20 Meter band Superhet Receiver (II)

I tried first experiment with eaty-beaty receiver but something got problematic and could not cure it in time so lost interest and attempted this receiver. have a look.

1. Front End
2. RF- Mixer
3. IF Amplifier
4. Product Detector
5. AF Amplifiers

AF Amplifier

My LM386 did not work ? I replaced atleast three new LM386. Was wondering what is happening. Ohh it might be Chinese dump. So took few transistors. made  complimentary pair small Audio amplifier. It works nice.

 

this is my first AF Audio amplifier made from all discrete components. It was just 20 minutes affair and worked at first time. But, power is low. Need to reduce the 470 ohm  resistor. But, that reduced the audio. So, it is good as it is. I used whatever components I had. Nothing special. only transistor AF amplifier. I feel it need some more audio gain in pre-amp. I increased the gain in front end RF amplifier. By shorting the 10 ohm degenerative capacitor. Oh boy it increased sensitivity.

 

BPF

The coils are made on standard 8mm drill bit. So, it can be reproduced anywhere all over the world. When I used 21 turns with 100pf it resonated around  10 mhz. Then empirically, reduced few turns one or two at a time and changed the pf to 68pf at one point it resonated. Finally at around 15 turns it gave resonance in 20 meter band. 14.200 mhz. That's okey. Same way done the second tank. Then linked them with 10 pf. That will give me enough bandwidth.


IF amplifier & Xtal Filter

IF amp Xtal filter

The If amplifier is simple two stage amplifier. I did not use the LC tanks. Due to non-availability of toroids/tuned cores etc. So, simple  resistor coupled amplifier are used. First Amp is classical class A with negative feed back. Used BC547b. Second IF Amp is a cascade one. Using two transistors BC547b+BC547b.

The xtal filter. I was little skeptical at first. The xtals were matched. See previous posts for xtal filter making. Its purely experimental. I have no instruments to measure the bandwidth etc.

xtal filter

I am not puritan. Whatever works is mine. So, this somewhat wide but okey for me. Only caution I took is short leads and clear soldering. Don't forget to ground the metal case. No extra shielding is needed. The filter is the "secret" of RC coupled amplifier.

VFO:-

4 Mhz VFO

Generally I use the  Collpit oscillator, Emmiter follower design. for base bias 100k resistor and at emitter 1k was used.  But, this time I used some different biasing method. A fixed base biased was used. 22k+33k. good result.

I used old trusted buffer with 470 ohm preset to control the RF going to mixer. This way I can somewhat control the mixer characteristics. Its stable. But, I have not measured its stability. Will put some slow tuning and box it up. Will use regulated 5 volt . LM7805.

Detector Stage:-


Sub Harmonics Detector
 



RA3AAE, sub-harmonics detector. See previous posts about it.

There is one common emmiter BC547b AF pre-amplifiers stage which feed audio to either the LM386 or discrete stage

Here is the ckt diagram of IF stage and detector.

IF stage & detector.

 

Front End BPF + Mixer

 

I will make pcb pattern and ckt diagram in deep-trace pcb designing program._

 

  

Receiver ( BPF, Mixer, IF amp, xtal filter, VFO, detector)

 

For further reading about these module just read my previous post. or email me. I will respond.

 

Further,

I will try to make one transistor audio filter. will make compatible 20watt cw transmitters using 4194 kc, 4286kc & VFO so I can be atleast heard by other hams. Once this is done, my "on air dream" is  over. Will try to modify it to DSB or SSB and will be end of days for  20 meter. And if by chance I get hold of DDS VFO, it will be good.

 

See you on air....

 

Boxed it. Performs reasonably good. I can say the stability is very good. Far better than my latest 40 meter transceiver. he he.....

73 friends.

de vu3inj.

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.