PM5324 oscillator

A recent question in a CircuitsOnline thread (link here), raised my interest in the oscillator section of this RF sweep generator. The oscillator section is around the (ECO) emitter coupled oscillator topology. This topology will oscillate at almost any frequency with almost any LC combination and is not critical with transistor types (of course using LF transistors won’t work at UHF..). The disadvantage is that the current through the common emitters needs to be carefully adjusted. if not the output won’t look like a sine wave output and there will be many harmonics (though this could be useful at sometimes). Also, because the transistors will saturate, the upper frequency is limited.

Emitter-couple- oscillator (ECO)

Not so, the PM5324 oscillator!

Continue reading PM5324 oscillator

LCR bridge

Continue reading LCR bridge

Scope probe storage

Usually the workbench is cluttered with oscilloscope probes, serial cables, programming adapters and the like. Before a cable can be used it first needs to be liberated from beneath a pile of projects. While doing so, you accidentally move a wire on your current project which shortens out an essential part of which you do not posses any spares in your junk box and of course it is Saturday 1701h so the shops have just closed for the weekend…. 🙁

Even it doesn’t describe your workbench, this could still be a very usefull project! It pays to be carefull with your oscilloscope probes. The tips are tiny and easy to damage and the coax cable to you scope is tiny and fragile…

VHS-HZ-200 cover
Continue reading Scope probe storage

L-meter

The usage of inductors in RF circuits is often intrinsic to its operation. Unfortunately, the measurement of small values of inductance is often difficult without specialized equipment. If, you have the ability to measure frequency, either directly with a frequency counter or indirect with an oscilloscope, this burden can easily be overcome.

Continue reading L-meter

Walkie talkie (2) transmitter

Below you see the block diagram for the walkie talkie transmitter.

Transmitter block diagram

The carrier oscillator is crystal controlled to guarantee sufficient stability. It is much easier to create a frequency stable carrier by means of a crystal than with an ordinary LC oscillator. The latter would require carefull selection of components and very careful construction to ensure sufficient frequency stability.
The minuscule voice signal from the microphone (a couple of millivolt) is amplified to line level in the audio amplifier. To have sufficient modulation a signal of circa 3- 4 Vtt is required. The bandwidth of the audio amplifier is limited to circa 3.5 kHz.
This is still wide enough for good intelligibility but restricts the used RF bandwidth.
Finally the output is filtered to remove unwanted harmonics.

The oscillator Q1 and modulator Q2.

Walkie-talkie (1)

Lately my 6 year old son has gotten interested in walkie-talkies. Now, I could go to the nearest toy-store and buy something but where is the fun in that? Since, he is getting more interested in technology it would be nice to design something that he can, at least to some extend, help me with assembling.

Features
Easy to build
Low cost
Crystal controlled
Sensitive Receiver

Design goals:

  • Usage of ham bands, so it is legal
  • No spurious emissions
  • Auto power-off (I think you don’t need to have kids to understand why … )
  • Low-power transmitter, just the end of the street
  • Sensitive receiver to match
  • Need to build at least two, so no exotic parts
  • Battery powered and thus low power consumption

The set-up of the transceiver will be quit simple:

The transceiver will by default always be in receive mode. Unless the Press-To-Talk button is pressed during which short time it will transmit. At other moments the transmitter will be switched off to conserve power. (The auto-power off function is not shown in the block diagram).

Policegun

Another Sunday afternoon project with my son. Of course, as possibly every 4 years old, he loves to act out as fireman and policeman. After a hospital visit we gave him a set of handcuffs but of course nog true policeman is complete without it’s own gun. So we spend some time in the shop and made our own.

The body is made of 18 x 44 mm pinewood leftovers. The top part is circa 150 mm long, the hand grip is ~90 mm. The two parts are just glued together with ordinary PVA wood glue. The body was painted grey with some cheap spray paint. The trigger handle was made from a saddle clip used to mount a PVC tube to the wall. All in all it took us 1 hour or so to assemble and we had some good fun along the way.

