Corona Virus Update

Corona virus, whats it mean to me and my home brewing? That is an interesting question and one i am asking myself daily. Sure it looks like I might have more time on my hands with the chance of being locked down growing daily. So that is the positive. The negative is I am also watching the economy tanking and along with it my income. I am a contractor, our clients are all pulling work so that means I will not be earning much at all. This is ok, I have some savings and will survive, but it means that I will lock down my budget to essentials and so I cannot see me starting any new projects for quite sometime.

However, I do have 4 or 5 projects already going on at various levels of progress, so i have plenty to do for now and I have a lot of parts so that is not going to be an issue. I think what will happen is that once i have worked through the projects in the cue, I will end up going back to doing manhattan builds with through hole parts. I have a lot of board and parts, so I am good for a couple years at least. About all it will really mean is that I wont be buying any fancy PCBs at all.

Oh and I have a lot of kits here also, so I can bring them out when things get desperate and have something to build. All in all, i will be ok, but if things get really tight, I might have to shut down my blog, or move back to cheaper VPS hosting rather than having dedicated server hosting. One stupid flu and the world is turning to shit.

Stay classy everyone.

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Its Working Again :)

So I pulled everything off the shelf to give this a test. Its working. What I have done in the pictures below was to use an DDS vfo as the incoming 7mhz signal. It run into as much attentuator as I have here, giving a final signal out of about -95dbm or there abouts according to the spec-an. This number is rather uncertain because that is right on the noise floor of the device and by my calculations, the actual signal is closer to -100dbm. Now I am still hearing a signal out of the speaker at that level. So its not an Icom, but its not totally deaf either. I do think i could use a little more gain in the audio stages. But, we will see how things pan out with some loudish signals on 40m this afternoon.

The receiver setup with the attenuators.
DDS VFO used as the signal source.
Function Generator being used as the VFO and BFO.

 

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Open Heart Surgery

 

Its still not working, but it is getting there. All be it, slowly. So i fixed the oscillation in the PA, replaced the fet and now at least the PA is all working as it should be. Now I am still not getting anything out of the Mic. Not sure what is going on there, but there is power and it worked when i bread-boarded it. Obviously something is not right, but I will work that out soon enough.

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Measuring Gain Bandwidth With NanoVNA

The NanoVNA is more than just a fancy SWR meter for checking your antenna. Its much more and a very useful tool for the home brewer building amps and filters and the like. Now i have been buying things like crazy for various projects that I would like to build in the future. Often these parts are spec’ed for bands not of interest to me. So what do you do? Well you measure them at the frequency of interest and see how they work yourself.

Below is a MMIC amplifier part that I found for really cheap. By cheap I am talking in the 40 cents per range, so i bought 100 of them. I mean why not, they are spec’ed for 100mhz to 3gig with +30db of gain. Worst case senario they are kind of useless at HF and I will have parts for when I actually want to build things at VHF and up.

So anyway I had a test board built with 4 different circuits on it for testing out various parts I have here and it includes Op Amp, Mosfet and BJT amp circuits. So i decided to start with the MMIC and see what it can do.

The good thing about MMIC gain blocks is the fact that they have such a low parts count. 2 blocking caps an inductor, bypass cap and gain setting resistor. Initially i set the bias resistor a little to high and was getting a lot of distortion, so I halved the value and boom it was providing 24dB of gain at 7MHz, which is my go to frequency for all these sorts of tests. Next though, I wanted to see how the gain bandwidth was. My bandwidth of interest is HF so 3 to 30MHz, so just for shits and giggles I measures it out to the 6m band.

The test setup was Port 1 of the NanoVNA to the input of the test board, the output of the test board to the RF Sampler i made the other day, which was also connected to a dummyload and then back to Port 2 of the VNA. Then an sweep of was performed and the S21 Gain was measured.

Things actually looked quite nice and rather flat. A few dB down at 80m and 1 dB down at 6m. That is pretty good for a part with a minimum frequency of 100MHz. So all in all, this part is a winner and something I can use in a project sometime soon.

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