A Project Under Consideration

[Sarasota Slim]

I have an old Realistic radio, sitting at home, that I don't particularly care about. It's not worth the effort of attempting to sell (or give away, even). However, it is a functional device, so I can't just pitch it, either.

So, I thought that it might be fun to take that radio, a cheap little amp, a cheap swr/power meter (I've got one of those lying around, too) and a low-pass filter, and combine them all in one enclosure.

The question is, how to go about connecting everything? I'd like to avoid using PL259 connectors (and their female counterparts), and solder in connections, instead. Would I use coax for that? And, if so, would a specific length be required?

The point of the project, aside from my personal entertainment and need to tinker, is to be a learning experience. That's why I'm using that particular radio (and other low cost components); if I screw up royally, it won't be a big deal.

If anyone has done similar projects, I'd love to hear thoughts on the subject. Actually, I'm pretty much open to any input, lol.

 

[Robb]

If it is a desirable model of a Realistic radio; it might worth being rebuilt. But that isn't for beginners. BTW - what model is it?

Putting everything in a box is done all of the time, it's called a 'radio room'. But to put it all in one metal box sounds like a waste of time and money to me. Never heard of doing that. Mostly because it would take up too much space instead of saving it.

If you want a decent project that you learn to do that is worthwhile, you can always learn to build your own homemade antennas. Not that hard to do, the materials are fairly cheap, and you can take some pride in the final product. You can make a simple dipole from scrap wire and some rope - for starters. Work great - too.

 

[Sarasota Slim]

The radio is a TRC-474. The highest price tag that I've seen on one was about $30. The average appears to be about $15. Not worth the effort, to me, lol.

I can see where one might think that building the "radio room" would be a waste of effort and finance. But, to me, it's not. It's just something to do. I'm using cheap stuff, and stuff that's just lying around, because I don't really know what I'm doing. I have an idea, but that's about it. Like I said, if I screw up, it won't be that big of a deal. Besides, that's my learning process; pick a project and do it. Most everything I know, is stuff I just figured out.

Another motivation for this project is that I have a pile of devices on my dash. It drives my wife nuts. I have a radio, a meter, an amp, a low pass filter, and an antenna matcher all up there.( There's also 2 phones, to GPS's, the qualcomm, the satellite radio receiver) So, this project is kind of like the practice run, with a goal of cleaning up the dash, a little bit.

I'll probably do some antenna projects, too. Tinkering around with antennas is something that I can do on the road, to some extent. My current antenna set up, actually, is another thing that drives the wife nuts. But, that's something for another thread.

 

[LeapFrog]

But to put it all in one metal box sounds like a waste of time and money to me. Never heard of doing that.

It's been done before, I don't know about a low-pass filter fitting inside the box though..
you might have to bolt that to the outside of the enclosure for space requirements.

I saw a DAKobra 29 on eBay once, nice build it was!
(A Cobra 29 LTD inside an old DAK Mark 10)
Very clean looking at first glance, it can be done!
Grab a low-noise power supply (like a true MegaWatt switching p.s.u.) or re-purpose an older PSU, find a suitable enclosure something that preferably has holes cut pre-cut for an s-meter and switches.

Keep any length of wires (for extending the controls to the front panel) as short as possible. My biggest concern would be electrical noise or interference brought about by extending wires, keep everything as short as possible.
Biggest issues I think will be:

* The channel select/indicator wire length

* Does the TRC-474 use a "floating ground chassis" (incorrect term) like a Cobra 29/25 where ceramic capacitors de-couple the pc board ground from chassis ground?

* Mic wire may need shielding if none is present, I think de-coupling everything properly in the new chassis will be the biggest issue to avoid RFI or mic feedback

* Various challenges while drilling/mounting the controls/meters


This is more of a month long project (if re-using most everything) rather than a weekend project.
It is fun to tinker, I can see the motivation for doing this with used parts.
I have a Cobra 25 just begging to be made into a base station radio, lol!

I'm going to let the Cobra 25 pc board sit in the original chassis/frame
(minus the covers and front bezel, so just the bare-bones "frame")
and mount that to the inside of my re-purposed enclosure. The SO-239 will have to be re-done at the rear wall of the new case, I might use a piece of 'micro-coax' from the pc board to the output connector (what ever kind I settle on, n-type or otherwise).

