Saturday, December 13, 2014


During the eyeballs visit with vu2upx had gifted me one SSB RX pcb along with other pcb and DDS VFO board , IC.

It seems to be R7 receiver. It is the simplest ssb receiver. I have plenty of the ta7358, 10mhz xtals and tools. Why I did not noticed it earlier. Anyway lets catch up with true things.....
here is the pcb & ckt diagram

Top side view the board::-

Componet side


Showing the links of the R7
The circuit diagram for the above pcb. The PCB is courtesy  OM Charudatt, VU2UPX. Thanks boss

Only components I don't have is the bf245. May be I will use 2n3819 which is on hand. For the varactor have to think or do some  juggad....instead of MV2109 I have BB139. Another bottle neck is the can used in oscillator and filter. I have plenty but not this one. need to modify it. All other parts are simple and one weekends project.

On the 13 dec started this project. lets hope I finish it and brag about it........
on 14-12-2014 done all the big parts i.e ICsockets, I cut 18 pin DIL ic-socket into half and got two 9pin SIL, On the rough edge, please file gently to make it smooth. As this sunday writing down the parts list to shop.
here is the list with my note. Click it on to make big.

1.Print the ckts. Study the ckt and pcb. See that you have all the necessary critical components. There is also help in the form of three pdf files at the fuji qrp website. Read it please. If possible characterize the filters, make LC tuned tanks before doing anything. These are the hardest element of this kit.

2.Ask the elmers, original builder or someone who built it for some insight. In every design there is always some silent points which needs to be adhered. My dear friend 2upx who gave me this pcb remined me to start from the back. Thats the way we all do ! Frankly this will be my first "RF KIT" build. I have always done my own design on perf boards, copper boards with giving some twist to the originals.

3. Study it again. see that you have all the tools instruments. Mulitmeter, 12vdc power supply, cutter, twizer,LC meter. See that y our soldering iron is very clean, if using ordinary iron then file it shining. As tracks are very close there is possibility of accidental shorting. Use MAGINFYING LENSE to do visual inspection. Before placing the components see that you are placing the right values, measure /check it( with mutlimeter, LC meter etc ). Once the components are soldered there is no way to know what it was and the trouble shooting will be very hard.

Lets begin solderig.

4.I first soldered the IC sockets, connectors. As a good practice you should use sockets , connectors.

5. Then Soldered the power supply module. LM7805, 1N4007, LED indicator.due to 1000mfd there should be good filtering. Important for smooth audio.

6. Then the audio stage. LM386. Mounted all the components. I wonder why there is no by pass capacitor (0.01mfd) at the intput pin3. Anyway i am not doing my own change. Try to stick to its original values. As it is the superhet design audio stage is not critical but it seems to have low gain.

Connect the Volume pot and 12v dc. Don't forget to put LS. See that there is voltage on pin6 of LM386. LED light is ON. Normally there should be only murmur/slight noice in speaker, But it should be not loud one. otherwise halt and investigate. Now do the finger touch test. There should be loud noise. All well, then proceed to TA7358stage.

(Gain is distributed all over the receiver. Still i feel that AF preamp for LM386 is needed.. I had to remove the 1k restor between pin1 and 8 of the LM386 to increase audio.)

7.When we do something in india we have to idianize it. in europe & america there are many local hams with strong signals. I dont have hams around me in 100km straight. So i have to make it more sensitive and need not worry for local strong signal.

8. At this time i had to choose the IF frequency. I had 10 pieces of the 5Mhz xtals and 10 pices of the half size 11.059 Mhz xtals. For matching the xtal i built a small oscillator. See the " filter making 1.html ". Noted the readings. Asked the seniour OM over internet for choosing the 4 xtals and one oscilator xtal. They unanimously chose. I put those xtals.

9. BFO was moving from 4999.8 to 5001.8 kc. Okey. At this time i should measure the bandwidth to put the BFO at right frequency. But, still i went on. This stage passed the finger touch test. Moved to the Front end mixer.

10. I just got the 4 pieces of the 680 pf of white styroflex variety. These are good for making a a very stable VFO. Used here. I could not find the 4.7micro henry coils for pin3 load. Can find only 100 micro henry and 3.9 micro henry. Got them. resontaed 3.9 micro henry with a capacitor in my LC Test Oscillator. with 68pf this coils resontates at the 6.9 mhz. I did not like a non-moving resonant tank , will replace it with 100 micro henry coil.

11. Went again to shop to purchase the few more henry coils and few pf values. Found the some old IFT like coils. Wound one IF with one turn. It showed teh 0.1 micro henry. So 11 turns were wound on the internal dumbell and it should be 1 micro henry. As was pushing it into the pcb for knowing whether it can fit or not. The pcb holes were very tight. So with small hard nail tried to winden it. But, still it stuck. As these coils very very old one leg broken during pushing & pulling. I said this will create a mesh. So, soldered it anyway and resonated to HF. it gave me about 22pf+68pf at around 12 mhz. Okey with me. With a varactor i can tune it. for entire 40 mete band. For the varactor i could not find the MV2109. I have BB139 but will try 33v zener diode or normal 1N4007 rectifier diode.

12. till now the luck was favouring me. I have spent atleast 1 hours per day for this little project and at the finale it is giving me trouble....

13. Need a resonant ckt at the front ends. Will have to wind the IFTs for 7 Mhz resonance. I don't have the BF245 FET. Well i can substitue the 2n3819 which is on hand Its not critical but it should be a FAT so that the tapping of the coils can be avoided. This stage is a must othewise the gain will suffer. All the RF selectivity is here. Hope gain of this stage migh make the receiver roarding.

14. I will Tune it with some xtal oscilator (7.159Mhz) and then conect antena & on air test. Hope i get the on air signals.

( Work in will be rewriting this soon24 DEC 2014)

1 comment:

  1. A simpler version of the same design, with DDS input, No BPF on board/PCB, Switchable USB/LSB crystals etc, is in the pipeline. More of it later.