?

I am looking for the original wire up instructions for the $59 bitx40 kit - I had an issue with mine part way through upgrading, and have gone back to start up (reflashed the arduino sketch) and need the original wiring instructions which I can no longer find on the hfsigs site. Then I will start to modify again!

Amazon has stainless metric screw assortments for under $10.


m73
Mark

btw already integrated the mounting points for this brace in my 3d printable sbitx case. Will upload it tomorrow!


--
AJ6CU/7
KD8CEC 2.0, Nextion Screens,? and open source uBITX Raduino boards for Arduino IOT, BLE, RP2040, Teensy 4.0, and Raspberry Pi Pico

would this help?

On Mon, Jan 22, 2024 at 4:36?PM AndyH <awhecker@...> wrote:

Probably, Raj.? Ultimately I'm trying to understand how to implement Farhan's mod.?

Since I don't yet know how to create the emitter follower he described, I'll go back to applying fiberglass to the bottom of my boat.?

Thanks, Andy

On Mon, Jan 22, 2024 at 12:22 AM, Raj vu2zap wrote:

Andy,

You are talking about a hard to get audio transformer!

Raj

On 22/01/2024 8:21 AM, AndyH wrote:

Could this be fixed with a 9T:2T transformer between C63 and the mixer pad, and rebiasing Q6 for a gain of 2-3?

And/or, could someone flesh out the emitter follower and specify which parts from the emitter of Q6 should be removed? (Just C62 and R64?)

? ?Thanks!
? ? ?73, Andy, KG5RKP/MM

On Sat, Jul 15, 2023 at 09:18 PM, Ashhar Farhan wrote:

Thanks for the analysis. There are two other significanr issues with the current mic amplifier.

1. The output impedance is 1000 ohms, the modulator needs a 50 ohms drive.

2. The gain is not less but too much. The electrer mic produces about 50mV of audio, the modulatoe needs less than 150mv drive. A gain of two or three is more than sufficient. The apparent loss is due to the mismatch between the 1000 ohm output and the needed 50 ohms drive.

These can be solved by adding an emitter follower with a 47 ohms resistor in series with the output of the emitter follower and removing the emitter bypass of the original mic amplifier.

- f

On Sun, Jul 16, 2023, 7:22 AM Dan Damon <dan.g.damon@...> wrote:

I've been working on the uBitx audio circuit for a while now and I think I've discovered a problem that I've never seen anyone mention before. If anyone has experience with this circuit, please review and let me know if I've missed anything. Here are my notes:

?

?Audio Amp notes.

?

The uBitx has always had challenges with the audio amp. It has insufficient gain for the condenser mic that is provided. Solutions include:

?

a. Use a mic with an amplifier built in.

b. Add an additional amplification stage such as the SSM2167.

c. Increase the mic circuit gain.

?

Mic amplifier circuit with suggested modifications. Also showing the load of the following stage.

?

SEE ATTACHED FILE

?

Analysis:

Given that the receive transistor Q70 is connected directly to the output of the microphone amplifier, the output of the mic amp must be less than 0.6v. We’ll say 550 mV to give us a bit of safety margin.

The input drive required to achieve 550mV out of the mic amp is 200mV. Most have claimed that the mic amp has a gain of around 20 due to the collector resistance of 1k divided by the emitter resistance of 47 ohms. This simple analysis is incorrect because it neglects the load impedance of the mixer circuit. Spice analysis and actual observation shows the actual gain to be about 2x or 3x.

A big problem with this mic amplifier is that it is incorrectly biased. With the originally specified bias resistor R61 set at 2.2k, the transistor runs out of emitter current at about 160mV of output voltage. In addition to limiting output, this causes distortion of the audio waveform. By increasing R61 to 10k, the circuit can easily output the 550 mV (1.1V P-P) originally suggested.

In my own uBitx, I have chosen to use the SSM2167 as a preamp in order to enjoy some voice compression. However, the simplest solution is to decrease R63 to 10 to 22 ohms. I’d advise not to go lower than 10 ohms, since that circuit should fully drive the mixer with a mic output of only 40 mV. But before doing anything else, increase R61 to 10K.

?

?

would this help?

