T&L Publications

It sounds like at least one of the amplifiers was an old piece of equipment, with a two wire line cord. New equipment should have a three wire cord with any exposed metal connected to the safety ground (green wire) and should not be a shock hazard. Old equipment (possibly referred to as "vintag...

The AD8210 looks like it is a good device to use. Switchboard shunts are usually calibrated for either 50 mV or 100 mV at full scale current. A 100 mV shunt would produce 200 mV peak to peak (depending on current direction). This, times a gain of 20 would give a 4 volt peak to peak output. This is a...

You might consider some processing before sending the signal to the microcontroller. One method would be to use two weighted resistor networks, one biased to the left and one biased to the right. The conductance of the resistors (reciprocal of resistance) would be proportional to their position. For...

The purpose of the series gate resistors is to damp parasitic oscillation. Even a single MOSFET can be subject to this problem. Vacuum tubes had similar problems. Most amateur transmitter designs from the 1950s on had parasitic suppressors as a matter of course. The parasitic oscillation might not d...

The stacked design that MrAl shows can be improved by making the high current connection at the top of the stack on one side and at the bottom of the stack on the other. This makes the number of joints in each current path equal. The resistance in each contact may be significant compared to the resi...

At 100 MHz, the reactance of 4 pF is about 400 ohms. This will require low resistance values to keep this negligable. In turn, the circuit will be "power hungry". About all you can do is minimize the capacitance and hope that the power still remains within reasonable limits. The MPSH10 wou...

Cork is more likely to be used as an absorber. If the frequency was varied over a wide range, an absorber such as cork might be needed to avoid the dips in the output that would occur when the reflection comes back out of phase.

The 2N3904 has a fair amount of collector-base capacitance (possibly 4 pF). This will start to be significant in the 100 MHz range. A better choice might be the transistors made for local oscillators in UHF tuners. These have better frequency response and much lower collector capacitance. The MPSH10...

The switching transient coupled into the signal channel may be of very low energy. It will be capacitively coupled, probably from the gates of two MOS transistors to their channnels. These are in opposite directions, so only the dfference will be effective. Thus charge is injected in less than a few...

The reflected wave would be in phase for spacings such that the distance from the transducer to the reflector and back to the transducer is equal to a multiple of one wavelength. This would occur at spacings of 1/2 wavelength, 1 wavelength, 3/2 wavelength, 2 wavelengths, and so forth. By enclosing t...

I don't see any discussion of power levels. If the load is a resistor of 4 ohms (3 A at 12 V), the maximum power in the 2N3055 will be 9 W (1.5 A and 6 V). This will definitely need a heat sink. If the load has a constant current nature, such as a light bulb, the dissipation could go to 36 W (3 A an...

The solution might be more in the way the circuit is used rather than the specific circuit. An old vacuum tube instrument, the Hewlett-Packard 411A, had full scale ranges from 10 mV to 10 V. The detector was a simple diode detector, similar to the conventional shunt rectifier. The trick was to use t...

On second thought, a CPLD may be all you need. These are available from Digikey for around five to ten dollars. For example, the XC9572 has 72 cells. Each cell has an array of gates and a flip-flop. A six digit counter will require 24 cells. A storage latch will require another 24 cells. Scanning th...

CRT displays have a similar problem, even at light levels well below daylight. There are several solutions which work to some extent. A circularly polarized filter may help, since the reflected light is pollarized in the opposite direction and attenuated. A filter that is matched to the color of the...

Most of the cheap digital panel meters use a dual-slope A/D converter. The signal is integrated for a fixed period (1000 counts in the case of the Intersil 7106). The integrator is reversed and the time required to reach zero with the reference voltage is counted. In effect, an internal counter is p...