I converted a power supply so that it now has a panel voltmeter and installed a voltage control on the front panel. Now when I need to adjust RF output a bit lower I can drop it quickly by lowering th

Replace 1 resistor. 470 ohms is a good choice. Saves a bit of current, makes the display last longer, less heat. Here's the link to how and where: http://www.nd6t.com/bitx/Backlight dimming I do this

I placed mine right at the output (wiper) of the volume control. I built mine from an LM380. I also placed a switchable 200 Hz wide CW filter between that point and my new audio amp. A throw of a togg

Hi Digger, Often the simplest of things are revealed as complex. As Jerry says, the delays are important. The values used allows the attenuation to smoothly increase and track the signal level variati

Daniel, check the voltage at the junction of C1, R3, and the gate of Q1 and Q3 when the PTT is active. That should be near zero. Q3 is the receive audio gate and should be open when transmitting. If t

#ubitx-help #ubitx

I have had 2 of the original volume controls with similar problems. The contact pin rivets had intermittent connections to the resistance substrate. They were going open. I changed to 10K audio taper

Pat, Just wire the PA power to the switch in addition to the rest of the radio. It was intended as a means to supply the RF power amplifier with a higher voltage if desired. That also makes it easier

Jim, Why a separate AM detector? When the reference oscillator is calibrated then you just tune to the carrier frequency and it is zero beat. I've been listening to broadcast on the BITX since I first

Hi Daimon, I would suggest that you switch it out. With FT8 you will have several signals present within the pass band, some quite strong, others below the noise. Any strong signals that reduce your g

Curt, Just to make sure, I opened up my uBIITX and checked voltages. With a 50 uV (S9, -73 dBm) there was about 1 to 2 millivolts RMS on the top of my volume control. But with 1,000 uV (about S9+27, -

I'm just sorry to hear that it isn't working for you. From your description it all seems correct. It would be nice if there was some substantial signal that you could tune to, something steady and str

What is the voltage on the base of Q1? What signal source are you using when you see no voltage output? Are you measuring at the junction of C3, R3, the cathode of D2, and the gate of Q2 to ground? Di

The discharge resistance is provided in the AGC circuits in the form of the AGC hold time resistors (R6 through 9 in the kit, R6 in the hand-made version). My concern is the analog reading method sinc

Peter, Here are the levels that I experienced: S3(.8 uV ,-110 dBm): 50 S9(50 uV, -73 dBm): 170 S9+20 (500 uV., -53 dBm); 300 S9+40 (5 mV, -33 dBm): 700 and S9+50(15.8 mV, -23 dBm); 800 Those values we

On one of mine it was the stock volume control. One end of the substrate seemed to have a bad connection with the pin. Swapped it out and it solved the problem. 73, Don

Try a 1458 instead. It has the same pin-out and is drop-in compatible with a much higher output capacity. I mention this since it appears that you are feeding a lower impedance than what it is capable

Sorry, I should have also included the place where the receive path is tapped on the BITX40. It is on a separate page here.

Yes, it works just as well on the BITX40. Instructions can be found on ND6T.com here.

I agree with you about getting the 5 volts from the 7805. It only pulls a couple of milliamperes and won't be noticed. That switching power supply, on the other hand, is a known noise source. A great

The AGC is a simple wide band attenuator, When properly powered and with a short across J1 there should be only about 0.6 dB attenuation (barely measurable). No artifacts. Check your wiring and your v