I have been held at gun point and arrested countless time by a very brave police officer 🙂

GDO circuits bonanza !

The Gate Dip Oscillator (GDO) is one of the most useful tools for the radio amateur. You can use it to tune LC circuits, as test RF source, check antennas, etc. This GDO circuits bonanza features many previously unpublished GDO circuits from (primarily) Dutch magazines and books.

Bouwen en luisteren – IAN R. SINCLAIR

This book in the “GDO circuits bonanza” contains many simple – yet very useful circuits. To help the constructor a simple layout sketch is given based on vero strip-board. The circuit is build around a single NPN transistor. The transistor (TR1) is set-up in common-base amplifier, the basis is held at a fixed voltage and is connected to AC ground via capacitor C2. This configuration is probably choosen because the input capacitance does not sugger from the Miller effect, which degrades the bandwidth of the common-emittor configuration. This implies that the collector and emitter from the transistor are in phase. Thus a simple small capacitor from collector (output) to emitter (input) is sufficient to provide positive feedback and hence start oscillation. The LC circuit comprised of L1 and VC1 only provides a high resistance and thus (high) amplification at it’s resonance value, which is given as ƒ = 1 / (2 * π * √ L * √ C).

For every component the position in the vero board is given, with the description from which to which copper strip the component should be mounted.

GDO circuits - Bouwen en luisteren - DIP oscillator - pag 58-59GDO circuits - Bouwen en luisteren - DIP oscillator - pag 60-61GDO circuits - Bouwen en luisteren - DIP oscillator - pag 62-63

 

Theorie en praktijk voor zendamateurs – J.L. Molema

Two other ones in the GDO circuits bonanza. This time from the book “Theorie en praktijk voor zendamateurs” (Theory and practice for radioamateurs), a collection of circuits and little background information on their workings. It features two GDO both based on junction transistors.

Theorie en praktijk – Afb.85

The first circuit is set-up around a PNP transistor, again in common-base configuration. The circuit itself is a little difficult to follow because, unlike current conventions were the positive rail is drawn a top and the ground below, it use the old drawing style were both the supply rail and ground rail are drawn next to each other. Both 3k3 resistors are used to set the base at half the supply rail and 6.8nF cap is used to connect base to ground for AC. The 820Ω resistor and 10nF cap are used for power decoupling the transistor’s collector. The meter read-out is different in a couple of ways. First the signal is taken from the low-impedance emitter. Thus the read-out circuitry will load the LC circuit far less than the design above. Potentially offering greater stability. The second-change is that a transistor is used to amplify the signal, thus a less sensitive meter couple theoretically be used. Finally the meter is connected to a bridge circuit, one leg being the 4k7 resistor and the transistor and the second being the 10k trimmer pot. Although, the circuit recommend using a trimmer here, a normal pot can be used to your advantage as well. With the 50K pot one can then set the sensitivity, with the 10k pot one can the shift the zero-point and thus zoom-in on a small dip.

One thing that should be pointed out, however, is that there is no protection for the meter M. If you are not careful you can easily destroy it when fiddling with the controls.

Coil details are given in the page scans below.

 

The second circuit is a more traditional design. If you are familiar with the classic Heathkit GD-1B and the Eico 710 models, you’ll probably recognize the circuit immediately. The emitter is held at ground via the 470Ω and 1nF. The LC circuit is connected between basis and collector. Basis and collector are in this configuration 180º out-of-phase. The LC circuit provides another 180º, because the mid-point of the capacitor is connected to ground. Sensitivity is set via the 5k log  potentiometer that changes both the base voltage and the collector. If the DC voltage is increased, the amplitude of the oscillation will also increase.  Th output is sampled from the collector and rectified. Because there is no amplification and more sensitive meter is required.

Theorie en praktijk – Afb.86

Coil details are given in the page scans below.

