Robs Receiver Build: RF Amp

So i have started to build the actual project now rather than build and test different blocks. Its about time that I actually built something from beginning to end. So lets start with the schematic.

A blank canvas all ready to go.

The first stage built, but not working in this photo. The J310’s i have, have a different pinout to the data sheet and i put a cap where a resistor should be 🙂

Got things fixed and working in this photo.

Maximum gain from the dual gate rf amp.

Minimum gain from the RF Amp.

So far things are going swimmingly and next job is to wind an output transformer for this stage and then start on the bandpass filter.

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IF Filter

So after building the IF Filter haphazard looking like a spastic, I connected up the test gear to run a Bode Plot to see the shape of the filter. I then proceeded to sit here wondering what i did wrong for the next hour as my 500hz CW Filter is almost 4K wide and probably ok as an AM Filter. LOL. Well, slow as slow can be it dawned on me, I grabbed 470 capacitors out of the box, thinking they were 470pf not 471 capacitors which are 470 pf. So in my haste and not thinking i have 47pf capacitors in my filter not what i originally planned.

 

On a positive note, the shape is not all that bad and not to much ripple even though the input to the filter is not correctly terminated. That is another headache, trying to get accurate measurements of in and output impedances and matching right when you have not built the preceeding stages. So I am going to switch to Termination Insensitive Amps for the IF and make my life easier.

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MPSH10 IF AMP

So i had another swing at the MPSH10 in LT Spice and what it says should happen and what actually is happening are 2 very different things. I got it sorted and it is working fine. But I am not sure if i run with this or revert back to the 2n3904. For now I will run with this and see how it goes, I just have to measure the input and output impedances. Which as of next week or so, will be easier when i have a vna. The circuit is a little different to what was in the schematic in the previous post. I will update the schematic if I end up running with these.

I build this a little different, I had these squares sitting there i made so I used them.

Oscilloscope output, green trace is the signal in, yellow signal out.

 

Output from the spectrum analyzer.

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Oh The Humanity

So i sat here this morning with a bag of 50 crystals playing a game of what is the resonant frequency. Thoroughly boring I can assure you and I am not sure how the ladies at uBitx Labs in India can sort through thousands to get sets of 8. But alas I have done enough for now to get 2 sets that are matched at a guess to within 50hz, being that my frequency counter is only good to 100hz.

One thing that I would not have predicted is the distribution in the resonant frequencies. Its like buck shot, all over the place and the other thing I would not have predicted is the number of dead crystals or ones with so low Q they might as well be dead being 8, that seems like a very high death rate to me. I still have 2 more bags to sort, but thats not happening today, i have 16 matched crystals I need for 2 filters and am moving on to the next thing.

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Crystal Frequency Tester

Need a tool, make a tool as they say. Well i need to sort these 100’s of xtals into groups of similar frequency for use in xtal filters for an upcoming homebrew receiver project I have started. I have like 200 12mhz to sort through, so i should be good for a few filters at least. Its just a matter now i sitting here for a few hours and sort them all. Not looking forward to that. 🙂

No rocket surgery here, just your basic oscillator and buffer circuit that can be found all over the internet. Its simple, it works and it is reliable.

Built it up Manhattan style on a scrap of copper clad pcb. Yeah i love MeSquares to all you MeSquare fan boys out there. LOL

The Joy Of Oscillation, it works. 3 xtals checked, 100’s left to go.

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Lab Power Supply Final Update

Just A Bunch Of PSU Modules?

All good projects need a name don’t they? Sadly I think just a bunch of modules has been taken by Pete Juliano for one of his many radio projects. Oh well, such is life. I was thinking Buck This or Well Switched or Ebay Wonder might also do. Anyway, i have now completed the project. It has its lid on and it works. Here are the final images, a couple of them are even hi-res using the SLR and not my mobile.

Here is one of those Tribal Knowledge moments that we often hear about. This is 6 core shielded computer cable, I used it to wire up the pots. It helps keep things nice and neat.

It worked out quite ok, next time I will spend some more time measuring then cutting just to the right size.

I do not like playing with mains voltage or anything that can kill you. It is why i went for a modular option, so that when I am done there is no exposed 240v anywhere inside the case that dummy hear can touch while doing da-finger-poken inside the case. Not that the lid will come off hardly every, i just am very cautious of anything that can kill me.

Here i have started to wire up the DC power side of things. I am not all that much of a neat freak like my friend Simon 6MSC, who can make toriod winding look like an art form, but I am trying to keep things somewhat tidy.

Now we are getting into the meat of it, things are all wired up and zippy tied all over the place.

All the power is done and dusted.    

An overhead shot of the whole guts of it.

Now i do not pretend to be a metal worker. I was really happy with the bottom half of the case. But, alas i turned the top half into an abortion. First off i folded the metal on the wrong side of the line and made it to narrow so that it would not fit properly. So I had to try and fold it flat and start again. Sure i could have scrapped it and started over, but hey, why waste such a large sheet of metal. So i folded it a 2nd time, this time it fit, but one side is 5mm short. I can live with that. I know that the next time i make a case, which will not be all that far away, will be much neater now that I know what I am doing. Thanks for reading, hope you enjoyed the project.

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Lab Power Supply Update

So i got in and did a bit more work on the lab power supply. Finished off marking out and drilling every hole for every component so i do not have to go back and make a mess inside when i start to wire things up. Other than 2 tie bars across the top, the lower half of the case was done in the image below.

 

Mounted the switch mode PSU into the case, its held in with 4 M5 bolts and is not going anywhere, the fused, switched power connector and EMI filter are also bolted in with M5 bolts. The earth wire will be bolted to the case also with M5 bolts as well as serrated washers, so it cannot go anywhere. Go over the top on safety is my motto.

 

Mounted all the front panel items. From here its now just a matter of wiring up the spaghetti and making it all work together. But that will be another day, i do not think i have any wire suitable for 240v ATM and will need to go and get a meter of 3 core to pull apart for the internal wiring.

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TSSOP Soldering

I just want to say that soldering TSSOP at home packages sucks big fat balls. What a pain in the arse this has been. I spent lots of tine chasing out solder bridges. But they are done now and I guess i can start to use them. Oh and if you want to know what it is, its a compander, to be used to make an audio compressor for the uBitx, Bitx and the receiver I am building, and maybe ALC as well.

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