I would like to add the audio AGC circuit from Peter VK3YE to my BITX40 (see ) but am wondering about exactly how to integrate it into the current version of the SMD BITX40v3. On Peter's schematic, I assume that the amp block shown at the "receiver audio in" is actually Q16. The 3.3K resistor in Peter's circuit doesn't exist in the BITX40 and I assume that it would have to be added between C115 and the high side of the volume control. The input to Peter's circuit would then come from the C115 end of the 3.3K resistor and the LDR would be placed across the volume control. The easy way to install the 3.3K resistor would be to lift the red wire from the volume control and install the resistor between the wire and volume control terminal.

Am I correct in my "assumptions" or did I miss something? His LDR version of an audio AGC looks like it really works well and would make a good addition to the BITX40.?? 73, AL - VE3RRD

OM Vu2RJW

Please let me know if its effective on Farhan's bitx 40

Also did you take audio in from Pin 1 (Red wire )of volume pot by connecting it directly to AGC and? audio out to Pin 1 of Volume pot

Thanks

73

Gaurav

After building several AGC circuits on solderless breadboards and tweaking each one for performance I settled on the VK3YE circuit and I am very happy with the way it performs. My Bitx is scratch built but the audio stage follows the Bitx40V3 schematic very closely.?

It seemed like the AGC circuit was loading the audio coming from the pre-amp a bit so I added a resistor in series with the AGC amp - 33K if I remember correctly. I also tuned the resistor that is in series with the LDR. My LDR has a resistance of about 1K when the LED is operating at 20ma.?

There are a lot of different LDRs out there with different characteristics. I used one that I got from Tayda and I used their super bright red LED with it. I tried a different LED that was a little better matched in wavelength (650nm) to the LDR but I went back to the super bright. I can provide part numbers if you like.?

I have just finished building the VK3YE LED-LDR AGC circuit, for an MST-Mk1 (not BiTx40), but a similar rig. ?Write-up and demo video here:?

W0PWE>?It seemed like the AGC circuit was loading the audio coming from the pre-amp a bit so I added a resistor in series with the AGC amp - 33K if I remember correctly. I also tuned the resistor that is in series with the LDR.

I noticed the same thing... connecting the LDR directly to the top of the audio gain control dropped the audio level noticeably with no signal present, so I also added a series resistor, but only about 2k2.

I used a high intensity white LED and a 4k-40k LDR, links in the blog post. ?I'm pleased with this circuit and will use it again. ?

73 from Paul VK3HN.?

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I used a high intensity white LED and a 4k-40k LDR, links in the blog post. ?I'm pleased with this circuit and will use it again.?

Nice write up Paul. I am very happy with the VK3YE AGC. It provides just the right amount of AGC action for my tastes and after many hours of operating with it in all kinds of band conditions I have not heard it do anything annoying. I put a switch in series with the LDR so I can turn the AGC off but it is always on.

I built my rig from scratch in a modular fashion and that audio board with Peter's AGC will surely get reproduced and used in my future projects.

Your white LED probably works as well or even better than the red one I used. The LED and LDR I used are:

http://www.taydaelectronics.com/led-5mm-red-water-clear-ultra-bright.html

73 - Jerry W0PWE