Crystal Clear
Posted: 10 Nov 2020, 15:54
Elsewhere on this forum, I describe how I am building a Remcon 12 Versatile “Reed” Tx, from scratch. My current task is acquiring the crystals. The hunt has created some questions and I wonder if anyone can educate me?
The 27MHz crystals to be used are specified as “3rd Overtone” and various third-party ads in RCM&E show that this is quite common.
Q1 Why the 3rd overtone? What was special about it?
Further, I’m guessing that the signal is attenuated with ever higher overtones.
Q2 Does this mean that, with these crystals, the “best” signal is going out on 9MHz, the primary tone?
Next, as early as Feb 1962, RCM&E published a newly-adopted crystal “protocol”. The adoption of this (Brown through Blue) enabled those with superhet receivers to fly 6-up, and no “waiting your turn”.
Essentially, the Tx “colours” were each separated by 50/60Khz, with the corresponding Rx using a crystal 455KHz lower, to produce the intermediate frequency.
Now, at least as late as 1966, Remcon released the “12 Versatile” with a designed tx/rx IF separation of 465KHz. I’m guessing this tied kit builders to Remcon crystals and might have provided a modest reduction in the chance of interference for Remcon receivers, but it would create a problem when “splits” (further dividing up the 27MHz band) were introduced, a few years later. (Indeed, my recently purchased “spare” Remcon Superhet receiver shows sign of its crystal being changed to the “standard” 455KHz separation, at some time).
So,
Q3 Is this 10KHz difference significant? Can it be “tuned out”, easily, in the IF coils?
I realise this historical information is a bit arcane, these days, but someone might know, and any answers will help me understand what is going on.
Q4 Am I in danger of taking all this a bit too seriously?
Many thanks,
John
The 27MHz crystals to be used are specified as “3rd Overtone” and various third-party ads in RCM&E show that this is quite common.
Q1 Why the 3rd overtone? What was special about it?
Further, I’m guessing that the signal is attenuated with ever higher overtones.
Q2 Does this mean that, with these crystals, the “best” signal is going out on 9MHz, the primary tone?
Next, as early as Feb 1962, RCM&E published a newly-adopted crystal “protocol”. The adoption of this (Brown through Blue) enabled those with superhet receivers to fly 6-up, and no “waiting your turn”.
Essentially, the Tx “colours” were each separated by 50/60Khz, with the corresponding Rx using a crystal 455KHz lower, to produce the intermediate frequency.
Now, at least as late as 1966, Remcon released the “12 Versatile” with a designed tx/rx IF separation of 465KHz. I’m guessing this tied kit builders to Remcon crystals and might have provided a modest reduction in the chance of interference for Remcon receivers, but it would create a problem when “splits” (further dividing up the 27MHz band) were introduced, a few years later. (Indeed, my recently purchased “spare” Remcon Superhet receiver shows sign of its crystal being changed to the “standard” 455KHz separation, at some time).
So,
Q3 Is this 10KHz difference significant? Can it be “tuned out”, easily, in the IF coils?
I realise this historical information is a bit arcane, these days, but someone might know, and any answers will help me understand what is going on.
Q4 Am I in danger of taking all this a bit too seriously?
Many thanks,
John