#350
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- เผยแพร่เมื่อ 8 มี.ค. 2022
- Bench project - adding an AGC function to the QRP-Labs QCX CW Transceiver. We take a look at the QCX circuit to see where the AGC will be applied and review the AGC circuit itself. We take a listen to the receiver without the AGC installed, and then again after it is installed. For more information, see the links below:
QRP-Labs website - great amateur radio kits including QCX:
www.qrp-labs.com/
Here are a few of the QCX kits available:
www.qrp-labs.com/qcxp.html
www.qrp-labs.com/qcxmini.html
...and the link to the ACG module:
www.qrp-labs.com/agc.html - วิทยาศาสตร์และเทคโนโลยี
I have been interested in these little rigs for a while and just purchased a used QCX Mini 20m. Has the TCXO but not the AGC module. So, this video is exactly what I was looking for. I have learned SO much technical info from your channel and I can't thank you enough Alan. You are a class act...73!
I added an AGC Module to my QCX Mini - I set mine by ear too, which worked just fine for me. It's a nice addition. Nice explanation on its operation - thanks!!
Everything Alan does produce a positive result!
I love my QCX+ but now have reason to love it even more. Thank you Alan for the demonstration, very helpful.
Alan, really really glad you put this out! Been hoping for a take on getting it done. -John Del Ponte
Hi Alan, you saved many of those who are venturing into designing an AGC for the QRP TRX.
Well presented as always.
Thanks on behalf of the many as I don't possess one yet.
De VU2RZA
Very interesting Alan. Thanks for another super video
As usual, nicely done and well explained.
Awesome, was just looking for this recently, thanks!
Your are Great Sir, this is absolutely marvellous.
Sir, My absolute pleasure.
Thanks for the well explained vid. Seems that this nice piece of equipment even got improved a bit. Never saw a curver tracer in action before. Your equipment pool must be HUGE
The Curve Tracer is a very useful piece - sadly not really made like this anymore.
Very nice. I did a similar project on my uBITX transceiver buy adding an aftermarket AGC board.
Just the circuit I've been looking for. I'll try a DIY version for my home-brew transmitter, but seems like the initial adjustments might be very tricky.
I have a "DSW-II" CW TRX (designed by K1SWL) which doesn't have AGC and NE-602 is saturated when strong CW comes in. Thanks to informing us a good idea of AGC on AF stage. I try to find your signal all the way from near Tokyo to the very distant east coast of USA. Good DX !
Of course, an AGC on the audio stage won't help with overload of the NE-602. You would need to add some gain control (or adjustable attenuation, maybe using PIN diodes) to the the signal path before the mixer in the NE-602.
@@w2aew Thanks for advice, Mr.W2AEW. QCX has very high gain after IQ mixer. so AGC may more difficult than I think. I try to read Sch again.
Thanks.
Can you make a video on how to troubleshoot AGC circuits in transceivers and receivers because when an AGC circuit is not working correctly it gets confusing when there is a Gain Loss issues because the AGC circuit will compensate in a loop to try to make the input to the output.
Dang it, man! Your vid made me look this rig up, and now I want one. $55 for a kit version? I have a $1,000 ic7300, and rarely do anything with it that this one wouldn't do. Looks like it would make the best hiking rig ever.
Thanks for the vid.
Note that the case is extra. The QCX-Mini is probably a better choice for hiking.
I have a QCX-Mini 30M version - about the size of a deck of cards, loaded with features (and yes, now it sports the AGC module I added last week). I have used it portable for SOTA activations, and /P in general - makes for a very nice, small package. Thinking about building the 17M version with the improving conditions.
I've installed 4 of these AGC units so it was really nice to see a description of exactly how they work. How did you arrive at the bias voltage setting for your radio? I ended up just setting mine to 1V based on the curve in the manual, but if you used a more experimental method it'd be interesting to hear about.
I did it a bit more by ear using the signal generator and attenuator used in the video. I adjusted it so that S9 signals were just a bit louder than S9-10dB, and made sure that S9+10 or S9+20 weren't too distorted (pops).
@@w2aew I should probably go through and do the same thing, now that I have the equipment to do so. At 1V the AGC "feels" very aggressive.
@@jburchm1 Next time I open up the rig, I'll measure the pre-bias voltage to see where it is. However, I suspect that a given bias voltage will give different results in different rigs due to the variation of MOSFET characteristics.
