Thursday, April 17, 2014

RA3AAE detector


I had tried serveral projects of ra3aae detectors PA2OHH and KE3IJ . Well before these projects, i had never worked or heard of it. Both hams have good projects on their website. worth to see it.


My experience of these humble diodes have been nice, diodes always provided me a reproduceable results.

During brewing of the  first 40 meter receiver and then second  48 mhz rx , i found that some peculiar problems. i.e noise, antenna mismatch, microfonics, sudden breaking of audio oscillations etc arises, i tried all my tricks to get something which others can use.. but i did not work. so left it.

( (6meter tx and rx (ra3aae) experiments. & RA3AAE detector )
(Please visit my earlier two posts to get reference of things i am stating here.)

RA3AAE detector has the reputation of "works on first trial". so little puzled  and after some rest and new lights, once again tried to tame it. here is the results.
hello cq cq can you hear me !

fsm meter , what a simpicity








































For starting the test,

i put these modules in the workbench once again.  gave cw tone okey. it works but it did not give the performance i wanted. Audio is little odd.

I said why not make another ckt to understand this ckt.

Then it was time to make my third detector from the scratch i started with audio amplifier first. hmmm, BC547B based af pre-amplifier stage, LM386 based audio amplifier. Ok.
 
Made a dedicated amplifer for the detector and then i tried to reduce the gain of lm386 presto ! sound is crystal clear.


Now ? let me first test it with existing detector. so, tested and within half hours understood what was the problem with earlier ckts - high gain audio amplifier.

LM386 problem and solutions.

10mfd placed between 1 and 8 pin is not needed. No need of high gain. How much high gain 200 times. Without 10mfd only gain of 20 times.

In AF pre-amp stage feed back of 100pf improves audio quality and reduces noice .

From 12Volt dc, 1amp capable power supply, whole radio circuit takes 40 to 140 ma. When i connected with 9volt pp3 batery it took 19.1 to 29.1 ma but on high volume it breaked into uncontrolled oscillations. may be with high impedance source i.e low current capcity-source. cure is to place 470mfd to 1000mfd capacitor across the power rails then af amplifier works better.
(kindly read handwritten notes will write it down shortly. Please.)
Antennas:-

a small piece of 1 feet wire was connected to the high impedance side of tank i.e top of it and signal came rouring. Night time BCB, other hams signals to be observed. In subsequent night observed. It is okey. there is slight BCB.But not too heavy. You can safely put headfone.

I want to connect the dipole and reduce the qrm so two tuned ckt will be employed in the front..( aantenna work is in progress, )
ra3aae detector problem solved

design on paper

af pre amp stages

conclusion too much gain in the audio stage is not needed as we are providing the bc547 based rf and af pre amps.


Failure of my ta7358 ( see earlier post)  might have the same problem, excessive gains. ???
(when i tested this theory later on ta7358ap has started behaving good )





Impedances:-

Here,ckt has been taken from pa2ohh. we are using the 470 ohm and another 1k pot with diodes so the impedances are high. Not just 50 ohms. Keep this in mind. So, when i tried the CB af preamp stage of KE3IJ it did not work with this designs. KE3IJ has intentionally made this cb amplifier to adapt the 50 ohm dipole antenna. wow.

Logic behind the designs.

when we adapt two stage from different design we should also take cognizance of the impedance they are looking and many of the time failure of the ckt is due to the mismatch in the impedances other wise individually they are working fine.

so, we have to first understand the logic used by the designer for the given module and for that we have to make the ckt as designed. they dont tell us variable ot the processs but it is possible they have worked hard to arrive at the single design after lots of other variations tried. My sincere thanks to all the designers.

Actual ckt diagram which works. 

After long long evaluations this ckt diagram is tested okey. I made it on perfboard. You can make a small pcb. If anyone makes pcb please let me know. I want to upload it so other hams, swl also benefit.


 
40 meter receiver using ra3aae detector.

At last i can say that these ckt works for the 40 meter.

(48 mhz will be tried after making suitable LC local oscillator of 24mhz.)

Local oscillator

For local oscillator i have used ceramic filter running a collpit oscillator..tuning is by a small variable capacitor. i have itentionally not given the oscillator ckt as also wants to test the other normal Lc Oscillator.To be frank tuning is very sharp some short of slow tuning mechanism might be need if you want ssb. otherwise for cw it is okey.

(as of 20april tested the oscillators and found that one with the ceramic resonator 3682kc , two terminal devices is more stable then LC oscillators. I was waiting for this test. thats the main reason did not write it first place. No two oscillators are same. I made three oscillators, one did not go to the desired low end freq 3530 instead it stick to 3639 one was going easilty and one stood at 3531kc ! so, first of all measre the frequency and then use it in receiver. make few oscillators and you will know which works and which does not. ckt is given below c1 and c2 are 1000p styroflex or any good capacitor, vc is variable capacitor use the radios gang .n.b i will upload the test result of the vwn tx done with the help of this radio and more on next post. thanks...... )


Other things.

Will be putting more musing on LM386, AF preamp of DC-40 of VU2ESE, oscillators.

I have no local population of hams so not tested ssb signal or cw signal of other hams. Also not connected big antenna. I want it be mobile to test my own transmitter and to check pheasibility of running SOTA . I live near Mount Girnar. One of the highest peaks.

 If, in sought india someone try this ckt and give me the result . i will appreciate the effort.

we can safely demo this ckt to childrens and novice hams for their first real receiver. Sound quality is real good.

In the end

Lo needs to be tweked, But, all other stage are complete and  there will be no further R&D.

Once again put into a permanent box and will let you know.

Thanks folks , lets use this wheel with great cheer. 

(During the testing my vwn tx on 7059kc gave me company and one of the days will be mobile with this rx and find out the range !...  and will conclude whter my tx is really low power or it works few km as i thought )

Let me cite the todays elixir from 
His Holiness the Dalai Lama,
the very purpose of our life is happiness, which is sustained by hope. We have no guarantee about the future, but we exist in the hope of something better. Hope means keeping going, thinking, ‘I can do this.’ It brings inner strength, self-confidence, the ability to do what you do honestly, truthfully and transparently.

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