I am using this AnyTone 144MHz 10/25/50W FM mobile device last years for local 144MHz traffic.
A lot of power from a very small VHF mobile rig
Though it will get very hot in longer chats at the 25 or 50W level
The RX-standby power is 0.25A
But sometimes it happens that sudden the squelch seem to open and a loud noise comes out.
The RX signal level showed 5 bars even with disconnected antenna.
The signal happens to be generated internal.
The noise/signal disappears when just touching the power cord or AnyThing(...) external at the device
Found internal a beautiful well build device with gold plated PCB.
I have no service document or diagram. Hard to believe that this professional build device would suffer from a self oscillating pre-amp stage, but i can't draw an other conclusion.
I could not see any malfunctioning parts. A wide-band design no tuning parts.
Suspect is the first RX FET to have a constant parasitic self-oscillation.
Hard to detect with my RF detector probe , the level is low and oscillation stops or changes when placing the probe at the receiver pre-amp fet. Close by at PCB left is the local oscillator that of course does show rf level.
I could move the oscillation frequency by hand effect near the RX input stage. It is a very weak oscillation , strange by nature an oscillator will work at maximum or not.
See Youtube recording below.
Having a test signal at 144.550 i could clearly hear an interfering floating signal passing by when approaching the PCB near i guessed it must be the RX pre-amp stage.
The UHF/SHF trick using a piece of anti static foam did not work.
Oscillation stopped with an 1/8W 1k5 resistor from ground direct to the drain of the FET
The receiving of the test signal did not seem to suffer by this rather rough approach.
Possible someone knows a better way to stop the parasitic oscillation but the parts are all SMD and i did not want to mess up the very clean PCB layout.
A few days standby now the annoying noise burst did not happen again yet.
Propagation 80m a bit restored last 24 hour sorry enough i had to remove my west Beverage due farmers activity's it was again cut by mowing machines.