BITX, Single Frequency Receiver-2

Peter VK3YE  made a wonderful signel freq transceiver based on the BITX. My previous experiment is here. http://vu3inj.blogspot.in/2015/06/bitx-singlefrequency-receiver.html write up looks similar.

Frequency is 14315kc , ( 20 meter band )

 I had one 14315kc transmitter and made two three single frequency receiver. Those receivers work for Testing my local signal only. I wanted something air worthy. Which can receive other hams signal. So, made this...

Lets start from back-wards.

1.AF Amplifier stage:-
LM386 In standard form with BC549C af preamplifier.

2.Product detector:-
Using subharmonics detector... he he... I don't have third 14.318kc xtals. So used the available 7.159xtal. Also did not had the balun core. If you have balun cores use them please. Another option is to use  differential 3 transistor Single balanced demodulator.

3.IF Amplifiers:-
 As given in bitx. As frequency is higher the gain will be low. Ohh this is the reason for Rx being so much deaf. Need to add one amplifier in Front end. { Read last para, finally found out the true reason, the xtal  had moved a little and loose connection happened. It works fine. No need of extra gain }

4. Front end band pass filters.
Even after making this working receiver I did not put the filter. Could not find the RFC nor a IFT. Was lazy to wind it up. One day legendary VU2DEV suggested to me K&R Filters. Here the tap is taken from the capacitor instead of the L.  My problem with filter was that I could not find suitable component for L and taped L does not work as receiver BPF. You can see VU2DEV use this type of filter for his JOTA, S7 trx, GR40, ISDR etc. Somehow I managed to make a suitable filter.

Have a look at his blog

5.Cabinet and Speakers.
All standard things.... I really homebrew cabinet.  In our kitchen we buy 15Kg oil in metal pack. So, when it is used up, I cut the metal box which is 2foot x1 footx1foot. So, it give a good one box for my projects. I buy paint from local store. Generally black paint . It is a thin metal, so I can do most of the mechanical work without any problem and it last more than 10 years.  After that give a pint job and it look new. He he. this tech is 15 years old.

The schematics and pictures will be updated. With full details.

PCB Sketching:-
I sometimes make the pcb very very old style. Using the oil paint, paint brush and Feric Cloride as etchant. It is no hole , surface mount type pcb. Of course for normal components. This is the process to make a quick prototype. Draw it, etch it, make it and test it. The prototype is ready within a day.


 Here AF amplifier stage pcb patter before it is etched. In the blank right hand side I have put the detector using manhattan style.

Af Pre amp + LM386 audio amp. 

RF amplifier, Second stage is cascade.

RF Amplifier with Xtal filter.

If I make further project then will integrate all the ckt in single board with replaceable filter assembly.

Schematics 
You will often see the similar ckt. reason is simple. The modules have given me time proven performance. So, they are innovated and used.





AF pre amp, LO,detector, IF2,xtal filter, IF1 Amp.

The last write-ups and this write-up looks similar. It should be as it is one and the same thing.
I intend to put up a BPF and do some on air test for my beacon. From one QTH to another QTH and measure its performance.

Testing:-

I  finally boxed up with last screw.  I want to make it as a black box. Literally its painted black. The VXO does not deviate much... I need to make some components change in VXO... add one rfc.

It is quite sensitive. There was one glitch. signal was intermittent. Did the screw driver test. I put screw drive at the second IF amp. It did sound loud. Then put at antenna side. No signal. so somewhere is dry solder. Pressed one xtal. Presto the signal boomed in. Did heat up all joints. Then suddenly once again signal went down. So, I looked minutely. Oh the real culprit was second leg of xtal. It was loose. So soldered it. And all is well.

Now.....Installing the bandpass filter. Installed and working fine. Will do some field test ..........



 

One  ham  VU3YFD, informed, he had also made the transceiver for single freq. But, I have not seen his ckt  nor the picture of that project.

 

VK3YE , Peter had made it and worked successfully. He has put it website. Both hams done transceiver in 40 meter, mine is just single receiver.

