40 Meter Receiver (7159kc)

Few days ago a friend asked me about the simple receiver to practise his CW Skills. Well, i have done few experiement with poliakov receiver and they have given a repeatable , proven results. I scanned indian products and could not find any thing for the small kids, new hams or something very basic minimalist, cheap devise. So, I filled in the space. Its better than pixie, tixies, foxx etc but less than well made DC receiver . Brainstorming started, I thought let's re-re-invent the wheel.....

here is the result

This requires minimum of time to make and its up and running within hours. It can be used to practise morse on air. It will certainly not bring the good dx nor it is frequency flexible.

See my previous posts, you will find many experients on this subharmonics receiver. It is still in development stage. You can have dip file from me. Just drop an email. I am making a suitable transmitter. In my mind is two way. One to use this LO and then use the doublers amplifiers to arrive at 40 meter so the hard to find find 7159kc xtal can be avoided and further 3560kc resonator can be used to give flexibility of freq. working on it. Tx might be three stage 3watt, along with relay change over etc.  Another tx will be using 7159kc xtal , class e two stage to arrive at 3watt.

Lets begin::: It all began with this ckt, have a good look. From this all other things are derived. First transistor is an RF amplifier. Two back to back diodes forms the sub-harmonics mixers. Second transistor is AF amplifier. The gain of This AF/RF amp depends on Rc/ Rb. If you find the gain is little low try experimenting with it. 470k/4k7 will give gain of 100.  The choice of transistor will determine the gain as well as noise. The RF transistor should have high ft ( gain bandwith product) that way it will produce good signal. In my experiments I found that bc547c, bc547b gave different gain. 

Small whip antenna works fine. For higher frequency please use some broad band transformer coupled RF amp. That will give good result in 20 meter. At present this ckt is good enough for 40 meter.

The diptrace schematics screen shot.





This is the diptrace pcb making software , This time I took time to make the schematics on this. EArliers I used make by hand and then scan. I realized to make a professional grade pcb, good quality image and parts making the pcb software is a must.

The ckt diagram

List of components

40 METER BAND RECEIVER

# RefDes Value
1 A1 whip antenna
2 C1
3 C2 100p
4 C3 100n
5 C4
6 C5 100n
7 C6 10 mfd
8 C7 10 mfd
9 C8 100p
10 C9 100p
11 C10 100p
12 C11 100n
13 C12 100  mfd
14 C13 1000 mfd
15 C14 33p
16 C15 10 mfd
17 C16
18 C17 100 mfd
19 C18 100 mfd
20 C19
21 C21 100n
22 D1 green LED
23 D2 1n4148
24 D3 1n4148
25 D4 1n4007
26 J1  speaker out put JACKPIN
27 J2 dc input JACKPIN
28 L2
29 L3 

34 Q1 BC549C rf AMP
35 Q2 BC547B af amp
36 Q3 BC547B Oscillator
37 R1 470k
38 R2 4k7
39 R3 470 ohm
40 R4 2K2
41 R5 120k
42 R6 2k2
43 R7 100 ohm
44 R8 120k
45 R9 2k7
46 R10 100 ohm
47 R11 47k
48 R12 470
49 R13 10 ohm
50 R14
51 T1
52 T2
53 U1 7805
54 U3 1/2 TDA2822m
55 Y1 3579kc
56 Y2 3579kc

Note of TDA2822m,

I always used LM386 but somehow I am finding difficult to get a good chip. All Chinese chips are faulty. So, tried TDA2822m  an 8 pin DIP ic. It is good one. It contains two amplifiers. This IC is a low voltage, low power  AF amp. So, use 4 to 5 volt maximum. When used with 12volt supply it starts heating up To reduce heating on IC, I used a ballast resistor of 200 ohm ( 100 ohm 2watt + 100 ohm 2watt) , so it stopped heating up. Remember this thing.  Only one part out of two is used.

Note on Antenna.

For making pcb from schematics , I put a two tank band pass filter, otherwise single tank with whip antenna is sufficient for all purpose.

Note on the Xtal Oscialltor- 3579kc

we need very small Rf injection to the diodes so single transitor osc is used. There is shown two coils and two xtals. I put it there only reason if someone wants to modify experiment , the same pcb will be useful. F6GQB. So, I can get 60k shift , more than enough for this set-up.  Except this two square I have not hidden anything. Only this squares have few extra empty parts.  Only single xtal is used, No RFC used.

If anything is missing please let me know.

You can make it, but remember its still in development stage. When I first put it on facebook there was two errors. one transistor part was wrongly labeled. And 12 volt and 5volt lines mixed up at 2822m. So, ckt on this blog should be final.

THE RECEIVER CKT IS FINAL. there will be no modifications. but revision of write-up , addendum will be added later on.

Input Band Pass Filter modifications. As of 17 may 2016 Modified the input filter system. Put fixed inductor 2.2 micro hentry with 215 pf =( 100p || 100p) + 180pf , tap taken from junction of both 100pf. The RFC of 2.2 micro henry can be used ready made or  made one 9 to 10 milli-meter dia plastic tube, I used felt pen, 30swg around 22 to 24 turns close wound, length will be 10 to 12 milli-meter.  Measure it with LC meter.  Plastic tubing former was around 3 cm long.  Will upload close-up fotos soon.

