04-01-2017, 10:44 AM
Hi Mike.
A very interesting thread, I'd like to add my tuppence worth.
Over the years I've made many different micro TX using transistors, FET's & Valves. What I have found is that trying to use a crystal by utilising the sub harmonics is a waste of time and effort. Sub harmonics are at a very low level borne out by you inability to tune into them, so by having a bandpass filter tuned to the frequency you are extracting you'd then need at least one or more stages to amplify the signal to a usable level.
I suppose I am lucky having a few crystals that fall into the MW band and don't forget a 1mhz crystal falls in the band too, OK it's not dividable by 9 but old radios are neither PLL controlled, a 1Mhz crystal is ideal for carrying out experiments and then you could move to one that is more acceptable.
I avoid third overtone crystals in my little TX's I stick to the standard fundamental ones.
Dividers, multipliers and other such circuitry adds to the complexity of what is essentially a simple device, the more you add the more you will land up with problems.
If you want Mike I can send you a 9khz dividable crystal for you to play about with, it might be pot luck though in your area for what is broadcast.
A very interesting thread, I'd like to add my tuppence worth.
Over the years I've made many different micro TX using transistors, FET's & Valves. What I have found is that trying to use a crystal by utilising the sub harmonics is a waste of time and effort. Sub harmonics are at a very low level borne out by you inability to tune into them, so by having a bandpass filter tuned to the frequency you are extracting you'd then need at least one or more stages to amplify the signal to a usable level.
I suppose I am lucky having a few crystals that fall into the MW band and don't forget a 1mhz crystal falls in the band too, OK it's not dividable by 9 but old radios are neither PLL controlled, a 1Mhz crystal is ideal for carrying out experiments and then you could move to one that is more acceptable.
I avoid third overtone crystals in my little TX's I stick to the standard fundamental ones.
Dividers, multipliers and other such circuitry adds to the complexity of what is essentially a simple device, the more you add the more you will land up with problems.
If you want Mike I can send you a 9khz dividable crystal for you to play about with, it might be pot luck though in your area for what is broadcast.