 

 I have tested and found working. Will try to design the pcb and offer kit also so that  others do not have struggle.

 

The wheel is re-invented  Worth try it.

eaty-beaty receiver.

I like well brewed homebrew things and also like to cook the food. In india many peoples are on air using the BITX. Well its the wave of the bitx after free gift of pcb at HFI2014. Somehow, I was not able to make the bitx. Only problem I had was pcb, input band-pass filter. vfo. I have not made any but on my bench I find two failed bitx & two bank pcb.  Whats wrong with bitx ? in my humble opinion, its a rig for the person who do not ask questions and just do soldering as directed. Well, I lack both that qualities. Many of new comer hams boast their bitx making. Well, its their destiny... i have to find my own........

I thought what makes them apart from my own super het receivers -dc receivers ? One thing I lacked until this day was the xtal filter making tech. After making the R7-Dayton receiver ( pcb courtesy-VU2UPX) I realized  the heart of the bitx or any good receiver is the xtal filter. Well, what if I can make the xtal filter and come up with my own receiver ?

For me, Its about enjoying the homebrew/food. Who cooks, it does not matter. On the net there was lots of discussion. I said why not make something of my own. Out of all this thinking the eaty-beaty receiver emerged. Atleast, I will be able to receive something to qualify as SWL....

Here is first shot. Not tested yet. Its evolving itself and i am not in its way. Lets hope it does what it promised....

eaty-beaty receiver.

Here is the ckt diagram. As it is evolving the values are not given.

First IF amp + Crystal Filter. 10mhz.



Second IF amp+ Dector+AF pre-amp+Audio Amplifier.

If it works, i will pass it on to others..... be rest assured.....wheel is being re-invented....please wait..... till then ENJOY.....

*date 21 april 2015:- today just powered up the stages. It gives a good loud sound. Nice. also passed the click test.  oscillator and if stage brewed. Need to test it for cw note of 10mh exteranal oscillator. It should work. Lots of ham friends are looking for it. Evening hours tested it works. filter is good. feeling its little wide but will deal with it later. Now time to make the Front end.

*date 22 april 2015:- I was looking or the first mixer from my homebrew files. I have used the transistors, diodes, ta7358 et all. I wanted something simple. I was not striving for the 1micro volt sensitivity. I want something that can receive faithfully. The plain copper board finally won. I don't want to make externa oscillator. There is not time for it. I want to finish it today or tomorrow. A date to keep. A dds vfo (yes sir arduino +ebay ad9850 board to be tested). To test my own 14194kc dsb transmitter. Its time i finish the receiver as it. So decided old faithful TA7358 with its internal osicllaotr. I will not use its internal common base RF amplifier. If needed I will use the FET amp. But I think even with this simple mixer it will give good signal.

 *date 23april 2015:- I tried the TA7358AP. Put the ckt on the copper board. Put a random inductor. Not measured. It was showing 7mhz. Oh I need 4.318kc as LO. then used another coil with ferrite slug. Thus Oscillator was trial and error.  Finally taken it to the 4.3mhz mark and presto I was able to beat the TX.  Singal is low. It need to be tuned up. I feel the IF filter is very wide. It needs to be narrowed down. Now I understood what narrow and wide filter means. After putting the mixer the sensitivity gone down.. mismatch.... this might use a good RF front end amplifier. Tried to listen to the on air signal, one cw station only.... ok this thing is working. It needs final tune up and boxing... lets see I am able to get on air signal or not.

*date 24april 2015:- Now I have tuned the radio. The Local Oscilator is giving me the trouble. Reason is simple. I don't have the frequency counter. The pic needs to be re-programmed. So beating with the oscillators. So exactly don't know where its beating.  This times calls out for good RF voltmeter and Oscilloscopes.... he he... if I had that much money I might have bought the rig itself.. who does this much labour ? As test is okey its matter of time when I put it togather in a box.... wait for two three days. Then I will test it. Put the tx and see how far its able to resolve the ground wave.  Able to resolve one or two am stations with howling of carriers ( he he)

now there is nothing left.... just patching here and there front end band pass filter, boxing and error free circuit diagram and possibly the pcb.

