Andy,
If your problem is microphone audio quality on transmit from uBitx V6 (and other versions), there has been a lot of forum discussion about using different microphones, or improving the microphone supplied with the radio.

I think some radios were supplied with Baofeng microphones, which had low quality electret mic elements. Audio was sometimes improved by finding a better quality compatible mic element.??

My uBitxV6 came with a different microphone. The internal circuit board is labeled "hamshack.in". The transmit audio was reported as very poor. I confirmed this by hooking the mic to my computer mic input through a simple circuit which provided dc bias to the electret mic, I recorded the audio as I spoke, then played it back. (The computer didn't supply proper bias.) In any case, the audio was muffled and nearly unintelligible.

I had a couple of used electret mic elements (quality and specs. unknown) in my junk box. I installed them, one at a time, and tested with similar results. But I noticed that, if tested outside of the microphone housing, all three mic elements had reasonably good audio. Apparently, there were echoes inside the hollow case. The fix was to add some soft foam padding inside the case (filling the lower case, with a thinner layer behind the holes on the case front, to cover the mic element, circuit board, and space in the upper case). I saw another forum thread where someone stuffed the case with cotton. The improvement was remarkable... and did not require any modification to the radio.

Also note that transmit audio can also be poor, if the BFO calibration is not right.

Simple bias circuit (for testing mic element with computer):? Use a 9 volt battery. Connect negative lead to ground side of mic element. Connect positive lead through a 10K resistor to the positive side of the mic element. Also connect a 10 ufd capacitor (+ side) to the positive side of the mic element. (These exact resistor and capacitor values are not required. Use the closest that you have). Bias circuit is complete. Connect to computer: Negative side of mic (and battery)? to ground of mic plug; Negative side of capacitor to mic input terminal of mic plug.

There emitter follower's base can directly couple to the original's collector.

- f

On Mon, Feb 5, 2024, 10:18 AM AndyH <awhecker@...> wrote:

Farhan,

? ?Would you sanity check this, please? It's the uBITX V6 mic amp through C63 with a buffer pulled from Eamon Skelton's book.? Did I translate your suggestion accurately?

? ? Thanks and 73,
? ? ?Andy



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.

?

?

?

?

Ok I'm gonna be a little bit brutally honest here about my experience with a EFHW.?
I got a MFJ-1982LP a 135' EFHW. I strung that up through my (purely evil) Pecan tree. The 49:1 Balun was attached to the eve of my house at around 9 feet high. The counterpoise/ ground wire was attached to an 8 foot ground rod that was installed for just this purpose. The middle of the antenna was in the tree at 37 feet off the ground (I measured the height) and ended at another pecan tree in the back yard. It is like my back yard was measured to fit a 80 meter dipole in, it is 140 feet from my house to my back fence. Through a weird quirk of planning my back yard is the biggest in the neighborhood. The end was held in place by a small weight that allowed the antenna flex with the movement of the trees. I gave it about 10 feet of movement. That was my first mistake. I live in Oklahoma City and it was spring time. That antenna lasted for 3 weeks until it snapped. MFJ honored their warranty and soon I got another antenna. They were out of the LP (Low Power) model so they sent me a MP (Medium Power) instead. Bigger balun, same 26 gauge wire. Instead of running it over the tree limbs, I got my trusty pneumatic? antenna launcher and launched a rope over the limb and pulled a pulley up to the limb and had the wire go through the pulley (Note: My first attempt with the antenna launcher was a little off on the aim and instead of the little projectile going over the limb it hit the limb dead on and pretty much vaporized it and the loud boom echoed through the neighborhood and i got a special visit from Officer Butler, Officer Butler thought it was funny but due to safety I will no longer use the antenna launcher in town. Now I use it for launching my fishing hook way out to the middle of the lake). Second antenna I made sure that it had plenty of room for movement. This time it lasted for three months before it snapped. Told MFJ about it and said that i didn't want a replacement but I am not impressed with their choice of wire. So they sent me the HP version (High Power) much larger balun, same 26 gauge wire. This time to keep it from breaking I had it stapled to the eve of my house. Now I think that it could work ok, but it really needs to be tuned and I can't do that because I can't get on a ladder. I would like to get some wire with a higher breaking point and try that.?
For my buddy I made him a 49:1 balun using a FT82-43 toroid and he has made a different wire cut for each band and he likes it a lot.?
I have been looking at making a cobbweb antenna but again my physical limitations and very small budget prevents me. So for now I have a 20 meter inverted V and it is working better than no antenna.?
--
'72