first understand the logic used by the designer for the given module and for that we have to make the ckt as designed. they dont tell us variable ot the processs but it is possible they have worked hard to arrive at the single design after lots of other variations tried. My sincere thanks to all the designers.

Actual ckt diagram which works. 

After long long evaluations this ckt diagram is tested okey. I made it on perfboard. You can make a small pcb. If anyone makes pcb please let me know. I want to upload it so other hams, swl also benefit.


 
40 meter receiver using ra3aae detector.

At last i can say that these ckt works for the 40 meter.

(48 mhz will be tried after making suitable LC local oscillator of 24mhz.)

Local oscillator

For local oscillator i have used ceramic filter running a collpit oscillator..tuning is by a small variable capacitor. i have itentionally not given the oscillator ckt as also wants to test the other normal Lc Oscillator.To be frank tuning is very sharp some short of slow tuning mechanism might be need if you want ssb. otherwise for cw it is okey.

(as of 20april tested the oscillators and found that one with the ceramic resonator 3682kc , two terminal devices is more stable then LC oscillators. I was waiting for this test. thats the main reason did not write it first place. No two oscillators are same. I made three oscillators, one did not go to the desired low end freq 3530 instead it stick to 3639 one was going easilty and one stood at 3531kc ! so, first of all measre the frequency and then use it in receiver. make few oscillators and you will know which works and which does not. ckt is given below c1 and c2 are 1000p styroflex or any good capacitor, vc is variable capacitor use the radios gang .n.b i will upload the test result of the vwn tx done with the help of this radio and more on next post. thanks...... )


Other things.

Will be putting more musing on LM386, AF preamp of DC-40 of VU2ESE, oscillators.

I have no local population of hams so not tested ssb signal or cw signal of other hams. Also not connected big antenna. I want it be mobile to test my own transmitter and to check pheasibility of running SOTA . I live near Mount Girnar. One of the highest peaks.

 If, in sought india someone try this ckt and give me the result . i will appreciate the effort.

we can safely demo this ckt to childrens and novice hams for their first real receiver. Sound quality is real good.

In the end

Lo needs to be tweked, But, all other stage are complete and  there will be no further R&D.

Once again put into a permanent box and will let you know.

Thanks folks , lets use this wheel with great cheer. 

(During the testing my vwn tx on 7059kc gave me company and one of the days will be mobile with this rx and find out the range !...  and will conclude whter my tx is really low power or it works few km as i thought )

Let me cite the todays elixir from 
His Holiness the Dalai Lama,
the very purpose of our life is happiness, which is sustained by hope. We have no guarantee about the future, but we exist in the hope of something better. Hope means keeping going, thinking, ‘I can do this.’ It brings inner strength, self-confidence, the ability to do what you do honestly, truthfully and transparently.

Tuesday, April 15, 2014

novice 90

You have transmitters or made one QRP.

WOW ! congratulations for hardwork. Lets have a QSO. You connect it to the dipole and presto there is no signal of 40 meter tx even 100k far ! You make another dipole. tweak it with magic formula found in net. It does not work. get frustrated. request for listening and it results in the downgrade of reputations !

Antenna Not Loading

and blame on your hardly homebrewed qrp tx.

No one is to be blamed except the murphy. The problem of QRP tx not loading on the antenna is age old. Even in the 1959 it was there. One of the ham friend has given the solutions in the form of novice 90 antenna.

please search the google and find the original novice 90 from the popular electronics pages.

I will be putting the source of these resources with note of thanks to original authors. I am trying to use the theory for my communications and writing it in a story style. Technique which works....... if it works for me , then it will surely work for you as i am going to make indepth analysis of it......

Now, musing over the antenna starts.
novice90
 Novice90 antenna roghly drawn.
lc tuners











Wow ! More i read, more i get confused. what is vital thing ? I feel like in a classical chicken and egg situations, You should have an experience before you get one. Pirates are doing fine with their qrp AM transmitters, and why we hams not able to use qrp 5watt, even though we have the previledge of cw also ?

I moved my self from the facebook and opened my eye towards the things around me.Brainstorming session starts. Series of question came.

What is transmitter power ? QRP or QRO ? what instruments you have ?

QRO amplifier uses dipoles , loops, uda-yagis, beams etc. they are balanced, they work better,even you can find commercial antennas, know how is easily available. most of hams use them. dipole are very user friendly.

