Was it just me or did I actually read or hear about that that transmitter actually did not have very good range for what it was? From what I heard it didn't do as well as they talking house transmitter does on a.m. with the wire antenna.
I listened to your demo using headphones and noted two things, both of which sound to me like what I hear at night at home using my outdoor antenna with the receiver tuned to a frequency where there are two or more weak stations on the same frequency. As we begin to hear your station there is a noticable beat frequency at about 1.5 to 2 Hz. This is caused by the carriers being off frequency of each other and alternating between reinforcement and cancellation which causes the receiver AVC to change the receiver sensitivity in step with the beat frequency. Note how the audio goes up and down at this beat frequency.
As you approach your transmitter and its signal becomes stronger this beating diminishes because your signal is now stronger than the other signal and the reinforcement and cancellation is reduced. But this is where you mentioned distortion which can be explained by the distant station's audio being added to the audio of your station which the receiver cannot separate. The addition of the audio from the distant station will distort the desired audio of your station since what you hear is the sum of the two (or more) signals. As you get closer your signal audio becomes stronger than the distant audio and the unwanted audio becomes a smaller part of the summed received audio eventually becoming inaudible leaving only your station's audio.
During daytime the distant stations' signals are not present so there is no beating or distortion due to audio summing. What I heard sounds like normal nightime interaction of several signals of about the same strength.
It is possible that I do not hear all that you do but you should consider that what you hear is normal and not produced by a problem with your transmitter.
Neil
From Reply #30 of this thread: During many years in hobby radio I have wished, along with many others, for a legal AM nighttime signal that would match the daytime signal. ... <snip, then this conclusion> 10X greater is a convenient number of about 1 Watt.
Unfortunately, increasing field intensity by 10X at a given location requires the radiated power to increase by 100X (other things equal).
Doing so for this scenario would require a 10 watt transmitter (again, other things equal).
Rich clarifies: "Increasing field intensity by 10X at a given location (seeking nightime equality compared to daytime) requires the radiated power to increase by 100X (other things equal)."
WAY beyond part 15!
Again... how many times do I have to repeat myself?.. this problem has NOTHING to do with carrier frequency and how far apart two or more signals are in frequency. From what I can see, the Procaster has great frequency stability that rivals licensed transmitters. There is no "beating" or "wavering" problem caused by two or more signals being a few HZ off from each other. The problem is PURELY AN AUDIO ONE but it only occurs when other stations (or even other sources of interference) are present on the operating frequency. If you don't understand the nature of the problem, please refrain from commenting. Thank you.
My Broadcast Engineer friend fixed my Sean Cuthbert
It had the worbling and it was to do with the PLL and Rob fixed it.
I am commenting on an old post because no one got this answer to the problem right.
When on AM and at night when another station is coming in on your frequency causing a tone or warbling it is because you are not spot on frequency and it creates this effect with the other station in the background. This is the beating that happens as the two stations aren't synchronized.
The Procaster has a frequency trimmer and you need a frequency counter that takes reading over the air and you have to adjust it to at least 7 digits to read like this if on 1630.....1.630000 mHz.
All the commercial stations are right on so you have to be also and that will solve the issue the poster asked about. Even a bit off frequency will cause beating at night when the skywave kicks in. This not noticed in the day when it's clear. If no frequency counter than as you are listening adjust the trimmer till the beating is gone.
I know because when I was using the Procaster I could create the problem and fix it by the frequency being "dead" on.
Licensed stations are required by the FCC to have Modulation Monitors, radios that show through calibrated meters the precise frequency accuracy and peak modulation level. Using a frequency counter or other calibrated radio is needed for a part 15 station to know the precision of its own signal.
I've never had that problem. I also have modulation monitor with frequency displayed.