Yeah, this is a little bit "out there", but...

[Omega-TI]

Hi,
Does anyone have a schematic diagram suitable for a basic homebrew scanner? I'm not looking for anything overly complicated, just something that could scan 2-6 channels. Construction would be old school style "thru hole construction" with discrete components, sort of like the old Radio Shack P-Box kits. Of course it would use crystals. I figure there would be no need for an O-Scope in aligning the radio because with a crystal of a known frequency one could tune it to match and be good to go.

 

[slicerwizard]

You're going to troubleshoot non-DC circuits without a scope?

 

[Omega-TI]

You're going to troubleshoot non-DC circuits without a scope?

Why does it have to be a non direct current circuit? Back in the day Radio Shack used to have an anemic little battery powered (DC) Aircraft/Police band tunable receiver, I figured of all places, someone here might have a little more sophisticated schematic lying around. I'm thinking it might be a fun little project to slap together.

 

[RFI-EMI-GUY]

Hi,
Does anyone have a schematic diagram suitable for a basic homebrew scanner? I'm not looking for anything overly complicated, just something that could scan 2-6 channels. Construction would be old school style "thru hole construction" with discrete components, sort of like the old Radio Shack P-Box kits. Of course it would use crystals. I figure there would be no need for an O-Scope in aligning the radio because with a crystal of a known frequency one could tune it to match and be good to go.

"back in the day", of crystal controlled radios like the HT220, MT500, MX300, Micor and Maxar's, there were simple add on boards and DIY circuits that used a simple clock and shift register to address channel selection of a radio by grounding a crystal. All that was needed beyond those circuits was a squelch logic detector to halt the shift register for a period of time. Google might help find schematics of DIY and commercial products.

For HT220 using flip flops:



These LED chaser circuits can be adapted to make a channel scanner:

10 Simple LED Chaser Circuits Explained [Knight Rider, Scanner, Reverse-Forward, Cascaded] - Homemade Circuit Projects

The article discusses the construction of 10 interesting yet simple LED chaser circuits, which not only create beautiful running light effect but are also easy to build. We also discuss […]

www.homemade-circuits.com

 

[techman210]

Many of the old school scanner manufacturers came with schematics, parts lists and alignment instructions as below.

Your real challenge is finding good crystals in small quantities. Crystals are not "lifetime stable" and will need some capacitive adjustment - if they haven't drifted too far. With most things narrowbanded now, you'll need tighter filters AND better frequency accuracy than in years past. Pay attention to the temperature coefficients that were used in the original product. These are most important in the oscillator stages.

One option is to use some of the programmable oscillators that have come on the market. Or get a programmable synthesizer board that has some sort of parallel frequency select bus that you can drive from the scan-select system that RFI-EMI provided above. And as pointed out above, doing this successfully without a scope and at least a rudimentary spectrum analyzer to see where things are- or are not oscillating will be a huge challenge.

Electra Bearcat III Scanner user manual – To Type, Shoot Straight, and Speak the Truth…

munk.org

Understanding Ceramic Capacitor Temp-Coefficients

A common question when looking at ceramic capacitors is what do the temperature coefficient numbers/letters mean? These numbers will generally break down to a temperature range and the variation in capacitance over that specific range. The first thing you need to understand with what standard...

forum.digikey.com

 

[merlin]

Back when I started working in the radio industry Channel elements (crystals) were the norm. Highbrid was waning for all solid state.
2, 4, or 6 channels. One could easily modify the channel switch with the 'knight rider' circuit above. Viola, a scanning radio.
Enter the world of PLL synthesizer for frequency control, only one crystal needed, and dozens to hundreds of channels. BCD switches for selection.
Radio got married to CPU, Now you have up and down channel, digital display. A port on the CPU handled the PLL.
Scanning, seeking included. Probably the simplest of the lot
You could get this far with a basic receiver with PLL and off the shelf CPU like PIC and Arduino.
Now you are in the world of embedded control. Scanners haven't changed much, just a lot more memory and a boatload of features. Multi band.
Even digital mobile radio and decoding.
I can't fathom effectively working electronics without a scope and for radio, add a frequency generator and counter.
A good DVM is like a must also. You could wire up battery packs but a better choice is a multi output bench supply.
I do just get by with all this:

 

[RFI-EMI-GUY]

There seems to be renewed interest in those old rock bound FM scanners. And rightly so, they were inexpensive and worked rather well. I might be interested in one If I could get the crystals I would need.

 

[Omega-TI]

There seems to be renewed interest in those old rock bound FM scanners. And rightly so, they were inexpensive and worked rather well. I might be interested in one If I could get the crystals I would need.

Yes, it does work well! The RCA 16S400 I have is way more sensitive than either my BC 800xlt or SDS100. Not only that, there is no underlying hiss on the channel. I'm fortunate enough to live in an area that is mostly analog.

About the crystals, most of mine came from Ebay. Just type in the frequency you want and it they might just pop up. Going price is about $10-$14 each.

Now building a simple one might be fun as well.

 

[ladn]

Now building a simple one might be fun as well.

Yes, the building part might be fun, but sourcing the components might not be. Long gone (for most of us) are the neighborhood parts stores (think Radio Shack as the lowest common denominator, but there were others as well). I wouldn't relish dealing with the likes of Newark or Mouser for small quantities of discrete components, and the cost would probably be pretty excessive. And, as @techman210 mentioned, narrowbanding will still be an issue in many areas.

Personally, I think it would be more rewarding to acquire and restore a vintage xtal scanner. There's still a lot of' them out there from Ebay or yard / estate stales and swapmeets.

Your mileage may vary.

 

[Omega-TI]

Yes, the building part might be fun, but sourcing the components might not be. Long gone (for most of us) are the neighborhood parts stores (think Radio Shack as the lowest common denominator, but there were others as well). I wouldn't relish dealing with the likes of Newark or Mouser for small quantities of discrete components, and the cost would probably be pretty excessive. And, as @techman210 mentioned, narrowbanding will still be an issue in many areas.

You may be right. Maybe it could make for an interesting group project though? If a simple enough schematic could be agreed upon, a BOM developed, and possibly even gerbers made up for a circuit board, I bet I'm not the only one who would get into this if only for the educational aspects. Not everyone one can design radio circuitry, but almost anyone can put components into a circuit board and apply some solder... provided it's not surface mount sized. I'm thinking more mid 1970's discrete components level.

<<-- About the level of complexity of this unit max.

Would anyone else be interested in such a project?

 

[Omega-TI]

You know, to keep costs down, I'd even be satisfied with removing the block that automatically scans and adding manual switch between two to four channels. Keep the receiver and amplifier section. Add pads for power, audio and antenna and leave the rest for the end user. Heck, at the very least it could make a decent weather radio!