Cobra 146 Frequency Mod For Switch Kit and Others

[ExitThirteen]

I'm going to ask a really dumb question, and please don't take it as an insult.

Are you wanting to get upper and lower channels out of the radio? Or are you wanting just the upper channels only (above ch.40)?

Just curious.


~Cheers~

 

[sdmahr]

I only want channels above 40.........I don't care about going below 1. I cannot get the radio to tune for the highest switch position. I'm awaiting a diode which is supposed to help.

One position of the switch tops out at 27.645 or so and the high position of the switch tops out at 28.045 or so. Its the high position I cannot get to lock.

 

[pushbiker256]

L13 in the cobra 146 schematic looks different to that in the galaxy N kit instruction posted earlier on in this thread.

In the cobra 146 it is a coil but in the galaxy N kit it is a transformer ?

Did you modify L13 so that is configured as the galaxy instructions ?

Not sure if this is important, just something I noticed while reading...

Still don't know how these really kits work..

 

[sdmahr]

I installed the kit exactly like the instructions show that came with the expander. I've all but given up trying to get the thing tuned for all three switch positions on the expander board. The best I can do is get 40 channels normal, 40 channels in the "LOW" position of the expander, and up to about 12 channels in the "HIGH" position of the expander before the PLL unlocks. I've tried all the recommendations given here and no dice. (Caps, diodes, etc.)

Covers off....sitting in the corner.....looking for ideas / recommendations. I've put several of these boards in other radios with NO problems at all....tuned up and work like a champ ! !

 

[Robb]

VCO voltage?

 

[pushbiker256]

Are your instructions the same as in post #20 ?

 

[Robb]

Yep.
See step #2 in 'Alignment'; the VCO Voltage adjust . . .

 

[sdmahr]

I've been through step 2 a hundred times. I can get it locked in 2 switch positions, but the 3rd is dead....won't lock. If I adjust it in, then when I go back to the opposite switch position its dead again....no lock. Its like the VCO / PLL isn't "broad" enough to handle the whole range I'm seeking.....which is channel 1 - 28.045 (what the expander is supposed to be capable of).

 

[Robb]

I've been through step 2 a hundred times. I can get it locked in 2 switch positions, but the 3rd is dead....won't lock. If I adjust it in, then when I go back to the opposite switch position its dead again....no lock. Its like the VCO / PLL isn't "broad" enough to handle the whole range I'm seeking.....which is channel 1 - 28.045 (what the expander is supposed to be capable of).

The answer is in your statement, Slick.
Now you have to get there . . .

 

[sdmahr]

Yes Robb, now I have to get there which in this case is 99℅ or more of the battle! So.....any pointers on how to get there?

 

[sonoma]

when you say it is out of lock is stating you have lost receive and trans both or is it that you just do not have any power out on transmit. when you key the radio will you get any freq reading on a freq counter when keyed.

 

[sdmahr]

Yes, when I say out of lock both TX and RX do not function. No power output, no green RX light, no red TX light when keyed.

 

[pushbiker256]

Have you seen this page ?

SECRETS OF BROADBANDING CB RADIOS

Since you have already tried steps 3and 4, the next step is number 5. Change the emiter resistor R98 ( Cobra 146) fom 1k to 220 ohms ??

When you modified L13 did you have to cut any tracks ??

 

[ExitThirteen]

If you can't get it to lock on the "hi" switch setting, you'll need to adjust L14 a smidge to lock it back in. Then re-adjust L13 again accordingly. L14 is your actual VCO can. L13 is the "tripler" can. Get L13 setup to where you have the "low" switch position working, and then flip to channel 40, with the switch on the "hi" position, and tune L14 until you get 28.045. When that occurs, go back to the center position on the switch, and go to channel 1. Retune L13 as necessary to dial in channel 1. Now check all switch positons, you should have full coverage from 26.965 to 28.045.

Hope this helps, good luck!


~Cheers~

 

[sdmahr]

Pushbiker256: thanks for the broad banding reference. I'm going to employ some of those techniques to see if I can get it there.

Keeping my fingers crossed......