Unless you plan on soldering your feedline coax directly into the radio, I would recommend you use some type of connector. In case the coax ever gets damages, you wouldn't have to re-open the rig and fire up the solder iron just to change it! (or if it is to ever be moved with ease again)

If you end up using the TRC-474 for this project, I would consider a 4 or 5 pin microphone jack conversion, those DIN plugs suck after an internal wire breaks you basically have to throw the microphone away or install a new DIN style wire/plug, way more effort than touching up the solder on a single wire that may break loose inside of a "Cobra style connector".

Best Regards
-LeapFrog

 

[Captain Kilowatt]

Putting everything in a box is done all of the time, it's called a 'radio room'. But to put it all in one metal box sounds like a waste of time and money to me. Never heard of doing that. Mostly because it would take up too much space instead of saving it.

Actually Robb it's done all the time. They are called slip seater boxes. Truckers use them to keep all their gear together in one easy to manage box when they switch trucks a lot. Some custom make their own and others buy ready made boxes.

http://www.bobscb.com/slip_seat/slip_seat_boxes.htm

 

[sonoma]

Well captain K I was just reading this and was waiting to see if any one was going to post some thing that has already been done. nothing new is it Captain K. I have built boxes like this for years. you could buy a small box built to add radios and other items to it, and yes it is called a slip seater. I use to build a box made out of an aluminum suit case for years. it would have the radio of choice, amp, am fm and cd player. 2 external speakers, swr meter and what ever the driver would want inside the case. only time the driver would open it up was when they would put the coax inside it for storage and then remove it to hook up the antenna. most would have the antenna mounted on a pair of vise grips. i have put a gps inside one, satelite radio and so many more items . it was all depending on what the driver would want. radar detector. goodness this is nothing new. so use your imagination and you can built it just about any way you want it and what options you want to put inside it. one driver I remember building one for had it mounted on a 2 wheel suit case dolly to move it from truck to truck because it was too heavy just to carry it. i use to buy the suit case from either Lowes or Home Depot to build it for drivers. like Captain K stated you can buy a box with all the partitions and cut outs for every thing you want to put in it. this could go on for ever using your imagination.

 

[Sarasota Slim]

@LeapFrog: You get what I'm talking about. Although, the finished product will still be a mobile unit, as opposed to a base station, and I will, most likely, fabricate my own enclosure, instead of repurposing an existing one. You've brought up some good points to chew on. Good call on the mic jack conversion. I know I don't want to keep the RS mic, but a jack swap hadn't occured to me. You mentioned something about mic shielding; how would I go about that?

Also, I imagine, with my schedule (I'm away from home 6-8 weeks at a time), this project is likely to take longer than a month, lol.

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@Captain Kilowatt and Sonoma: A slip seat box is not what I was talking about. I'm a team driver, and I stay in the same truck for about a year and a half, so I have little need for such a thing. There have been times, however, that one would have been useful. I may build one of those, too, to keep on my top bunk, just in case.

 

[Captain Kilowatt]

@LeapFrog: You get what I'm talking about. Although, the finished product will still be a mobile unit, as opposed to a base station, and I will, most likely, fabricate my own enclosure, instead of repurposing an existing one. You've brought up some good points to chew on. Good call on the mic jack conversion. I know I don't want to keep the RS mic, but a jack swap hadn't occured to me. You mentioned something about mic shielding; how would I go about that?

Also, I imagine, with my schedule (I'm away from home 6-8 weeks at a time), this project is likely to take longer than a month, lol.

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@Captain Kilowatt and Sonoma: A slip seat box is not what I was talking about. I'm a team driver, and I stay in the same truck for about a year and a half, so I have little need for such a thing. There have been times, however, that one would have been useful. I may build one of those, too, to keep on my top bunk, just in case.

Yeah OK well with out any other info it was hard to tell what you are looking for exactly. It certainly can be done but the size of cabinet to house everything in would make for a pretty large mobile rig when finished. You might be able to stack the radio and amp boards to save some more room but you have to be careful about shielding. Some screening between the two would work. You could save more some room by eliminating the low pass filter. There is really no need for an LPF when running mobile anyway. Any interference you may cause while passing thru some place would only last a minute or less generally. The percentage of mobiles running LPF's is likely in the order of 0.0001%.

