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Author Topic: CB conversion to 10 meters  (Read 11073 times)
KJ4RQV
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Posts: 130




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« on: May 28, 2010, 05:16:25 AM »

Ok, let's start off by agreeing that I AM cheap! Also understand that I do not want to break any laws! I would like to add a portable rig to my shack.

I have a Johnson Messenger 23 channel crystal controlled cb that was given to me as well as a Cobra 146 GTL and I have never used either one of them. I am seeking advice as to the feasibility of converting one of them to SSB 10 meters.  I suppose the SSB part leaves the Johnson out but I am really unsure about this idea and its practicality. As I said, I have never been on CB and am focused on the ham bands. I currently own a FT-101ex (with 10 meters), A Yaesu 2900 and am building a Small Wonder Labs PSK20 for digital when I up grade to General.

I hope to take and pass my general test in two weeks and this seemed like a fun project plus I don't like to just have this stuff sitting unused. Thanks for your thoughts on this.
Don
« Last Edit: May 28, 2010, 05:32:08 AM by Don Bukar » Logged
K0PD
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Posts: 60




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« Reply #1 on: May 28, 2010, 05:35:46 AM »

All i did was put Cobra 146GTL Mod in my search engine and got all kinds of info on converting your 146. It does appear tho that 27.860 is as high as it will program. The old Johnson not worth the effort. So just enter Cobra 146GTL Mod and that should answer your query.
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WO4V
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« Reply #2 on: May 28, 2010, 10:09:23 AM »

I did a bunch of these conversions back in the day when you could get good CB ssb chassis to work with. A radio with a pll02a or upd858 processor chip would be an excellent candidate. Nowadays, they are getting scarce as back in the 80's the gubment forced the CB manufacturers to use frequency-determining chips that could not be externally modified for increased frequency coverage. Keep in mind when you embark on a modification project that if you smoke one of the old chips that can be modified, you are basically SOL as they have not been made in many years...

You will need a "SAMS" repair manual for the 146...these are still around on ebay and such...trick is finding one for your model.

Basically (very basically!) such a mod involves locating the frequency-determining circuitry and "re-wiring" the PLL (phase-locked loop) chip so you can change the programming logic voltages. You will have to look up the chip and its pinouts. A good source of information is Lou Franklin's publications, among them "The CB PLL Data Book", "Understanding and Repairing CB Radios", and the classic "The Screwdriver Experts Guide". Lou's business used to be called "CB City International". You can google and see if he is still in business and if these publications are still in print. If not, you might be able to find them on ebay, and I have seen them (rarely) at hamfests. The old "Secret CB" publications are great sources of info on modifying these old rigs (and ham rigs, too!) and I have seen them in CD format on ebay. Lots of reading on these conversion techniques will get you up to speed on what you are trying to do. The "Screwdriver Expert's Guide" actually carries you through some mods step-by-step...many of the old chips such as the 858 were extremely broad-banded in their frequency-generating capabilities because they were used in equipment other than CB's.

Keep in mind that since you are jumping the radio's frequency coverage UP one Megahertz or so, you will most likely have to go through the receive and transmit chains in the radio and re-align them for better performance, or your rig will be extremely lame (deaf, and low power) in BOTH receiving and transmitting response. Common tricks (beside basic alignment) include modifying some of the inductors (in the receive chain) for lower "Q" (broadbanding their frequency response). This is not as daunting a task as it may seem, as it generally means changing a tap on the inductor via cutting traces on the pcb and jumpering, etc...speaking of cutting traces and jumpering, you will need an X-acto knife and some very small wire, as well as a soldering iron with a small tip in th 15-20 watt range. Desoldering braid is a necessity (if you do not have access to a commercial grade solder-sucker) a good magnifying glass with a light, and lots of high power reading glasses, especially if you are an OT like me. I no longer tinker with stuff like this due to loss of eyesight...and remember when you are cutting and jumpering that rare old pcb, if you screw it up sufficiently, a replacement may not be easy to find!

