Ramsey Electronics FZ-146 Specifications download pdf (Page 115)

FX-146 • 115

Easy enough! Whenever you want a transmit offset that is higher than the

receiver or repeater output frequency, simply find the the N number for the

offset and program it on the offset matrix.

Here's one more example. Let's say we want a + 1 MHz offset.

1 MHz = 1000 KHz. 1000 ÷ 5 = 200 = N

Converting to binary: (Obviously 200 is less than all values from 8K through

256, meaning that we need no diodes in those positions.)

Can we subtract 128 from 200? YES (Therefore diode at 128)

200 - 128 = 72

Can we subtract 64 from 72? YES (Therefore diode at 64)

72 - 64 = 8

Can we subtract 32 from 8? NO (Therefore NO diode at 32)

Can we subtract 16 from 8? NO (Therefore NO diode at 16)

Can we subtract 8 from 8? YES (Therefore diode at 8)

This +1 MHz TX offset is set up easily by diodes at 128, 64 and 8!

Programming of Minus offsets is covered in the Reference section of your

manual.

ADDITIONAL CIRCUIT NOTES:

The 19 100K resistors at the frequency programming matrix and the 14

100K resistors at the offset matrix are called "pull down resistors" and are

required to ensure positive logic switching action of U6.

Transistor Q15 and its associated switching diodes ensure that the desired

offset is switched in during transmit, that offset programming does not

interfere when simplex is desired and that the offsets do not interfere with

receiver operation . . . and that receiver programming (21.4 MHz lower) does

not interfere with transmit operation. Obviously, these simple parts must be

installed correctly, or major PLL problems would result.

Stage H: PROGRAMMING MATRIX ASSEMBLY

There are two diode matrix programming areas on your PC board. The

obviously larger area is for frequency channel programming. The second

space is for offset programming added in by U7-U10.

Correct assembly of the following section permits Q15 to switch off all three

transmit offset programming lines while receiving, allowing only the RECV

programming to be in effect. Be certain to orient the diodes correctly.

Install the following resistors:

 H1: R68, 1K (brown-black-red).

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Ramsey Electronics FZ-146 Specifications Page 115