• You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

Mods

Walterlu

New Member
May 21, 2022
1
0
1
50
‎Hello good night, someone save how to modify a cobra 146 gtl, for the band of 10 meters? 28mhz, thank you very much.‎
 
Last edited by a moderator:

The PLL in that radio requires both a new crystal and an oscillator circuit for that crystal. In addition, the kit's oscillator must contain its own clarifier circuit. The factory clarifier will not function properly by itself outside the 40 CB channels.

The internal frequency feeds into pin 4 of a mixer IC. The channel-expansion circuit feeds a larger signal into this same pin. This larger signal takes over and hijacks the PLL to a new range of 40 channel frequencies.

The crystal you will need to cover 28.305 to 28.745 MHz would be 16.72 MHz. I have no idea if anyone sells that frequency. And if you can find a crystal for a frequency near this, it should work okay. But of course you'll need that oscillator circuit as well.

The dominant product sold to do this for decades was sold under the brand name "Expo 100". The kit sold for this radio was their type "N". If you can find a "N" kit, you'll find two crystals inside with cryptic letter markings.

Simply substituting your 16.72 MHz crystal for one of them will be a good start.

You will be moving the radio's frequency coverage by nearly 1.5 MHz. This will make full alignment of the radio necessary. Most of the tuning-slug adjustments will probably have sufficient adjustment range to reach the new band. But you'll probably need to follow a complete "dead radio" alignment procedure. Naturally that will start with making the PLL circuit lock onto the new operating frequencies. Once that is achieved, you can find out if the tuning adjustments in the receiver and transmitter circuits have sufficient adjustment range to be peaked properly for full performance.

This can be done, but very little published wisdom seems to be available for coping with the setup challenges.

Best of luck and 73
 

dxChat
Help Users
  • No one is chatting at the moment.
  • dxBot:
    Tucker442 has left the room.
  • @ BJ radionut:
    LIVE 10:00 AM EST :cool:
  • @ Charles Edwards:
    I'm looking for factory settings 1 through 59 for a AT 5555 n2 or AT500 M2 I only wrote down half the values feel like a idiot I need help will be appreciated