I designed a ~3Mhz 2 BJT, receiver and demodulator, LTSpice agreed it should have peak gain at that frequency. But in real life on a proto-board, it's peak gain was about 4.85MHz. I'm guessing it's mostly the BJT's that are different in real life, some of it could be the caps/ and inductor too.
So for a TX, I started with a low gain 4.9MHz Colpitt's oscillator, and then noticed all the FM radio stations were a lot closer to my signal strength then I wanted. I could swap or change the Colpitts caps, and get much higher gain, but I haven't.
Instead I added some RC and LC filters, between some more amplifier and buffer stages, and it works well enough in LTSpice.
But in the real proto-board circuit, the AM and FM radio stations, got stronger, and no were near as weak as in the sim by the end.
The dBVrms levels in sim and real circuit match pretty well, until the Q4 buffer emitter. The sim has about
-100dBV for 800kHz local AM
-44dBV at 4.9MHz
-165dBV at 100MHz local FM radio
The real circuit has -46dBV for 4.9MHz, but the AM and FM stations are only about 7-15dB less at Q4 emitter. So I'll have to un-solder some stuff, simply swapping the upper and lower cap in the Osc, will get me much more more gain, but I wanted a clean signal, not a strong signal, at this point.
Is this a lack of shielding over the circuit, like the green through style inductors ? Or the BJTs, Or the layout ? It's 5 BJT's , all pretty neatly packed, more or less like on a beardboard, with V+ and V- parallel and directly adjacent to each other.
The image order should be sim C3 /E4 C5, for collector and emitter, and the the real ones