The question however is why they selected 10.7 etc. in the first place. Would 10.5 have worked, or 10.9 etc. The IF switch feature is a great tool but I don't know why specific freqs were chosen in the first place.No.
Changing IF frequency changes the location of birdies. If you have a selection of IF frequencies to choose from, you can move a birdie away from a frequency you want to hear. For example, if you have a birdie at 460.000 MHz and want to monitor that frequency, changing the IF frequency from 10.80MHz to 10.85MHz would move the birdie to 459.950MHz. That allows 460.000 to be monitored without interference.
The x36 scanners have this feature, it is under the Miscellaneous tab of the Profile Editor, the button labeled Intermediate Frequency Exchange (IFX). You can list frequencies that have birdies using the default IF frequency, and the alternate IF frequency will be used for those frequencies.
Crystals for one manufacturer's scanners will not be on the same frequency in another manufacturer's scanners that used a different IF. I don't know if that was intentional.The question however is why they selected 10.7 etc. in the first place. Would 10.5 have worked, or 10.9 etc. The IF switch feature is a great tool but I don't know why specific freqs were chosen in the first place.
WA1NIC explains well the reason for 455 KHz. so I assume there was some similar thought behind the 10.7 (Regency) and 10.8 (Electra) choices made for scanners back in the day.
I've heard/learnt the same thing but for 10.7MHz and I guess that's a reserved frequency for europe and 10.8MHz are for US? So when Uniden makes a european model they change the IF from 10.8MHz to 10.7MHz and that's the major change between EU and US models? Nowadays the scanners are so good RF screened that it's seems unecessary to do that.i heard in high school that the frequencies were left unoccupied so that they could be used for just this reason.
Back in the crystal scanner days we used to chart what freqs Regency (10.7) crystals would result in a Bearcat scanner and vice-versa. Usually it resulted in something 5 KHz off but that was close enough in those days. When you have a lot of crystals but they were expensive ($5 then, like $30 or so in todays dollars) that meant you could hear a different channel if the freqs lined up.Crystals for one manufacturer's scanners will not be on the same frequency in another manufacturer's scanners that used a different IF. I don't know if that was intentional.
Thats as good an explanation as I ever heard, makes more sense than anything else.It was a group of engineers who decided that 455 Kc and 10.8 Mc should be the freqs used for the IF circuit. More or less a "gentleman's agreement". This was the reason given to me many years ago. True or not, I'm not sure.