But,for QRP transmitters with dipoles i am not able to transmit. looked into the web found lots of things. there are many camps and theories and formulas. Mind boggling things. End feds, Half waves, Shortened dipoles, Long wires.....

 Ok Ok. what about my question "i am not able to load the transmiter ?" i litterally typed similar words on the google and one solutions came -use Novice90. then Monoband verticals, Long wire etc.

For qrp, first experience,antenna should be resonant.
What you mean by resonant ? half wave, quarter wave, exactly measured and then trimmed ( increased or decreased the wire length practically).

antenna have self capacitance. Due to its structure and nearby objects, EARTH etc it has an inherent capacitance. dont blame elements but use it. here you will need a good earth or counterpoise.

two things, first- antenna should be tuned (resonated) for your band/freq.
and second- impedances should be matched for optimum transfer of power from transmitter to antenna.

So, this power goes to other ham's radio.

For antenna tuning you need antenna analyzer MFJ259B, GDO. (If your club or nearby hams have ! then your all problem end within an hour............).

For impedance matching you need LC tuner with some sort of SWR meter. These things might be in your transmitter or you have to make one.

Fsm is also vital for this verticals, sigle wire antennas.
If you have a portable scanner or second ham ins some distance or a friend who can tune into your signal then its better to listen to your signal and estimate the Signals stregth. In the south india there is density of hams are high compared to my gujarat state , western part of india ! so, they have success in ham radio.

quarter wave antenna has low impedance (in the range of 25 ohm etc), half wave antenna has high impedance (3k around)

Using formulas , for a given frequency a wavelength is calculated (that is called electrical length). If your physical antenna ( wire !) is shorter then this calculated value then your antenna is short. If it is longer, then  your atenna is big. for short antenna inductor has to be added and for large antenna capacitance has to be added to 'tame' it down to your frequency. there are all sort of formulas. For us imperical values will suffice.

For insulation, end insulators or support you can use "white pvc water pipe" used in water plumbing. Please remember "white". If it is grey or black, dont use them.

(for this antenna) lower swr alway does not mean that it will radiate more, check with FSM, (Emperical) little mis-match on swr but high FSM reading is okey with qrp.

what is VSWR ?  standaing wave. answer is complex ! but practically be understood by little experiment. put a water in a bucket, with a little stick or pen -vibrate up and down with a constant motion, you will see the waves propagate to corners and move back to centre and due to this to and from movements of waves there is a pattern on the surface. this sort of things happens with rf in antenna, coax etc.

the power which does not get radiated due to this VSWR comes back to the coax, tuner and heats up the coils, capacitors and make complex things... that's the reason for qro amplifier swr should be 1:1, our goal should be to throw last bit of rf power onto the ether....

wave travels in duality. up-down, if we are using single radiator there should be some sort of earth to compensate it. counter poise is a piece of wire which provide earth for radiating element. remember the famous parasets. they used halfvave wire as antenna and quarter wave as earth. good. Military is using this comm. we should carefully see their wwII radio antennas were....

in our novice90 tuner is supposed to be near the transmitter, also the earth is nearby. Warning- long coax line is not encouraged. it will create problem due to return currents, heat, TVI, harmonics interference to (the legal services, very bad , if your shortvave tx harmonics interfere  neraby police  station vhf ! an ugly situations is ready for you. wpc is will be late but they will reach to you first with siren blaring wehicles ). hence we dont find this antenna in a full power or medium power transmitters, commercial transceivers. Thats the reason most hams don't use this atenna.

This is your first antenna. and with upgradation you have to migrate to other antennas. happy ! thats why you will not find anyone using this antennas but it works mirculously first time and any time, good for camping, temporary, clandestine work (he he) etc ......Don't loose hope. It worked for 1959 American Novice and even today it will work for you, me with just 5 watt.

Make a good earth. How?. Make a deep trench of 2 feet deep. Soil should be moist. Bury the old unsused cloth iron plate and few small metal, copper etc things with salt and black coal deep into the earth. dont forget to wrap copper wire for more contact. rod etc. pour water from time to time and you are done. Main element is, there should be no gravels, sands, stones etc, it should be wet. and if not sufficiently wet, then you got to insert a pipe to pour water before use. With multimeter measure the voltage. There should be no drop of line voltage and you are ready to go.