*date---25april2015:- The problem identified. The 4mhz local oscillator is not oscillating coil was resonated with the help of one external oscillator.  Tuned it, then in the ta7358 it was not working ? reason might be the 1000pf+1000pf emmiter feedback capacitors. yes sir, it should be the problem. In my last experiments only 680pf worked. why did I forget ? I should have consulted my own notes first. I do keep the log of all my tinkering with all the comments. Its worth reading.

Here is the picure of IF strip. Its working nice. I have to re-work tweak the Local Oscillator.

If its not tamed I might use external oscillator.







*date--- 29april2015:-
One thing I observed that the  RC coupled amplifier for the IF and RF amp is good when you are using it with low gain and with xtals filters.  Good I will be using them in my designs.

I will be making the receiver once again. Still there is issued with the front end. Coil need to be wound. I will be using the old IF / RF cans.... that consumes times....  but will make it......

*date 03 may 2015:-
The input BPF is really giving me headaches. I had made the bpf atleast two ways. Missing the alladin formers. I have few RF cores but they give me high inductance. Somehow I think the receiver will come to its logical end. RF pre-amp instead of amplifying it does attenuations.....

*date 04 may 2015"- It has reached its logical end. Mixer needs to be improvised. Which will take its own sweet time. there is need of tuning up of the front end or in other words good signal conditioning is needed. The receiver is able to get 59 signal as 53 signals. Will put one RF amplifier. Then its over.
I will not publish the ckt till I make another receiver using the same components.

*date 05 may 2015:- at night time I changed the rf amplifier and presto the signal came booming. Receiver was very deaf due to the RC coupled amplifier. I needed more gain. Now audio also sounds good. But xtal filter is wide. It needs to be narrowed. The time signal is ticking in with carriers. So it needs to be tamed. I should have chosen the 11.059mhz or 4.000mhz or any If where there is no constant signal i.e... ok it works.....  BPF needs to be little modified.  Box it and use it for signal testing receiver for the experiments of dsb tx .

This receiver was worth all the effort.

The wheel has been re-invented. But first I will use it myself only. thanks guys.

14194kc DSB transmitter

The most of beautiful band for me is the 20meter. I fell in love with it reason most of the time I can get plenty of the station for listening DX and local. Some are QRP/QRPp/QRO.

Its time, I make the DSB Modulator and be on the air. Lets see how much I fare.
Started the 2Watt linear.

This will be my third prototype. First stage is the 2N2218, Second transistor is IRF510 both working on the 12vdc. This time I will be making the power-supply little up 14 volts. ie LM7812 plus LED.

Plan is to drive the VXO of 14318kc, one DSB 14194kc, 3.68mhz ceramic VFO plus Quadrupler. And the DC receiver integrated with it.......

***
VU2ESE has designed this linear and it gives about 5watt when carefully made. But ,I call this 2watt as to me it gives me just 2watt without any special care. Happy, this is best for our use.  I could have tried broadband RM96 1watt amp, but that needs more toroids/components
my toroid/ferrite source ( I do recommend VU2PTR for toroids)  (For balun core I bought from tpsonline )

Here we can use the simple plastic pipe for IRF510. And just one balun for its driver. For RFC use the CFL lamps cores. What else you want ! This ckt is best made on the veroboard ( Yes sir !).

A small heat-sink is needed. 2inch by 2inch (5cm by 5 cm square or rectangle aluminum will suffice). But don't over do here. use small piece as heat dissipation will be low.

