I was bitten by that bug too. In the mid-2000s I got a Landmark Technologies FM stereo transmitter. This was a time before all of the inexpensive digitally tuned transmitters started to be sold out of Asia direct.
The Landmark was PLL, binary rotary switch controlled, and had good audio specs, and was somewhere around $200 I think. It was common to use institutionally, like in rest homes and penal institutions.
Well, I had it sitting on a window sill, with a dipole antenna stretched diagonally across the glass of the picture window and broadcasting. There was a storm outside and lightning.. normally I would have disconnected if the antenna was outside, but thought it was safe, and the lightning didn't seem too close. There was a strike nearby, and the signal was suddenly weak in a monitor radio in the room.
I thought oh no, and turned it on and off, it was no use, nothing but a 15 foot signal range. Opening it up on the bench, the final was one of those blasted 4-lead devices, a black pill the size of a rice grain. Touching a probe wire to the output side of it, there was a little bit of signal to a radio, but there was more signal on the input side, so likely the output amp was blown.
I wondered why they used something that was so fragile. I can see why they'd want to use something like that chip, taking less board space than a transistor, with fewer support parts, and controlled input and output specs. I guess they never thought to test it for electrostatic discharge across the output.
It seemed like this bad design choice propagated to other companies, and I'm sure it hurt their reputations. I'm glad there's a fix with the 2.2 microhenry choke across the output. Did Ramsey ever do anything about the the issue, like send a choke out to buyers, or redesign their output sections?
They should stay with a good old bipolar transistor output stage, something that's worked for decades, and the transistors only cost a few pennies. Here's the radio taken apart, showing the top side board, the final is under where those coils are on the lower right.
The output is under those coils!? How the $%# are you supposed to get to it to replace it? And those tiny surface mounts are not fun trying to replace and easy to screw up and have to just throw it away. Yup, old fashion transistors with the few extra through hole components would not take up much space and would be more durable and very easy to replace but still I would protect from static/electrical surges like close lightening and a shock from your finger.
Hi OldiesWMRK, well, the output chip is on the opposite side of the board from where those coils are and pretty much in the clear. You need a small tipped iron, the right tools and magnification for surface mount.
I'd only used the transmitter for a matter of hours before it went out. That was the first real broadcast, and I had a friend over and a live studio. Likely it 2005, and when it broke I just put it in a box and thought about it recently again.
I have to wonder if the ICs used are really made for use as final amps in transmitters. Usually devices made for the final stage are ruggedized, not just for electrostatic discharge, but for high SWR (which can cause the RF voltage to soar on the final), like for operating with no antenna or shorted output.
Maybe the GAL 5 is made for input amplification, RF amp stage in receivers, or as an interstage amp, not to have its output connected to an antenna? It might need even more protection than the choke, like a zener diode across the output, and a resistor.
Thanks for taking a look at it guys! I'll see what the part number is in my Landmark and if I can find a replacement.