Kinda like Christmas morning....

[nomadradio]

So here's the next piece of this puzzle to get addressed. Different slice highlighed in purple this time.

Got all 50 of this one built. Now still need to add wires for the carrier control.

This one goes into AM-only CB radios like a Cobra 29. The wire jumper that feeds power to the driver transistor gets pulled out. The two bare wires on this module go into the two holes where the jumper was removed. It comes with a piece of industrial-grade adhesive foam on the transistor. This stuff is called "VHB" and sticks like elephant snot to a clean surface.

It's best to swab the surface of the heat sink where it will be attached with your favorite non-residue solvent. Rubbing alcohol works fine in a pinch.

Any tech who doesn't want to be a Kevorkian will inspect both sides of the mica washer under the final transistor before making any high-performance mods, or even turning up the modulation limiter. This one was nearly dry on the heat-sink side.
Typical.

The two bare wires on the PNSVK module go into the jumper-wire holes. They're marked "JP36" in this version of the radio.

A good squeeze is necessary to bond the VHB's adhesive to the heat-sink surface.

I used the radio's front-panel "SWR Cal" control to attach the three contr
ol wires. It's a tight squeeze to get them soldered, but doable.

What remains on the top side is to strip a half inch from the end of the green ground wire and insert it into the handy hole at the rear corner of the pc board.

The reason for stripping so much from the end of the green wire is that you'll have to lap-solder it to nearby component leads near that hole.

All that remains now is to set the minimum carrier power you want with the SWR Cal knob all the way to the left. That's what the trimmer pot on the PNSVK is for.


I hate to disable a radio function even when I hijack a control on the front. The SWR meter can still be used by installing a 5.1k or 4.7k resistor here, with the clockwise and wiper wires at one end, the ground wire at its other end.

Slide a sleeve over the mess to keep it from getting into trouble.

Of course, all these loose wires need to get zip-tied down securely. Shouldn't need a pic for that detail.


This one's not ready for Ebay yet, but that's the idea.


And yeah, it works in pretty much any 40-channel AM-only CB. Not recommended for a 23-channel radio. Makes a lot of them get squirrelly.


73

 

[sonoma]

so far it looks to be a very clean addon for a AM radio. reminds me of the MD1 modules that are out.

 

[Handy Andy]

Nice Job Nomad - excellent!

Should be made into a "How To"...

I don't know if it will put you into contention with "Shark Tank" but I can imagine several countries overseas are reviewing this thread heavily as we speak...

 

[sonoma]

the more I look at it the board reminds me of the variable power mod for the transformer modulated radios that is in a exploded view on cbtricks. not having one here to see close up at least has some versions of that mod but just a lot cleaner install.
this should sell good on ebay for do it your selfer radio mod guy's.
is the trans on your board a tip120 trans?
this kit looks good and a lot of planning going into it.

 

[711]

Same thing is the dial a watt but I like Nomads board a lot better. makes a cleaner install. I do this on a Uniden 880. Nice work Nomad

 

[nomadradio]

I'm still skeptical of how the "Ebay-nomic" price will fly for a single unit. My plan is to include a 5k panel control that can be installed in the front panel (or wherever) of a Cobra 25 or 29-type radio. We have seen more than a few radios with that control burned out from an ill-informed talkback or a previous carrier-control mod. The control is not expensive in a batch of 100 from China. Gotta figure the aggravation it would save is worth the cost of including it with the board.

Like the keying board, a single one will seem expensive. But a quantity of two or five will have a more-attractive unit price.

It will be up to the installer as to which is easier, swapping the new control for the old one, or wiring up to the existing SWR Cal control. But adding that part does drive up the cost a bit.

The transistor in this batch is a TIP122. Just a higher-voltage rated version of the TIP120. I watch for a deal on that part in quantity. The TIP120, 121 and 122 are interchangeable in this setup. The major difference between them is the breakdown-voltage rating.

The whole "planning" angle has more to do with the previous four or five versions. We originally built these solely to save labor when a customer wanted a carrier control. The first few versions had some "clumsiness" issues with the layout.

But after this many iterations, I think we have it pretty well ironed out.

Just one boo-boo in the pic. I didn't actually hook this radio up and try it until the next morning. Found the diode in the pic is backwards. Oops.. Worked a lot better after I turned it around. Copying what you see in the closeup pics won't work, if you were to duplicate it on perfboard as seen above. That diode has to point the other way.

Works "a treat" with the diode turned the right way.

73

 

[nomadradio]

NEXT!

Next in line is a 600-ohm audio isolation transformer.
Highlighted in purple here.

Pretty mundane, yeah.

This serves to isolate the ground in a transceiver's mike-audio circuits from an external audio source. This came up to simplify the job of installing the Motor Mouth Mauldulator in a case with the power supply, controls and output transistor. Works in a radio for "Direct Inject" hookups, as well.

To use a quarter-inch 'phone plug for the external input, it's important to use one that has a plastic bushing. You don't want any connection between that jack and the radio's chassis. The output side of this transformer will usually go to a toggle switch, so you can still use the radio's original mike socket, or the direct input.

The two ferrite-bead chokes and the two bypass caps serve to keep stray RF energy in the room from sneaking into the radio through the 'direct' input jack.
The solder side isn't particulary interesting. Was the only place I had room for the ID and copyright notice.

I checked the frequency response of this transformer with a 600-ohm load resistor on it. It rolls off below about 50 Hz, and above 10 kHz or so. More than "wide" enough for any radio it may get used in .

This is another "too cheap to sell" sort of Ebay item. The single-unit price probably won't look terribly attractive. But in quantities of five or more it will compare favorably with hooking up all this stuff manually.

Maybe.

73

 

[711]

Nice work bro, I like the isolation board too. I built a few "Ibox" boxes. Your board is nice and compact. I get the cheap TM018's. Id buy a few of your boards, each on definitely solve lots of problems

 

[Shadetree Mechanic]

I would like to get one of the variable power boards as well as an audio isolation board. I will be keeping an eye on your eBay page for sure.

 

[Shadetree Mechanic]

Any update on the other gizmos? I put the Peel N Stick in a couple of radios, works great.

 

[nomadradio]

The isolation transformer has become a victim of "software-itis". Proper directions really count.

Turns out that you have to install it correctly to get the desired result.

Easy for me to say, I already know how. But getting the buyer to fully insulate the audio-input jack from the chassis of the radio turned out to be a tough sell. I started looking for a cheap source of quarter-inch phone jacks with a plastic bushing. The more-common jacks with a metal bushing require a pair of insulating washers, the way the headphone jack on the front of a Cobra 2000 is mounted.

The plastic bushing takes care of this. Never did buy a big-enough batch of them, to pick up where I left off. Clearly this needs to be packaged with the board.

But the users who installed the input jack for the direct audio would simply mount the conventional metal-bushing jack on a grounded metal rear panel. This totally defeats the whole point of isolation. Caused all kinds of odd feedback-squeal issues.

Oops. That's what this thing is meant to prevent.

The other detail that just jumped out at us like a costumed trick-or-treater was the need for a relay, so the computer audio doesn't get force-fed into the receiver's audio. You really only need it while transmitting. We hand-wired a relay into the radios that needed it, and key it from the radio's internal transmit voltage. But this doesn't seem like a winning strategy for folks who want a self-contained solution.

Development is always a slow process when I pay for it myself.

73