One thing I remarked that we need 24swg copper wire with just 2-3 twist perinch for biliar winding. When I gave more turns about 6-8 turns during the winding (sliding the wire from cores) I feel insulation was cracking. not joking. I realized the mistake but somehow if this does not work I need to rewind the toroid for IRF640 ( the after burner power amplifier)

05-feb-2015. Finished most of the components. Winding the second set of coil incase the first coil does not work as it has low number of turns. Prepared the heatsink from aluminum. It was in L-shape. Cleaned it. Flattened it with the wood batten and small hammer (250gm). Then with the help of Jig made it into the U-shape. Filed the aluminum surface clean and fat. As the transistor has to made the contact with it. So, it must be flat atleas the contact area. Then put the drill. The heatsink should be outside the pcb not near or on the 2n2218 transistor. Otherwise feed back may arise. I did not had the insulating kit but will use small plastic piece on top bolt to isolate it from Vcc.
Lets hope it works as I am trying an old tech in the days of the DDS Microprocessor controlled VFO........

But my hunch has proven right sofar.....this will also work

All the fun is in making and using it to drive a big amplifier. Yellow are the biasing network for IRF and 5volt dc supply. In blue,The crown heat sink is the driver transistor. In he tblack is the IRF amplifier stage. In corner  black LED to indicate the DC supply...........

One thing I noticed that in the previous two attempt the preset was atleast 2 hole apart from the two 100 resistors... here that is the mistake. So if you are making atleast put the preset 3-4 holes away from the 100 gate resistor. This way during the tuning the screwdriver just don't hamper the coil.

 

 

Please use the dedicated LM7805 here. As the work is in progress  at the input and output we need to put one 470 mfd, 25volts each. This way It gives a good stable 5volt. There is one LED placed so it burns the voltage during switched off and reminds me that there is voltage.

I have made a point to add atleast one LED per board so that quickly I can know atleast there is voltage and power supply is not at faults.....





Now the back side of the vero-board.

Here it is important that the IRF510 is soldered in the back side to reduce the lead length. IRF is not inserted into the holes. Just placed over it. If the lead length is big it will sure to oscillate, be it in the copperboard, etched pcb or any damn thing. Make sure the lead length is small. also notice the gimmick 10 ohm resistor on the gate of IRF510. I have also used the 100k+0.1mfd capacitor for negative feedback. This reduces the possibility of the parasitic oscillations. I did not have the insulation kit for transistors, so using the mica washer only. Of course the heat conducting paste is liberally applied. The gates impedance is 100 ohm so it needs more drive from 2n2218. That's okey.

I could not find the round ferrite core used in the CFL lamp. So used its transformer by breaking its half E core into a C and then placing a small slab on it so it becomes sqare bobbin. I also liberally applied the plastic adhesive used in the water pipe / plumbing.

work is in progress will be update from time to time.... whatever the outcome.....

07 Feb 2015.
Working on the Quadrupler and Amplifier. May be today or tomorrow it will be ready. At this time only one band will be operational. But will make it for two bands.

3.68 mh Ceramic VFO + Quadrupler is almost ready. Two Coil needs to be tested/ tuned for 20meter band.  One small amplifier will be added which  will drive a CW as well as DSB modulator plus DC receiver. Lets see......

Actually I wanted to make this for  20 & 40 but in a bit hurry to be on air.... anyway will make dual band also. On searching the net I found somedifferent filter which has the 50 ohm terminations impedance using the capacitor divider method. That's good. So, we don't have to put a tap, that results in physically strong coil. When we put the tap it slacks a little bit.... whatever works is okey for me. So when you re-produce make sure it  works for you.... I don't intend to make another or repeatable thing. Each prototype will be little different, learning from failure and success of the previous modules and new information.

The modules first tank i.e quadrupler required extra 47pf. That means it required (47+68+150)=268pf total with 13 turns 20swg copper wire wound on the 1/4" drill bit. I chose the dril-bit as it is a very precise tool then lots of other available items like sketch pen, plastic tubes etc.

On second thought I think a small 2db pad will solve a harmonics problem. 470 ohm 10 ohm 470ohm preset to control the RF. This was quadrupler get minimum power required without producing excessive harmonics. I will not put the signal directly to tx stage. Instead make one class-A tune amplifier with emitter degenerations. So that harmonics are down further. Will also use more filtering at the  small linear stage.