 

[firerunner]

Not exactly what your talking about but sort of. i have put it in my pickup and gone to a hill and made contacts.

 

[firerunner]

In the finished setup i have a power supply also. More of a to go box i guess.

 

[Sarasota Slim]

Sorry if I came off a little sharp, Captain. Also, sometimes communication is not my strongest attribute, lol. (Just ask my wife!)

I currently have a low pass in my current set up; it seems to help with some other speakers in my truck.

The radio, itself, isn't very big, nor is the filter that I have in mind. I also found a small amp kit that didn't seem to take up much space.

Once built, this thing will likely be tested, then set on a shelf. So, if it ends up bigger than planned, it's not a big deal. This is really just something to do, to see if I can do it.

 

[Sarasota Slim]

@firerunner : That's not exactly was I'm looking to do, but that's a spiffy setup, nonetheless. A mobile box for camping is a cool thing.

Lol, I started out with one project in mind; now I have three. (Original project, slip seat box, and mobile camping box) Ahh, fun stuff.

 

[Captain Kilowatt]

Sorry if I came off a little sharp, Captain. Also, sometimes communication is not my strongest attribute, lol. (Just ask my wife!)

I currently have a low pass in my current set up; it seems to help with some other speakers in my truck.

The radio, itself, isn't very big, nor is the filter that I have in mind. I also found a small amp kit that didn't seem to take up much space.

Once built, this thing will likely be tested, then set on a shelf. So, if it ends up bigger than planned, it's not a big deal. This is really just something to do, to see if I can do it.

No you weren't sharp. I just misunderstood what you were looking for. I am surprised however that you say the LPF helps regarding the speakers. An LPF simply eliminates or reduces harmonics and unless those harmonics are getting into the stereo and being heard normally an LPF will have no effect whatsoever on audio amps and speaker related issues. That's just the way physics works. No amount of LP filtering in the world will cure front end overload or audio amp issues. Sounds like there may be more at work there than it seems. If it works it works is the bottom line but I suspect it is working because of something not fully understood and it may not be as it seems.

 

[Sarasota Slim]

Captain, you may be right. To be sure, there is much that I do not, yet, understand.

The speakers that I refer to are the speaker in my tv, some cheap computer speakers that I have hooked to my tv (that tv is too quiet, especially when I'm pulling reefer), and an unused speaker that Volvo installed for the purpose of being an auxiliary speaker for the tv. (It's fairly useless)

All of those were picking up my radio transmissions, and now they are not. I had read that harmonics in my particular amp could cause that, and that a low pass filter might help. So I bought the filter, put it in the line, and it seems to help. It's entirely possible that something else changed, I guess, but I'm not sure what it would have been. The physics of it all, I don't quite have a grasp on. But, that's one reason I'm here; trying to absorb as much knowledge as possible.

 

[LeapFrog]

You've brought up some good points to chew on. Good call on the mic jack conversion. I know I don't want to keep the RS mic, but a jack swap hadn't occured to me. You mentioned something about mic shielding; how would I go about that?

Yes on some Realistic radios I have seen them use a small pcb (behind mic input), others they have the DIN receptacle soldered directly into the main PCB, I think this is what you will find inside your TRC-474. If the jack goes directly into the main PCB you may have to get creative, and add a wire with shielding for the audio line plus an extra cap or two on the rear of the 4/5 pin to chassis to help de-couple things.

On a TRC-431: The DIN receptacle is soldered into a small pcb with the with the factory chokes and de-coupling caps placed on it, for the conversion I simply reused the existing pcb, by adding wires in place of the original DIN pins, these wires extended a few inches longer to give me wiggle room during install. And I simply matched the pinout of the DIN plug to the desired "Uniden/Cobra" style pin out, and I'm able to use almost any standard CB microphone.

Another way to do it would be to mimic (or relocate) some of the components that are directly on the board but rebuilt in a "deadbug" or "manhattan" style free-floating construction off the back of the microphone input jack, closer to the *new* front panel.

