I decided to occupy myself with 1000 kHz oscillator crystal transmitter temporarly until I can get a kit or assembled part 15 tranmitter. I am not going to be on 540 kHz that much, my new frequency is AM 1000 on 1000 kHz. Same programming, but a different frequency. Soon I might buy me a new AM transmitter kit and return back to AM 540 kHz.
The main reason why I have to use 1000 kHz is because the audio and stability of a crystal oscillator sounds better than the “toy” lab kit transmitter circuit. The good thing about this is that it’s narrowbanded and does not require wideband tuners to hear the audio.
Rock Bound
is a radioman’s phrase for crystal controlled transmitters with the bound part coming from the pre synthesizer days when you were literally bound to a frequency according to the crystal you had.
The LC oscillator type of transmitters used in “lab kits” are OK but they do drift, often when the capacitance seen by the antenna changes. I started in this hobby with a tube KnightKit AM broadcaster which used an LC oscillator with no output buffer. Surprisingly, once warmed up it held frequency fairly well but the problem was at night when other stations appeared on frequency there was a beat note present. I chanced to have a 1320 kHz crystal available and wired it into the KK and solved the drift and beat note problem. Been “rock bound” ever since on AM.
Back in the day of analog tuned receivers it didn’t matter much if you weren’t exactly on frequency but with digitally tuned AM radios this can be a factor. Once you upgrade to a synthesized transmitter you will be pleased not to have to contend with drift.
Meanwhile, your 1 MHz oscillator project sounds interesting. Are you modulating this oscillator? If so, be careful about spurs and harmonics which usually result when using an oscillator to transmit. Keep the power low.
Keep us updated.
Neil
No Harmonics
No harmonics, they are already been taken care of using .01 uF capacitors on the input and output of the crystal oscillator and LM-386. The transmitter power is kept low and when I hear the station in the living room it’s very weak.
Hello Gccradioscience
Cool.
Your original transmitter was probably
FMing – in other words, it was transmitting
a combination of AM and FM. A lot (or maybe
all) LC RF oscillators tend to FM when you
apply modulation – so they sound really wide
when you try to tune them in on a radio.
I had a Ramsey Electronics AM-1, which used
an LC oscillator – and it FMed like crazy –
and drifted badly as well.
I built a crystal oscillator circuit for 1700 kHz,
and I wired it into the front of the transmitter
where the LC oscillator used to be.
That took care of all of the problems.
Yup – let use know how you are doing.
This is good stuff.
Bruce, The Dog Radio Group