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Path: utzoo!watmath!clyde!burl!ulysses!allegra!mouton!karn
From: karn@mouton.UUCP
Newsgroups: net.ham-radio
Subject: Re: TS-430 frequency display; mods
Message-ID: <157@mouton.UUCP>
Date: Sat, 22-Sep-84 15:43:25 EDT
Article-I.D.: mouton.157
Posted: Sat Sep 22 15:43:25 1984
Date-Received: Wed, 26-Sep-84 03:58:13 EDT
References: <12149@sri-arpa.UUCP>
Organization: Bell Communications Research, Inc
Lines: 22

I don't know about the TS-430, but on synthesized VHF radios such
as the Kenwood TR-9000 (which I have) there is a mechanism which
explains small frequency calibration errors.

Very few radios are actually synthesized to such small frequency
steps such as 100 hz; this makes the phase lock loop design much
more difficult. Instead, they typically have two oscillators which
are mixed to generate the final LO signal: a "coarse" synthesized generator
which operates on, say, 10 khz steps, and a "fine" conventional analog VCO
which is operated over a relatively small range (10 khz) with a control
voltage generated by a D/A converter.  This means that while the
frequency accuracy over a wide range will be fairly good, there may
be small (several hundred hertz) errors which cyclically repeat due to
nonlinearities in the D/A converter or the VCO (which is often a crystal
oscillator and a variable capacitance diode.)  There can also be
nonlinearities when tuning through a "coarse" frequency step, e.g.,
a 10 khz boundary on the TR-9000 when the PLL synthesizer changes
its output by one step and the analog VCO must sweep from one end of
its range to the other. This is particularly noticeable on the TR-9000
in lower sideband.

Phil Karn