Your local electrical store can provide you the brass plates and little more know-hows,even a handy-man for a price.
In the railways they still make earth for signaling purpose. Ask a friends in the signals department (the PWay inspector or Signal Inspector). They have measuring tool like "megar" a resistance measurement tool. only thier instruments are regularly used in fields.

What wire should be used for L ? for antenna use any wire easily available say "1/18 " electrical wire inside the insulating coating there will be a single copper wire of 18swg. It seems electric wires copper is little different from the motor windings copper...,

Use of copper enamalled 22swg, 20swg is ok, still better is 18swg. copper enamalled will cost less then common electrical wire. You can scrounge the copper wire from burned winding of big electrical motors. but buying new is really cheap.

peoples have used the normal aluminium pipes in the telescopic fashion (fitting one end inside other pipes end) with success as monopoles. here you dont have to worry about supporting the wire or buying the bamboo. this is also a good option. but care should be taken to tight fix the aluminum. as it can not be welded. better mechanical works gets good results.

40 meter is all day night, all time band. terresterial. (neighbour hood band if there is no local qrm due to mobile tower smps etc) for a given place,situation one antenna works and for different place situation that does not work!

There is also another third options. As the legendary spy set and paraset transmitter used. halfwave as antenna and quarterwave wire as counter poise. I think i will try this last antenna first and then other things. or may be make all the antennas.... or may be somehow use the QRO-linear..... and not try any of this.

Brain storming ends here. What a topsy turvey journey.still there from where we started. thats called chicken egg problem.

Now,,,,,I am making ANTENNAs and will  upload more fotos, end results. And possible first contact.using vwn tx.


mp-10, minipig
 this is the simplest bridge to handle the qrp tx.

I intends to make this led based bridge to get hang of the swr meter.
antenna and tuner coil. short antenna whip, vertical, half wave , long wire.... all sketched on paper same but, there is big difference.....






(to be continued.......)



Saturday, April 12, 2014

80 meter transmitters

In the early (around 96 to y2k) i had designed few transmitters.
 (later on will be  changing the writing in logical order its just mumbo jumbo at present...... )
My pirate Radio projects.

 Actually when i applied for amateur radio license, it took really long long years to get one license. I gave exams in 94 with vu2lex.

After it was boring  and nothing to do, so made this transmitters. two shown. there is one more. Its not original, but i have not exactly copied anyones ckt. different modules were taken from different sources and made compatible to work for me.

My first 'elmer' was vu2lex om faram khambhata, he allowed me to copy his amerikan book.it contained ckt of w1fb. his set up was all home made 1 watt cw tx diode dc rx, frequency counter using hct ic.cmos keyr with memory. atu, rf probes and a full 2foot by 2foot crate of various ckt modules he made.He never came on fone. After two visit i lost touch with him. he went somewhere for mqth and i also became busy.

Second guide 'elmer' was vu2atn ckt and few other articles copid from practical wireless etc. I made first receiver by duplicating vu2atn 20 meter cw tx. although it never worked on air, as there was no instruments. frequency counter, rf experience etc to tune it up.....when i fed mc1496 with QRO SIGNAL it gave audio note, i was happy, project successful, examinor happy, someone got the marks for engineering project. thanks. (i wish to have eyeball one day with vu2atn)

Then by chance, i made diode detectors and they worked for me. Those were my starting days. I did not know how to wind the coils, even how to solder ! but i learned everything. thats another story.

transmitter circuit description


This is a very low power xtal controlled AM transmitter capabale to provide one way reliable link over few hundred meters.

a sturdy metal cabinet.built in dc power supply, microfone (power supply),xtal oscillator, af amplifier, modulator, one stage rf amplifier. actual rf power is in the few milliwatt range.

few fotographs and ckt diagrams is given here for reference.If time permits will trace out components value  and make a list. Not used since a decade. I hope to revive it and gift ( i dont need money for it) to someone (if s/he wants to vu3hm* in rajkot city) for local (h)AM Experience.

As one transistor oscillator did not give me long range with small antenna i made this big ckt.

Antenna:- i used approximately 30feet long wire as antenna. No care was taken to measure rf or tune anything. I did not have ATU, simply connected the wire to the collector of pa and presto am signal came out very clearly. Litte tuning of pa core furtheer increased the clarity. I was able to receive the signals in portable am,fm radio plus cassette recorder ! This was placed into our second home and it was my bug, a private radio and a caretaker of intruders.