Receiver sounds good. Housed in the home made box. Other modifications like painting, putting nut-bolts that will happen as per need but electrical ckt is finale.  Am breakthrough is very minimal. AF filter might be a good idea. But the simplicity beats all. Make this receiver and please wait for compatible transmitter.



BPF

so, till then enjoy, the wheel has been re-re-invented, take a ride.
de vu3inj.
 here is a link to my youtube chanel. on similar design made the 20 meter one. have a look at https://www.youtube.com/watch?v=G4LTTf-waVc please
NB;- you may write down few words please.

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.

VFO SLOW TUNING

now a days peoples  are using the dds vfo and all sort of digital techniques in the vfo. The days of slow vernier drive and band-spread coils etc are gone. Also there is no more production of this mechanical devices. We still love those metal gangs and slow drive !  But unfortunately we could not find them easily.... here is the todays solutions.

Now peoples use the varactor diodes. This varator diodes need to be given some DC voltage. One solution is to use the multiturn pot.

You can use the fig.1 ckt. I used it but it did not give a very clear and broad range.
Then somehow, I got hold of this ckt in PY2OHH, the Brazilian ham. In one of the VFO he used  I liked it. I am going to implement into all my vfo.

It gives a very clear and very slow drive. It can work with the 33v zener used as varactor. Earlier is used the 1n4007 as varactor. The voltage is not linearized. The two 100k pot has to be linear ( not the logarithmic) for further very slow tuning you can use a multiturn pot. How much shift it gives just enough to resolve the 5khz shift. Ok when you are using the homebrew rx/tx.

You would like to use the MV2109 etc etc varactors. Here nothing is hard and fast rule. Use whatever is on your hand.

The values of the slow tuning is given in the ckt itself.  Wire as shown in the ckt.  Don't forget where the ground is taken from ! (Will upload the fotos laters on ... ok see below )

That's it folks wheel have been re-invented successfully.
 

Direct Conversion Receiver

direct conversion receiver

80 meter oscillator & buffer

dc receiver front view

This is the working direct conversion receiver. I am using along with 80 meter xtal transmitter for test purpose. Initially it was made to test whether Diode Product Detector could be used or not. I was skeptical about diodes product detector but ultimately i beleived in these diodes.




It contains four stages.
1.   LO with buffer to drive the diodes. which requires 7dm power.
2.   Product detector of Four diodes, as shown in previous post.
3.   Active AF Filter, this is also shown in some post in this blog.
4.   Standard LM386 af amplifier.

All stages are operated from 12 Dc regulated voltage.It needs antenna (dipole)  and BPF at front end.

For 20 meter some sort of Rf pre-amp is a must. I had used the Cascoded RF amp with filter. LO was same but one stage of Transistor multiplier amplifier was used to drive the dbm. That was my best receiver to operate. I used it extensively  during the y2k as valves receiver required more power consumptions and this was just a small size receiver.

In the front panel, on left corner there is unmarked socket it gives the output directly from filter so that it can drive external AF amplifier.

Enjoy the simplicity.
***************************************************************
Here is the circuit.

 The block diagram. This is the typical diagram. All the direct conversion receiver follows this stages.

Product detector. This is standard circuit. I was making the receiver and little skeptical of passive diodes. For the sack of go or nogo test connected the diode dbm and presto it worked first time. It lacked the audio so i put the resistor as shown and it became my favourite. It is given in the QRP Notebook also.

How to wind the core ? Make a trifiliar wire. Three wire is taken and twisted for 5 to 8 turns per inch by handdrill. then wound the 15 to 17 turns. One side wire end are labelled as 1,2,3 and their other ends are labelled as a, b,c. Test for dc continuity. 1-a,2-b,3-c and no other pair should show the zero. If it shows then wire enamel is broken and it needs to be rewound using new wire. Connect 2and a and your transformer is wound ok. Becareful with scrapping the enamel.

to be continue......

Boat Anchor Receivers

broken dial cord

inside the chasis

Yesterday i once again tried the old favourite sait MR 14501. It did not give me results. I worried. I opened up my S-129 and wound the dial cords. Tested it. working ok but cord once again sleeped from dial so will have to open up once again and wind up band spread cord.

Later on i found out that my wire was 'broken'  so it did not worked in first time. Soldered it and presto gives out loud signals.

75 meter , 4 Mhz receiver

Original hand drawn ckt, Later on it is redrawn. See, the end of this post.

This was developed with intention of testing 4 Mhz IF of  Superhet Receiver design. I  check the 4 mhz DSB modulators signal and CW tone of 4 Mhz oscillators . Using  Xtal of 3.579 Mhz or any 80 meter band xtal  and  changig input tuned ckt of band pass filter (capacitor values) it can be used in the 80 Meter ham band.

In the earlier ckt diagram there was some mistake in showing 9th pin of audio ic (actually it is 8pin DIL package !). Now, it has been corrected and uploaded. pin 6 of ta7358 has load resitor of 1k.

Nb i was not able to use it as IF in my superhet receiver project design. I need to change input bandpass filter for IF.  As for 4 mhz cw, direct conversion receiver this is good.