Other equipment that is useful for this sort of tinkering:

A good multi-meter (a necessity).
A good 60 MHZ or better 'scope.
A frequency counter.
A good dummy load.
A good signal generator.
A second receiver or transceiver (general coverage)...a receiver can be used in a pinch in place of a frequency counter and a transceiver can do that AND replace a signal generator...(sorta)
Desoldering equipment.
Ground strap for your hand....
Grounded soldering iron...
Assorted hand tools for really small stuff...cutters, pliers, x-acto knife.
A good lighted workbench.
Jeweler's eye piece.
Head worn magnifier (look in arts and crafts places for these).
Small alligator clips and jumpers...
Small diameter solder for pcb work.

I do not want to discourage you as this kind of stuff will really teach you a LOT about how radios operate and how to repair and maintain them, as well. I learned most of what I know about electronics and radio from doing just what you are contemplating. Watch where you stick your bare fingers, as even though a 12 volt rig might not be lethal, you can still get a nasty RF burn if you transmit into a finger! A tube type rig can kill you! My first rig was a converted SSB CB and I made a lot of satisfying contacts on 10 with it's 3 or 4 watts output. My second rig was an FT-101ex, like yours...boy! what an improvement over the CB! I wish I still had that rig. Yeah, I know you can still find them, but I have a lot of stuff to tinker with on my shelf, and my interests have shifted nowadays...

Good luck, read a lot, and have fun!

73, Dave

WO4V
« Last Edit: May 28, 2010, 10:23:02 AM by David Kyles » Logged
KD6KWZ
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Posts: 276




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« Reply #3 on: May 28, 2010, 10:38:03 AM »

There's a Yahoo Group with this in mind:

http://groups.yahoo.com/group/CB2HAM/

Note you DO have to be a licensed ham to join them. They are not helping "freebanders".

Then, another site has some good xtal charts:

http://www.cbcintl.com/docs/xtals.htm

I'm looking to convert a Cobra 138 AM/SSB to 10 or 12 meters. You do have to look out for the "odd"  10, 10, 10, then 20 kHz frequency sequence jumping of the established CB channels. 

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AD5X
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Posts: 1430




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« Reply #4 on: May 28, 2010, 12:27:50 PM »

I published a detailed conversion of the Cobra 146GTL to 10 meters in the June 1990 issue of Ham Radio Magazine (their last issue) - pages 30-33.   If you have the Ham Radio Magazine CD ROM, you'll be able to find it there.  If not, contact me off line and I'll see what I can dig up.

Phil - AD5X
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W5FYI
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« Reply #5 on: May 28, 2010, 01:03:03 PM »

I've done several CB-to-10 conversions. Just recrystalizing is fine for the FM band, but is too restrictive on SSB for my tastes. One of these days I'm going to convert a spare Cobra or Sears Roadtalker by replacing one of the crystal oscillators with a VFO (and I think I may have Phil's article stashed away somewhere).

When we've got sunspots, 10 meters is a blast! This week's sole spot will shortly rotate around the sun's western limb and out of sight. You'll have fun converting the rig to 10 meters. GL
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W3LK
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« Reply #6 on: May 28, 2010, 03:45:22 PM »

You can pick up used RS 10m rigs for far less than the effort of converting a CB radio, not to mention that a real 10m rig has a VFO, not channels.

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KJ4RQV
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Posts: 130




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« Reply #7 on: May 28, 2010, 04:38:49 PM »

Wow! Thanks for the replies. I think that this is more than I can handle at this level of the skills I have. I would probably be better off selling the Cobra and just saving for a good used multi-band rig. I do appreciate your opinions. That is why I asked!
Don
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KD8GEH
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« Reply #8 on: May 28, 2010, 07:16:37 PM »

Hi Don,

Had to put my 2 cents in as well.  I have a 148GTL converted to 10 with a jump switch and clarifier mod. Works pretty good, but its a little of a pain to keep track of where you are without a counter. I have a couple other rigs that have digital readout, work just fine on a tight budget.
Contact me direct my call at arrl dot net if your interested.
See you down the LOg.

73,  Dave KD8GEH
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AC5UP
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Posts: 3875




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« Reply #9 on: May 28, 2010, 08:18:39 PM »

A few years back I found a web site with a collection of mods... Can't find it tonight, but aside from that it might be worth mentioning. Two or three of them were for generic Cobra CB's and used an interesting technique when dealing with the typical three-rock PLL synthesizer.