ONE TRANSISTOR transmitter

In facebook, my friend vu2uuu gave me a hand drawn sketch of one 80 meter tx from his own experiments.


Let me reproduce his ckt. I am thankful to OM Kaustava saha for taking out the time to hand draw , fotographa and publish it in facebook. that really reflects his love and care for fellow hams. Thanks OM Saha.
one transistor transmitter by VU2UUU

Considering your need for Local Ragchew on AM mode, I think the choice of 20m X-Tal is not a good one. You must use 40m X-Tal for Local Ragchew. Also, the Amateur 40m band is present (but not highlighted) in SW 41m band, and it will be available in any normal SW Radio. So you can use the SW radio as a Receiver. In case you use a 20m X-Tal then you need to make a AM receiver too,
I had seen a circuit on internet & it works very well. I am sharing my hand sketched circuit diagram for reference. On the antenna side, you can make a standard 40m antenna (prefered) or a random long-wire will also be OK. Take a 500pF variable capacitor & fix the L2 coil.
The L2 coil is made on a 0.6cm former using 10 turns of 22 SWG Cu wire, as shown, to form a tuner circuit in between the 2 section of the 500pF variable capacitor.
The L1 coils is made on a Ferrite Rod, with a 1.5cm dia former & 10 turns of 22 SWG Cu wire. Dont forget to use a good heat sink with the BFY50. The X-Tal needs to be 40m for better local activities, but you can use 20m X-Tal without changing any components. Use a 12v Battery Power supply, because a AC-DC adapter will generate considerable humm in your transmission.
Hope the circuit suits your requirement.
Best 73
de VU2UUU

Kaustav Saha



This all flooded nostalgia. I also had made similar looking ckt from "123 projects"- a book containing the 123 various projects related to the af, rf,digital  gates etc. .

Please dont reproduce my ckt i have dismantled it due to poor performance. but, i taught me lot. Instead use vu2uuu ckt it will works.


my version of one transistor tx (DONT COPY)

Carbon mic was hard to find. I requested a fone repair guy and he gifted one carbon mic for a free from a broken fone. wow !

When i made one transistor ckt with 2N3053 (a very good rf transitor) , only 1 meter telescopic antenna was connected. 3.579 kc xtal did not worked, then changed freq to 27 mhz cb xtal it gave me a range of about 30 meter on 12v batery, but i did not realize that real problem is small antenna and very very low power. i used 100k for base bias. when you use 15k as base bias, the current increase so does the power.

And there is real antenna, tuner and ground. ATU and very long antenna. Now, i realized why i did not got the (range) a decade back !

ATU

When my dsb tx on 14318kc was not loading OM vu2kd told me to take a gang and wind a few turns air coil and put coil between it and tune it with diode two diode and led detector. He explained over fone in length but I could not grasp it ( beleive me please !). but vu2uuu drawing gave it clarity. I will certainly try this LC ATU. I am not yet understanding its theory but if practically it works who cares for theory !

Story of 80 meter:-

There is an interesting story. During my second transmitter testing with small wire antenna (may be 30feet) i was puting some morse code practise to nearby radio for learning and suddenly some reply was coming through. I could not understand it, but gave out my call sign (?)  and signed off. I never had intended to radiate more than 300 meters. Next time never heard him. poor fellow ! but i never received any rst report or any QSL card.  but that proved my second transmitter was working nice, pumping out few watts (!). but, i never tested it again with wire. beauty is that during this whole testing-time this transmitter was connected with dummy load and as a leak-wire / gimmick antenna was connected ! when this happened ! dont remeber the year. Dummy load had become very hot, it burned my finger so i remeber. I had used IRF510 as PA.

i had qsy to somewhere in pursuance of mqth.total about a decade years (2004 to 2012) So, when i started putting things back togather in 2012, that is the reason my tech is little old (10 years) and you find no digital things.... but, it is going to improve. only one aim is to be on air.

i  once heard the vu2pua from bhopal.might have audio recording also. he used just 300mw and tuned vertical.  i regularly hear vu2kd with just 5 watt bitx homebrew, i also hear regularly vu2seg with homebrew 15watt bitx. so, QRP is possible. my friend vu2isr also helped  in checking my signals on air as he is interested to show that even with qrp, west to south qso is possible.

someone has promised me to give an atu. lets see when i am able to get it............