QUADRUPLER MODULE

One friend recently asked why taking this much pain. I said I have in the last year spent atleast 20k in buying old marine receiver ( lasted 6 month), LRR40 receiver ( that piece never worked from day one), VHF DR150 that guy cheated me. So I don't trust. I will not buy anything from the hams. Only VU2PTR & VU2KD was able to give me something which worked as they claimed.

So I am making this much effort to be on air. First will be the CW/DSB tcvr 15watt. Then will move towards the other band.

The receiver was tested with this quadrupler module. It gave me good quality signal in speaker even with 15cm wire as antenna. It has too much gain so there is need of proper shielding and filtering plus 3db resistive pads....

08feb2015

At night time again tested the linear module. There was short developed due to the that green capaciotor. Removed it. There was no connection/ dry connection on Vcc rail....
need some work..... there is some carrier leakage...

This is the first time TA7358Ap module is leakage of RF. On verobaord it was very nice. It might be due to the  copper planes instead of small pin socket...(. it needs some pads / resistor to curb the leaks...)

09feb2015

finally plugged the problems. At the 150 mw pre-driving amplifier on the  DSB modulator put one 10k resistor across the 4:1 transformer. Then things settled down. It still producing more power so will have to put some pad at the IRF510 output. Signal is very clear and clean. Will put one filter after IRF510 amp... Starting to brew the after burner (using IRF840) and the cabinet, VFO. So I will have three things on this TX/ CW full band, DSB on 14318kc xtal and DSB on 14194 kc ......

Half success...One day one day, I will be transmitting ham....

work in progress........

(this ends here, next will be actual on air test and other things.....)

THE WHEEL HAS BEEN RE-INVENTED use it as given.

( Till August 2015 not tested it on air. oh the damn 24 Vdc power supply.Will drive a big linear with it. )




 

DSB Modulator,20 Mb

The Modulator,
               After perfecting my system with the 14318kc transmitters, cw. dsb and linear amplifier , push pull amplifier and wasting so much time and energy on making, learning,teaching things it is my time to be on air finally or forget the dream forever.

DSB Exciter

             So making it with my time proven modules. I have previously made the single ic modulator and mixers. Now giving it a little twist making on the copper plane. I call the copper board as a magic carpet. Better than pcb. It gives me the creative edge how to shape the project.

             For working on the copper board you need small hacksaw, big hacksaw, triangular file, round file, sharp knife, marker pen, steel ruler or straight bar, some crocodile clips, little vice. one sharp steel pin, de-soldering pump & good Magnifying lence,

As for 04jan2015 see the foto

I soldered the transistors. Used BC549c. Tried to use same components so that inventory can be good.

06jan2015:- soldered all the wires, jumpers, extra capacitors.

07jan2015:- At the modulator state fixed/measured the LC valued in the Test oscillator with the frequency counter.
Soldered it.
15jan2015:- finished up.



27jan2015:- Tested OK, slight careers leakage is there, but which need  to be reduced...
01feb2015:-uploaded the ckt diagram.

MY write-up for the contest.

14,194kc, 20 meter DSB MODULATOR by Indrajitsinh, VU3INJ,

For 20 meter only xtals widely available is 14318kc . Sometime we also get the 14166kc but not always. But this is far from the crowd. Most of the excitement is around 14200kc fone part. So this idea was born.

The DSB modulator using the two simple cheap easily available xtals and two TA7358AP, the 9pin SIL, FM mixer IC. Its widely available it contains one RF amp, Gilbert cell mixer and oscillator. It also cheaper than NE612 . Using two ta7358ap is a little bit over kill for a single frequency dsb exciter. Only advantage is simplicity, no critical tuning. When you are using the QRP the stability of signal is utmost important. Due to use of the DDS VFO and narrow xtal filters even 100hz deviation go dutch for some operators. This will give us a good solid stable signal and our friend will know where to find us.

            First IC is TA7358ap which modulates the signal. Internal coll-pitt oscillator between pin7& pin8 is used. Xtal here is 4.194kc. not pulled much. One stage bc549c used as MIC AF amp with 4k7 preset as crude af level control. Another af amplifier stage used is within ic. The DSB signal is taken out from pin6 by resistor to make it simple. So it does not effect the mixing/modulating much. But, a tuned amplifier is used to clean the signal, filter out harmonics & amplify. Common BC549c is used will give enough gain here. No need of RF transistor.

