Wednesday, August 24, 2016

4 transistor 80 meter receiver

My friend Pat Pending sent me this one. It is worth a look. I would have to make some changes to build it with my materials on hand. Diode tuning mainly.

Sunday, August 21, 2016

op amp radio update

My first post was an op amp radio. It used a LM741 which is a 1Mhz amp. I built it with a NE5532 which is rated at 5Mhz. It was designed to drive a small speaker and it will. I'm using it with an earbud  and have to be careful to keep the volume down. The NE5532 is a dual amp chip so why not add a RF amp? The only circuit modification for the NE5532 was the pin out. Here is the modified circuit.

 The original to compare.

The NE5532 output is pin 1 . The NE5532 power is pin 8. Changing those two pins is all that's needed.  Pin 5, 6 and 7 are the second stage. They could be used for an AF preamp, IF or Rf stage. This circuit gain is controlled by the ratio of R3 to R6. 1,000,000 / 10,000 = 100. the circuit gain could be adjusted by varying R6. If we change R6 to 1,000 ohms then 1,000,000 / 1,000 = 1000. The gain would be 1000. If we leave R6 at 1,000 ohm and add a 10,000 ohm pot with the wiper tied to one end between R6 and the tie point between R6 and R3 we would have a gain or volume control. It would adjust between R6 + 0 = gain of 1000 as just calculated to R6 + 10,000 = 11,000 ohm. which gives 1,000,000 /11,000 = 90.9.  Adding a 100KOhm pot would allow you to adjust the gain down to around 10. Because the op amp is so flexible I'm abandoning the hearing aid amp for the time being. If you only want a low frequency amp you could also use a LMx58. The LM358s are about a dime apiece and are rated 1 MHz.

Friday, August 12, 2016

playing with the balanced mixer again. The Gilbert cell actually.

A slick little circuit made with 6 transistors, 2 resistors, and a transformer. It is available as an IC but what's the fun in buying a chip when you can build your own? Don't laugh at my breadboard, I made it too. Here's the chip version.

If you could find them it would probably be better than my home built but it's only 6 transistor so here we go.
Same circuit but the IO ports are labeled.
Not much to look at. All the jumpers cover it up. Let's see what it does.  With some signals applied. I don't have a lab but I have a little digital function generator and a grid dip meter. I put the function generator on the LO input and coupled the dip meter to the IF.

You can see the signals are interacting.
I changed the signal a little and it look good considering I don't have lab grade equipment here.
I turned on the frequency display The purple spikes are the input signals. One is dead center, the other to the right. Nice envelope being produced.
This looks much the same but note I have lowered the signal. The spike is to the left now.
My scope is not the best I can only step through the adjustment but here you are seeing the same signal as before but the time base is changed. Note the frequency reading is the difference.
Here I really made some changes to the display same inputs.

Cleaning up a little here.

I pulled the clip leads away and this is the circuit. The round red thing is the transformer I had on the negative supply lead. The junction between the two resistors are the positive supply point. That's it 6 transistor, 2 resistor, and 1 transformer = Gilbert cell.
My project at this time is an 80 meter receiver I might build that circuit into it?

I made a couple of long tailed amps using 2SK2539s and they worked quite well. Now I'm looking at a Gilbert's cell using the JFETs.

Wednesday, August 3, 2016

Examining unknown toroid core.

10 for $5.65 0.87" OD doesn't sound bad BUT what are they and what can they be used for? The reviewers give good reviews but no one knows the material. First I download Mini Circuits mini ring program. Second I wind 40 turns on one of the cores. Third I measure the inductor I just wound. Fourth I insert the data in the program.

After entering the data I press the button at the upper right screen.  Done with that step. Now how to use the data obtained.

From unknown to usable. Back in the main program click copy AL from tool and click Copy Dimensions from Tool. The data is set enter desired inductance, in this case 121 uh and click the =>. The program tells you how long the wire needs to be and what the max size can be.

All that's left is to put a couple of turns for a primary and send a signal through the transformer formed to observe the frequency response. It looks very promising if it will work at the frequency range desired.

As my final test I did put 7 turns on a core and it checked good. It would be good to check frequency response.