80meter am transmitter


inside view of 80 meter tx


another transmitter based on similar to "two fer" tx
This is another transmitter. first i made mighty michigan and then added the pa stage consisting of bd139 and then found a small modulator transformer 1k to 8ohm used in small af amplifier. with help of lm741 and push pull transistor i drove it will success.
af amplifier, transformer as modulator,


My problem was not able to load the antenna. 

 Has anyone faced the similar problem. 

Various answere came, like , go to  a seniour hams, have atu, use swr analyzer etc etc. i dont have access to these tools ! do you have any idea ? it seem most of guys are using the commercial ones. okey.

 but i searched teh net and found something which is older than me. even i was not borrn at that time. Hams had faced similar problem for a "first time".loading the antenna .. we all face problems in the first encounter. have a look at 1959 popular electroncs . NOVICE 90. then there is endfed half wave ckt of recent origin not requiring the physical ground etc....





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

06april2014
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.....

Saturday, April 5, 2014

coils winding direction

In the year Y2K i made few transmitter ckts. Only resources available to me was old analogue communications receiver with no digital dial (!), AM SW RADIO and simple-calculator, logaritham tables , formula book ( i collected the formulas and made  my own book ! ) on those days there was no internet. If we forget something, then we had to consult the engineering books. I had lots of books of theory, practicals and my own konsultations papers.

In one of the scrape-book i had drawn this ckt.

coil winding 

At that time alladin former was widely available in the form of SW,MW oscillator and antenna coils.

Another type of coils were the metal cans. KANK type, metal can type was only available for the 10.7MHZ fm radio if, 5.5mhz TV FM Sound if and 455KC if coil set, but those were very hard to make/change for other frequency. as they had internal capacitor. Coil wire size was very thin say SWG45, So, we used this alladin former for all experiemnts.

When i was replicating the VU2ATN  20 meter CW Transceiver,  I had to find out the hot and cold property . It was hard for me to understand at that time. I put RF probe on both secondary ends and was puzzled to find they both were showing RF. Hot. He he he. Log time After that experience and further reading got to know that Hot and cold means the  sinusoidal phase directions the rf is taken or given.

After that i made few more 20meter, 80 meter transmitters. valve transmitters. It was easy. In those days in the smae locality we had two big big homes. I had two radio room with big antennas on both houses ! So, whenever i did tx experiments i did not ask other hams to listen to it. I tuned up and do the listening test myself. gone were the days. I regret that on those hay-days i could have bought my own 50k transceiver. Anyway this is life.

On the marry note:- I should have married some  bhavangar girl, so on social visitation to her home, i might have found some communications receiver, tranmitter from ship-breaking yards. Fact is that beautiful womans uncle had one yard in alang. Year was 1992-94. Both were precious. Woman and com equip.








guarat earth quake

in the year 2k1 there was richter scale 5 to 6 magniture earth quack all over the saurashtra peninsula and kutch regions of the gujarat state. Its epicentre was near the bhuj city in kutch but after shock and effect was felt all over the regions. Even my home was also damaged in Junagadh. During this time i had only valve receiver and marine modified vhf which did not worked properly.

I did not go to the are but i did what i could. I monitored the signals and maintained the records.One of my friend when we had the eye-ball qso at my home and saw my logbook copied few entry. He remarked, we did only roughly maintained the log book at g'nagar control room, as it was very vital to keep communications going on. your book is correct based on this we will verify our own !. Thanks for compliments.

few pages








Thursday, April 3, 2014

Tuesday, April 1, 2014

6meter tx and rx (ra3aae) experiments.

     Small transmitter

48mhz canned oscillator

local oscillator
pin details of can
Why this receiver

              There was a need to make  small RF oscillator for code practise and demo.  It was my deep desire to know far the small canned oscillator can work as some hams claims ! Is there any justificatins in the claims. Only way to know is test it yourself or beleive them.

             I had some 48Mhz canned xtal oscillator. Also i bought from metro, few 24Mhz fundamental xtals. This does not fall into the ham band but if you have the canned oscillator worth to try it.

     After initial successful testing 40 meter receiv er (PA2OHH design, see the march 2014 post) it was found that in the receiver, audio is bit noisy.

