Sunday, April 19, 2015

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.