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 Post subject: Anybody remember the penlight signal generator?
PostPosted: Jul Thu 21, 2016 3:58 pm 
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Location: Hutchinson KS
Back in the 70's I remember using a pocket sized device that had a locking pushbutton on one end and the other end had a probe that would inject "noise", both rf and audio frequencies to use as a signal injector. Took two AA batteries I think and it sure looked like a pocket penlight at first glance. Anybody have a clue what I'm talking about? Was very handy in troubleshooting AM transistor radios.


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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Thu 21, 2016 4:09 pm 
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Sure do! That was the "Mosquito" manufactured by the Don Bosco Company.
They're absurdly pricey on that infernal auction site. I built one in a pen-sized,
plastic ladies' reading glasses case that works well. PM me and I'll give you my
address---SASE and I'll send you the plans.


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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Thu 21, 2016 4:36 pm 
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Image

http://www.antiqueradios.com/forums/viewtopic.php?t=109446

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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Thu 21, 2016 5:14 pm 
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Yes! That is it!


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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Thu 21, 2016 6:13 pm 
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Location: Aurora, IL
Used the D.B. "Mosquito" myself back in the day and can't tell you how many sets I quickly diagnosed using it. One of my regrets is not purchasing one for myself. I used the shop one and never bought one for myself. The other service tech I worked with was smart though and bought one for himself.. probably still has it. But no... wouldn't spend the kind of cash I've seen these going for now.


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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Thu 21, 2016 6:29 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Wayside, NJ Monmouth
I just got done rebuilding one I own, Call the Buzz-It. Runs on one AA battery. Works from audio up to a few megahertz.


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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Thu 21, 2016 7:18 pm 
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I "oh, so skillfully" managed to take out two 1 volt tubes with the Radio Shack form of the critter, while troubleshooting a Columbia(?) portable radio back in my teenage years. Back when "I knew everything"...

Best part was, that a 10¢ resistor turned out to be the culprit, and I was forced to shell out almost $5.00 for the replacement tubes (prominently stocked by the electronics supply house which I then frequented, and which I never expected to see disappear along with most others).

Those penlight signal generators were quite useful!

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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Thu 21, 2016 11:42 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Minneapolis, MN USA
Try DIY.

Real easy to make a working injector. Simple circuits. Much tougher to package them cleanly.
Here is mine with a tilt switch to turn power on / off.

Image


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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Fri 22, 2016 10:16 am 
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Is that the original circuit of that “Buzz-It” signal injector? My two examples are based on a one-transistor blocking oscillator, with a tiny ferrite-core coil, and small light bulb in the translucent red tip. They also have a twist switch rather than a push-button, so perhaps they represent a different version.

It is amazing how useful a signal injector can be. The Micronta circuit, shown on the forum page cited by Nortronics, is in many ways the most effective design for radio work; but any of these devices will work well. The original form was a simple electro-mechanical buzzer, with a small-value condenser connected from the junction of the coil and contact point, to the probe tip. The D.C. (or D.C. / A.C.) version of the very compact Lungen #15 buzzer will work very well, and produce a potent wide-band signal.


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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Fri 22, 2016 3:01 pm 
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Very useful thread. I see a construction and machine shop project in my future. :) Any tips on making the coil in the Micronta circuit?

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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Fri 22, 2016 8:42 pm 
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Here is one that is just mechanical
Image


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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Fri 22, 2016 10:38 pm 
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Location: Wayside, NJ Monmouth
Made these two from the ARRL Handbook. One on the left uses a Crystal, the one on the right is a Signal Injector. I used plumbing fixture fro Home Depot.


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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Sat 23, 2016 7:37 am 
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I should certainly like to add an electro-mechanical signal injector, like the one Lou has shown above, to my collection. It seems that the probe type buzzer injectors were made only briefly, before transistor circuits took over. But the concept originates over a century ago. Professional grade crystal receivers and wave-meters were often provided with a little battery operated buzzer (usually a Century or equivalent) to facilitate adjustment of the crystal detector.

The coil for a signal injector based upon a blocking oscillator circuit is not critical, though it should be tapped. Many surplus ferrite core inductors of various values can be used to produce a functional injector. The transistor blocking oscillator is likely the most forgiving of all oscillator circuits, and will also work at a wide range of voltages.