            In the KE3IJ (160 meter/40meter receiver design) there is one Common-Base amp stage. His callsign also contains 3IJ , my callsign is 3INJ ,what a remarkable co-incidence ! we both are brewer.
 
Transmitter
              Now, soldered the oscillator-transmitter and RA3AAE receiver. Will test it for range, antenna and all. 

Testing
          Powered up the tx. Switched on the rx and no tone. On increasing the volume it breaks into the oscillations. There is less noice unlike the common emmiter configurations but it breaks into the oscillations due to the  high gain of common base amplifier stage ! solutions- decouplings. or once again use noicy CE stage.  Ok. This receivers AF stage works. switched on off the QRPp tx (!). but there is no CW tone. RF probe shows tiny lights as it is very low power ( may be 10 miliwatt its not an issue).  Are they on right frequency ?

        Measured the freq. 

        48Mhz canned oscillator. reading shows stable 48.000.30 . thats OK.

        24mhz xtal oscillator shows some what like 24.020.5x

 OK. That means 24.020Mhz after the 24mhz it is up by 20k and on doubling it result into the 40k. No human being can hear it ! only BAT can hear hello cq. 

solutions, due to the VC (trimmer) freq is up,  Try to pull it down with L- a small inductor. But, this 24mhz osc is little wobbly in 100hz range. Put a little filter rc in the +vcc of osc.done not much improvement.

25march2014
         I am writing this on, day by day but will publish after all process is successfull. As one of my friend remarked is it working or not ?
28march2014

the thing which started out as the fun and simple is turning to be a major challenge. Reasons are two. Oscillations very-low freq motor boating due to high gain, and xtal oscillator (LO) is not coming down to even 24.001mhz. I need only 1k to 2k audio tone. Very strange. Tried lots of L and C combinations. It took my whole 3 hours. But, could not bring it down to the 24.005 Mhz. 

So, i will be leaving it and try to cure the audio motor boating first. Then test with the vfo 24mhz instead of the xtal. I think will make it in a bigger board with good audio stage utilizing the LF411, a pin compatible but better than LM741 op-amp ic.

(31march2014)

Deoupler circut :-

I saw this type of decupler in the ARRL dc radio R2 and Farhans(VU2ESE). Well now a days, i am seriously looking into the farhans fone stock website. What he has used and how its used. then look from my collections of the ckt compiled over the years (4 years) from the net. And then at-last the web. But, generally i find the answere from the compilations.

de-coupler
 This decoupler simply reduces the hums, noice going into the low noice pre-amp. It prevents noice coming from line to get into the input and amplified. Its design in not critcal, but use is higly recomended in the direct conversion receivers af pre-amplifiers. You will feel the difference.

VXO

vxo

I did not use the oscillator with two xtals as Low side shif was needed. An inductor was put to pull the frequency down toward 24.000Mhz but i can only manage to get the 24.005 Mhz with inductor -(10 turns,22swg, with ferrite core). So, it is not zerobeating the 48.000Mhz xtal QRPp tx. 

This will be ok with the sound cards-i.e. software radio but for humans ear s  up to 4k  tone is needed. 

So,it will be replaced with normal coil for 24Mhz and beat heard and the project will be declared success. in the front will put a cb rf amp with small whip.

Problem with this type of detectors are when a longish antenna is connected overloading is present and short antenna is not good enough. 

1april2014

It has become april, and project is taking time due to the morning QTH & other activity. I also have to do my share of chores....

Most probably, as shown in the G-QRP magazine SPRATs Mouse Trap receiver, will put a 1k pot in the input for the test.

8april2014 once again got the courage and put it on the table. heated up the soldering iron for an hour. changed few things.Lastly measured the voltages. Hmmm on the collector is less voltages then the base i.e first af stage is not amplifying. needs to change the bias net work. second discouragement was that 24mhz oscillator was not coming down to less than 24,005kc. so, still i will be not able to hear the audio note (10kc) for the test. Tried everything i knew on oscillator includin super oscllator style but no way.... Atlast removed the oscillator and will try it once again. If the compuer was used as receiver i might be able to see the 48kc wide spectrum. Hmm  from that wspr i had taken the ckt ! any way tx stage is okey. rx stage is also ok but they are not matching..... so, project ends here will try to put 20mhz can and with small antenna and batery will test the range. actually this was what i wanted to see.


(to be conitued........................)