On Mon, Jan 22, 2024 at 4:36?PM AndyH <awhecker@...> wrote:

Probably, Raj.? Ultimately I'm trying to understand how to implement Farhan's mod.?

Since I don't yet know how to create the emitter follower he described, I'll go back to applying fiberglass to the bottom of my boat.?

Thanks, Andy

On Mon, Jan 22, 2024 at 12:22 AM, Raj vu2zap wrote:

Andy,

You are talking about a hard to get audio transformer!

Raj

On 22/01/2024 8:21 AM, AndyH wrote:

Could this be fixed with a 9T:2T transformer between C63 and the mixer pad, and rebiasing Q6 for a gain of 2-3?

And/or, could someone flesh out the emitter follower and specify which parts from the emitter of Q6 should be removed? (Just C62 and R64?)

? ?Thanks!
? ? ?73, Andy, KG5RKP/MM

On Sat, Jul 15, 2023 at 09:18 PM, Ashhar Farhan wrote:

Thanks for the analysis. There are two other significanr issues with the current mic amplifier.

1. The output impedance is 1000 ohms, the modulator needs a 50 ohms drive.

2. The gain is not less but too much. The electrer mic produces about 50mV of audio, the modulatoe needs less than 150mv drive. A gain of two or three is more than sufficient. The apparent loss is due to the mismatch between the 1000 ohm output and the needed 50 ohms drive.

These can be solved by adding an emitter follower with a 47 ohms resistor in series with the output of the emitter follower and removing the emitter bypass of the original mic amplifier.

- f

On Sun, Jul 16, 2023, 7:22 AM Dan Damon <dan.g.damon@...> wrote:

I've been working on the uBitx audio circuit for a while now and I think I've discovered a problem that I've never seen anyone mention before. If anyone has experience with this circuit, please review and let me know if I've missed anything. Here are my notes:

?

?Audio Amp notes.

?

The uBitx has always had challenges with the audio amp. It has insufficient gain for the condenser mic that is provided. Solutions include:

?

a. Use a mic with an amplifier built in.

b. Add an additional amplification stage such as the SSM2167.

c. Increase the mic circuit gain.

?

Mic amplifier circuit with suggested modifications. Also showing the load of the following stage.

?

SEE ATTACHED FILE

?

Analysis:

Given that the receive transistor Q70 is connected directly to the output of the microphone amplifier, the output of the mic amp must be less than 0.6v. We’ll say 550 mV to give us a bit of safety margin.

The input drive required to achieve 550mV out of the mic amp is 200mV. Most have claimed that the mic amp has a gain of around 20 due to the collector resistance of 1k divided by the emitter resistance of 47 ohms. This simple analysis is incorrect because it neglects the load impedance of the mixer circuit. Spice analysis and actual observation shows the actual gain to be about 2x or 3x.

A big problem with this mic amplifier is that it is incorrectly biased. With the originally specified bias resistor R61 set at 2.2k, the transistor runs out of emitter current at about 160mV of output voltage. In addition to limiting output, this causes distortion of the audio waveform. By increasing R61 to 10k, the circuit can easily output the 550 mV (1.1V P-P) originally suggested.

In my own uBitx, I have chosen to use the SSM2167 as a preamp in order to enjoy some voice compression. However, the simplest solution is to decrease R63 to 10 to 22 ohms. I’d advise not to go lower than 10 ohms, since that circuit should fully drive the mixer with a mic output of only 40 mV. But before doing anything else, increase R61 to 10K.

?

?

Thanks Bob!? I have been using any number of things to tilt my sBitx and should have thought of this.? I fired up a 3D printer after lunch and voila!? Fits like a glove and just what I needed.

73, Mike
KD4MM

Hi Evan,

I really do appreciate the advice and reasons that you have stated. Since I really like rtty/bpsk style modes as well as cw, I will most likely go for the sbitx model. Also, if modification is needed to bring the ubitx up to what I want, then I am best to start out with the sbitx. I do enjoy ssb from time to time too though. When on a limited radio equipment budget, planning is needed. Not sure of the portable antenna yet, but it will most likely be no larger than a 20 meter inverted vee so that it will fit in a camp site with our pull behind camper at state parks. I might try making it multiband with a tuner and twin lead cable.
Many thanks, 73

Scotty