The tubular style Micronta injector (made in Japan and sold under several brand names, even in kit form) is different from others in that it employs a relatively high-Q coil shunted by a condenser to make a tuned circuit. The injector circuit—

Image

—actually oscillates at an audio frequency (1,335 cycles per second in a specimen that is at hand) that is chiefly determined by the values of the 0.022 mF condenser and the 20,000 ohm resistor. When the transistor shuts off during the cycle, the energy stored in the magnetic field of the coil gives rise to ringing of the tuned circuit, at its resonant frequency (463 KC in the same specimen), with the amplitude declining logarithmically, until the next pulse occurs. A damped wave train looks like this:

Image

The radio frequency is near to the I.F. of most modern A.M. broadcast receivers, but the signal is extremely rich in harmonics.

It should be possible to wind a coil on a small piece of ferrite rod, that comes close to the Micronta original, the dimensions and value of which are given on the signal injector forum page:

http://www.antiqueradios.com/forums/viewtopic.php?t=109446

I should think that a typical transistor radio loopstick could be employed. The tap can be obtained by connecting the main and the coupling windings in series, in phase.

Note: Edited to correct audio frequency unit from KC to CPS.


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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Sat 23, 2016 1:39 pm 
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Philip Colston wrote:
It should be possible to wind a coil on a small piece of ferrite rod, that comes close to the Micronta original, the dimensions and value of which are given on the signal injector forum page:

I should think that a typical transistor radio loopstick could be employed. The tap can be obtained by connecting the main and the coupling windings in series, in phase.


Perfect. I have about 10 NOS ferrite rod antennas that came in a box of stuff that I bought. I kept them "just in case" I needed them. :lol: Now to see what other junk I have on hand to use.

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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Sun 24, 2016 1:13 am 
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I have an Eico like Nortonics has. Got it in the proverbial box-o-junk, as I recall, at a hamfest or something. All external marks are worn off but it does work fine. Even used it a few occasions. Thank goodness the N type batteries are still available for in it. I felt kinda lazy or cheating using it after all these years of meters and scopes and such but for quick and dirty it lets you know where things are rotten, fairly quickly.


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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Fri 29, 2016 4:27 pm 
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Got one of the Archer ones...haven't used it lately, because one wire to the battery box came off...and the fix is very low priority. But it's not exactly penlight size.
RW

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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Jul Sun 31, 2016 6:32 pm 
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radiowizard wrote:
Got one of the Archer ones...haven't used it lately, because one wire to the battery box came off...and the fix is very low priority. But it's not exactly penlight size.
RW


I have this one from Radio Shack. Is it one of these?
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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Aug Mon 01, 2016 11:41 pm 
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Philip Colston wrote:

The tubular style Micronta injector
Image



I made one from this schematic using an inductor on a ferrite antenna core wound with #24 enamel wire (had both in the junk box). Coil was just over 2" long. Used a generic cheap germanium transistor. Not a picky circuit at all. Works fine with signal into the RF, IF and AF coming through on an AM radio. Still on the breadboard and not in a housing yet. This is a really simple build.

Rick

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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Aug Tue 02, 2016 3:43 pm 
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I found a small project box in my junk box and a blank PC board with solder pads. Built the circuit with point to point wiring. Used a terminal post for the output so I can use a probe, wire, alligator clip or whatever to connect to the radio. Being a pack rat I found a surplus Blackberry charger in my stash. Perfect use for it since it is 5vdc and pretty small. Decided I did not need a battery operated pen sized device so this should work for me. Checked it on the scope and looks like the circuit is working properly. The only part I had to buy was the transistor. Had everything else as junk / spare or in my regular parts inventory.


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 Post subject: Re: Anybody remember the penlight signal generator?
PostPosted: Aug Fri 05, 2016 6:53 am 
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That’s excellent work. Your circuit has considerably less decrement in the ringing (in other words, a more persistent R.F. waveform) than most of the Micronta style injectors I have tested. I am pleased to see the original germanium transistor.

Although I have assembled a reasonably comprehensive collection of vintage signal injectors, I have obtained an anodised, extruded aluminium case to construct a Micronta style injector from scratch, to optimise the function, as you have done.

This is an excellent, simple project for any-one interested in restoring or repairing vintage radio sets. The usefulness of a signal injector can not be overstated. And this particular circuit produces a waveform very like that of a spark transmitter of the wireless era.


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