Modified CB Radio for AM Band Broadcaster

[loverboy]

In the 90's a GE CB Radio (PLL2) was modified into an AM band low power (10 watts) broadcast station and was actually used in a remote coastal town of Mindoro, Philippines during a local election. Small AM radios were given away to several barangays in favor of some candidates so they won in that election. This has opened door to the importance in tidal and typhoon warnings in the area.

MABUHAY from the Philippines!

[formulamojo]

WTF??????

[QRN]

Originally Posted by loverboy

In the 90's a GE CB Radio (PLL2) was modified into an AM band low power (10 watts) broadcast station and was actually used in a remote coastal town of Mindoro, Philippines during a local election. Small AM radios were given away to several barangays in favor of some candidates so they won in that election. This has opened door to the importance in tidal and typhoon warnings in the area.

MABUHAY from the Philippines!

Having been a radio operator for 31 years, a ham for 18 years, an electronics tech for 25 years and a commercial broadcast engineer with experiance in AM and FM broadcasting for 22 years I would REALLY like to see that mod. Until then I shall say . It's a very,very long way from 27 MHz to 1.5 MHz or thereabouts and it would have been easier and better to simply build an AM transmitter than to TRY and mod a CB radio for that band.

[loverboy]

OK, I did not know that this would attract people. It’s really a simple task that it took me a day to figure out as well as build it. A GE CB radio model B (and others) uses a PLL02 synthesizer. The phase lock loop signal that goes to this chip can go below 1.6 Mhz in 10 Khz channel increment. I just buffered this signal using capacitive coupling (like an audio amp) directly to the finals. The product gain bandwidth of the final (easily go over 10 watts) at this frequency is good so I just windup a broadband ferrite to step up the collector impedance (20 to 40 ohms) for best power transfer and load it to a simple low pass filter. I lowered the output and add more cooling fins since it’s a continuous duty. That simple, really. The antenna was much harder to match as per the installer.

I modified (without transverter) over a hundred CB radios (majority were SSB) from 75 up to 6 meters and do mono as well as multibanders. My favorite modification was using a 7.8 Mhz intermediate frequency (cobra, president, etc) to operate at 40 meters. It was my greatest challenge since at night it becomes noisy (image) but was able to resolve by using a 7.8 Mhz crystal that acted as a sharp (over 30 db) band trap in the front end.

Mabuhay from the Philippines

[park]

OK, I did not know that this would attract people.

Of course you didn't...............