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I see the Kit Projects AGC boards are no longer available from Kit Projects. Does anyone have one sitting around they are not going to use.

Please reply to me at djwilcox01 at gmail dot com.

Thank you.

Dave K8WPE

David J. Wilcox’s iPad

I too would like to buy an AGC board for ubitx6.

Could this work for you?

Joel
N6ALT

They made these open sourced so you can download the gerber files and have them made. I ordered 5 pcb boards?
from Jlcpcb but I didn't know that they would populate the boards too and I'm not sure how that works on there website.
Maybe someone that has ordered from Jlcpcb before will chime in about it. You could get a group of people together
and make an order(I think there's a minimum quantity of like 5).

When I ordered just the pcb I didn't realize how tiny they are and how difficult it would be to put the components on.
It's all smd and my eyesight and not so steady hands have a little trouble with the tiny parts.
This is a link to the files?/g/BITX20/files/Kit-Projects

73's
Dave

Can someone compare the Kit Projects AGC board with other AGC mods, such as
the TIA-AGC (suggested by N6ALT, several posts earlier in this thread), or
the VK3YE LED/LDR AVC/Audio Limiter (or the adaptation by K4LXY)?

I was leaning toward the last of those, because of its simplicity. But I'm open to other options on my uBiitxV6.

Thanks!

Hi DaveW,

I have done three different AGC mods to different uBiTx versions.??
1 - The Kit Projects AGC
2 - The AmateurRadioKits.in AGC included with the v5 Nextion display case kit
3 - The VK3YE as describe by Curt Milton WB8YYY with modifications

Of the three, I liked the VK3YE the best for operation and ease of build.? Here is the way that I built it (I used LTSpice as a schematic editor):



The key with the LED AGC is to select the correct LDR.? You need one that can get down to 1kOhms when fully illuminated by the LED.? The LED did not seem to impact the results much, as did the LDR.

I built it on a perf board with pads connecting a female DuPont connector.? This could then plug into the Audio connector on the uBiTx mainboard.? I also mounted R3 on the front panel to allow for AGC adjustment.

The next best was the Kit Projects, with the least favorite being the AmateurRadioKits AGC.? I have not done the TIA-AGC, though it does look interesting.

I have found that the RF or IF-based AGC seems to impact the receiver sensitivity or is not as capable of reducing very large signals.? Since these were for others, I have little on-air operating use to define differences further.? The information is from my testing.

73
Evan
AC9TU

You could replace the Light Tube with a H11F1 opto-coupled FET...Full on-state resistance is 470 ohms and off-state resistance is very high...Jim WB2LHP

On Sat, Nov 11, 2023 at 11:15 AM, Dave K0DLP wrote:

They made these open sourced so you can download the gerber files and have them made. I ordered 5 pcb boards?
from Jlcpcb but I didn't know that they would populate the boards too and I'm not sure how that works on there website.
Maybe someone that has ordered from Jlcpcb before will chime in about it. You could get a group of people together
and make an order(I think there's a minimum quantity of like 5).

When I ordered just the pcb I didn't realize how tiny they are and how difficult it would be to put the components on.
It's all smd and my eyesight and not so steady hands have a little trouble with the tiny parts.
This is a link to the files?/g/BITX20/files/Kit-Projects

73's
Dave

I've not done it on my own from scratch, but just had some boards made by JLC with gerbers, etc provided by another individual where they did also install some smd parts for me. The additional pricing is amazingly minimal..I was prepared for a bit of sticker shock, but not the case. There is a bit of work to create what's called the BOM file (using LCSC part designators) and a centroid file, that guides placement. It can be done in most tools, Kicad, etc., the guide here gives some additional insight using Kicad, which is usually my tool of choice: https://jlcpcb.com/help/article/81-How-to-generate-the-BOM-and-Centroid-file-from-KiCAD

I ordered a couple of these to use in VK3YE's AGC, ? but never got around to building the circuit. They would take the place of the LDR and LED and make for a nice small package.

Joel
N6ALT

Hi Joel,

I ordered a similar part and tested the operation with a controlled power source and ohm meter to measure the output.? It was very non-linear, which would be OK, except it was either on or off with a tiny band between.? ?I do not know if this part is similar.

Any of the packaged LED/LDR devices could work in theory.? I have had good results with only the separate LED/LDR.? This combination seems to have the best attack/decay response.? This could be adjusted in the circuit components.? I have not tried that.

73
Evan
AC9TU

Evan,
Your comparison of various AVC circuits is very helpful.
I'll stick with the VK3YE version (or some similar variation).

In the circuit diagram that you provided, the sampling point is nearly at volume control high. (TP21 is on the other side of a 1K resistor). It seems like placing the LDR between volume control high and ground would produce a lot of interaction between the input and output of the AGC. Other diagrams? show the LDR connected to the volume control center. In either case, the rest of the circuit remains the same. A little experimentation should reveal the best placement (which may depend on the LDR characteristics).

Thank you.

Hi DaveW,

The original design had the input connected to a resistor upstream of the volume control.? TP21 was the best point that I could find without modifying the board.? My thought was to keep the signal at the top of the volume control constant to reduce the volume control interaction with the AGC.? I have seen the connection that you are proposing.? It is not that difficult to set up a jumper on the perf board to select either TP21 or the MID value of the volume control.

73
Evan
AC9TU

Evan,

I hooked up one of my Vactrols and made some measurements, I found it to be quite linear, (I think). Without the LED on it shows 24Meg, with the LED fully driven at 15ma it shows 95 ohms. I can steadily bleed the voltage off of the LED and the resistance changes at a smooth linear rate. I think this would work very well with VK3YE's AGC circuit. I think I will build it and try it out on my V6.

Joel
N6ALT