Would you please make a video on via shielding on PCBs?
nice vid and nice model, i always assumed that agc would be applied with j fet never thought a nmos would be a subtitute due to limited ohmic variance unless this is a new mosfet i dont know of, if i had to guess i would assume its n7002
The circuits uses a 2N7002. The device I showed on the curve tracer was a 2N7000.
could u make a short video about peak detectors using diodes alone and using them combined with op amps, thanks in advance
@@bumohamedubualooy7111 I did, many years ago. Have you seen this? th-cam.com/video/Fn5kHhNRsz0/w-d-xo.html
how do I become as acknowledgeable as you are. I'm an entry level RF engineer and struggle with these concepts
All it takes is a fair amount of experimenting, testing, designing, failing, succeeding, and experience. I've been playing with electronics for well over 45 yrs, and for nearly the last 40yrs of that professionally. There is still a LOT that I don't know - I learn something new nearly everyday. Don't get discouraged...
👍🙏👍
Very nice receiver if it only did more than one band.
Please do a show on QCX+ firmware update using both the ardrundo and other methods. There is not very much on that on TH-cam
Thanks for the video, this is exactly what I need. I didn’t know they were available Mike G4VQH
Nice job Alan, what kind of wire are you using? Is that wire wrap wire?
Yep - love using wire wrap wire for this - the insulation is very temperature resistant, and it is good quality wire, easy to solder.
Quadrature stuff is hard for me to understand. Do you have any videos on that topic?
Check out videos #170 and #171 on my channel.
@@w2aew thank you! And thank you for making these videos for us
@@w2aew I just never understand how phase modulation can work, how can a receiver detect a difference in phase - I guess you have to use a PLL of some sort?
@@researchandbuild1751 A PLL is one way. Another is to use a mixer along with an unmodulated signal at the same freq as the LO- then the output of the mixer will be the phase changes.
Why not attenuate the rf signal entering the front-end?
Does the front-end cope with so strong signals without saturating? If yes, how is that possible? How large is its dynamic range?
There are a lot of ways to implement gain control, this is the one that this designer chose. There is no front-end preamp in this design. The RF goes directly into the Tayloe quadrature sampling detector, which is nothing more than a dual 4:1 bilateral switch (MUX/DMUX), so it has a very large dynamic range. The output of the QSD goes into an audio grade op amp. I haven't tested the overall dynamic range, but 20dB over S9 is still well within the operating range.
Is there a way to have a higher gain on an anytone at6666? It's awful quiet.
Sorry - I don't know anything about the AT6666. Is it quiet because it has a very low noise receiver (a good thing), or is it quiet because its sensitivity is poor (a bad thing). It would have be tested to be sure.
Has anyone tried this on the new QMX? I’m wondering if it’ll fit with all the new components they packed in there.
I and Q aside, do you think the Tayloe mixer is superior to, say, a diode ring mixer, like a mini circuits SBL or whatever? I was building a 6 meter xvrter, and kinda can't make up my mind. W3IHM
Does the qcx + have same display size as the mini ?
They're both 16x2, and according the the website "...the LCD is the same size and style as the original QCX/QCX+ kits", although the Mini is yellow/green while the + is blue backlit.
Why wouldn't you use small FET directly on antenna input ?
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De VU2RZA
- the goal is to control the audio.
- it's easier to work with audio
- it would raise the noise floor.
- it would screw up antenna match.
- it's a transceiver you'd have to get it out of the circuit on xmit.
@@anullhandle But by controlling just audio you don't solve problem of saturating previous stages.
Antenna match shouldn't be an issue for a receiver when signal is unpleasantly high. In other situations all that you'd have is a small capacitance of a closed small MOSFET, which could be compensated for, if it would even be needed.
When MOSFET is closed ( which would be in any normal situation), noise also shouldn't be a concern.
First thing after the antenna is a Rx/Tx switch. So he could have placed right after the switch on the RX side.
Or, he could have it antenna and simply keep it closed during Tx.
@@brane2379 I didn't catch him say he had a saturation problem. If a front end is getting hammered it's either stepping on your desired signal and oh well or its off frequency and you'd want a filter that doesn't compromise your desired signal.
My fear is to mess up...
You
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