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Strong signals are way too loud with headphones.? What is the best way to deal with this?

The problem is mainly with high power stations chatting about their amps and beams.? Some powerful signals are breaking up so as to be unintelligible.

I have done the c113 cap delete and the c102 capacitance reduction to 28 pF, that may have something to do with it.? However, I also had issues before I did the c102 mod.

From Ashhar's post 18062:"The capacitor between pins 1 and 8 of the LM386 can be removed if you prefer headphones to speakers."

Check the LM386 datasheet if you want further info on this. Though I'd think if it were just an issue with audio gain, that could be cured by twiddling the volume control. ?Perhaps you need an RF gain pot going into that first RX amp at Q1.

Jerry, KE7ER

Also check out Ashhar's AGC circuit here:

???

Discussed in the thread around post 18986

A switch between R15 and R16 will act like a 20 dB attenuator. Or insert a 10 K variable resistor there for continuous control from zero to 17 dB.

-Don, ND6T

No. A rheostat (variable resistor) from R15 to R16. Check the BITX Hacks blog.

Lift the end of R15 that connects to C14 and insert the rheostat. Or the switch. The idea is to reduce or eliminate power to the first? RX RF stage (Q1) to reduce gain.

Grounding it would release the magic smoke, wouldn't it?

-ND6T

Don's got a very nice trick there, and I plan to use it. ?But I needed clarification as well. ?Cutting power to an amp entirely is a rather unusual way to reduce gain.

> A switch between R15 and R16 will act like a 20 dB attenuator. Or insert a 10 K variable resistor there for continuous control from zero to 17 dB.

I replaced R15 (10 ohms) with a 100 ohm resistor, but it is still loud.? I will open it up tomorrow and check my work, see if there is a solder bridge or something.

Then I will do this:

Yes, the bithacks blog explains it fairly well.

Q1 gets powered from 12v through the 10 ohm R15 and the 220 ohm R16, a total of 230 ohms.

Now that you have replaced R15 with 100 ohms, that figure is 100+220 = 320 ohms, which might reduce the gain of Q1 a little bit but likely won't be noticeable.

Here's Don's original post:

??A switch between R15 and R16 will act like a 20 dB attenuator. Or insert a 10 K variable resistor there for continuous control from zero to 17 dB.

So if you remove R16 entirely (or put a switch in series with R16) so Q1 gets no power, you will still get enough signal through the Q1 stage to hear stations but they will be reduced by 20 dB. ?Being able to select between 0 attenuation and 20 db of attenuation might be all you really need

Alternately, you can replace the 220 ohms at R16 with the series combination of the original 220 ohms plus a 10k pot stolen from an old transistor radio volume control. ?Then RF gain will be continuously variable from what it is now to something 17 dB down from that. ?Facing the front of the pot with the pins pointing down, I'd tie the center pin of the pot to the left side pin, and use that as one node into the pot, and of course the free pin of the pot is the other node, ?That way fully counter-clockwise rotation is maximum resistance (10k) and minimum volume.

Reducing RF gain up front like this will keep the first stages of the receiver (the Q1 ?and Q2 amps and the diode ring mixer) from being overloaded by nearby stations. ?Once we get through the crystal filter, all those other stations will be filtered out and no longer a threat. ?

Another AGC idea. ?

Uses an LED & LDR. ?Louder signals brighten the LED which reduces the LDR's value which reduces the volume, so compressing the audio.?

https://www.youtube.com/watch?v=IQ5JEPRiPoM

R15 serves as part of the stage supply filtering. I would leave it. If you want to remove R16 then be sure to install a 220 ohm resistor in series with the switch or control. That will limit the current. A switch works very well, don't discount the simplicity and utility.

I would recommend that you only do this at this one stage. The others need to provide the proper terminations to the crystal filter. -ND6T

Using a pot between antenna and ground, center wiper into the receiver, seems the most obvious thing. ?The ideal place for such an RF gain control would be in the wire between K2-14 and K1-12, an attenuator there will only affect the receiver. ?Pot should have short wires to it, or use coax.

Should also work fine to put a 1k pot in front of C11, as output of the transmit amp at Q4 would then only see 1k to ground regardless of the position of the RF gain control. ?Also, that node is free floating with DC blocking caps in all directions. ?But can't be on the Q1 side of C11, as that would muck with the DC bias into the base of Q1. ? ?

What's the best way to do AGC here, such that it affects the RF gain and not AF gain?

Does Don's trick of cutting power to Q1 make that first RX amp go non-linear, and introduce crud into the received signal?

Send an email to hfsignals at gmail dot com stating you're an old customer and would like the Raduino upgrade..

Do it now, they were offering the upgrade to old customers for $14, but seems they were cutting it off right about today.

I'm sure it works well enough. ?My concern is that the diode ring mixer is non-linear, but normally only the 40m signals from the antenna get passed on to the 12mhz crystal filter because the bandpass filter up front strips out everything except 40 meters. ?Now if Q1 goes non-linear, we've got all those 40m harmonics plus all the vfo harmonics mixing together, likely producing a few birdies. ?(That's just as true for those of you with carefully groomed sine waves out of the VFO, cuz the action of the mixer is very not linear.)