Member postings for Dodgy Geezer 1

It is old - but people who look for vintage parts are often searching for years, and I thought that it was also worth putting this data up on the web for any others who might be wondering why apparently matching crystals that work in one radio set will sometimes not work in another...

The key point is they don't need to be Macgregor crystals, any brand will do as long as they are intended for remote control....

The above is not quite an accurate statement.

Crystal-controlled receivers are usually 'super-hetrodyne' designs. This radio technique converts the received frequency to a lower 'intermediate' frequency signal which is easier to manipulate. As part of this process, the receiving set uses a crystal which has a slightly different frequency from the transmitting crystal.

The transmitting crystal can be any frequency in the 27MHz band, though you will find that 27MHz crystals are invariably on one of the 'spot' frequencies (google for precise data). Later sets were capable of using frequencies in between these 'spots' (called 'split' frequencies). It is true that any specific spot crystal will do for the transmitter.

BUT the receiver will need a crystal which precisely matches the frequency offset that that receiver is designed to operate at. The radio control community developed a common standard for this - it was 455KHz less than the transmitting frequency. So a transmitter on the RED spot frequency (27.045MHz) would have a corresponding matched receiver crystal at 26.590MHz.

So far, so good. Now we come to the problem. The early Macgregor sets did not comply with this standard, and used an offset of 470KHz. IF your set is an early Macgregor, then you will need a receiver crystal of 26.575 MHz if your transmitter is on RED, as an example. The set will probably not work with a 26.590 receiver crystal, which would be the common RED Futaba receiver crystal. Certain other manufacturers also had different offsets, but your problem is finding out whether this set is an early Macgregor, and, if it is, finding a pair of matching Macgregor crystals of that vintage...

Edited By Dodgy Geezer 1 on 12/11/2019 06:49:17

If anyone is looking for a resource aimed (amongst other things) at introducing youngsters to model boat building, they might be interested in this site:

**LINK**

It provides plans for the old Keil Kraft 'EeZeBilt' series of model boats, which were designed by a craft teacher to give kids practice at making boats sucessfully without adult help...