           After that the signal is given to a mixer second IC TA7358AP. Here 10.000 mhz xtal is little pulled up higher / to change the frequency few kc upwards, trimmer capacitor is used. But a small panel mount 50pf will be good. You can try also the varactor diode. Single stage tuned amplifier using BC549c follows the mixer ic to select the sum product i.e 14.194kc. Our goal is to arrive near 14200kc.

          Afterward this signal is filtered and given to the linear amplifier. Whole strip is driven from the 5volt regulator. Current consumption is about 45ma.... Signal is clean. There is not much tuning or testing. Except setting 4k7 trimmer for good sounding audio in receiver. Use whatever mic you have and accordingly modify the mic bias resistor. All the tanks are pre-tuned. i.e means the LC components were used as a tank in the collpitt ocillator. By adding standard capacitors values to arrive empirically at the given freq. The freq was measured by the counter. Now, this same components were soldered on the board. This is emperical and quick method of putting the fixed frequency coil for BPF work. To simplify 2.2 micro henry ready made rfc used as first tank. For second tank I could not find suitable candidate in commercially made RFC. Its 22swg wire,1/8 inch dia ( a metal dril bit used as a former) to wind it. 12 turns, tight wound. Then with the adhesive it was made rock solid.

         I had made two prototypes. First one a year ago on vero-board and another this time on copper board. This second prototype was mechanically more challenging than the veroboard. I had to cut groves on the copper plane , solder the copper pad with adhesive on copper board. But happy in the end that it worked. To solder/brew it took me three days But, testing required little more time as my receiver was not working....

        Components details, values and ckt diagrams follows. Please also see the PY2OHH & various TA7358 design on the web.

(x)indrajitsinh, vu3inj. Copy right. If you find this ckt useful please enjoy and pass it on with your refinement and above all enjoy the brewing.

Block diagram

Ckt diagram:-


DSB MODULATOR 14194KC



 

Two prototypes:-

Bill of Material:-

Resistor	Value	Note	Capacitors	Value	Note
R1	1M		C1	0.1
R2,R5,R8	100		C2	1000pf
R3,R6	470		C3,C6,C14,C21,C22, C23, C24,C25	0.1
R4,R7	47K		C4	100MFD
R9	10K ---100K	Choose as per MIC	C5	10 MFD
R10	100		C7	0.1 / 10 MFD
R11	10K		C8	NIL
			C9,C10,C16,C17	100 PF
			C11,C13	47PF
			C12,C19	* TEXT
			C15	33PF	TRIMMER
			C18
			C20	10PF
			C26	470 MFD, 25V
			C27	1000 MFD, 16V

Transistor	Value	Note	Diodes	Value	Note
Q1,Q2,Q3,Q4	BC549C	NPN transistor	D-	LED
IC-1,IC-2	TA7358AP	FM Front-end IC	D-	1N4007	reverse polarity protection
IC-3	LM7805	Voltage regulator

Other items & hardware...

Mic & PTT switch, Relays.

Copper wire,20swg or similar for connecting the stages.

Copper islands cut for placing the components

Adhesive tube used in plumbing to join the water piples.10gm.

Fone pins, plugs,

Aluminium sheets to cover the entire units. Some paper for insulation.

Special note:-

Please make sure the Vcc is 5Volt dc .

How many contacts I have made with this ? None,

Is there any AM signal ? Yes there might some leakage of carrier due to the gain stages and absence of the xtal filters.

What development I can make ? well nothing much, in this one. if you don't like the tuned stage, please use the resistor as load but then there will be no harmonics filtering. This is just a simple DSB modulator. Take it as a basis for your own design.

Can I use the external VFO, DDS:- No need .its made for simplicity. If you want to use vfo/dds then it will be more rewarding to make a complete trx set of bitx.