IEEE Consultants' Network of Long Island

A Puzzle - John Dunn, Consultant, Ambertec, P.E., P.C.

This can really be set up on the lab bench and demonstrated to within the specified accuracies of the test equipment. Take a look at this first sketch and figure out what is inside the box. 

Don't look down yet for the answer until you've either figured it out or given up.

DZIF: HOW IT RELATES TO ILOD-----Carl Schwab

The ZIF portion of DZIF refers to “Zero Intermediate Frequency” and it is just my favorite abbreviation for homodyne or synchrodyne. They all mean the same and are technologies that evolved in parallel with the superheterodyne around the 1920-1930 period. The  “D” part of DZIF refers to double conversion meaning that a high IF is used in addition to the ZIF.

In the hobby industry, the double conversion receiver had become standard and the usual design employed a 10.7 MHz FIRST IF and 455 KHz SECOND IF and the modulation most times was PPM FM. This design(S) evolved from about 1980 up to and beyond 2000. From a mechanical damage standpoint the 455 KHz transformers were the weak link. Also there were design missteps in gain distribution between the FIRST IF and the 455 KHz second IF.

Coil Shielding Choices - John Dunn, Consultant, Ambertec, P.E., P.C.

The choice of which conductive material to place near to or far away from a coil can affect that coil's electrical behavior. The effect on a particular coil of wire of placing a non-ferrous metal (a twenty-five cent coin in this case), placing nothing at all and a placing small piece of ferrous metal is illustrated as follows: 

ILOD IMPLEMENTATION-----Carl Schwab

ILOD is an acronym for “Injection Locked Oscillating Detector”. The schematic below shows on the left side figure the ILOD Block Diagram, while the right side figure show the actual circuit implementing the ILOD concept to develop a +- dc error voltage. In this implementation ILOD circuits were used to demodulate 4 subcarriers to produce dc error signals to drive analog servos.

Dual-Resonance Coil Testing - John Dunn, Consultant, Ambertec, P.E., P.C.

If you need to measure a transformer winding inductance in situ, while the transformer is all hooked up to its operating circuitry, that surrounding circuitry may interfere with getting the measurement done if there is a large capacitance present across the winding in question. An LC meter I once tried to use in that way simply could not ascertain a transformer winding's inductance because there was a large capacitance being reflected into that winding from the transformer's other windings.

However, there is a way out of this problem using the test fixture as sketched below. 

Injection Locked Oscillating Detector -- Carl Schwab

ILOD DESCRIPTION

First let us explain what ILOD stands for-------Injection Locked Oscillating Detector— ILOD. By injecting a locking signal of the correct value (actually range of value), the detected output responds to the input signal frequency in an extremely linear manner over the pullable frequency range. The following diagrams hopefully can clearly describe the fundamental action that makes it inherently linear over the pullable frequency range.

Key attributes are------

1) Its output over its "pullable range" is not only linear, BUT its slope measured (delta volts/delta frequency) is a computable CONSTANT.
 
2) I have used it for center-frequency ranges from 300 Hz up to 60 MHz.
 
3) Inherent to its design, its input level is best restricted to +-4db amplitude range. This is easily done with ordinary AGC if working behind a radio OR leveling amplifier working over 'phone lines.

4) Hard limiting, as a means for level setting, is to be avoided because of generation of troublesome intermodulation products.  

Dip Oscillator and Dual Resonance - John Dunn, Consultant, Ambertec, P.E., P.C.

A dip oscillator is an oscillator whose oscillation vigor is monitored on a front panel meter. When the exposed inductance of a dip oscillator is brought close to an external tank circuit whose resonant frequency equals the oscillation frequency, that tank circuit draws energy away from the oscillator, diminishing the oscillation's vigor which is then seen as a "dip" in the meter reading.

Going back to vacuum tubes, this kind of device was called a "grid-dip-oscillator" and later, when these things were made using tunnel diodes, there was the "tunnel dipper".

I happen have dip oscillator in the basement, but apart from that, I haven't seen one of these in industry in quite some time. Still, a dip oscillator can be quite handy to have at times.

To Zero Cross or Not To Zero Cross - John Dunn, Consultant, Ambertec, P.E., P.C.

Turning on AC power to some load by making switch closure at the zero-crossing of the input voltage sine wave sounds intuitively like the thing to do, but that may not be proper or wise.

We use recursive differential equations to examine the settling behavior as input power is applied to a sample circuit.  

Equipads - John Dunn, Consultant, Ambertec, P.E., P.C.

Imagine having to attenuate a fairly high power signal, high enough in power that one single attenuator pad can't handle the power dissipation requirement. We can use a cascade of attenuators, but we want to spread the burden, so to speak, so that each attenuator in the cascade will dissipate an equal share of the total power dissipation.

The following derivation shows how to calculate the dB values for this: 

Type-K Thermocouples - John Dunn, Consultant, Ambertec, P.E., P.C.

Thermocouple tables are published from which you find the relationship between millivolt (mV) measurements and thermocouple temperature, typically in degrees C. That relationship between temperature and mV, in the case of a type-K thermocouple, happens to be approximated as an 8th-order polynomial.

The GWBASIC program below uses that polynomial to find an approximation of thermocouple mV output given a specific temperature in degrees C. This can be useful in making simulations where you really don't want to have to deal with a real device sitting on your workbench at multi-hundreds of degrees.

Some tabulated results from this program are as follows: