Recent content by nomadradio

NGP antennas are a half-wavelength stinger. The feedline length is an odd quarter-wavelength. The coax braid does not connect to the antenna. This makes the coax a step-up impedance transformer. The loading coil on the stinger makes it functionally a half-wave radiator with a high feedpoint...

Does L22 have a well-defined peak? I have had my share of aggravations with a bad L22. Beware of the slug being dead-flush with the rim of the hole when it appears to show a peak. That would indicate L22's internal capacitor has failed open. 73

Just wish I could remember what color wire on the mike socket is the receive-speaker circuit. Taking that wire loose might reveal trouble on the mike sockets pc board? 73

Oops. Didn't pay attention to that detail. The 2SC1419 AM modulator transistor is a famous point of failure in that and other similar radios. If sideband is okay, there's no reason to pay any attention to the final transistor. I'll betcha DTB is right. 73

Get a can of "duster" from the office-supply store. Key the mike until the transmit fails, then turn the can of duster upside-down. Now squirt the final transistor with the can inverted. This will spew liquid onto the final transistor and chill it severely. If the wattmeter jumps back up...

The italian Prosistel rotator used a single worm gear with the motor's axis sticking out the side of the tower. This guy went one better, driving the main worm gear with a second one parallel to the tower. Looked bullet proof to me. Just can't remember the product name. 73

There's an understatement. The one with two worm-drive gears would probably be apropriate. Can't remember the name of that one just now. 73

Back when we repaired linear-regulated power supplies, the S_T brand 2N3771 from Mouser worked like it should. Most likely what they're selling now. Oops! Just checked, not in stock. Been a while since we bought any. Used them to repair the suicidal power supply in the Galaxy...

You would think so, but not in practice. This is a routine mod for truck driver radios that have acoustic feedback howl from the talkback. Doesn't seem to result in audio-chip failures that we see. 73

If this were spurious oscillation coming from an amplifier stage, the frequency would not be stable. It would wander randomly. The transmit mixer in that radio can simply pass through harmonics of the 7.8 MHz carrier frequency if the local-oscillator input is disrupted, but the second harmonic...

The "515"? Is this the one that has a single bald tube that drives two tall tubes, driving five more? 73

This radio hasn't been converted from the original 5-pin mike socket to a 4-pin socket, has it? 73

Here's the pre-mosfet 2517 info page. https://cbtricks.org/radios/galaxy/dx2517/ 73

Q57 is the AMC detector. VR16 is the AMC trimmer, D106 is the diode between VR16 and the base of Q57. Full schematic and plarts placement diagrams are at cbtricks.org. 73

Unplug the mike with the antenna connected and see if you hear weak receiver audio. If so, there is a resistor wired between the sleeve side of the external speaker jack and ground. Somewhere in there. 73