Instead of changing out the 11.275 MHz crystal it was left in place and a small PC board with a common 12 MHz CPU crystal, trimmer cap and buffer transistor was added. The clever part of the mod was that after cutting only one trace the new oscillator fed the 1st RX mixer and final TX mixer while the PLL circuit remained unchanged. In effect this moved the rig ~1 MHz up band without affecting the PLL and was easy to un-mod.

As a bonus, if the 12 MHz rock was tweaked to 11.995 MHz the new channels would all be on "0" frequencies.
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N4NYY
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« Reply #10 on: May 30, 2010, 06:47:36 AM »

I's not a matter of being cheap. First of, most talk is done on USB. Secondly, the you need a VFO, as there are no "channels" on 10M. Also, the filtering is nice, and CBs don't have it. Take it from someone that does both, 10M and CB for local rag chew. Get a cheap used HF rig.

Lastly, stay away from the 23 channel crystal rigs. Theyir crystals drift like unanchored boats after 30 years, and are way off.
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KI4SDY
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« Reply #11 on: May 30, 2010, 07:24:47 AM »

Why ruin a good CB radio to make a less than wonderful 10 meter rig? Huh If your not going to use the CBs, sell them on eBay and buy a good used Radio Shack or MFJ 10 meter rig. I own both and they perform very well. Then, you can concentrate on building good antennas for them. You will be much more successful and get to enjoy all that ten meters has to offer, cheap! Grin   
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N1YRK
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« Reply #12 on: June 17, 2010, 12:36:30 PM »

So, I have a pile of old CBs. Most of them are AM, old xtal mixing types. The sole SSB radio is a Sears SSB. This is not labeled 'roadtalker', so it's older I guess. Model 61-36772, with a built-in power supply...but I need to find the pinouts for the power jack, as the cable wasn't included (anyone have this?) My desire is to use this as a PSK31 rig, so it needs to be lifted to 28.120 Mhz.

The crystals are soldered. My idea is to cannibalize one of the AM radios for a crystal, and replace one of the ones in the SSB radio, to bring it up over a Mhz. Of course, I'll need to re-tune the filters and so forth. Luckily, this radio was made before large-scale integration was the norm, so many inductors have tunable slugs.

I am wondering, firstly, if anyone has experience with this radio, particularly in 10 meters conversions. Next, if someone knows what the mixing scheme is. Thirdly, any crystal sources which are useful - either from other radios mixing, or microproccessor cyrstals, or what have you. I'd also like to get an idea of what I need to tune. Perhaps a schematic would be useful.

If I don't get any info on the mixing scheme, I'll get out my dentist's tools and start to read the xtals, hopefully they are marked. And I'll do that for the AM rigs I have as well. But before I do anythnig, I should probably test these would to see that they are functional CBs, and the ones that aren't get marked for canniblization.  I'll post the model and test results here, for anyone who wants to help me to see.

73,
N1YRK
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OH2FFY
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« Reply #13 on: June 22, 2010, 11:03:38 PM »

Why ruin a good CB radio to make a less than wonderful 10 meter rig? Huh --

Nothing will get ruined if the conversion is carried out properly.
The performance will be more than acceptable, again, if the conversion is done properly.

A converted CB doesn't mean a poor performing dog. !
My 20 meter conversion is coming along well, with some final work still needing to be done on the PA.
The RX is perfect, and it is more sensitive than my Ham gear.

The idea behind CB conversions is not a way to get a cheap radio.
It is the technological challenge of the work involved.
Technical understanding, challenges and experimentation are the basis of the Ham radio hobby, perhaps some have forgotten that.......

The CB conversion process will make you curse , scream , pull your hair , pull your wifes hair , pull the dogs hair , , all out of frustration.
But in the end, you will have achieved something which others feel , , is just a bit too hard for them.

For those Hams that aren't appliance operators or scared of a challenge, join up to the group--
http://groups.yahoo.com/group/CB2HAM/

Regards

gregW:-)  OH2FFY
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