Added RF Gain to my Cobra Ultra III

[cooljay]

Since the U3 board is the same board as the DX IV which has RF Gain switch, I hit up srtga for some pics of the inside of his DX IV for the wiring, pulled up the schematic for the DX IV and added RF Gain to my U3. Over all it was a fun project that took me a couple of days to complete and the results are better than I expected. I took the squelch pot/switch from a spare U3 I had laying around and the parts I needed to add.

The people you hear in this video are at least 20+ miles away.

[ame="http://www.youtube.com/watch?v=L3xK3tY9GSI"]YouTube - Cobra Ultra III CB RF-Gain mod[/ame]

[trailtow]

any chance of a diy on the upgrade

[cooljay]

I'll get a write up and some pics of how to do it and get it posted some time tonight

[trailtow]

sweet thanks man cn't wait to do this mod to my old cobra which is now in my friends truck

[cooljay]

I'm trying to write this in easy terms, the best I can so if you get confused or lost just reply or PM me and I'll help you out.

What you need to do this mod:

1x 50K-Ohm Potentiometer
1x 1N4148 Diode
1x 10uf 16v Capacitor
1x 47-Ohm resistor (1/2W is all I can find at RadioShack)
Some 22AWG wire, I used multi-color to easier ID each wire.

Now you can solder your wire to your Potentiometer either before or after you solder your wires onto the board, what way you wish to do it is up to you. The order for the wires is:

Pin #1 on the pot -> VR2D
Pin #2 on the pot -> VR2C
Pin #3 on the pot -> VR2G1

All these are right around the front where the squelch wires, volume/power are at. See picture below, Green = VR2D Red = VR2C and Black = VR2G1 (right next to VR2G).



Next, at the back of the board near the antenna hookup and the coils you will see 2 empty spots labeled DR2 and CR19, line up your diode so the dark strip of the glass on the diode is at the end of the arrow on the board. If this is confusing you can look at the other diodes on the board to better understand what I am saying.

After the diode is soldered into place, place your capacitor into place with the negative side placed on the side with the filled in white and solder it into place.

Now, on the SOLDER side of the board RIGHT below where you solder the capacitor on, you should see a square marked RQ3 with a little bit of solder on there already, this is where you need to solder your resistor to.

Now power it on and give it a try, if everything is correct you should now be able to adjust your rf gain.

[yamaha1]

VERY COOL!

I may just have to add this to mine! Nice write up!

[Stealth Stalker]

You've inspired us all with these mods, guys! So I have started a DIY archive sticky at the top of this forum to keep track of these threads, as well as links to off-site mod pages. Thanks!

[srtga]

Looks and sounds great! Cool modding these cheap-o radios aint it

Oh yea, adding the DIY was a great idea. I've done most of the mods and they're cheap and easy to do.

This is a pretty good SWR tutorial:

http://www.firestik.com/Tech_Docs/Setting_SWR.htm

I like it because it shows how to adjust the different types of antennas.

[cooljay]

Just be careful if you turn the RF Gain up all the way you just might hear TOO much! The skip is pretty strong today and had the RF Gain all the way up, listening to 19 heard truckers in GA asking Northbound traffic about Florida and talking about how it was clear for him most of the way thru to SC! So you just might hear a bit TOO much with this mod