The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

Hi Grease Monkey.. Why is it that everybody wants to use a BIG radio with a small amplifier? Consider that most single-stage amplifiers (one without a built-in driver stage) will multiply the radio's power by a factor of roughly ten-to-one. This suggests an amplifier with about 800 Watts peak output...

Uh, that little problem is "built in" on the 8-band Galaxy radios. What you are hearing is the second-harmonic frequency of the so-called "offset" crystal in the radio's PLL section. The PLL uses a crystal to "mix down" your VCO frequency in that radio. On CB channel 1,...

That echo board shouldn't pull much more than 15 or 20 mA. Won't overload TR28.

73

Bum external speaker jack?

73

Simplest solution tends to be the best one.

73

Does the receive/transmit LED on the front panel light up green? I'll guess that it doesn't change to red when you key the mike. Makes me suspect that they used different wire colors in the two radios. If they came from different production runs, or from different factories you may not be able to ju...

Electric fuel pumps cause a lot of trouble like this. Turn off the motor, and compare your noise level. The additional noise you hear with the motor running can not be filtered inside the radio, but only at the sources where the noise originates. A pain in the neck to install, mostly. And the risks ...

The receiver speaker audio goes up the mike cord, through the switch, and back down the cord's ground wire on pin 1. A bum mike cord can kill the speaker audio. Is the S-meter bouncing around on channel chatter in a normal kind of way? Or is it laying down the low end of the scale? This could point ...

The small pc board has filtering components on it. They prevent RF from inside the radio from "leaking" out and radiating from the mike cord. It's a legal requirement the radio's design must meet before it can be certified as a legal USA CB radio. In practice, those parts also keep stray R...

That's more than a little weird. There is a capacitor in the "Relative Power" circuit that feeds the meter on transmit. Well, when the "mod" button isn't pushed in, anyway. If your Jackson has PC board type number "PB-042", it's C176. My CBC International schematic does...

Ummm, Okay. To start, the schematic "callout" numbers you mention are not universal, but will be different for every radio brand and model. "R123" is not a meaningful description without identifying the radio, and expecially, the circuit board used in the victim of your experimen...

Well, I found the guy a manual. http://bama.edebris.com:81/download/swan/1200/swan1200.pdf You might prefer to right-click on "Save Target As" with that link. A left click will launch Adobe reader as a browser plug in. A shaky proposition with some browsers.... Not a wise thing to stick yo...

Boy, did I ever blow the chance to hawk a product.... Don't know if you found the data you need. But if the high-voltage section has flamed itself from the first 5 years of use, we have an improved replacement. http://www.nomadradio.com/HDHV Single HV board, replaces the two side-by-side boards used...

Don't know if the 'mod' created your talkack, or if another failure is causing it. I'd suggest that first you tighten ALL the mounting screws on the main printed-circuit board. They tend to come loose, and can cause this all by themselves. If enough of the ground connections on those screws come loo...

Microphones break far more frequently than radios. The cord is the number one failure, especially where it enters the mike, or the plug. If you don't have another mike to try on the radio, or another radio to try on the mke, this is a lot more trouble. Taking apart something that isn't 'broke' could...

Hi Rick, I want to thank you for carrying my water here for so long. I'm still listed as 'moderator', but life and business got, well, busy...... I'm pleased to see so many pats on the back posted above. My personal preference has been to conduct troubleshooting discussions on the main board, rather...

Hi Max, That thing sure is old. They used two types of relay. First was a flat, opaque-plastic relay made by Potter and Brumfield (P&B) marked "R50-E2-Y2-12VDC". This part was used for both the main and the preamp relay on early models. After a while they figured out that the "R50...

Uh, calibrating a frequency display is a lot like calibrating any other kind of measuring tool. You compare it to a high-precision reference and adjust the trimmer cap until both units display the same frequency. The counter's calibration is only part of the picture. In that radio two frequencies ar...

Umm, I would recommend holding out for a description that's edited to agree with the part layout and ID markings in your radio. "Same as the Cobra 29" means looking at the schematic diagram for each, and "translating" parts that have the same function in each model. Trouble is, p...

Less tricky solutions include using a so-called "noise-cancelling" mike. They tend to reduce feedback. Even less tricky method is to use a radio with a mike gain knob. That Cobra model doesn't have one. Turn the mike gain down far enough, the howl will stop. If you put the speaker far enou...

Like MrSixString says, you have to readjust the "Cal" knob for the higher power level before you can read SWR with the amplifier on. And if the SWR is still high once you've reset the Cal knob, it means that your amplifier is putting out extra harmonic frequencies. Since most of them conta...

Yep. It is connected to an input on the custom computer/channel-selector chip in the radio. Changing that one part causes the chip's internal program to now deliver all the frequencies that WOULD have made it illegal to sell in the USA. The simpler they make it, the better the radio will sell, as a ...

Um, okay. I gotta ask. Did you try Ebay?

Or, you could try Yahoo auctions.

73

Umm, turning them around the wrong way will definitely pop them, and fast. If the amplifier has a bias circuit, it could have been damaged. If so, it could feed way too much DC bias current into the RF power transistors' base leads. THAT would pop them too, but usually not quite so fast. If you remo...

Um, there is more than one manufacturer making RF power transistors, and more than one type made by each of the folks who do. And the power rating on the transistor's specification sheet is not the whole story, either. Some amplifiers using two so-called "60-Watt" transistors will deliver ...

A decent wattmeter, like a Bird with a PEP adapter, a 'scope with response to 50 MHz, a counter with an external 'probe' input and a decent signal generator should get you by. A stable, precise 1 kHz tone generator with a speaker on it is the easiest way to set SSB transmitters on frequency. Had to ...

Before you know it they'll be asking how to stretch the duration of the RB to two or three seconds after they unkey.

Where will it all end ? ? ?

It's madness. Madness, I say!

73

Hi SLim Jim, Rather than reply direct by e-mail, I tend to just post a reply here. The single largest supply of low-power FM broadcast hardware here in the states is http://www.ramseyelectronics.com I'm just assuming that FM broadcasting in Z-land occupies the same approximate frequencies as here in...