Simple AGC Experiments

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@philippejard5310 3 жыл бұрын

I Love the cute modules and enjoy the spirit of your projects. In the same context you could try a Gilbert cell mixer made of matched 2N3904 and compare the performances with your new Siglent SSA. There's a lot of flexibility in that mixer and it's a joy to play with a discrete one where you have access to all nodes, vary gain and modulation schemes.

@CharlieMorrisZL2CTM 3 жыл бұрын

Thanks and I'll look into that Philippe. I've used Gilbert mixers in the past, but not using discrete transistors. That could be interesting as you get the added bonus of gain!

@philippejard5310 3 жыл бұрын

@@CharlieMorrisZL2CTM yes, and spot to plug some AGC circuitry.

@richardchambless12 3 жыл бұрын

Great video. AGC is the next step for me on my home brew rigs. I will have to experiment with your opamp circuit. Thanks!

@CharlieMorrisZL2CTM 3 жыл бұрын

It works well for me Richard.

@brianharper9798 3 жыл бұрын

Very nice, even sat here at work listening on my phone that makes a huge difference especially on the srong signals. With no AGC they are a little distorted, over driven. But with it on they sounded really nice even though the small speaker on my phone.

@CharlieMorrisZL2CTM 3 жыл бұрын

Thanks Brian. It certainly works well. Best I solder it up today and put in the TX bypass.

@jerryfankhauser2959 3 жыл бұрын

Very effective and much simpler than my dual gate fet IF amplifier. I'm also adding a LM13700 transconductance audio preamplifier to increase the dynamic range, a single stage gives about 20 db control I may try 2 stages. Thanks again ! WA8HTO

@CharlieMorrisZL2CTM 3 жыл бұрын

That sounds interesting Jerry. I had greater dynamic range when i used the 1N4148 versus the 1N4001. The smaller junction area certainly helped.

@Zeus-ub2zp 3 жыл бұрын

Charlie, Please can you provide a link to that attenuator for purchase? Thank you!

@diddleize 3 жыл бұрын

Very interesting, to use a simple diode as a variable resistor. The problem is I guess it is non-linear, so in effect you have built a limiter, not an S meter which should have a logarithmic response of -6dB/S point. I am thinking that to provide a log response needs something more sophisticated like an AD8307 log detector (and them an Arduino...)?

@CharlieMorrisZL2CTM 3 жыл бұрын

Absolutely, this is just a simple gain control circuit. The meter is just there for show. Adding an AD8307 could be another upgrade IDC.

@scharkalvin 3 жыл бұрын

Amazing that a single stage agc controlled has such a good effect at a constant voltage output (after a point). But the AGC does limit the available gain quite a bit.

@CharlieMorrisZL2CTM 3 жыл бұрын

Yes it's a tradeoff. I have plenty of spare AF gain which i may look to use (not yet). I'll keep playing with it for a few days and fine tune it.

@scharkalvin 3 жыл бұрын

@@CharlieMorrisZL2CTM Using a diode to control the amount of bypass might be limiting. Perhaps an FET might give more range.

@phonix6494 2 жыл бұрын

I have a question about the dimensions of the RFC. How large should it inductance be and on what does it depend? Thanks for helping out

@willharris2100 2 жыл бұрын

Charlie, I know this is an older video, but would you mind elaborating on how/where you tapped the signal for the AGC detector? It seems like you tapped in the IF chain instead of in AF like most receivers. I'm trying to implement a simple AGC in one of my receivers, but I'm trying to decide on the best place to tap the signal and how to do it without loading down the preceding stage. I've read in Solid State Design and the W1FB Design Handbook, but just wanted to see how you did it, since those texts tend to focus more on IC amplifier chips like the MC1350. Thanks for the work that you put into these videos; they have been a tremendous resource for me.

@CharlieMorrisZL2CTM 2 жыл бұрын

Hi Will. I tapped the IF for this rig. From what I can see in the literature this is the best approach. I've also used AF, which to be fair worked well too.

@101blog 3 жыл бұрын

Hi Charlie, liking the layout and comparison with the SDR as a Panadaptor. Have you considered using the ADC/DACs on maybe a DSP32 to do all the heavy lifting including maybe filtering. You could change all the parameters of the AGC from S/W at that point!.. Keep it up

@CharlieMorrisZL2CTM 3 жыл бұрын

No not for this rig. I have made a couple of SDR rigs using the Teensy, which worked well. I'll look into though. Cheers.

@Gw0wvl 3 жыл бұрын

That's working nicely ...👍

@curtstacy779 3 жыл бұрын

For something you say is simple it sure looks like its works very well to me. I love it! This is what I thought you could use this radio for. you could have a new series and add to it as you feel the urge. The Radio Extra's hour with Charlie Morris! lol If you decide to use the Arduino for more things not only do they have I/O expansion boards but they have Analog expansion and also a true analog out. check them out. Aliexpress has the breakout boards. I'm sure Amazon does also. 16 Bit I2C ADS1115 Module. MCP4725 DAC I2C Digital to Analog Converter Module (This one is rail to rail 2.7v to 5.5v supply).

@CharlieMorrisZL2CTM 3 жыл бұрын

Thanks Curt. I'll look into those.

@bundylovess 3 жыл бұрын

Nice job Charlie big thumbs up 👍

@CharlieMorrisZL2CTM 3 жыл бұрын

Thanks Alan. Just playing around.

@acestudioscouk-Ace-G0ACE 3 жыл бұрын

Good to see and hear the progress. If you were to box it, would you move the panels closer to shorten lead length as well as physical fit...or wouldn't it make much difference given the style of construction?

@CharlieMorrisZL2CTM 3 жыл бұрын

Yes, I'd rewire the whole radio as required. I do like it open though. I like to see all the components.

@gorillaau 3 жыл бұрын

@@CharlieMorrisZL2CTM mount the boards into a pizza box style case. :) Like these videos.

@daviddavidson1372 3 жыл бұрын

Interesting stuff.great video

@CharlieMorrisZL2CTM 3 жыл бұрын

Cheers David.

@philippeversailles2170 3 жыл бұрын

Hi Charlie. You said: "Simple" ACG experiments …. In fact this is not simple at all and you have done a really very inspiring video. Thanks for that. Would it be a good idea to use a pin diode?

@CharlieMorrisZL2CTM 3 жыл бұрын

Thanks Philippe. I used a readily available 4148 vice a pin diode. Having a small junction area certainly helps in getting the widest dynamic gain out of the IF amp. I also tried a 4001 which worked ok, but not a well as the 4148. I'll have to keep playing.