This is all anecdotal, but what I can tell you for sure: How to go about it really depends on how that particular radio was designed, If you see ceramic capacitors from the metal frame to the pcb ground I would say you would be fine following a Cobra/Uniden 4 pin schematic.
[photo="medium"]4458[/photo] .
The TRC-474 may have a brother radio that was built by Uniden (usually 4 pin) in that case I'd copy the factory arrangement of the similar radio. Not all models sold by R.S. came from Uniden, but the ones that did... I can guarantee a huge chance exists the same radio was sold under a different model, with the same PCB inside.

An example of what I mean, the Realistic TRC-427 is basically just a Cobra 25 GTL/Uniden PC-66 without the mic gain control.

So I would copy the way the factory did it on the Cobra/Uniden and "clone that setup"
into the Realistic radio, this should work for you just fine. Not all Realistic TRC radios were made by Uniden; so in the end you will need to get creative! (You'll need a 4 or 5 pin female jack) the last Realistic I converted got a standard 4 pin jack, on some radios you may need to use a 5 pin!

Depending on your selected case size, perhaps you could simply buy an adapter instead (if room permits) that'd be a quick and easy way to use a more common mic.

From Wikipedia:

The term harmonic in its strictest sense describes any member of the harmonic series. The term is employed in various disciplines, including music and acoustics, electronic power transmission, radio technology, etc. It is typically applied to repeating signals, such as sinusoidal waves. A harmonic of such a wave is a wave with a frequency that is a positive integer multiple of the frequency of the original wave, known as the fundamental frequency. The original wave is also called 1st harmonic, the following harmonics are known as higher harmonics.

So round-about 27 mHz is the fundamental (or 1st harmonic), and the 2nd harmonic frequency is roughly around 54mHz, third order harmonics exist, and so on. For our purposes we like to keep the 2nd harmonic to a minimum, way down in the mud/noise floor as possible, the third order would not be an issue then. The higher in multiples of the fundamental you go, the weaker the signal becomes.

The factory service manual (not available for all models) explains the alignment procedure.
The point is we don't want our signal heard anywhere except the fundamental frequency.

From what you describe, that radio may have been "peaked and tuned". I have heard of radios causing these issues without power ("barefoot") because the 54 mHz TVI suppresion trap was fiddled with for an improper "tuneup"; the results (or so I here) were a lot of TV, radio, & computer speaker issues as you described, bleeding into other (much newer) devices.

A LPF will help block anything over 30mHz (depends on your filter) but the meter will show less output if the LPF was placed between the radio and meter.
(assuming the TVi trap has been fooled with.)
When some places "peak & tune" radios they incorrectly adjust or damage the 54 mHz harmonic suppression circuit, this causes the watt meter to show an increase in power. BUT I'd rather be clean, instead of showing a few extra "ghost watts" on the power meter. As the 54 mHz harmonic is measured by a watt meter (and added to the fundamental freq. power reading), but the added power is not even remotely on frequency. So any gains by doing this are false, and will lead to RFI/TVI issues!

In the wonderful world of 2-way communication I find that CB radio has more myths and folklore attached to it, than any other another 2 way service in existence. Peak & Tunes (crappy ones) are a subject for a whole another thread, but let's just say it is possible your radio may have been fiddled with in the past!

Not caring about possible splatter is always a negative attitude in radio, I don't feel that you want to splatter and it was a good call on using the LPF!

Unless you are interfering with the vehicles engine controls/electronics, you could in-theory get-by without a LPF in a mobile setup.
As a stickler (almost 11 meter purist) I 100% agree with Captain Kilowatt, if you are on the road and moving the issue could still be there but will not be as crucial as if in a base station (stationary) style operation.

If you pull the lids off the radio, do you see any coils that have been squished/spread into a slinky shape? Or a Brown/White cylinder with copper coiled around it, missing a ferrite core in the center?
Look towards the back of the radio, near the SO-239 antenna connector.

Also, if this is not going to be a base station unit when done.. You wouldn't need to concern yourself with a power supply, I was not 100% sure what direction this project is headed in when I mentioned buying a power supply. (Just run a 2 or 2.5 amp fuse in-line somewhere & you should be fine)
Also attaching a traditional s-meter to this radio will require some poking and prodding as I didn't notice this model uses an LED bar graph style meter.


Sorry for the long post!
Best Regards
-LeapFrog