Crystals

 

Crystals, always abbreviated to XTALS, were of several types, and were treated as permanent stores of considerable value. Click on the following thumbnail

Click to enlarge

which will give you an idea on how difficult it was to get a quartz crystal.  The XTAL holdings was mustered every six months and were listed as "Attractive Items -  Routine Musters."

In the days before synthesisers and Wadley Triple Mix [1960], transmitters and receivers had their frequency of operation controlled by a plug-in XTAL, which either in isolation or in concert with a VFO [variable frequency oscillator - tuneable free running] controlled the frequency determination.  This latter method was known as PCC [partial crystal control]. However, this method of frequency determination did not last that long when compared with pre and post determinations. XTAL's became familiar units only with the introduction of the 601 series transmitters and the receivers B40/B41 [1950's], with retro applications made to WW2 [essentially American] equipments like the 89.  This is not to say that the 601 series introduced XTALS, far from it [see below to crystal controlled wavemeters in 1938], but their ubiquitous fitting brought the XTAL, hitherto the exception rather than the rule, to the fore. Before the introduction of 'modern' equipments like the 601/B40, tuning transmitters and measuring the frequency of incoming signals for receivers was done solely by Wavemeters, and there is a section of them on this site. This is what is says in the February 1954 edition of BR 222 [Authority SD1051/54], The Users Guide to Wireless Equipment, quoting from Chapter 6 page 271, where, true to the story, there is no mention of XTALS as a stand-alone piece of kit. {Sadly, for me that is, the book is stapled with an enormous chunks of metal so it can't be pulled apart for scanning, neither do the pages which are 13 inches long [as opposed to A4 which are 11 inches long] lend themselves to scanning, and yes, they are printed in light type from top to bottom and right across the page into the spine}.

"WAVEMETER OUTFITS.

1.      GENERAL

[a].    The introduction of modern transmitters and receivers such as the Type 601 and B40/41 with crystal control, reduces the necessity to fit wavemeter outfits in ships.

[b].    The present requirements of the Fleet, for the accurate setting up of transmitters and measuring the frequency of incoming signals, can be met by the equipment listed below and by the use of modern receivers.

[c].    Future requirements for accurate measuring equipment are being met by equipment now under consideration.

[d].    The revised allocation of present equipment is as follows:-

Class of Ship Outfit
[i].     Capital ships, Aircraft Carriers, Cruisers and Depot Ships GJ
[ii].     Squadron Leaders, Destroyers, Fast Minelayers, Frigates,
                    Surveying Vessels, Monitors and Minesweepers
GN
[iii].    Submarines GY
[iv].    LST[3] GN
 [v].     Maintenance Ships GN/2

The wavemeter outfits shown [as were outfits GH onwards before WW2] were XTAL controlled, so in effect, we have a direct reversal to the FS [frequency standard] of today. Then, all the ships transmitters and receivers which were VFO controlled were compared to the output of the, say,  GN wavemeter to measure accuracy which was crystal controlled.  The FS, taking the place of the wavemeter, feeds its accuracy to all transmitters and receivers as a common reference signal which is used to build up the synthesised frequencies required - local oscillators, sub-carriers, output and input operating frequencies etc.

Thus, in summary, frequency determination was done from the very beginning of our story by wavemeters [VFO and crystal controlled], interrupted by the use of the individually used quartz crystals fitted into each piece of equipment, supplanted by the synthesiser and frequency standard  [which uses just the one crystal in a highly stable, temperature controlled environment].  Putting a time-base in the summary is easy, if only approximate, when we can say that the wavemeter ruled for 46 years [1904 - 1950]; the XTAL for 10 years [1950 - 1960] and the frequency standard/synthesiser for 46 years [1960 - 2006].     

Crystals came in several sizes, none larger than a small match box with some as small [but not as thin] as a postage stamp. They had two male connector pins at the base and some were plugged into an equipment as a single crystal {89Q, B40 etc} whilst others were plugged in as part of a bank of crystals  {86M, PTR 170} and others.   Some crystals were built into glass envelopes and for all intents and purposes they looked like thermionic valves with multi-pin bases.   Each equipment differed and documented its own requirements, and often the XTAL frequency [clearly stamped on the side of the crystal] should equal the transmitted or received frequency, but others might say that the XTAL used should be a half or a quarter of the output/input frequency to be used.  XTALS, though much less cumbersome than a wavemeter and generally more accurate, did have potential problems as the following article shows - click on thumbnail   

Click to enlarge

 The 'normal' XTAL was the type A or type L, which was either black or brown in colour.  Also used for the 5AB [601 series of transmitters] were "Marconi" types - wide spaced pins  - and "Salford"  types narrow spaced pins which were more accurate.