[Boatanchors] crystal question

[Al Klase]

Geeze Ray, did you have to ask THAT question? :-)

There were three frequency bands for FM in the WWII era. In addition to 
pioneering this mode, the Signal Corps chose to crystal control most of 
the radios. There's whole story there. The total US production of 
crystals before the war was about 100K units, and it didn't take much 
calculation to realize that millions were going to be needed. Most of 
the raw quartz came from Brazil past the U-boats. But, I digress.

Armor 20.0 - 27.9 Mhz Channel Numbers 0 - 79 Ch. No. = (Freq (MHz) - 20) 
x 10

Artillery 27.0 - 38.9 Mhz Channel Numbers 270 - 389 Ch. No. = Freq (MHz) 
x 10

Infantry 40.0 - 48.0 MHz Channel Numbers 400 - 480 Ch. No. = Freq (MHz) x 10


Crystals:

Tank Sets: SCR-508/528 - 20.0 to27.9 Mc (Armor) SCR-608/628 – 27.0 to 
38.9 MC (Artillery)
These used the Armstrong System. Signal from a crystal oscillator at 
about 400 KHz is modulated by a phase shifter, then multiplied up to the 
operating frequency. Receivers are not crystal controlled, but have 
car-radio-style push-button presets.
Crystals are the FT-241 type. Resonant frequency is Ch. Freq. divided by 
54 for Armor, and Ch. Freq. divided by 72 for Artillery.

Jeep Radios: SCR 509/510 : 20 to 27.9 MHz (Armor) SCR 609/610: 27 to 
39.9 MHz (Artillery)
Crystal-saver architecture. The crystal frequency is multiplied by 4 to 
provide the local oscillator for a receiver with a 4.3 MHz IF. In 
transmit, the DC output of the receiver's FM discriminator is used to 
frequency lock the TX oscillator to the crystal controlled RX frequency. 
Crystals are FT-243's. E.g., (8000 x 4) + 4300 = 36,300 KHz.

SCR-300 Walkie Talkie (Infantry)
Similar architecture to the jeep radios. However, the receiver local 
oscillator is free running with a single crystal in a separate 
calibration oscillator providing manual calibration points.

Hope that helps.

Al


On 12/7/2012 1:33 AM, Raymond Cote wrote:
> You also listed ch numbers. What do the channels mean?  Some of my FT-243 rocks have channel no. listed.
>
>
> On Dec 6, 2012, at 21:58, "Al Klase" <ark at ar88.net> wrote:
>
>> For the technoweenie historian:
>>
>> These were the jeep radios developed by the Signal Corps Laboratory in conjunction with Galvin Corp. (Motorola).  They use the so-called crystal-saver architecture.  The crystal frequency is multiplied by 4 to provide the local oscillator for a receiver with a 4.3 MHz IF. In transmit, the DC output of the receiver's FM discriminator is used to frequency lock the TX oscillator to the crystal controlled RX frequency.
>>
>> E.g., (8000 x 4) + 4300 = 36,300 KHz.
>>
>> Al
>>
>>

-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/