 

Ontvangers – F.A.S. Sterrenburg

The next book in the “GDO circuits bonanza ” is probably one of the best books on radio receivers available in the Dutch language. It describes almost every aspect of radio reception: radio propagation, receiver principles, receiver specifications, planning and construction, antennas, receiver inputs, oscillators, IF amplifiers and the list just goes on and on…! It is all written down in an easy to read concise format, with many many examples. I bought his book at a library selling off some surplus books some 20+ years ago and it is still my go-to book for many aspects. It really is a pity it is only available in Dutch!

Of course being a book of 1978 many new techniques in receiver design, such as H-mode mixers, DDS VFOs, SDR and new modulation techniques as WSPR, are not covered. But then you cannot run, if you cannot walk, can you? So, I would definitely recommended this book to any youngster planning on building a receiver.

In chapter 15 “Meetinstrumenten” (Measuring instruments) many principles and some simple to build tools are described including two dippers. The first one is build around a EM87 tuning indicator tube, very cleverly using the triode portion of the tube as the oscillator. Oscillator and indicator are all in one tube. Although the author, very politely, doesn’t mention it, the circuit is from it’s own hand. It was originally published in the Dutch magazine Radio Electronica 1974, page 49. The author goes to great length to describe how to build the circuit, enclosure, which coils to use and how to calibrate the circuit.

Dipper with EM87

After the previous circuits, the oscillator configuration itself should be becoming familiar: an LC circuit connected between a tube’s grid (gate) and plate (drain), the central part of the capacitor grounded to provide the necessary 180º phase shift. The second half of the tube (the actual indicator) is then used to display the amplitude of the oscillation. In the original article you can find a great deal of information about the construction and the coils used.

The second dipper described in the book is totally different. It is a transistor dipper, again in common-base configuration. However, now a couple of diodes are used to rectify the output and stabilize the amplitude of the oscillator signal. This agc signal is then also used to indicate the dip.

The use of a negative power supply looks maybe a bit strange but it is actually quit clever. In this way one half of the LC circuit can be connected to the ground, minimizing hand effects. I am not sure if the actual rectification circuit around D1 and D2 is drawn entirely correct. It seems strange to put D1 in anti-parallel with T2…

You can find more information in the page scans below..

 

Kleine zenders en oscillatoren – Herbert Brosch

This booklet is written by German amateur Herbert Brosch (now SK), who has compiled a collection of many simple circuits about oscillators and small transmitters. The GDO feaured in this book is classic Collpits based GDO with a J-FET and uses a sensitive meter to display the rectified gate current. Not even a basic 100nF buffer capacitor is included in the schematic….

Kleine Zenders en oscillatoren – dipmeter

You can find more information in the scans below:

Although I am not a great fan of this book, it features some nice and unorthodox circuits, like this Push-pull oscillator:

Push-pull oscillator

Super Fine Tip test probes

These test probes wereld made several years ago and have proven to be very useful in many applications. The small tip allows you to probe even the tiniest SMT components.  Because the tip is really, really sharp (don’t ask me how I know… ouch) it allows you to breach residue of solder flux or even penetrate the outer isolation of a cable.

Continue reading Super Fine Tip test probes

SMT DIP adapter PCB from TI

PA3COR TI SMT DIP adapter EVM

If you like prototyping but find it’s a nuisance to mess around with small, all too common, SMT packages, the Texas Instruments SMT DIP adapter kit might be something for you.

The DIP adapter kit supports six of the most popular industry-standard packages, including:

  • D and U (SOIC-8)
  • PW (TSSOP-8)
  • DGK (MSOP-8, VSSOP-8)
  • DBV (SOT23-6, SOT23-5 and SOT23-3)
  • DCK (SC70-6 and SC70-5)
  • DRL (SOT563-6)

There are six coupon boards per supported package type,  so in total 30 adapter PCBs. It comes complete with terminal strips. Best of all it costs only $10.00 USD!

You can find more information or order the SMT DIP adapter kit HERE

PS
I don’t have any stock or interest in TI, nor do I get paid, I just found it a neat and cheap solution.